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  #1  
Old 05-17-2016, 03:51 PM
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Tube Rolling

I have a rolling project that will require making a continuous oval approx 25" wide and 60" long.

I can calculate the theoretical arc length required to make the radii, but I'm afraid I won't hit my target radius after performing the roll bend due to material deformation, inconsistencies in start/stop locations from one roll iteration to the next, etc.

I thought of starting with excess material and rolling until I achieve my desired radius. Cut to a 180 arc, repeat for the other side, then join the two arcs with pieces of straight tube. I can't help but think it would look like garbage though, as the transition from rolled tube to straight tube wouldn't align perfectly (rolled portion would be slightly deformed).

I have a HF roller with the Swag weld-on wings. Considering my tooling, this is most definitely an art opposed to a science.

The material will be 1" x .120" wt 304 stainless round tube. What would be your approach?
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Old 05-18-2016, 10:10 PM
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Wow, that's a challenging project. I'd try it all out of one piece. If you can get it done in four tries I'll be impressed. You have four bends, a large radius, small radius, large radius, small radius, all continuous. I'd add another large radius bend that overlaps the first, then cut the first and last and weld them together. How accurate do you have to be?
You gotta post pics as you do it.
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  #3  
Old 05-18-2016, 11:33 PM
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Having never done it before, I would spend months tirelessly researching the topic, find videos of the most incredible automated machinery available for production work, compile pages of calculations, and eventually give up from over thinking it. Yup I think that's pretty much how I would go about it.

That said, and with all my usual disclaimers about not knowing a thing about this, I would try out two things to try for repeatable, predictable bends. First, I would attach a long throw dial indicator or at the very least a steel rule with small graduations in order to measure the position of the adjustment wheel. Second, I would mark the side of the tube with measured tick marks (say every two inches) so I could consistently travel to the same start /stop points. Finally I would bend I few test pieces, writing down the start/stop positions and wheel position, then measure the actual piece to see where it ended up.
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Last edited by TheBandit; 05-18-2016 at 11:39 PM.
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Old 05-19-2016, 09:04 AM
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Are you making an oval shape that is two radiused ends connected by straight sections, or is the whole thing curved (ellipse)?

I would probably do this as two 180's. If it's supposed to have straight sections in the center, instead of cutting in the curved section, I would try to hit the angle so you have straight stubs on the ends of the 180's, which should allow you to have pretty round tube where you're trying to weld.

I agree with TheBandit, anything you can do to help repeatably position the top roll will help your cause (dial indicator, scale, etc.). I also like Clint's idea for marking the tube. That would go well with a pointer...you could even do something quick out of welding rod, just to have a good reference on where to stop.

I almost pulled the trigger on a SWAG Hulk machine this week for a paying project...but the same project also required tight radius bends in 1" square, so I wound up buying a die for my bender instead. I'm going to try multi-shot bending to hit the larger radius (it's only a 12" CLR, 60 degree bend) and see where that gets me. Someday I really want to build my own manual roll bender...I like the concept and price of the SWAG machine, but the one thing it won't do is a complete circle (or close) in a fairly small radius, and I have visions of making some steering wheels and stuff someday.
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Old 05-19-2016, 09:24 AM
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Thanks for the input, guys. This is an oval opposed to an ellipse - two straight sections and two radiused ends.

TheBandit's comments definitely hit home. This is part of my endless research before I ultimately throw up my hands and give up from over thinking it.

It seems like everyone is in the same boat, and there isn't a tried and true process for this type of work. I have indicators/scales/etc to try and accurately locate the top die, however the top die itself isn't the most rigid piece on the machine. You guys will know what I mean if you've ever messed with a HF roller - it's a bit sloppy. Regardless, having an idea of where I'm at will help for sure. Marking the tube and rigging up a pointer so I know my start/stop points is a good idea as well.

I already have material on hand, and I might have enough excess to perform 1 practice bend with the actual material. I have a decent amount of low carbon steel in the same thickness though. I may make some test bends with the cheap stuff and try to figure out the required start/stop locations to achieve a 180 at the radius I need. Hopefully that information would transfer to the stainless quite well. Tolerance is loose on this one; on the order of +/- 1.000". If the transition from carbon steel to stainless yields results within 1", I'm golden.

Ideally I could make both bends in one piece, then complete the oval with a single butt weld midway through the last straight.
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Old 05-19-2016, 09:49 AM
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In theory, the amount of tube in the bend is going to be pi times the bend radius for a 180 bend. That would get you close on your stop/start points and tube length, but you're probably going to have to adjust a bit from there for tube deformation. I would think that would translate pretty close from mild to stainless, but your top die position is going to have to be lower for stainless because there's more spring back.
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Old 05-19-2016, 09:56 AM
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Most definitely. I'm sure the theoretical calc will be slightly off as well due to the change in cross section during the rolling process (material deformation). It'll get me close though, then hopefully I could nail it on the second try after making adjustments.

I think I'll make a template to check my radius in addition to measuring the top die location. The more info the better.
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Old 05-19-2016, 12:02 PM
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I didn't realize you were doing a "racetrack" shape as opposed to an ellipse. If you want to eliminate some variables in trade for more welding/fitup, perhaps you could plan cutting and having weld joints at each end of the straights. This way when you do your rolling, you don't have to get a specific swept angle, you can just make sure you roll at least 180 degrees of sweep, adjust until you get the radius you need, then cut out the 180 degree sweep section for welding when done. In this way the only thing you have to work about for rolling is the roll radius. I would make a simple fixture out of plywood that you could go back to to compare radius, then use it as a tack-up and/or final weld fixture once all the pieces are ready.

Roll "candy cane" shapes so you end up with just two welds in the final part. Here's an illustration. I think the only potential issue with this is if the rolled section becomes significantly distorted, there might not be a perfect transition where the "candy cane' gets cut.

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File Type: jpg roll bend racetrack.jpg (30.8 KB, 483 views)
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Last edited by TheBandit; 05-19-2016 at 12:10 PM.
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  #9  
Old 05-19-2016, 12:07 PM
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Yep, that was going to be my initial approach, but I'm worried about fit-up issues where the cutoff rolled portion meets the full section round tube.

I'll do some testing with the mild stuff and go from there. I have high hopes of pulling it together with 1 weld seam.
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Old 05-19-2016, 01:29 PM
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Valid concern. Here is an alternative that would require finer control of the start/stop points, but still probably not too difficult and would allow you to cut on the bend which would give you a good fit-up for welding. Using this method, I would measure the overall width of this thing as your target dimension when you do the bends. Even if the radii are slightly off, once you cut and fit up it should be close enough.

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File Type: jpg roll bend racetrack 2.jpg (29.7 KB, 477 views)
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Last edited by TheBandit; 05-19-2016 at 01:32 PM.
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  #11  
Old 05-19-2016, 01:39 PM
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Now you're thinking outside the box. I like it. I'd still like to try and hit my target, but if I fail, that may be my preferred method. Even though it's mid-bend, the cross sections should be the same.
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Old 05-19-2016, 02:04 PM
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I like that as well. I would bet the transition for a weld would be less obvious there than in a straight section.
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Old 05-19-2016, 10:50 PM
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I also thought you where bending an ellipse type oval. A race track type will be much much easier. With a test bend and marking the tube well, you should be able to pull this off with one weld.
When you put the tube through the roll bender never stop at the same spot. It will make a drastic deformation spot and an ugly transition from bend to straight section. Stop a half inch or so closer to the bend each time. Less bend each time and more passes will help.
I've also found it necessary to mount a digital angle finder on the end to keep it going straight through the bender. A muffler clamp and flat plate work. If you mount it level and it gets off a couple degrees it will read 2 but you won't know quickly which way it is off. So mount the angle finder at angle, say 30, so it reads 32 or 28.
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  #14  
Old 05-20-2016, 12:04 AM
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Interesting. If I move the start/stop locations with each iteration, how to I ascertain exactly where those locations are? Seems like it would be more of a guess and check process, requiring multiple test pieces to really dial it in.

I've rolled a handful of tubes, but most weren't size critical. Even so, I usually tried to hit the same start/stop each time. I know what you're saying in regards to deformation, but I'm OK with that so long as it gives me accurate results.

I'll be using a POB bracket to keep it from spiraling for sure.
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  #15  
Old 05-27-2016, 11:25 PM
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I'm still pondering this project. I met with them to nail down exactly how they want to mount the piece, and it looks like mitered joint legs located mid bend was the winner.

They want the super large radius front piece as well, but that's far easier to handle than the main hoop.

I have a 14 bolt to re-gear and move out, then I'll be getting serious about rolling some tube. I'll keep you guys updated as things progress.

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Old 06-09-2016, 10:28 AM
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The axles are out of the shop and I rolled up some thinner wall stainless for a less critical (in regards to start/stop location) job. I ran my numbers and the resulting diameter was over 1" larger than what I calculated.

In theory, I could shrink the distance between my start/stop by Pi (approx 3") and be good to go. Unfortunately I only needed to make one bend, so I didn't get the chance to prove out the theory.

I've also realized that my method for measuring rolled bends is inadequate. Tape measuring to the approximate centerline isn't sufficient anymore, and I don't want to layout and cut templates each time I make a rolled bend to a specified radius.

With all of that in mind, I splurged on a nice set of large radius gauges.

http://www.trick-tools.com/Arc_Maste...t_RG_3600_1341

I look for them to arrive tomorrow. Hoping to make some progress on this project this weekend.
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  #17  
Old 06-10-2016, 12:12 AM
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Those radius guages look awesome. Let us know how well they work out once you get them.
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  #18  
Old 06-11-2016, 03:09 PM
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The main hoop is complete. I used TheBandit's method of splicing mid-bend. Turned out great. Dead nuts on target width. 1/2" short on target length. I'll take it.

The radius gauges are the awesome. I'm very glad I picked them up.

I'm building the feet this afternoon. Hoping to post up a more detailed build description and pics tonight.
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Old 06-11-2016, 10:43 PM
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I calculated the theoretical tube length used for each 90* bend, then added a couple inches to ensure I was safe. Cut the tube to length, then rolled the first bend, checking with the new outside radius gauge.

My current shop is tiny, so I have to pull my 'workstation' outside to roll the long length stuff.



I was able to check the radius while it was still in the roller, but I snapped a pic of the gauge after I removed the piece to show you guys. Highly recommended if you're doing any precision rolling.



Once I had one 90* bend at the specified radius, I laid it on the floor and measured the true distance from the outside of the bend to my mark where I started the roll. Found out it was about 1/2" shorter than expected; 1" total for both sides. Due to that, I pushed my bend start location out 1" for the second roll.

Completed that roll bend, then loaded the second piece to make a clone. My roller failed as I loaded up the die. Pulled the threads right out of the top plate. Made a quick run to the hardware store to pick up some 1"-8 all-thread and a couple nuts. Pulled out the stick welder and burned the nut on top of the plate, modified the all thread as necessary to make the drive screw, and I was back in business.



After completing the second piece, I set the pins in my table at the target width (25") and put the two sides in place. I cut off the excess and clamped it down for welding. With one side clamped up flush, I was just over 1/8" off at the other end. Not too shabby, and easily pulled into position for welding.



Taking this approach to the build allowed all of the welding to occur at the same location, keeping the remainder of the piece pretty clean. I set it up, built the feet, and welded them on. (still getting the hang of TIG)



And the final piece, fully supporting itself.



I plan to clean up the outside corner welds a bit tomorrow morning, then deliver the piece tomorrow afternoon.

I'm quite pleased with the outcome. No regrets regarding the build progression. Thanks for all of the insight guys.

Last edited by Bray D; 06-11-2016 at 10:46 PM.
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  #20  
Old 06-11-2016, 11:43 PM
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Really looks nice.
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