[rp74]

See attached, brake backstop mod for my G0556.

Alu is 6061-T6 cut on my CNC'd Sieg X2 mill. Guides and strips are teflon. Brass threaded rod ends were turned on my mini-lathe.

The goal of this mod is to provide precision positioning of material. It's square, and depth is adjustable. I have a screw for setting mechanical zero.

I looked around on the 'net for adjustable backstops with some kind of accuracy, all I found were huge CNC-controlled shop presses.

[doorknob]

I'd be interested in hearing more about how you built this (and perhaps a photo of it in action, and/or more of an overview photo or diagram about how it works).

I have a larger brake (still in the shipping carton) and have wondered how to get precise and repeatable operation from it, and it looks like you may have an answer.

[rp74]

Here's a bit more info...

In the pictures, the backstop is sitting on a piece of alu sheet to keep it from scratching my desk - not a part of the backstop.

In this image, the sheet extending farthest left is the backstop, an edge to butt sheet up to. It's cut down to .040" thick on the end to fit under the fingers of the brake, as I intend to a good bit of short bends in .040" alu. The sheet I'm using is .080" thick, and is used on the top, bottom, backstop, and scale bracket. Under the backstop sheet on the left you can make out 3 of 4 holes that will mount this to the brake.



This end is to be situated farthest from the brake fingers. The bar stock between the top and bottom plates is .250" thick, 1" tall, and about 3.2" wide (about the limit of my Y axis ballscrew using a 1/8" end mill). I have a small flanged bearing situated on each end of the threaded rod - I left enough room in the top and bottom cap screw holes through the plate to snug up the bearings against the turned rod ends. This end of the brass threaded rod will get a knob once I cut one. The holes left and right are from fixturing when cutting out the part. Here, you can see the white teflon rails and adhesive strip that the backstop plate slides in. The teflon rails are held down with strips of .080" alu sheet. Screws are 4-40 all around, except for the two 8-32 screws holding down the scale.



This is a side view. You can see the brass threaded rod, this is turned on both ends to fit the flanged bearings. If you follow the brass rod to the left, it meets a nut press-fit into the follower block (.250" thick plate). The follower block is mounted with countersunk screws underneath through the sliding backstop sheet. The top of the follower block mounts to the scale. In the top left in this pic, you can see the black plastic of the scale and the .080" thick scale bracket and one of the two screws that mount this bracket to the scale.



In this view, you can see two of the holes that will mount the backstop to the brake on the bottom sheet, these still need to be countersunk. The backstop plate is situated between the teflon rails. You can see the edge of the bearing with the brass rod through it. The horizontal screw under the top plate is a zero stop, this is to be used to set mechanical zero of the backstop, right up to the edge of the bend on the brake. The scale will show length of the brake-clamped side of the bend. You can see the follower block protruding through the slot in the top plate, mounted to the scale bracket with one 4-40 screw.



Materials:

All screws are 4-40 except for the 2 screws that mount the scale to the top plate. Screws holding strips down on the teflon rails are threaded into the bottom plate, these are .5". The rest of the 4-40 screws are in tapped holes and are .250". Where screws pass through, a .125" end mill was used to make the hole. Otherwise, the appropriate tap drill bit was used.

The two screws that mount the scale are 8-32, about .5" (too long but not a problem).

Aluminum used is 6061-T6 throughout, using .250" thick plate on the follower block and the two end blocks. All sheet is .080" thick alu.

All .080" sheet was 3.5" x 7.5'", some parts were right up to the edges of the material.

All .250" parts were cut from a 1.5" x 12" bar.

Threaded rod is brass, 1/4-20 thread, ends manually turned on the lathe.

The scale is from Shars.com, it's a horizontal scale.

All alu parts were CNC'd on my Sieg X2 mini mill, most of the work was done with a .125" carbide 4 flute end mill, the rest was a done with a countersink bit and a few drill bits.

Why I Did This:

I tried bending aluminum by hand, but I didn't get the results I wanted - cracks, splits, etc. Short bends were difficult to make square. I bought the G0556 to get better bends, which it does. I was using a fixed backstop: I mounted a plate to the brake, then clamped a bar to the plate to reference the back edge of the material being bent, then I used spacers from the known position of the bar to get the required distance from the bend. This was tedious and problematic. So, I came up with a design for a slide and a scale - and that's what I have here.

Some Build Info:

I left about .002" of vertical room between the teflon rail and the adhesive teflon strip for the sliding plate to slide nicely, this worked out well. For side-to-side adjustment of the rails, the .125" holes for the 4-40 screws left plenty of adjustment room.

When I cut the teflon rails, I surfaced them with the same bit I used for notching the rail (inverted from position in the pics), leaving a precise notch for the sliding backstop plate. I measured the thickness of the teflon tape without backing and compensated for this depth and the thickness of the backstop plus .002" when I cut the notch in the rail.

The nut in the follower block was press fit, I undersized the hole in the alu block by about .015" in radius. I pressed the nut into the block in a vise, and used a socket to recess it slightly (it's a bit less than .250" thick). The alignment of the nut was adjusted by inserting a 1/4-20 screw (not the threaded rod, it's too soft) and pushing into position such that the nut wouldn't bind on the threaded rod once installed on the slide. This was tested on the slide until it was good enough.

There is some backlash, but this is to be expected - 1/4-20 isn't really meant for linear actuators. The only caveat is to approach the bend as a last adjustment to elminate the affect of backlash. The backstop is quite rigid as tested by pushing on the stop and watching the scale after setting a position - the most I've seen is .0005" of movement from the scale.

In total, there is 4" of travel. With the backstop mounted with full extension right up to the bend, I am set for a maximum of 4" (with some adjustment room) of sheet length clamped in the brake. The backstop is 2" wide, which is sufficient for the work in my immediate future. If I need a wider backstop, I could go back and mount a bar across the end of the backstop sheet.

The backstop plate was fully cut from 3.5" x 7.5" sheet, it is perfectly square. When mounting this mod to the brake, I will make sure to keep it square to the bend.

One last comment - on the G0556, there is a flat bar built into the brake that acts as the clamping surface. This mod was designed to reach over that bar up to the actual bend. The mod itself is to be mounted behind the bar.