What's Best Method to bend square aluminum 1x1" tube into circle diameter=20"?

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I am currently using a harbor freight tubing bender. finished circles are +/- .125" I'd like to get that down to +/- 1/16th if possible. Below are photos of my first attempt.I started with a 24' long of 1x1" square AL tube 16 gauge. I wanted to make 4 perfect circles each with a radius of around 20"I originally had the bender lying horizontal on the wooden palette so one person can manage it. After bending the tube into approximately a 72" diameter I rotate it to vertical.Successive bends were pretty easy until the circle was getting down to about 30" and then it obviously had to start a helix due to the pipe length.When I got it down to 24" the helix was getting so tight and narrow the pipe started deforming and becoming trapezoidal instead of staying square.At this point I just cut the tube into 4 equal lengthsI cut a few inches off each tube so that it had a circumferance of 70" and then bent/rolled them until the two ends met.It is quite diffcult to remove this circle from the bender once it is made. I had to take out the bottom roller, and then offset the circle and slide it off just like you slide a key off a keyring.Just wondering if there is a better method?Next try I think I will mark the tube length at 70" first so I can cut it where the mark is instead of trying to wrap my tape measure around the circumference of the bent tube.I also would not helix the tube as that causes it to distort. After I got it rolled down to 6' diameter I would just cut the curved pieces at the premarked spots and then further bend them down.any suggestions are appreciated. This is for a custom point of display type structure. It will be 6' tall and made out of 4 rings with white polycarbonate and some flashy LED lights inside. The circles will form the skeleton of the kiosk.finished circles are not perfect probably plus or minus 1/8" of an inch. I can make it work, but it's annoying!!!! if I can get it down to plus or minus 1/16th than I'll be happy.Last edited by AluminumWelder; 03-10-2013 at 10:37 PM.Reason: images not linked correctly
Reply:If you are using the rollers that are in your photos it will be hard to get a nice bend. You need to have rollers that are shaped for what you are bending. IMHO
Reply:duplicate postLast edited by AluminumWelder; 03-10-2013 at 10:35 PM.
Reply:they are square rollers, obviously I took out the round ones which are on the ground.
Reply:Looks like you are rolling exact measured length for the circumference.  If you roll more than you need you will eliminate the apparent flat spot, the cut where need to for  the ring.  You might be able to roll a continous coil and make a cut to make multiple rings.  Might need an open face roller to roll a coil?There also might be benefit in rolling half and the welding rings together.  Anyway might help your precision.  The flat spot might be where you are losing it.
Reply:Imo for what your doing and doing it with I think your results are great. To get a nice tubing roller to do exactly what you want will cost you several thousand. I also agree with making the circles in half's to eliminate the flats but think for what your trying to accomplish your doing great.
Reply:If you roll more than you need you will eliminate the apparent flat spot, the cut where need to for the ring. You might be able to roll a continous coil and make a cut to make multiple rings. Might need an open face roller to roll a coil?
Reply:I am impress with the rings. What is the diam of the smallest ring?  What happens if you pull/spread the end of the material out of the bender before it passes back through the roller. Then you could loosen the rollers roll the coil out of the roller?
Reply:they are all 20" or so in diameter.
Reply:Have you seen the Swag Offroad roller? It uses the same HF tools, but they have a "wing" arrangement that facilitates faster roller changes. Also, Swag has specialty dies. [ame]http://www.youtube.com/watch?v=OM_QyvTCsyk[/ame]
Reply:Also, DBTindustrial has an upgrade to the HF bender. You can see thumbnails of ther improvments at http://www.ebay.com/itm/Air-hydrauli...item3ccf9fd315.
Reply:Yes I have a lot of swag stuff but honestly for the thin al I bend no need for their wings
Reply:+ or - an 1/8" is pretty darn good.  I don't know how you would get closer with the machinery you have.  Maybe if you had an excact form you could put it on while making the final tack.  Other than that, it's more accurate than I could do.
Reply:I can appreciate your wanting them perfect, but like others have said, yer damn good being as close as you are. Is the job/ pay worth spending the time getting them that little bit closer? Just something to consider. It's the benefit of not working on the space shuttle.  Sorry I can't help any.200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.