A bending question

S

spike7638

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I need to make a piece from 1/8"-thick x 1/2" wide stainless bar. Here's what it looks like:
PXL_20220620_004849095.MP.jpgPXL_20220620_004845103.MP.jpgPXL_20220620_004906628.jpg

I need to duplicate this, except that the overall distance between the hole-centers needs to be 1/4" more than it is now.

The locknut attached to the back? I can do that with some JB-weld. The holes? No problem there, either, esp. since reading a discussion from H-M about how to use center-drills better.

But that zig-zag bend has me troubled. There's a bender at the shop, but it's for sheet-metal, and can't handle something like 1/8" stainless. There are a couple of arbor presses that I could use, and I've even got a 20-ton Harbor Freight hydraulic press at home ... but I don't really know how to use them to get what I want.

I figure that I can take a scrap piece of steel and cut a notch, rotated 45 degrees, making something like a vee-block. Then I can put my stock on top of it, and then put a rod on top of that, and press down on the rod so that it pushes the stock into the vee to get a decent bend. But then I need to flip it over and bend the OTHER way, and I don't see how to do that without interference with the rest of my "vee block".

There's also the challenge that the amount of offset is critical. It should be 0.5", although 0.45" would still be OK, I believe. More than 0.5" would be bad though.

The good news is that I have a fair amount of stock to practice with, and I figure I'll make the bends before drill the holes, etc.

Can folks suggest how to make a reliable amount of offset, and how to make the "zag" after I've made the "zig"?

By the way, you can see that this zig-zag isn't exactly 90-degrees -- more like a pair of 120-degree angles. And in fact, those angles aren't at all critical. I'm not sure whether that helps or not. I'd like to think that if I bent it 90 degrees, and found the offset was 0.6", I could "unbend" a little and make it 0.5, but my experience with work-hardening of stainless is that this will be more or less impossible.

BTW, the stainless I've got says "T-304L".

My gratitude in advance for any help folks can provide.
--John
 
I would machine a die with the z bend in it.
a top and bottom that matches but allows for the material thickness + 10 thou.
The die would have a landing cut in it for the start of the piece to butt against so it doesn't move out of position.
I would use some dowel pins to make sure the 2 dies line up.

Then I would press it in your hydraulic press with the material loaded.. I would probably lubricate the surfaces so the metal could slide a bit into position.

that's how I would do it.
 
As you have found out, it's not easy to make a shape like that with just a bench vise. The factory probably had a jig made for it.
What you can do, and I've done, is to make the first bend toward you at 90 degrees. Then loosen the vise and lift the part up a certain amount, then reclamp.
Now take a piece of flat steel and hammer underneath the bend away from you so that the piece rises to a vertical position, then you have your S shape.
You'll have to experiment with how much to lift the part after the first bend.
-Mark
 
Thanks to everyone for your ideas. They've all given me something to think about for later similar challenges

benmychree: The "solid block" approach would have been great...if I had the solid block to start with. But since I'm hoping to get this made today, I'll have to use a different approach.

Nutfarmer: Bend first, then locate was definitely my plan. The JB-Weld is a good-enough solution here, while my welding skills are at best laughable, which is why I'm going that route. (Also: that nylock nut might not survive the heat of welding, at least not the nylon part of it!)

markba633csi: Your plan sounds like one that's worth trying to get the job done well enough, and done today. I think that getting the right amount of offset is going to be a challenge, but that's life.

woodchucker: I really like this plan for its precision and repeatability. If I needed more than two of these things, I'd definitely go with this approach, and refine the die until it was exactly right. I suspect that was what the original manufacturer did. The key insight here (from my point of view) is that you can sometimes do two machining operations in a single step, which I'd never considered before.


--John
 
Make a piece with a step the size of the joggle offset. Cut the corners off as shown @ 45 degrees. Cut it in half to make a punch and die. Press the strip to form the part. Cut part to length and drill.
The two parts will align as pressure is applied.joggle.jpg
 
I make offset bends like that in a vise with two pieces of bar stock. The thickness of the bar stock is equal to the amount of offset. I make up a sandwich of the three pieces , allowing enough material for the bends and tighten the vise. Not quite as precise as what @Parlo is suggesting but the same effect and quick and dirty. Having the hydraulic press will make the job easier.

I wouldn't use JB Weld alone for fixing the blind nut. If you ever have to remove the fastener, it will break loose and if you haven't access to the nut , it can ruin your day. If you have access to the nut, just forget the JB. If not , a captive nut would be preferred. Another approach could be to mill a shalow groove, the width of the nut flats to prevent the nut from rotating. JB can then be used for holding the nut in place.
 
you have a sheet metal bender. no reason it would not work for something that small. i bend 1/4" on my diacro 16 ga bender (small pieces of course)
 
I would make one bend, machine the bent leg to get the necessary offset, then TIG weld a straight tab to the the bent leg. But that's just me, I machine better than I weld and I weld better than I bend.
 
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