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Old 01-01-2019, 02:46 PM
BruceConner BruceConner is offline
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Default Bending square tubing with 3 roller bender

I need to make some simple U-shaped pieces out of 3/4 square tube (.063 wall). I've got dies for my 3 roller bender, but I wanted to check with the collective intelligence of the group on getting my layout correct before messing up some material.

Here's the question - Is there any shrink going on when using a 3 roller bender, or is it all stretch? In other words, if I measure the length along the inside radius of my curve (inner radius 8.25 inches, so 25.9 length), will that give me the length of bent area I need so that my U comes out with the correct distance between the legs (18 inches across to the outside of the legs, so not a super tight curve or anything)

-Bruce
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Old 01-01-2019, 02:59 PM
Ken Hosford Ken Hosford is offline
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From my experience when I have rolled it will squash the tube worse the tighter you go not bad on gentle arcs . figuring cut length is rough easiest to do after , if trying to roll with tangents it is a tough challenge .
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Old 01-01-2019, 03:26 PM
Gareth Davies Gareth Davies is offline
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There’s more shrink than stretch on square section and you’ll find the inner face yields into a concave profile, that’s been my experience anyway. I’ve used my rollers on 50 x 50 x 3mm mild steel, 50 x 30 x 2.5mm mild steel and 3/4” x 3/4” x 16g aluminium box and all have behaved the same way. Depending on the gap between the sets of bottom rolls is what controls how much the sides flex out but, if you have them too tight you get lots of scoring, so there’s another down side. The outside profile tends to stay pretty good for dimension and looks but it’s always the throat that suffers. If you want to see what I mean, take a look at the big material trollies at a DIY store and you’ll understand how much it will affect what you’re trying to achieve. Hope that helps!
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Old 01-02-2019, 11:18 AM
billfunk29 billfunk29 is offline
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Default square U bends

I have never been able to get square(or rectangle) thin wall tubes to bend without getting concave. I have not used a mandrel though. Never seen one, but it should be possible. If I want to have a square tube after bending, I cut it in half and bend each half separately. Then weld them back together.
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