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bending 3 x 4 rectangular tubing

Tooly236

Plastic
Joined
Mar 16, 2013
Location
Canada
Hello all, I found a large rotary draw bender. I have searched all over google and I can not find anthing about this size of material being bent. With a inside die what radius do you think I could get away with without crushing, I am bending to about 75 degrees. I am bending it the easy way and the Wall is .188. Any help would be appreciated.
 

gbent

Diamond
Joined
Mar 14, 2005
Location
Kansas
I have never bent anything that large on purpose. One trick to avoid crushing the corner is to use a piece (or two) of flat stock inserted into the tube so it is bent (hard way) in the joint. Bend the ends of the flat stock so it lays at the right height in the bend, and use a pusher to get it positioned lengthwise in the correct location.
 

johnoder

Diamond
Joined
Jul 16, 2004
Location
Houston, TX USA
We tried something similar, easy large radius in plate roll. Total disaster - the weld seam just opened up

Enpro Systems back in the nineties
 

Chip Chester

Diamond
Joined
Dec 13, 2007
Location
Central Ohio USA
Sounds like boat trailer territory, except they usually don't do it without deformation. There's a dent on the inside of the bend. Stateside, Indiana seems to the the nexus of trailer manufacturing, although Wisconson area was heavy in trailer boat maufacturing. I have a Snowco boat trailer from the mid 60s with about 1' radius bends in the front frame section that are nicely done. They are pretty dent free though. Maybe look for trailer websites showing shop pictures/videos, and make some inquiries.

Chip
 

adama

Diamond
Joined
Dec 28, 2004
Location
uk
Never bent square tube yet, but do a lot of round, is the bender setup for a mandrel or not? If mandrel bending you can go a lot tighter as your very much controlling the distortion. If the weld seam opens then its better to find a different steel supplier, because its fundamentally flawed tube. Good tube and the weld seam should not be a issue till you approach the fail point of the parent metal.

What makes tube bending hard is theres a lot of variables at play at once, tube od, wall thickness and center line radius, theres various calcs for round tube that let you kinda predict how it will go and how much you need to support it, as to weather you need a wiper, mandrel or can simply just bend it with a follow block and skip thoes extra parts! im sure the same applies to square or rectangular material too, just probably with a different correction factor.

Probably supported in a die and follower the material should never crush, just more a question of kink comes into play and what your preprepared to accept distortion wise, if it was round tube, at that wall you would be wanting to use a manderal for internal support at more or less any radius, this is the best place i know for this stuff and there calcs hold true in my experience, all be it thats all sub 1" erw sub 14G wall thickness’s. Not sure what they have on square bending though!

http://www.bendtooling.com/bending_formulas.htm
 

Tooly236

Plastic
Joined
Mar 16, 2013
Location
Canada
I am sure the machine has the power. It has a 10 horse 3 phaze motor with a industrial 50-1 reducer. The pinion to the main gear is 100-1. The main gear is 5 inches thick by 38" diameter. It is a rotary draw so I could put a mandrel in it. Anybody know where they sell mandrels that big or advice on. How to make one
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
I am sure the machine has the power. It has a 10 horse 3 phaze motor with a industrial 50-1 reducer. The pinion to the main gear is 100-1. The main gear is 5 inches thick by 38" diameter. It is a rotary draw so I could put a mandrel in it. Anybody know where they sell mandrels that big or advice on. How to make one

Is this a "one shot" (or limited number of bends), or will you be making many of these? Does the material have an internal seam? It might interfere with a mandrel unless you allow for it (broach or otherwise remove seam, or notch mandrel). If limited number of bends, you might try the old packed sand trick, but it's likely not going to be as successful as for round tubing. Making follower blocks might help, but perhaps dependent on the machine construction and where you'd anchor them. Any pics of the machine available?
 

Graham Gott

Aluminum
Joined
Jan 26, 2010
Location
Denver, NC
If it's a one-off thing, you might contact Art Morrison. They mandrel bend rectangular tubing for chassis and it looks great. No distortion of the walls at all. I'm pretty sure the sell chassis with 3 x 4 rails, but I'm not sure of the wall thickness.
 

adama

Diamond
Joined
Dec 28, 2004
Location
uk
Is this a "one shot" (or limited number of bends), or will you be making many of these? Does the material have an internal seam? It might interfere with a mandrel unless you allow for it (broach or otherwise remove seam, or notch mandrel). If limited number of bends, you might try the old packed sand trick, but it's likely not going to be as successful as for round tubing. Making follower blocks might help, but perhaps dependent on the machine construction and where you'd anchor them. Any pics of the machine available?

Its pretty std just to notch the manderal at the weld seam in round tube bending, that said, the weld seam does have to then be aligned with said notch, but thats a feature you need to be controlling the location of any how. Not sure if the weld seams always maintained in the same location on box section or not? Never ever even looked at or considered it. Unlike round you can not just rotate it!

Worth adding depending on your chosen radius’s - accepted distortion, a mandrel may need be little more than a sutably shaped plug, you oftern don't need segments trailing around the bend if you can accept limited distortion + have the plug positioned deep enough into the bend! Because in my messing about it seams the plug part realy does most of the work, by the time the tubes left that, it should be formed. It needs to be a surprising distance past the centreline to get the best out of it though! I have only mandrel bent some alu tube, just used a simple nylon bullet like shape with the radius of the point matching the internal od bend radius, worked well at preventing the tube going too oval in the forms, Not sure if nylon would be strong enough for your tube, but that said, done right it does not see all that much force, seams to be more a case of supporting the tube - making it stretch not letting it pull in as it stretches around the radius - stopping it collapsing than actually being strong enough to cold work the material.
 

Limy Sami

Diamond
Joined
Jan 7, 2007
Location
Norfolk, UK
I've said this before .

I've BTDT and still have the scars, easiest way is to fab up the curve out of 4 sections of profiles and bent plate, - weld together and dress up - done carefully you'd be pushed to find the joins - and the finished job looks as near perfect a curve as you could wish.

IME&O you would have to spend a lot of time and even more $ to get that job right - when those sums run to 4 figures you can fab a lot of bends for the same $ and sleep easily.
 

PDW

Diamond
Joined
Jul 24, 2006
Location
Australia (Hobart)
I've said this before .

I've BTDT and still have the scars, easiest way is to fab up the curve out of 4 sections of profiles and bent plate, - weld together and dress up - done carefully you'd be pushed to find the joins - and the finished job looks as near perfect a curve as you could wish.

IME&O you would have to spend a lot of time and even more $ to get that job right - when those sums run to 4 figures you can fab a lot of bends for the same $ and sleep easily.

Or, if there's only a few bends and a little irregularity is acceptable, cut out as many pie shaped wedges as needed from the inside and sides of the bend, bend the now dead easy to bend outer section, weld the closed up wedge seams, grind & paint.

Standard thing we were taught to do in first year welding, both for RHS and pipe.

PDW
 

Ries

Diamond
Joined
Mar 15, 2004
Location
Edison Washington USA
I have had pretty good luck rolling both square and rectangular tubing- assuming the radius is not too tight.
But thats not a rotary draw bender.
I use 3 roll angle rolls, with a set of different sized dies and spacers, and multiple passes.
 

Inferno

Plastic
Joined
Mar 26, 2016
Location
Portland Oregon
1) Fill with wet sand. Freeze. Bend.
2) Fill with just water, freeze, bend
3) Fill with molten plastic, allow to solidify, bend, melt plastic back out.
4) Fill with steel shot, bend.
5) Fill with molten lead, bend, melt lead back out.

Just a few suggestions.
 

Limy Sami

Diamond
Joined
Jan 7, 2007
Location
Norfolk, UK
Or, if there's only a few bends and a little irregularity is acceptable, cut out as many pie shaped wedges as needed from the inside and sides of the bend, bend the now dead easy to bend outer section, weld the closed up wedge seams, grind & paint.

Standard thing we were taught to do in first year welding, both for RHS and pipe.

PDW

Yep BTDT AKA ''Lobsterback bend.'' :)
 

tft1987

Aluminum
Joined
Feb 26, 2014
Location
North Kingstown RI
1) Fill with wet sand. Freeze. Bend.
2) Fill with just water, freeze, bend
3) Fill with molten plastic, allow to solidify, bend, melt plastic back out.
4) Fill with steel shot, bend.
5) Fill with molten lead, bend, melt lead back out.

Just a few suggestions.

Saw an episode of how its made where they were using hydroforming to bend tube. Weld caps on end, fill with liquid, pressurize (no idea what the pressures needed would be)Then bend...
 

vanguard machine

Stainless
Joined
Dec 20, 2011
Location
Charleston and NYC
with Ries here,
you don't say, or maybe i missed, where you state your desired radius. if big enough rolling easy way would be a cake walk on 3 x 4 3/16 wall.
make yourself up a set of delrin rolls that the tube fits into semi tight so the walls don't collapse too bad. ive done a bunch of mild and alu, and a little bit of ss this way, on a POS old clapped out pyramid roll, with really great results.
 








 
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