A No-Mar, Low Stretch Bending Fixture

[Nakedanvil - Grant Sarver]

Making a simple rolling die fixture.


Probably the first thing people build after they get their press going is a little “V” bending fixture. Usually weld a couple angles or round bars down and press stuff down in between them. First thing they notice is the backside gets a little scarred up. Next they notice that the material stretches out thin around the bend. Usually they just chalk it up as normal evils of the process.

Well, I pondered this back before a lot of you were born. Here’s what I came up with. If you look at the drawing you’ll see it’s simply a box frame with two half-rounds captured. It consists of a four-sided frame with a floor. The half-rounds just sit loose inside the frame. Spacers are shown, as sometimes you need to make width adjustments depending on work thickness, the diameter of the half-rounds or the bend radius (you move them apart for larger radiuses). You should be able to understand from the drawing.

This method produces three benefits that I’m aware of. One, the backside of the work stays perfectly smooth, even round bars have enough bearing to avoid flat spotting almost entirely. Two, the work doesn’t stretch as thin in the corner. With the angle setup, when you start pressing, the part digs in to the angles hindering it from sliding and scarring the backside. The rolling dies move with the work. Third, it effectively increases the power of your press, really! The rolling blocks “give way” as the ram advances requiring a relatively longer stroke. The same force applied over a greater distance is the principle of leverage.

I used to have a setup like this that consisted of a box fabricated from 2” plate and was about 24” square. The rolling blocks were 10” diameter. With this setup in my 100-ton hydraulic press I could bend really heave stuff. One time I (hot) formed 4” 4140 24” wide on a 2” radius nearly 180 degrees. Ten years ago I was getting $400.00 each for those. A similar setup for a small press might use a box six-inches square with 2” half rounds. Really worth taking the time to fabricate one of these. No reason a guy couldn't make a miniature setup for a small press either. Note that the one pictured uses a loose round bar in combination with a shallow "V" top die. Full round bars can also be used to advantage in the box as they will also rotate, unlike the welded down ones.

EDIT: The thinning in the bend that you get bending round stock is mostly on the inside caused by the "pusher" tool. Best way to minimize thinning on round stock is to use an inside form tool like they use on pipe benders to cradle the work.


Just a little bit of the “S.T.O.C.K.”*


*(Stuff The Old Coot Knows)

Edited June 24, 2009 by nakedanvil

[jeremy k]

Grant - I've seen those in the fabricator magaizine (for large presses) - I bet they do work swell. - Do you need to have them oiled or greased on the bottom of the half rounds so they don't stick? or is it not a problem? - JK

[dablacksmith]

good idea! i dont use my flypress for bending usually but that looks slick!

[Nakedanvil - Grant Sarver]

jeremy k: Yeah, them %$#@$'s copied my idea! Pretty hard to come up with anything that hasn't been done before. I build 'em quick and dirty, and yes, lotsa smokin' grease. That why I use bacon fat in the shop!

[Frosty]

Bacon fat . . . Mmmmmmm.

Slick bender. Another STOCK idea for the book.

Thanks Grant.

Frosty

[Nakedanvil - Grant Sarver]

You sound just like Homer Simpson! Bacon fat. . . Mmmmmmm. Doesn't lubricate all that well, but it sure do smell good!

[Charlotte]

Thank You! Just added that to my enormous list of really great things that I wish I'd thought of.

[Frosty]

You sound just like Homer Simpson! Bacon fat. . . Mmmmmmm. Doesn't lubricate all that well, but it sure do smell good!

You do keep up with the times don't you?

Bacon makes ANYTHING better.

Frosty

[AndrewOC]

Ah youse Americans and bacon!

Great idea Grant, thanks for posting it. The workshop i work in has a 60 ton hand pumped hydraulic press, i'll eventually build one for it. What thickness steel would you suggest for the floor and sides of the box? It would be used on top of a platen thats 'bout 1-1/8" thick.

Ta
Andrew O'C

[Nakedanvil - Grant Sarver]

Oh heck. I usually just overbuild things. 1" would probably do fine. Hey, wait a second, I thought you guys dint use "imperial" measure.

[AndrewOC]

Hey, wait a second, I thought you guys dint use "imperial" measure.

Ah we have split personality when it comes to adopting standards of the world! Part of the psyche. I've had bit of an Imperial measures morning.

And yes 25.4mm plate would be easier for us to find

regs
Andrew

[arftist]

Grant, thanks for taking the initiative to post this and other original ideas.

[nuge]

That's a gem, thanks.

[Nakedanvil - Grant Sarver]

AndrewOC: 25.4?? Sounds like "soft" metric conversion to me.

[JNewman]

Here is a picture of a top pusher tool that is contoured to the round bar that it bends like Grant describes. Above it is the bottom tool that I may replace with the tool Grant describes above. After I use this tool I have to true the bar up in a die under my hammer which also upsets the corner a little. Thanks for this STOCK answer Grant, using your fixture may save me from having to use the hammer. These tools have formed over 4000 parts, not bad for mild steel eh.

[Nakedanvil - Grant Sarver]

JNewman: Good looking set up, man. The rolling bottom die may help, but that sharp corner top die does have a tendency to "cleave" into the part. Of course the rolling die can also be made with that half-round groove which will help.

I can think of two other ways I might approach this part. I think you mentioned that you upset the corner a little before bending. Trouble is, it's hard to get it to bend in the upset, it wants to bend either side of the upset. One solution is to flatten the upset before you bend it, then bend it in the rolling die fixture. One thing you'll notice with the rolling die is that the work is supported directly under the top die, no forming in "air". This will leave it thin but wider at the bend. Forge the sides back down and press in your current fixture. Of course this will yield a part that is not round cross-section in the corner.

The second approach requires the same upset, but instead of bending it we forge the corner, as shown in the illustration. If you look, you'll see that the corner bend is done. This avoids a lot of the stretch in the corner. Now you just put it in your current bending die and bend both of the legs up.

[JNewman]

It was a different part that I upset before bending. After bending these I have a bottom block that bolts on my hammer with a vertical hole and horizontal swage I drop the part in and hit the top with a swage. This straightens any slight bent in the shank, trues the corner up to 90 and upsets the corner slightly. The top tool is 90 but it overbends the part because the metal seems to bunch up a little in the corner when I first did these I tried just making the top tool wider than 90 degrees but that did not work I was thinking if I used the rolling die for this part I would cut the round into into a dedicated set of half rounds. I may still have to do the second step but it should keep the short leg straighter and give me a better finished product.

After I made the first thousand I looked at my customers tooling as he used to make these in house. His die set bent the part the same way mine does but then they removed a stopper block then die springs hold the top part of the bending fixture down but allow the second stage of the die to push down on the short end of the part upsetting the corner. Their set up is slick and does a slightly better job than mine but they have been happy with the parts I have been supplying them with and their tooling is probably worth what my annual sales are to these guys.

[Nakedanvil - Grant Sarver]

Long as the customer is happy and you're happy...........

[JNewman]

Things have been a little slow here so I made one of these bending jigs. I used a 6" long piece of 4.5" dia. stock for the rounds. I have a job that I have been told is coming for the last few weeks that I will be using it for. I have to prebend 200 3/4" round bars before I bend one end into a hook. This will eliminate the marking from my old bending jig.

If some things I have been thinking about work out I can see myself using this jig quite a bit. I was thinking about what effect if any the saw kerf and cleaning up the face of the half round would have. In thinking about this I reallized that if I bolted half round swages with stops on top of the half round about 1" above the center of rotation the distance between the stops gets shorter. So THEORETICALLY this will upset the corner as it is bending. It may still need cleaning up in a swage but should get more material in the corner. I am going to take a skim cut off the faces of the half rounds on the mill so that I know they are parallel and then put 2 12" dowel holes and tapped holes in the ends so that I can fasten swages and other tooling on top of the half rounds. If I countersink these holes slightly I dont think these will mark up flat stock when being bent. I am also thinking if I get a little inventive I may be able to bend my hooks on the press much colder and faster than my old way of a bending jig on the platen table

[JNewman]

I forgot to attach the picture

[Nakedanvil - Grant Sarver]

Good job John! Glad you like it. Not sure you'll get the upsetting you're looking for though. As you move up from center the ram has to push harder causing more pressure in the corner. Certainly worth trying. Center-to-center distance changes things too. Contour top tools really help. For repeat bends it's nice to have a top tool that is like a radiused "V" to define the intended angle. Sure bends smooth and easy, doesn't it?

[stretch]

Thanks Grant. Excellent idea.I think I will upgrade to this bottom tool, looks good. Here are some pictures of what I used and the product I made with them. I have made quite a few of these joist hangers out of 1/4" and 3/16" material. Now I will try to post the pictures, I am new to this. There pictures on. I use this on a 10 ton Hframe flypress. Works real good. Would rather have a Cframe press, I think it would work better.