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.

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…

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

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!).

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)

Operational!

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.

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.

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.

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

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.

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.

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.

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.

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.

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).

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!

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.

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…

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