A scroll bender has been on my list of tools to acquire for quite some time. I have looked at all manually operated ones available to the home guys and those on a budget. They all operate pretty much the same and involve no more then bending some flat, or round bar, around a scroll die. I keep waffling between purchasing one or building one. I think the biggest challenge with building one is constructing the die itself as you will see if you read on.
Normally I start my posts with an introduction, continue with the build, and finish with the result. Well sit down and hold on cause today I am switching it up! Let’s start with a video shall we? I’ll show you what I came up with and then you can decide if you want to read on. The following it a video I shot after building my own version of a scroll bender. I bent a ½” x 1/8” piece of hot rolled flat bar. Take a look.
So now on with the build. What was the criteria? Well I wanted it to be a universal contraption. I didn’t want to build something dedicated to one die, I wanted to ensure I could switch things up if need be. I also wanted to keep my working envelope clear. Many of the commercially available scroll benders use a T handle attached to the center of the die to allow the operator to turn the die. I wanted to come up with some way to keep things as clear and open as possible.
So I started to rummage around to see what I hand kicking around for metal. I had section of 3” x 1.5” x .065” rectangular steel tubing as well as some old bicycle gears and a chain. I was also able to dig up an old broken ½” ratchet extension that may come in handy. Looks like I have everything I need except for a couple of 5/8” flange bearings as with some 5/8” drive hubs. A trip down to the local supplier got me the remaining components and I was good to go.
So as you can already figure out from the video I had planned to integrate a countershaft to drive the main shaft with. I used a couple of sprockets off an old bicycle cassette and machined a couple of drive hubs down to fit the sprockets. The sprockets then got TIG weld tacked to the hubs. The welds were laying on so nicely that instead of tacking the first sprocket I ended up running a complete bead around it. Mistake…I should have known, the sprocket looked the taco’d front wheel of my mountain bike after I hit that tree last year. Yeah…too much heat for the little guy to handle, it had no choice but to warp. No problem, lots of cassette gears to spare. I machined the wavy sprocket off and tacked on a fresh one, much better. As far as gearing went I did not get too scientific about it. The benders typically use a 1:1 ratio coupled with a Tee handle. The tee handles are not huge as there is not a large amount of mechanical effort required. I used a 24 tooth for the drive sprocket and an 28 for the driven giving me an overall 1.16:1 ratio. I figured going just under a 1:1 would be more then sufficient.
In order to drive the gearing I opted to adapt a ½” extension onto the drive gear mechanism. I had an old broken ½” extension laying around so I machined down the extension to fit into a machined 5/8” hub. The two were married with the TIG welder officiating. The drive hub now joins up with the drive gear via a 5/8” keyed shaft.
With the gearing and the leverage taken care of it was time to move onto the die making. I was going to have to support the dies as well as build something to allow me to use different tooling. I opted to build a 9.5” diameter 3/8” thick base plate. This way I could drill holes into the plate as required to accommodate different dies. The base plate was plasma cut from a scrap plate using my homemade circle cutter. The edges were cleaned up and a 5/8” hole was drilled in the center to allow the plate to rest on top of the 5/8” driven shaft.
The dies were next and these proved to be a huge challenge. I do not know of a way to mathematically build a scroll in AutoCAD, I am sure it is possible except I do not have the know how. I ended up finding a picture of a scroll that I was able to enlarge on paper and the cut it out to act as a template. It took a lot of staring before I could figure were to cut the scroll in half to allow it to be used as a 2 piece die. There was also a certain amount of guess work when it came to building the die to allow for proper clearances of the scrolled flat bar.
Using a ½” thick plate I traced out my scroll die, grabbed the plasma torch, took a deep breath and started blowing out molten metal. My initial plan was to build an MDF template as a guide but in the end I opted to free hand the scroll cut. When cutting ½” steel I have a little more time when handling the torch as opposed to sheet metal. The cutting is much slower in the thicker material which gives me more time, and better control, of the cut. With the scroll die rough cut by hand I then chopped it in half and trimmed the larger die to allow for bent flat bar clearance.
I worked the die edges over with both the 4 ½” grinder as well as the belt sander. It came out fairly round however it did have a few flat spots. To look at the die it was fairly obvious that it was not CNC, or machine, cut. I figured the few flat spots would not create too much of an issue. Well I was wrong…more on that later.
So I need to somehow connect my starter die with my 5/8” keyed shaft as well as construct a way to hold my flat bar in place while performing the bend. I used another hub and cut out a ½” x 1/8” wide slot in it to allow me to hook the flat bar into it. I was able to TIG weld the hub onto the smaller die section.
Next it was time to attach the 2 dies to the base plate. The smaller one got a 3/8” hole drilled through it and then a threaded hole cut into the base plate which would allow bolting of the smaller die to the plate. The larger plate was going to need to be installed, and removed, quickly and easily as to allow for quicker rolling of the scrolls. I opted to press in two 3/8” cold rolled pins into the die and then drill mating holes for the pins to drop into onto the base plate. I allowed for a little bit of slop to ensure no binding, or prying, would be required.
Last component on the agenda was a support roller to allow the flat bar to bend. I dug through my junk and came up with an old timing belt roller, perfect! It had lots of height to allow for larger flat bar plus it wasn’t too large in diameter. I machined a steel spacer for it to bolt onto therefore allowing free movement of the roller. A hole was drilled in the steel rectangular tubing base to allow for mounting as close to the 9.5” base plate as possible. I ended up using a 5/16” threaded rod to secure the roller, unsure if this will be heavy enough.
So with all the components fabricated it was time to put the bender to its test. With it clamped down tight in the vise I went and found myself some scrap ½” x 1/8” hot rolled flat bar. Using a 48” section I marked off a tick at every 6 inch increment. I wanted to know how many inches of bar was required to make the bend. I proceed by placing the flat bar end into the center hub notched section and started cranking on the ½” ratchet. Effort to bend was incredibly light, no issues there. The actual shape of the flat bar with the starting bend? Not so great. The flat bar would not make a tight enough 90 degree bend at the center hub slot to allow it to tuck up nice and tight to the first die. Ok…I guess the bending will require a 3 stage process. Round number 2. I started off this time by bending a starter 90 degree bend into the end of my flat bar. All I did was clamp it down in the vise and, using a hammer, gave myself a clean, crisp starter bend. Back to the scroll bender and with my flat bar locked in place into the center hub I started cranking. The bar hugs the die beautifully, in fact too well.
Earlier I was whining about how I had flat spots in my hand cut dies. Well I thought that the spots may go unnoticed in the bending process. Turns out I was wrong. The flat bar hugs the dies so tight and close that every imperfection in the dies become evident in the finished bent scroll. So now what? I suppose I have a couple of options. First one is to build up the low spots with the welder and then keep smoothing the curves out by hand or get the dies CNC cut. For now I will opt for the cheaper of the two options and spend some time reworking the dies. I suppose I could still go back to my original idea and build an MDF template as a guide. Either way I will try and perfect the process in house first. For now the tool functions fantastic, no mods required. Once the dies are sorted out things are good to go.
As far as the completed scroll goes it used right around 30 inches of material. There is some spring back experienced, this is expected, however it’s not a factor. I am unsure if I am happy with the actual shape of the scroll, it looks a bit too uniform. I think it needs to be a bit tighter around the first die. Anyway…I would call my first prototype a success. I will continue to improve and hopefully come up with a solid method for building dies.