the importance of sketching

I’ve often talked to students, young designers, and colleagues about the importance of sketching as a part of the design process, whatever flavor of design that might be. I like to think that I practice what I preach, but sometimes I forget.

I have been struggling with the design of an enclosure for my CNC mill that would allow me to use flood coolant and contain the mess of metal and plastic chips this machine can create. I had a rough idea in my head, and looked around at existing enclosures, so I immediately jumped into CAD to sort out the design. For days I iterated on-screen, unhappy with the results but trudging through each new concept until I hit a wall.

sketch

So last night as I sat on the couch I opened up my laptop to give it another go, only to find technical issues that kept me from launching my CAD software. Frustrated, I shut the laptop and pulled out my sketchbook. Within minutes I was teasing out the solutions that were so elusive on screen, and by the time I shut off the lights I had my design roughed out.

So, one more time, especially so I remember: Never underestimate the importance of sketching. CAD is an invaluable tool, as are rendering packages and Illustrator and Photoshop, etc. But for quick ideation, brainstorming, breaking through a mental block, or simply communicating with your fellow designer/engineer/marketing person, nothing beats sketching.

Thanks for humoring me. And stay tuned for my next rant, titled mock it up before you fock it up

home made chuck key

This weekend I spent a lot of time in the shop machining parts for my CNC mill, and ran into a problem with the lathe. The four jaw chuck has these adjustment screws to move the jaws in and out, but I can’t find the chuck key needed to adjust them. They use an inverted key–it’s and innie, not an outie, like most chuck keys–and it’s almost impossible to adjust without that particular tool.

I had a leftover piece of steel rod, so I made my own:

9x20 lathe chuck key CNC machined

The ends were machined on the mill, clamping the piece upright in the vise. The shoulder was turned on the lathe (in the three jaw chuck!).

9x20 lathe chuck key CNC machined

I milled a socket into the other end for a 3/8″ ratchet, although the fat body makes it easy to turn quickly by hand. (I tried to knurl the end but I still don’t know how to knurl properly, so I just mucked it all up)

9x20 lathe four-jaw chuck

 

Operational!

sneak peek! hot shop styles for 2012

This new milling machine creates a lot of tiny shards of aluminum. And apparently those are not good for a toddler to eat, so I’ve had to take steps to reduce the amount of aluminum chips I drag into the house from the shop. I think my solution is pretty stylish…

shop coveralls G0704 CNC mill

CNC surface machining

I’ll be posting more about exactly what this part is in the near future, but for now I’m super excited about making my first surfaced part on the mill…

This is ABS, which I’m using to test the program before moving on to brass. Good thing too, because one of the last commands jammed the end mill down into the part… I pressed the reset button just as the bottom of the collet was carving out a pocket in the ABS and nothing was damaged, but if I was using brass things would have been ugly.

The end mill is a 1/4″ three flute uncoated carbide ball end mill. The spindle speed was around 2400 rpm and the feed was 7.5 ipm.

CNC milled PC board

One of my goals for the CNC mill has been to help fabricate PC boards, primarily in terms of cutting out the overall shape and drilling any through holes. For simple boards, however, it is possible to machine the circuit traces into the copper and avoid the entire photo-etching process altogether. I recently had a chance to try this process out, and the results were quite good.

This particular board needed to be circular, and needed to have a rectangular opening for a switch, so CNC routing the outline is really the way to go. The circuit is relatively simple, so it also lends itself well to routing the traces. If I were to etch this circuit the usual way with photoresist, developer, etchant, etc. etc. it would have taken three times as long.

PC board layout in Cadsoft's Eagle

 

The board was designed in Eagle as usual, but I then used an add-on to Eagle called PCB-gcode to generate gcode from the traces. There are a number of settings to specify depths, tool settings, speeds, etc. but it is fairly self-explanatory.

PCB-GCODE screenshot

I chose some pretty basic settings, which resulted in the following preview:

PC board layout in PCB-GCODE

I was never able to figure out how to generate the outlines using PCB-gcode, so I re-drew them in Mastercam and went from there. PCB-gcode is supposed to have that ability but there appear to be some bugs in the software that limit its ability to deal with circles and arcs. If anyone has made better progress than me I’d love to hear about it.

CNC machining a PCB on G0704 CNC mill Anyway the final product came out pretty good. I was pretty pleased with myself having tightened up the backlash to only .004″ per axis, but after machining .024″ wide traces I realized how bad that is. Under the right circumstances this is a good technique to save time, but I wouldn’t try to machine extremely fine traces or tight-pitched pads until I work those last few thousandths of backlash out of my machine.

 

 

 

 

 

milling machine modifications, part __?

In this minor modification I added a 50 lb. gas spring between the column and the head, meant to assist the Z-axis motor in lifting the weight of the head.

gas spring modification G0704 milling machine CNC

The stock part is a 50 lb. gas spring with ball-joint fittings, McMaster part #4138T621. I simply drilled a hole in the column (and tapped it for 5/16-18) for the lower pivot, but the upper pivot point wanted to be above the top of the head to allow for a full 12″ of travel. I designed and machined a simple aluminum part to extend the upper pivot point and mounted it to the head. While I was at it I also machined a nice little cap to cover the hole where the Z-axis crank was.
gas spring modification G0704 milling machine CNC

The backlash in the lead screws has been giving me relatively poor surface finishes, so I bead blasted these parts to even them out. I like the look, but the “toothy” surface really grabs onto dirt.

I was hoping to double the rapid speed I could get out of the Z-axis, but I didn’t quite make it… It went from 15 in/min to about 25 in/min, although I just bought some better way oil so we’ll see if that makes up the difference.

first CNC movements

Manual entry of G-code, with a Sharpie mounted in the drill chuck…

antenna ball

For the ham radio operator on my gift list…

antenna topper turned 9x20 lathe aluminum

After eyeballing the spherical shape using a mixture of cutting tools, rasps and files, I wet-sanded the tool marks off and polished it with red and green compound. Then I parted it off (pictured above) and drilled the mounting hole. I was going to measure the sphericity I got by eye but decided I’d rather not know.

CNC mill parts

Tonight I finally finished the metal parts for the CNC conversion. These were made from a subset of the “phase 1″ plans I purchased, and are all the custom parts I need to attach my stepper motors to the G0704 mill.

aluminum and steel parts for my G0704 CNC milling machine conversion

Most of these were pretty straightforward. The standoff-looking parts are steel rod, parted off to length and then drilled and tapped. The fatter bushing-looking things are aluminum, also round rod that was drilled out then trimmed to length. The big flat aluminum parts were a little more challenging, requiring some milling, but the holes were all center-punched and drilled on the drill press (I still don’t trust positioning on the mill due to the backlash in the screws).

steel part for my G0704 CNC milling machine conversion

This cylindrical steel part took several hours. Starting from a 1.5″ steel rod, I first turned the skinny stem part, then flipped it around to bore out the inside. The tricky part was getting the piece clamped into the lathe so it was perfectly concentric to the shaft I already turned. Apparently my three-jaw chuck is not perfectly centered, so I used the four-jaw chuck and aligned the part manually using a dial indicator attached to the cross slide. According to the indicator I got within half a thou for concentricity… good enough!

steel part for my G0704 CNC milling machine conversion

Once it was centered I bored out the inside and put the little shoulder on the end. Next it was drilled and tapped (for set screws), then off to the mill to make the flats on the shaft.

The most challenging part was probably this aluminum bearing block, shown here in the four jaw chuck. Again, concentricity here is key, so a lot of time was spent getting this guy aligned when I flipped it around.

aluminum part turned on a 9x20 lathe for my G0704 CNC milling machine conversion

Technically I’m ready to mount the motors to the mill, but I’m hesitant to start the process. I’ve gotten used to having a milling machine available, and once I take the handwheels off it’ll be out of commission until the CNC conversion is complete and working! Here we go…

Mach3 setup

I’d love to say that getting the CNC controller software (Mach3) to talk to my stepper motors went quickly and flawlessly. It didn’t, but to be fair there are several hardware steps between the two and I don’t blame Mach3. Anyway by the end of the day I had gotten to this point:

Next step is mechanically attaching the motors to the mill, then addressing the whole Arduino safety system.

CNC controller – assembly & wiring

Assembly of the controller box has gone very well. The PC components (motherboard, hard drive and power supply) all mount to the monitor’s VESA holes through a flat aluminum bracket, and the monitor attaches right to the front panel. The keyboard gets sandwiched between a flat steel plate and the front panel, with some minor modifications to its silicone cover to make it fit.

small form factor PC and touch screen built into custom CNC controller box

The rest of the assembly revolves mainly around the PCBs and front panel controls. Before mounting the PCB assembly I installed the small USB daughter board that provides a USB port on the front panel.

USB daughter board for custom CNC controller box

The rest of the assembly mounts over this, aligning the tact switches to the button actuators. The remainder of effort went into managing the many wires neatly into the cabinet.

custom CNC controller box

The lower cabinet assembly was much more straightforward:

stepper motor drivers for G0704 CNC milling machine

stepper motor drivers for G0704 CNC milling machine

Of course I wanted to fire it up as soon as possible, even though nothing was connected. The Arduino IC was not yet programmed so none of the UI elements were working, but I was able to transfer files through the USB port.

custom CNC controller box for G0704 milling machine

This is far from complete, but I’m ready to start integrating the Mach3 software with the electronics and make sure they can talk to each other.

CNC mill – metal fabrication

With the CAD design more or less complete it’s time to make some parts. I generated some 2D views of the various parts and plotted them at full scale, then spray-mounted them to some sheet metal, most of which I had cut to size beforehand.

fabricating parts for the custom CNC controller box

As a result, most of the fabrication involved simply drilling and tapping the right sized holes in the steel:

fabricating parts for the custom CNC controller box

But some of the more complicated parts required cutting out larger areas of material. I did most of this very slowly with the jig saw and a metal-cutting blade. But some of the rectangular areas allowed me to use the mill!

fabricating parts for the custom CNC controller box

I quickly realized that this machine will be challenged by steel, as even this thin material caused the whole column/head to flex as I cranked on the wheels. I think it will be possible to machine steel, but the feeds will need to be very slow and it will definitely require copious amounts of coolant.

Here’s the “lower cabinet assembly”–the part that will house the motor drivers and their power supply–welded up and primed:

fabricating parts for the custom CNC controller box

The front panel of the controller box required extensive modification, done entirely with the jig saw and drill bits (the large holes were made with a step drill). I couldn’t wait to dry-fit the assembly onto the mounting arm:

fabricating a custom CNC controller box

The front panel also required a fair amount of welded parts on the back side, for mounting the monitor and keyboard. Notice how the thin sheet metal warped after welding:

fabricating a custom CNC controller box

Final fitting before priming and painting:

fabricating a custom CNC controller box

Next step, assembly…

controller box mounting arm

I don’t usually build as I go, without detailed planning or at least some sketches. But one Saturday a few weeks ago I had several hours to myself and I was itching to make some physical progress on the CNC conversion, so I took a quick inventory of my metal stock pile and just started building.

custom CNC controller box welded steel The mounting arm for the CNC controller box–that physically attaches the box to the mill–is a very simple part with well-defined parameters. The controller box has four mounting holes on the back side and the column of the mill is a thick iron casting that can be drilled & tapped basically anywhere. I knew approximately where I wanted the box to be, so it was a simple connect-the-dots part design. I had a 2′ length of square steel tube and some angle iron, so I started chopping it up and dry-fit it to the back of the controller box.

MIG welded steel

I MIG welded it together (still practicing that welding… getting better) and cleaned it up, then primed it with some Rustoleum, then did a quick test fit on the mill.

custom CNC controller box mounting arm

custom CNC controller box

A couple of coats of black lacquer and it’s good to go!

custom CNC controller box mounting arm

CNC mill phase 4: PCB fabrication

By now I’ve got a pretty good system down for fabricating PC boards:

1. print artwork onto transparencies
2. laminate the dry film resist onto copper
3. expose the board on the UV light box
4. develop the film, rinse
5. etch the PCB in a tupperware in a sink full of warm water (I’ve been experimenting with acid cupric chloride, but my go-to is still ferric chloride), rinse
6. strip the film off with acetone & tin plate the board with Tinnit (also in container in warm water), rinse with ammonia solution
7. drill & trim board
8. dab on solder paste and place components
9. reflow solder in the toaster oven
10. hand-solder through hole components

This is basically the process I followed this time, but this was the biggest PC board I’ve made to date at around 11″ long. To start with, I couldn’t fit the whole thing on a 8-1/2 x 11″ transparency out of my laser printer, so I had to print it in two pieces and tape them together.

PCB artwork transparencies

I also couldn’t fit the board in my typical etching tray, so I had to use our good Pyrex baking tray for the etching and plating. Otherwise the process went smoothly. I intentionally sized the board to just fit into my reflow toaster oven, and despite using expired solder paste the boards came out pretty good.

PCB - ready to etch

CNC mill phase 3: PCB design

In my CNC controller design most everything is handled by the PC and the off-the-shelf breakout board and motor controllers. But there is an ‘optional’ hardware layer that provides a measure of safety–both for the user and the machine–and a degree of feedback as to the status of the system. This is where a couple of custom PCBs come in.

The design of this subsystem is based off a sample from the excellent Mach 3 controller software documentation (without permission to reproduce it, see page 4-24 of this pdf document). Essentially the system monitors a series of limit switches–designed to prevent the machine from trying to move beyond its mechanical limits in any axis–and one or more E-stop buttons, which together are called the ‘interface’. It also listens for a 12.5kHz electrical signal that the Mach 3 software generates when it is running normally, and if any of these conditions are abnormal the power is cut to the stepper motors and the machine’s spindle. The Mach 3 example does this in an analog way with a clever series of relays, and includes LED indicators and a reset button to provide system feedback to the user.

I realized that a microcontroller could do the same job and offer some more flexibility, and ultimately be simpler. At the heart of this board is a standalone Arduino–basically an ATMEGA 328 and a small handful of discreet components. The IC just to the right of that is a MAX232 chip for serial communication with the PC. This is certainly not necessary, but I figured I have a PC in the same enclosure, so why not enable it to connect directly to the Arduino, either for reprogramming purposes or for some future physical computing need related to the CNC mill. To the right of that is an HEF4538 monostable multivibrator IC and the rest of the ‘charge pump’ circuit provided by Geckodrive’s Mariss Freimanis, which turns the 12.5kHz signal from Mach 3 into a logic high or low into the Arduino. To the upper left is a simple 12VDC (from the PC power supply) to 5VDC power supply, for the ICs and the C-10 breakout board in the lower cabinet. This 5V and GND and the rest of the lines between the Arduino and C-10 board connect to a pin header, shown directly below the Arduino.

CNC mill - main board schematic

On the very far right is where the E-stop and limit switches will connect to an Arduino I/O pin, and a pull-down resistor to keep the pin from floating. The E-stop and limit switches are connected in series and set up in a ‘normally closed’ configuration. This is an added measure of safety as an inadvertently severed wire will indicate a fault, rather than fail to indicate a real problem should one arise. As configured here, a normal condition will read as ‘high’ on the I/O pin.

On the upper right is a series of switches and indicators: MACH OK and INTERFACE OK indicators, INTERFACE RESET and MOTION OVERRIDE buttons (each with their own indicators), and a PC POWER button with power and HD activity LED and a PC RESET button. The latter are not connected to the Arduino at all but go directly to the PC motherboard.

pushbutton The reason the other buttons and LEDs are part of the PCB is that I had a handful of Klockner-Moeller illuminated switches. Except that they are not actual switches and they are not illuminated; rather they are the actuator in a larger assembly that includes switches and lamps. Being real industrial controls, these full assemblies are extremely expensive. Also, I am dealing with signal-level voltages and currents and don’t need anything heavy-duty. So I designed my board to sit just under these switch actuators and provided a couple of small tact switches that are depressed when the big button is pressed. In the middle of each set of switches is two LEDs that will fire up through the middle and illuminate the button.

On the lower right and directly above the Arduino are two headers that connect to the relay board. This is where the AC power terminal block is, and where the relays that switch AC power reside. The first three relays are for switching the main power to the lower cabinet and AC power to two different (future) coolant systems. The other two relays replace the original power switch on the mill (it is a DPDT switch) so the controller box will now have control of the mill’s spindle.

CNC mill - relay board schematic

Since my PC board far exceeds the maximum size that the free version of CadSoft Eagle allows, I designed the Arduino board in two halves and joined them together in Illustrator. The large cutout for the E-stop button provided a nice natural break between the two halves. The upper half was also too big, so I designed it with much less vertical space between buttons and simply stretched the image out later.

CNC mill - PC board artwork

Note: if these images look very slightly skewed to the left, you don’t need to check your eyes. My laser printer warps the transparency film as it’s going through the hot printer, so double-sided PCB artwork doesn’t line up when flipped to face each other. So I printed two copies of a square grid and flipped them face-to-face, then measured the offset so I could compensate for it. Now as a last step before printing transparencies, I skew the entire page in Illustrator horizontally by -.179 degrees, and I end up pretty close every time.

Here’s the relay board, and a small daughter board for the USB connector on the front panel.

CNC mill - PC board artwork

Next step: PCB fabrication!

CNC mill phase 2: CAD

With the system map complete and the major components sourced I set about the mechanical design of the enclosures. I originally intended to design and build a custom enclosure for the computer and drivers, out of brushed aluminum/stainless, etc. but came to my senses. Sometimes you have to recognize when to go all out, and when to just get it done. So in that spirit I found a suitable electrical pull box from Automation Direct and probably saved myself a month of fabrication and finishing time. That’s not to say this box will work as-is off the shelf, so there’s still plenty of opportunities to fabricate and modify.

enclosure This is the main two-part enclosure after the extensive modification required to mount the PC and monitor, keyboard and PCBs. Since the enclosure is steel I opted to weld as much of it together as possible in the interest of simplicity. Most of the front panel is cut away for the monitor and keyboard, so the ribs that are welded in also add rigidity. A continuous steel hinge is welded to the front panel and then bolted to the enclosure to join them together.

The touchscreen monitor will mount to the ribs on three sides, allowing the PC components to attach to the VESA mounting holes on the monitor through a simple, flat aluminum bracket. The keyboard will be sandwiched against the inside of the front panel with a flat steel plate.

front panel assembly 1

The interface elements on the right side of the front panel are connected to a large PC board that includes the Arduino and charge pump circuitry. A smaller board isolates the relays, most of which will be switching AC power.

front panel assembly 2

The original concept was to pack everything into the controller box so it would be a standalone assembly, but I came to understand the risk of packaging higher DC voltage components (like stepper drivers) into the same box as sensitive logic-level components (like a PC). So the motor drivers and their power supply moved into the base of the milling machine, mounted to a welded steel assembly that will mount into the base through an opening cut through the back. The pink datum planes in the screenshots represent the interior space available in the upper half of the machine’s base, which is pretty much consumed by the electronics.

lower cabinet assembly

Next up is the PCB design for the interface board in the controller box…

CNC mill phase 1: planning

While I have understood the basics concept of CNC machining–and have utilized it in my work–I never fully appreciated how complex a system a CNC machine is until I set about designing and building one. There are many software and hardware layers are involved in the process, and each of these layers offers nearly endless options to choose from… CAM software, controller software, steppers vs. servos and their torque specs, power supplies, motor controllers, breakout boards, encoders, etc. not to mention the mechanical modifications to the manual mill.

So as a first step in converting my milling machine to CNC I looked at a lot of other people’s conversions with this and similar machines, especially in the copious posts on CNCzone.com and specifically the great work that “Hoss” has done. In the interest of not re-inventing the wheel (for now) I chose one of Hoss’s recommended stepper motor configurations from Keling, and bought his plans for the mechanical conversion from a manual to a motor-driven G0704 mill.

From there I started to sketch out a system map, detailing the wire-for-wire connections between the different components to best understand how this might go together. This also helped me to think through the available options, like physical interface elements such as emergency stop buttons and limit switches.

CNC mill system map

The lower area will exist in the base of the machine and will include the higher voltage DC elements that actually drive the stepper motors. A KL-600-48 power supply provides 48V to the three KL-5056D motor drivers. Control signals from the PC come through a C-10 breakout board, which serves to isolate the PC from the motor drivers. It seems that keeping things separate like this is good practice and tends to avoid funky interference or crosstalk problems with the PC.

The upper area represents a “controller box” which will hang off the side of the machine, and will enclose a small form factor PC, a 15″ touchscreen monitor (eBay!), a ruggedized keyboard, and a small cluster of buttons and indicators. The I/Os will include a main power cord, a ‘switched’ power cord to feed the lower cabinet, a DB25 to connect the PC’s parallel port to the breakout board in the lower cabinet, a DB15 to connect other signal to the breakout board, a series of connections for limit switches, three relay connections to control the mill’s spindle and two different coolant systems, and USB and ethernet ports to communicate with the PC.

CNC front panel

A main switch on the front panel controls the power to the entire system– PC, monitor, and the motor power supply in the lower cabinet. “PC power” and “PC reset” switches are connected directly to a header on the motherboard, as are LEDs to indicate power and hard drive activity. A USB port on the front panel is intended to be the main method of getting files on the PC, as I intend to use a pared-down Windows installation with a bare minimum of extras (like network access).

The remainder of the controls are dedicated to the safety system, which is based roughly on a scheme provided in the Mach 3 documentation but adapted to work with an Arduino microcontroller. The first part of the scheme monitors the emergency stop button and limit switches (what they call the “interface”) to make sure the machine and operator are OK. The second part, called a charge pump circuit, reads a 12.5kHz signal that the controller software produces when everything is functioning normally. These functions are monitored on I/O pins of the Arduino, and if either condition reports a problem the Arduino cuts power to the lower cabinet and the milling machine’s spindle (via relays) and lights the appropriate indicator(s) on the front panel. After a limit switch or e-stop event, the “interface reset” button will give the controller software the all-clear and resume power.

The “motion override” button is one that I threw for my own comfort. Say I’m running a program and it comes to a point where I need to change to a different sized end mill before continuing. The program would stop the spindle and pause and wait for me to go in there with my bare hands to switch out the tool. At this point I’m relying solely on software to keep the machine from firing up the spindle and plunging the razor sharp end mill through my hand and into the table (for example). Not that this is likely, but I don’t trust software… after all, robots will kill you. So the “motion override” button tells the Arduino to cut power to the spindle and controller until I press the button again. I know what you’re going to say… the Arduino that’s in control is also running software. Well, Arduino is benevolent and would never try to hurt me.

With the system laid out and all the components chosen, the next step is modeling it up in CAD.

new workbenches & cabinets

This one has been a long time coming. Ever since we moved into our new house I’ve been slowly turning our unfinished, unheated two-car garage into a respectable workshop… insulation, drywall, lighting, heat, climate control, etc. etc. I’ve put a lot of effort into the “bones” of the space but I’ve been hesitating to start building the work surfaces and storage. IMG_0920 In a way it’s good that it took three years to do this, because in that time I’ve gotten to know the space through cold and hot, from woodworking and welding to painting and machining. I know where the floor gets wet when it rains a lot, and I know where the good light comes in at 7am. While I was still hesitant to commit to a design, I felt that I knew enough to take a best guess at what I need now (and what I anticipate needing in the near future) and go for it. Besides, stepping over and around piles of tools, hardware, and raw materials for three years is a miserable way to work.

For me, the first step for this kind of project is CAD, and this is one of the few things for which I actually recommend Sketchup. In my experience Sketchup is a poor tool for modeling anything with curves or circles, or cylindrical or 3-dimensional surfaces. In most cases I would also prefer feature-based modeling (with a modifiable history tree) and parameter-driven modeling even for simple rectilinear objects. But I’ve modeled my house (and garage) in Sketchup for a few reasons. shop_sketchup_1For one thing I’m not designing my house, I’m just modeling it– I enter a dimension once and I never need to go back and change it. The shapes are all rectilinear, almost without exception, so the surfacing shortcomings of Sketchup are irrelevant. Sketchup has a fairly good set of textures to apply to the model and I like the look and feel as you spin a model around. But I think what sold me–particularly for architectural modeling–is the ability to drop your model into Google Earth, in the right spot. At that point you can see the model in its landscape context and even play with the daylight at different times of the day and year and see how the shadows change, etc. Very cool.

So I settled on an overall size and shape that would be reasonably inexpensive and worked well with my shop layout (also mocked up in Sketchup). The construction is a bit of a hybrid between traditional kitchen cabinetry and a typical 2×4 workbench, with a little of my deck-building experience adding some flavor as well. The benchtop is a single 3/4″ sheet of plywood, supported by copious amounts of 2×4 framing, finished with laminate. The front edge is thickened to 1-1/2″ with a second layer of plywood, overhanging by a couple of inches to allow clamping to the bench, and simply painted to match the rest of the cabinets and drawers.

I copied each of the elements in the Sketchup model and pasted them into a single plane so I could arrange them into 4×8 sheets, trying to maximize the yield of each sheet. I did the same with the 2×4 pieces, and color coded everything so I would know which piece went where.shop_sketchup_2

I chose AC plywood (EDIT: I actually used BC plywood) for cost reasons, knowing I would put the “good” side out and paint it, constantly reminding myself that these are garage workbenches and not fine kitchen cabinetry. Still, in hindsight I wish I had sprung for hardwood plywood, as I found that the AC sheets are not flat, resulting in some poor door and drawer face fits.

Good planning leads to quick progress, and the framing came together quickly. These first assemblies were lag-bolted to the wall using a laser level for positioning, then eventually supported along the floor with small 2×4 feet.

IMG_0921

The cabinets were next, using strategically placed 2x4s for strength. Note there are no “backs” to any of the cabinets (simplicity = lower cost). Next I primed the whole thing with Zinsser B-I-N shellac-based primer, tinted gray to more closely match the final color.

IMG_0964

Drawer bodies are not typically 3/4″ plywood but I found the small pieces were a good use of empty space on my sheets, so it turned out cheaper to maximize the 3/4″ plywood sheets than to buy separate 1/2″ plywood. It is typical however to make the drawer face a separate part, as it makes the final fit & alignment much easier.

IMG_1051 IMG_1052

Doors and drawers were notched for a nice extruded drawer pull, which I bought in an eight foot extrusion and cut to length myself. There was some extra work (and router fixturing) involved in getting the notches just right but I think it was worth it.

IMG_1053

The final paint job was porch & floor paint in an olive-drab green. I left the insides of the cabinets in primer, as I suspect the shellac-based coating will be more durable for horizontal surfaces where things will be resting on it. The bench top is white laminate, which I’ve found is a great functional work surface– you can easily see small screws and stuff and it resists attack from glue and other chemicals. I’ve had similar melamine surfaces on my outfeed tables, which were dismantled to provide their melamine particle board for the shelves inside each cabinet. Generally I don’t trust particle board for shelves, so I cut some 1″ angle-iron, painted it white, and screwed it to the front edge of each shelf to prevent sagging.

IMG_1320

The final product…almost. The trim bit I used to rout the edges of the laminate took a bunch of paint off the front edges of the countertops, so I need to go back and touch them up. Next task: fill up the cabinets with all my shop stuff.

IMG_1386

IMG_1385

This lowered area is for my miter saw, which matches the height of the step in the bench. This way I can let long material run across the 8′ bench to the left.

IMG_1384

makin’ chips

Finally got to making some chips with the mill today. ABS and aluminum scraps with a 1/2″ HSS end mill, just facing the rough edges to make rectangular blocks. So basically turning chunks of stuff into slightly smaller (and geometrically regular) chunks of stuff.

I also tried some simple features like slots and pockets. I’m finding the backlash in the screws to be frustrating– .004″ in the Y axis and .008″ or more in the X. It’s hard to measure the Z but there’s definitely some there too. The CNC controller software can compensate for this, but until then it’s up to me. Also I definitely need to mark the handwheels with which direction they move the table.

I’ve already got some manual milling projects lined up, including the CNC controller enclosure. Still refining the design but I’m getting there. Can’t wait to have a metal-cutting robot in my garage!

our new addition

Oh, and we also had a baby. But even 6-month-old Izzie is excited about our newest shop addition, a Grizzly G0704 milling machine.

I just got it bolted down to the floor and assembled. Next step is the extensive cleanup and break-in, followed by some manual milling to get accustomed to what this little guy can do. Coming soon: full CNC conversion.

Arduino UNO

Sweet!

MakerBot Cupcake assembly

I spent the weekend assembling my new MakerBot Cupcake CNC, which went very well. Of course I had to document the build, so I set up my old webcam on a tripod over the bench and used Gawker to capture a frame every 30 seconds over the 11 hour build:

This is certainly not an over-engineered machine. Rather, it is designed to be just enough — finding a careful balance between cost and functionality — and that is what makes this such an elegant solution. The design of the MakerBot is very clever, primarily using laser-cut plywood that bolts together. The X and Y sliding suspension parts are ground rods and plastic bushings, which is a little loose and may be a source for some inaccuracy… we’ll see when I get it fired up.

finished MakerBot

The best part about the MakerBot is its open-source nature and the community of hackers that are constantly tinkering with it. I can already see room for improvement, and I plan to get busy on it too. For starters, I moved the Plastruder PCB off to the side of the assembly so I can see the mechanism working.

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Also, I cracked several of the acrylic Plastruder parts by tightening down too much on the screws. I might have chosen polycarbonate instead ($$) for strength reasons, but I understand the cost trade-off.

I can’t wait to start making stuff… this is an awesome little machine!

Cupcake CNC transformer

So Make: recently introduced a contest to give away a Cupcake CNC FDM machine kit, and I came up with this entry…

What’s cooler than transformers? A Cupcake CNC transformer with a Bre head? This is a fully articulated assembly that transforms from a Cupcake CNC to a Bre-bot.
I started with a snap-together design (see the attached concept sketches) but migrated to a bolt-together kit or various reasons. The final design allows for fine adjustment of the joint tension so the transformer can stand in any position but still be movable, positionable, transformable!

Buildable in two Cupcake CNC builds (see screenshots), this transformer is assembled with commonly available 6-32 (3/4″ long) flat head machine screws and corresponding lock nuts. NOTE: may be substituted with M3.5 x 20 screws and nuts. 15 sets of screws and nuts are required.

Download the .stl files at Thingiverse.

UPDATE: Thanks a bunch to Frank for printing one!

UPDATE: Here’s another print:

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LED lighting, part 2

tin plated My first attempt at using the tiny Luxeon Rebel LEDs taught me several things, among them how difficult it is to hand-solder them. I also realized that I would need to experiment more with the different white LEDs that are available, or potentially using red green and blue LEDs to produce the white I’m looking for (or a combination thereof). So I designed two new PCBs… a new six-LED board with individual control over each of the LEDs, and a tiny single-Luxeon Rebel breakout board so I can mix-and-match different combinations quickly and easily. To both designs I also added very tiny dots at the corners of each LED location to help position the LEDs. These designs are two-sided, with the back side consisting of a large copper field to help transfer heat to the aluminum heat sink.

I made the boards the same way as before, except that I tin-plated the finished boards with Tinnit to protect the copper from tarnishing and to improve the solderability.

For this batch of boards I decided to finally try my hand at reflow soldering, using the skillet method described by the Sparkfun guys. I bought an inexpensive skillet at Target, an infrared thermometer at Lowes, and some no-clean solder paste. The solder paste came in a syringe package but didn’t come with any needles, so I squeezed a little paste onto a paper towel and carefully dabbed it onto the PCBs with a toothpick. Using a pair of tweezers I placed each LED into position and pressed it into the paste, which held the component fairly well.

Before trying any soldering I looked up the reflow profiles for both the solder paste and the LEDs, and experimented with the skillet to see what settings would yield the target temperatures. I may one day build an Arduino temperature control for the skillet to more precisely control the profile, but I think these reflow characteristics are pretty flexible and for now it’s working just fine.

reflow skillet reflowing

I put the PCBs into the middle of the skillet (I got wildly different temperature readings from different spots on the skillet) and turned it up to “LOW”, watching the temperature with the thermometer. As the temperature leveled off at around 165°C the boards began to smoke and I turned it up to “MED”. Within a minute or so the solder liquified and flowed nicely, in some cases shifting the LED into perfect alignment with the solder pads (apparently a result of the solder’s surface tension).

soldered assembled with headers

I made breakout boards of several different LEDs: “warm white“, “ANSI 2700K white” (an even warmer white), “amber“, and red, green and blue. After the skillet reflowing I hand-soldered on a couple of header pins for the breadboard.

breadboard

This breadboard setup allows me to swap out different combinations of LEDs to evaluate the color of the light (here I have six 2700K Rebels installed). For this mock-up I used a 24VDC desktop power supply powering a BuckPuck LED driver, switched with a momentary pushbutton. I’m getting closer to the color temperature I want, but right now these are all on (full power) or all off. The next step will be PWM control over individual LEDs or groups of two or more to start precisely dialing in the settings.

home carbonation

I love seltzer, but I don’t love spending money on bottled seltzer and carrying 50lbs of it home at a time. I recently bought a CO2 tank and regulator for the keg at Crushtoberfest, and I’ve been looking for other uses for it ever since.

It turns out that making seltzer at home is very easy, and once you have the basic equipment the cost-per-bottle is extremely low. Here’s how I set it up:

home-made seltzer

The tank and regulator kit are from Micromatic. The rest is just a handful of fittings from McMaster-Carr, screwed into a hole drilled into a seltzer bottle cap. Here’s the parts list:

part #
quantity
part source
cost
1 1 5lb. aluminum CO2 tank, empty
Micromatic
$59.95*
2 1 tank filling
local welding supply store
about $10-15
3
1 double gauge CO2 primary regulator
Micromatic
$59.95**
4
3′ red vinyl gas hose – 5/16″ ID
Micromatic
$5.55
5
2 hose clamps (pack of 10) – part #5388K14 McMaster-Carr
$5.28***
6 1 Brass Barbed Hose Fitting Adapter for 3/8″ Hose ID X 1/8″ NPTF Female Pipe (pack of 10) – part #5346K34 McMaster-Carr
$18.95***
7
1 Lincoln-Shape Hose Coupling Plug, 1/8″ NPT Male, 1/4 Coupling Size – part #91455K51 McMaster-Carr

$2.78

8
1 Lincoln-Shape Hose Coupling Socket, 1/8″ NPT Male, 1/4 Coupling Size – part #91455K52 McMaster-Carr

$8.38

9 1 Electric Panel Hex Nut 18-8 Stainless Steel, 1/8″-27 Nps – part #91862A306 McMaster-Carr
$3.11
10
1 bottle cap
your recycling bin
$0
11
several empty one, two, or three liter bottles
” ”
$0

TOTAL
$178.95

* you may need to turn this in for a full tank, although some places will fill your tank while you wait
** I bought a good one, you can get these cheaper
*** unfortunately you sometimes have to buy 10 packs (or more) from McMaster. You can get individual hose clamps from your local hardware store.

Here’s how it goes together:

I drilled a hole in the cap (#10) that was just big enough for the threaded end of the coupling socket (#8) and assembled them together with the nut (#9). I used teflon tape in between parts 6 and 7. I also use my CO2 bottle for a keg when necessary, so I got a second set of part 6 and 8 and attached it to the hose coming from the keg tap. This way I can connect and disconnect from one system to the other.

One thing I learned, and this is VERY IMPORTANT: Apparently there is a chemical reaction between the CO2 dissolved in water and copper (or copper alloys like brass) that creates a toxic substance that will make you sick. Never use brass or other copper-based fittings with seltzer! All of these fittings (or at least the ones that will be in contact with the seltzer for any length of time) are either zinc-plated steel or stainless.

The carbonating process is simple. Fill an empty bottle with the liquid of your choice and refrigerate it. Replace the cap with the special one you made and attach the quick-disconnect hose to it. Make sure the shutoff valve on the regulator is closed, then slowly open the main valve on the tank until the regulator shows pressure. Adjust the output pressure to about 45psi and open the shutoff valve, pressurizing the bottle. Now loosen the cap on the bottle just slightly while squeezing any air space out of the neck of the bottle, then tighten the cap. This will purge any air from the bottle and replace it with CO2. Now shake the bottle vigorously for about 20-30 seconds; this will help dissolve the CO2 into the liquid faster. Shut off the CO2 at the regulator and disconnect the hose from the quick-disconnect fitting. You can now remove the special cap (slowly, the contents are now carbonated!) and replace it with a regular cap.

So on the first day I made seltzer water. On the second day I carbonated apple juice, grape juice, and Gatorade, and ended the evening with a carbonated vodka martini (nice!). What else can I carbonate?

LED lighting, part 1

I’m in the process of designing some new lighting for the house, which I’ll get into in detail later. For now I’m experimenting with Luxeon Rebel LEDs to evaluate the different colors and white temperatures. I started by getting a handful of “warm white” and red, green and blue Rebels. I expected the white ones to be too “cool” in temperature, so the R G and B ones could be individually adjusted to provide some warmth to compensate. I designed a simple PC board that takes three white LEDs and one red, one green and one blue one.

transfer sheet toner applied etch-resist layer

I designed the board in Illustrator and laid out several together on a page, then printed it onto a sheet of toner transfer paper (from Pulsar). I laminated it to a copper-clad board and ran it through again with a “white TRF foil” as an etch-resist layer, as the toner alone tends to be somewhat porous.

etching etched

I then etched the boards with ferric chloride in a Tupperware dish floating in hot tap water in the bathroom sink, agitating the dish continuously.

drilled & cleaned

After about 25 minutes in the etchant I rinsed the boards, drilled the holes, divided them up and removed the toner from the remaining copper with lacquer thinner and a scotch-brite pad. I soldered the LEDs onto the board, along with a female header to connect wires to. For testing purposes I connected two C batteries together and plugged them into the header.

Luxeon Rebels are designed to dissipate heat through a large “no connection” solder pad directly under the chip. There are specific guidelines for the design of the PCB to draw this heat away from the LED which include a multitude of plated vias to increase the copper surface area. I’m unable to create plated vias in my homemade boards, so my intent is to mount the board to an aluminum plate, using an aluminum machine screw to draw the heat through the hole in the middle of the board.

assembled board test run

I learned some important lessons from this first attempt. The main problem is hand-soldering these tiny surface-mount LEDs to such a large copper field, which resulted in a sloppy, lumpy mess of solder. I also realized that I may need to experiment with other combinations of LEDs to get the color right. This first try produced a pleasant white light (and yes, red, green, and blue light does combine into white…I know the theory is fundamental but seeing it happen before your eyes is pretty exciting!) but compared to incandescents and even some of the warm CFLs in my house it still looks very cold.

A good first effort, with room for improvement…

55-gallon drum smoker, part deux

I’ve had some questions about the details of the smoker, so here I’m posting the CAD model and bill of materials as a reference. NOTE: the CAD model is incomplete… I modeled the major structure (barrels and doors) and then ended up building off the cuff as the smoker took shape. Things like the grates, drip tray, feet, hinge and latch locations, etc. were not modeled but just figured out as I went along. If anyone has questions about the details let me know and I can elaborate.

CAD files:
smoker.stp
smoker.igs
wood_rack.stp
wood_rack.igs
charcoal_basket.stp
charcoal_basket.igs

And here’s an unmodified 55 gallon drum model (minus some of the details, like lid and caps, etc.) in case you want to create your own design:
55gallondrum.stp
55gallondrum.igs

Here’s the bill of materials:

quantity
part source
cost
2
55 gallon barrels local junk yard
varies
various
16 ga. sheet metal pieces welding class supply room
$0
≈10′
1/2″ square steel bar (for fire grate) welding class supply room
$0
various
expanded steel sheet (for charcoal basket) welding class supply room
$0
13
1/4″ x 8′ long round rods, 304 stainless (for cooking grates) onlinemetals.com

$78.66

(delivered)

12×12″
18 ga. 304 stainless steel sheet, item #8983K38 (for dampers) McMaster-Carr 

(mcmaster.com)

 

$8.34

36″
maple dowel rod, item # 97015K82 (for handles) McMaster-Carr 

(mcmaster.com)

 

$4.92
5
304 SS hinges, item # 1549A57 McMaster-Carr 

(mcmaster.com)

 

$18.95
3
304 SS draw latches, item # 1889A37 McMaster-Carr 

(mcmaster.com)

 

$15.18
1
quart of Rustoleum High Heat paint Lowe’s
$14.98
1
3″ BBQ/smoker thermometer amazon.com
$21.99
various screws, nuts, etc.

new engine for the snow blower

my new toy Last fall I bought a snow blower that was made in 1974, like me. It’s a 32″ Ariens and it’s big and rusty and awesome. The guy I bought it from admitted it needed a carburetor rebuild, but it was only $250 and I saw an opportunity for a minor project. So I rebuilt the carb, which went pretty well, but it still didn’t seem to be putting out the 8hp it was designed to.

I thought about doing an battery-powered electric conversion, but quickly found that the components alone would run me over $1000. I found a guy in Minnesota that did a cool corded electric snow blower conversion that could be quite inexpensive, but I would really want the portability of battery power.

So I gave up the ambitious plan and bought a replacement Tecumseh engine from  Small Engine Warehouse, which I recommend for this kind of thing. I couldn’t find a direct replacement for my machine on their web site but the guy I talked to on the phone gave me three different options. I was disappointed about the electric plan not working out so I upgraded to this 11hp beast:

the new engine

It took two trips to the local lawnmower place — I couldn’t get the sheave off the old engine and then found the traction belt was worn out — but it bolted right on and fit perfectly, if a bit tighter than the old one. We still have some snow on the driveway so I took it for a little test spin. I was expecting to be launching snow onto the neighbor’s house with all that extra horsepower, but the snow is now icy and chunky so I wasn’t getting the distance I was hoping for. Next fresh snowfall I’ll see what this baby can do.

first test run

A few photos from Crushtoberfest ’09

image002

The Selleck Striker ready for action.

image003

Lisa about to show it who’s boss.

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Beer pong!

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That’s a lot of facial hair.

55-gallon drum smoker

This past fall I took an evening welding class at a local technical school and got very excited about making things out of metal. I already had an old stick welder that I didn’t really know how to use, and I ended up buying a MIG welder–the Hobart Handler 140 from Northern. After making lots of small assemblages out of scrap metal  I managed to build a stool and a couple of plant stands, but I had bigger plans.

There’s something special about creating useful objects. A smoker is a nice combination of supremely useful (preparing sustenance) and slightly frivolous (do you need a smoked pork butt to survive?). There are certainly faster and more efficient ways to cook food, but damn smoked meat is good.

I looked around at commercial smokers and custom hacks and talked to a few connoisseurs, and decided the Weber Smoky Mountain was a good design to start from. It’s simple and effective, and in the end it mostly convinced me that the design need not be complex.

Something appealed to me about using the iconic 55-gallon drum as a building block, so I went out and bought a couple from the local scrap yard. One of them even got immediate use as a beer barrel at Crushtoberfest!

A little sketching on different configurations, and I decided a ‘T’ shape would be simple, stable, and functional, and provide plenty of opportunity to practice the MIG on some thin sheet metal. I laid it out in CAD, which made it easy to generate the intersecting curve between the two barrels.

I printed the curve at full scale and wrapped it onto the barrel, traced the curve, then cut the barrel with a jig saw. The first dry fit was amazingly close (way to go, CAD!) but there was still a lot of grinding here and there to accommodate the ribs in the barrels.

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I measured and marked the door openings on the barrels and cut them out with the jig saw.

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The next step was grinding the paint off. The last thing I wanted was burning paint fumes getting into the food, so every bit of paint needed to go. If I were to do this again I would find another way… sand blasting, chemicals, burning it off, etc… anything but taking it off little by little with an angle grinder. I’ll admit the Gator brand paint & rust remover discs I found at Lowes were very effective (if a bit pricey at 9 bucks a piece). But my shop is now coated with a thin layer of green paint dust, much of which ended up in my nose and likely my lungs.

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On the first day of grinding I wore a respirator and glasses but nothing else. After washing my hair three times in a row to get the paint dust out I learned to don more protection. For the insides of the barrels I also used an LED headlamp.

As the barrels were made of surprisingly thin metal (20 gauge) the door openings needed to be reinforced with some angle and rolled sheet metal strips, which were plug welded from the outside and tacked from the inside.

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The doors also needed reinforcement, in the form of sheet metal ribs tacked onto the undersides.

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I welded small pads onto the barrels and doors for the stainless steel hinges. These pads were ground flat then drilled and tapped.

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After grinding the rest of the paint off I welded the two barrels together. This was a challenge, since the metal was so thin and the fit was far from perfect. To prevent burn-through and warpage I used a “stitching” technique where you put a quick tack weld across the joint, wait a second or less and put another tack next to it, continuing like that for about an inch at a time. Apparently this puts less heat to the metal than a continuous bead, but the end result looks very similar. With a little practice I was even able to bridge relatively large gaps between the barrels with short, controlled beads that build on each other, kind of like ants crossing a stream.

IMG_5078 IMG_5079

I shopped around looking for off-the-shelf replacement grates that would work but none of them were big enough for this guy. So I bought about 80 feet of 1/4″ diameter 304 stainless rod (from onlinemetals.com) and cut it to length on the abrasive chop saw. I scored a piece of 1x pine on the table saw at the proper spacing to use as a jig, and clamped the rods down. The MIG would have been perfect for welding the grates, but I would have needed to buy stainless wire and a separate tank of tri-mix gas (65% argon, 33% helium and 2% CO2). The stainless itself was already pushing my budget, so I bought a handful of stainless welding rods and used the arc welder.

IMG_5080 IMG_5081

Next I drilled holes for the dampers– two sets of three holes at the top and two sets of four holes the bottom. The top ones were made like typical grill dampers with a round rotating plate. The bottom ones needed to be on a curved surface, so they slide along the surface rather than rotating.

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In both cases the moving damper is retained by screws, so I drilled holes and tacked some steel nuts behind them.

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I then drilled a series of holes to allow the smoke and heat into the top barrel. My step drill bit did an amazing job, but the cordless drill still went through two fully charged batteries getting the job done.

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Next I tacked on some small support tabs for the grates and six small sections of square tube as feet.

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After a thorough deburring, wire-brushing and degreasing with alcohol, I set about applying a high-temperature grill paint. There are several available but Rustoleum High Heat Brush On was a) available at Lowes and b) didn’t require curing at a high temperature like most of the products I found online. Unfortunately it only comes in black, which is actually slightly brownish. They recommend only applying one coat, which I agree with after trying to touch up a few spots after drying, resulting in some weird gloss differences. I then tried the spray can version of the same paint, but found it to be flat finish (vs. the brush-on which is satin). The lesson here is get it right with the first coat because you really can’t go back and hit it again.

IMG_5108 IMG_5110

While the paint was drying (24 hrs… it’s oil-based) I fabricated some handles out of a 1″ maple dowel. I don’t have a wood lathe but the metal lathe did the job. A few coats of Polycrylic and they’re ready to assemble.

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The smoker can be used in one of two different ways– with charcoal in an expanded metal basket or with wood on a traditional fireplace grate. I suppose I could retrofit some gas burners or even electric heating elements, but that’s a project for another day.

IMG_5128 fire_grate2

And last, final assembly. I bought a 3″ smoker/grill thermometer online, and used some nickel-plated chain for the lid stays. I also fabricated a sheet metal “drip tray” to cover the holes under the food and deflect some of the heat.

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I figured my brother-in-law Pete would make much better use of this than me, so we gave it to him for Christmas. Here he is opening it…

Pete getting his present