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Die Design to Crimp Small Diameter Stainless Tubing with Minimal Deformation of the surrounding OD


Feb 11, 2014
The ask: I need to crimp some stainless tubing, approximately .125" OD x .040" ID so that minimal liquid passes through (not liquid tight, no pressure requirements, just "less liquid than gets through now when it drips on the far end"). The kicker is that I need to keep the tubing as straight as possible (12 ft bars with one crimp approximately 6" from one end), and I'd like to keep the material from bulging as much as possible (which may not be very much).

Equipment available: 2 Ton arbor press for now. If this goes to fruition, I could probably purchase just about any sort of mechanical press I could want.

I've tried: I just cut up 2 blocks of steel 1/2" x 1/2" x 2" and cut the tops into a flat topped V shape with the crests being .125" wide, threw em in the arbor pressed and crimped some tubes. This made a flat crimp that worked decently for stopping airflow under pressure, and I think would work well enough, it did bulge the material approximately .020" on either side, and the bar became slightly less straight, but likely still workable.

The engineer asked if I could deform the material surrounding the crimps less. So I used a 1/16" ball endmill to cut a radius approximately .015" deep, perpendicular to the .125" width of the V on the dies, and used the same endmill to put a radius on the downslopes of the V, so the material could flow outward along the length of the material more, rather than bulging toward the OD. This produced a worse crimp.

The question: Got any resources I can read on crimping, or suggestions for a better shape to add to some simple dies to crimp tubing with minimum OD deformation in the areas surrounding the crimp?

I have an idea for a simple jig with a slip fit hole that supports the OD for say 75% of the circumference and a piston that comes down through the open 25% to perform the crimp. I just don't know what shape to make the end of the piston, if anything is better than a simple flat topped V.

Something that just occurred to me... Is there a simple handheld tool that could do this that's already available off the shelf? Like the crimping portion of a pair of wire strippers, but slightly heavier duty?
I've never done this before. But my best guess is to have a solid die that closes up around the tube with a hole for a punch pin to indent the tube to close off the cross section.

The advantage of an indent is the cross section can collapse into a shape that fits within the original diameter without having to significantly compress the material.
Cable rail crimper/swedge with radius relief on semi circles. Crimp 3/4 of the way, rotate 90 crimp the rest to avoid ears.
Two dies, easy to make. 2 blocks of steel tacked together, drill a hole to desired od smack down the center of the two. Untack and sand in relief radiuses.
Going to need more than 2 tons unless working hot.

Gullitine fullers work too. Less tonnage, more small rotations and hits.
Would it be acceptable to have an insert in the end of the tube, slightly smaller (snug slip fit) inside, and then swage the OD of the tubing down onto the insert? You could profile a couple of grooves on the OD of the insert so it locks in place.
I thought about this, but man that tubing is like big girl thick. Dunno if can do by hand. :D

I've used a pipe cutter to mildly swage 316 and 304 tubing before. Like retain a ball bearing to make a check valve kinda thing.

I don't know how much he needs to decrease the ID of the tubing. If he needs to go from .04" down to .02" I bet a dulled tubing cutter would do the trick pretty good. If he needs like a .005" hole then I don't think that'd do.

Wouldn't hurt to use some high pressure lube on the tube cutter as well.
I actually do this to some 7/8 13ga tubing. Probably wouldn't scale for shit but we have a roller that we put in a scissor style knurling tool. It is basically the same concept as the tubing cutter. Really rolling the seam in these parts would be the easy part for me, controlling a 12ft stick of spaghetti in the lathe would be the hard part.
Hi TeachMePlease:
Are you planning to turn hollow parts from these tubes and just want to keep the cutting oil from dripping out the end and soiling the bar feeder?
If that is your goal, I'd plan to just plug the ends of the tubes.
Instead of crimping the tube ends I'd just turn up some stepped aluminum plugs and make them maybe + 0.0005" compared to the tubing ID and -.01" compared to the tubing OD.
Or maybe just give the stem a little straight knurl so you get 0.0005" or so of interference.
If you put in a nice lead-in taper on the plugs you can probably just tap them in with a small hammer...no press needed.
If you think they're going to be a PITA to handle, just leave them on a stem and part most of the way through them so you can pop them in the tubes and then break off the ends

If this is not what you intend, then my apologies for wasting your time.



make you some of the collet pieces to your flavor.
over kill!!!:willy_nilly:

That would be very difficult to get a nice result with over a rotary method. Hydraulic crimpers displace a lot of material between the segments. Just the nature of that design.

Swaging machines are not a squeezing down segments kind of machine. They are a rotating process, kinda like how a cone crusher works to crush rock.
I would try doing a split die with a tube od hole centered on the split then on the bottom half of the die I would dill and tap a through hole centered in the die and use a grub screw to hold a ball bearing protruding up into the split hole.
this would allow you to raise the ball bearing until you get the closure you need while fully supporting the tube around and both sides of the actual crimping process this should keep it reasonably straight
There are some good size electrical contact crimpers out there. I have a couple with interchangeable dies. Your success might depend on how annealed or not the tubing is. Also Nicopress tools, again there are several different die sizes.
My guess is to make a rotary swaging tool, rotate the tubing and use two support rollers and one moveable/adjustable roller to swage the tubing as it rotates- kind of like a tubing cutter except with a flat wide roller rather than a sharp thin wheel.
I once visited a firm called brush power, they were doing electromagnetic crimping of fuses, no distort just an electromagnetic “ swage”, went bang btw!
Smooth crimp. Interesting even if impractical for small volume.
Here's a custom tool that sounds like what you're talking about:

These folks are squeezing hard enough to sever the tubing, but same idea. A problem is that they say the confining die block needs to float, so it's not like you can just clamp it with a 2-axis press to avoid the screws.

Is there a simple handheld tool that could do this that's already available off the shelf? Like the crimping portion of a pair of wire strippers, but slightly heavier duty?

There are handheld interchangeable die crimping frames. I use one from Daniels that relies on leverage alone, but that's not going to have enough oomph for this. There are hydraulic, pneumatic, and battery operated versions that might:


Greenlee also makes this kind of stuff.
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