DIY tube-bending tool
Saturday, 19 January 2013
My plans for the milling machine oiling system call for some small-diameter bent brass tubing. I looked into the various tools designed for this, but the high end is too expensive and the low end looks pretty cheesy. I also wanted a small bend radius, which is hard to come by in off the shelf tools. It seemed easy enough to design a simple bending tool, and besides there’s nothing I like better than making stuff that makes other stuff.
My tubing has a 3/16″ OD and I was aiming for a 3/8″ bend radius (to the centerline of the tubing). I only anticipate needing 90 degree bends, but it didn’t seem any harder to allow for 180 degree bends. With these parameters I modeled up a simple design in CAD and ordered a few pieces of brass and steel from onlinemetals.
The first step was to grind a lathe tool blank to a 3/16″ diameter half-round shape. With this I turned some 3/4″ brass round rod into a set of rollers that closely fit the 3/16″ tubing.
I then milled the end of a 4″ length of 9/16″ square brass bar to accept the smaller roller, and drilled it for a tight fit to a 1/4″ dowel pin (1″ long).
I then drilled two 12″ lengths of 1/8″ x 3/4″ mild steel to accept the two rollers and welded two more shorter lengths of steel to create a rectangular tube handle. Done and done!
The square brass bar is clamped into the vise, and the tube to be bent is gently clamped to the brass bar with a rubber-jawed clamp. The first test worked perfectly!
The bends aren’t perfect– there’s a small amount of collapsing, probably from the small bend radius and the imperfect roller profiles. But I sawed through one of the bends at the thinnest part to see how much collapsing there was, and I think it’s acceptable for my needs.
Here is the collapsed section (top) next to the normal tube section for comparison. Not bad!
Next step: experiments in brass soldering.