This pandemic isn’t going away, so I decided to try a careful return to the workshop a few weeks ago. I cycle to and from, so there’s no public transport, and once I’m there the only sticking point is the shared toilet, but overall it’s been going well. I don’t have a lot of work on at the moment, and I’m not keen to take on any big orders right away only to find a problem with a supply chain or something, so I’ve been working on an infrastructure project I’ve been meaning to do for a while; an improved roll bender.
I have a tiny roll bender, one of the common Chinese ones that will do a maximum of 25x3mm flat, or about 6mm round bar. It’s really good for this smaller stock, but I wanted a bigger one. Bigger ones are catastrophically expensive, or not very good, or both, so I decided to try and build one. I wasn’t much good at fabrication then, and this is what I ended up with:
look at this nonsense
The lower carriage would balance precariously on a 2 tonne bottle jack, while the upper bearings were static. Sound in principle, in that the two lower rollers moved in opposition to the upper roller, but the span of the upper shaft was far too great, and given the poor alignment I achieved when mounting the bearings, under pressure the whole thing would twist, which will probably result in rolling a helix or something rather than a circle. It did manage to do this to a piece of 40x10mm steel flat bar, though:
“I’m straight.” “So is 40x10mm steel flat bar until it gets rolled into a semicircle by a questionable machine”
Anyway, it didn’t work very well and then it sat under the welding table for a couple of years, unfit for purpose, before I decided building a new one would be a good project to get me back into the workshop life.
Day One
The first thing I did was to take all the bearings off the original machine, and clean them up. These were the only part I paid for (I think it was about £80 for all six); the rest was all made from scrap I had lying about.
Then I had a dig through the steel I had on hand to see what I could build the new machine from. When I built my welding table, using 150x10mm flat bar slats for the top, I ordered ten lengths from my supplier, but two of the ones I got sent were badly bent which is no good at all for a welding table. My supplier sent out some replacements, but didn’t want the bent ones back. The bends in this case were perhaps 3mm out at most, so they were still usable for less critical applications, and I put them to one side. Now their time had come. I also had some 40x10 and 50x10mm flat bar, though not enough of either to avoid having to mix and match. I did some cutting, and laid the bits out on the table to get a rough idea of how it would all go together.
the red thing is the bottle jack that will provide the bending force in the finished machine
I wanted to have two possible positions for each of the lower bearings, to allow for a greater range of radii that I could bend things to. Meanwhile the two upright bars would provide a track for the upper shaft to ride in, and be in tension as the bottle jack pushed the upper bearings down. I ground some bevels on the ends of the uprights for welding, and then started marking out and drilling the holes in the lower plates. To make sure the hole pattern aligned correctly in both parts, I tack welded them together and drilled through them both at once.
The bolt holes for the lower bearings, plus the pilot holes for the shafts.
I now needed to drill clearance holes for the shafts, but for that I needed a 26mm annular cutter, which I didn’t have, so I drilled out pilot holes and left it there until I could order the cutter.
I then made up the plate that would hold the upper bearings, and against which the bottle jack would push. From the previous bender I had two pieces of plate with holes drilled to accept the pillow bearings, so I just took those and welded a new plate between them to make them into one piece.
the upper bearing carriage ready to be welded up
That was about as much as I could do without the annular cutter, so I ordered it, did a test fit of the bearings, and left it at that for the day.
the upper bearing carriage with bearings in place
Day Two
With the new annular cutter ready to go, I got started drilling out the clearance holes for the shafts (in the front frame only, since I only need to be able to remove them in one direction). I then drilled smaller holes concentric with the shafts in the back frame, for pushing the shafts out from behind, and also some central holes near the top of each frame which I then cut out into slots, which I would need in order to bring the carriage down far enough to bend tighter radii.
H O L E S
Next, I clamped everything in place, and welded in the uprights, taking care that the uprights on each frame lined up with the other, and had a consistent gap between them, to allow the upper shaft to move freely up and down, but not side to side.
the two frames- note the narrower 40mm flat bar for the front uprights, vs. the 50mm in the back
I wanted some kind of support to stop the uprights flexing side to side, so I dug through my scrap pile. I found some scraps from a job where a customer wanted a mitred frame made from 150x12mm flat bar, so the 45 degree offcuts were just right after a little neatening up. At this point I decided to put the shafts in place, and the central carriage, for a test fit:
the carriage is resting on a scrap of flat bar resting on the lower shafts, which is what you see sticking out at either side
Everything fit very nicely, which was tremendously pleasing, so I cut some more parts- two end pieces to join the frames together on either side of the base, and a few bits of angle and some channel to form the top of the frames, which the bottle jack will push against. The angle I welded in place, but the channel will be bolted- once I’ve rolled something into a circle and the ends meet, I’ll need to be able to remove it from between the frames.
And that’s where we’re up to! Next time, I’ll bolt the channel in place, build the mount for the bottle jack, as well as for a return spring, cut a keyway in the central shaft, make some dies, fashion some kind of handle to drive the whole thing, and start bending!
everything in its right place
once the carriage and jack are in, this will be the last thing the steel sees before it stops being straight forever
Part 2 is now here.