ring roller

savarin

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I am in need of 2x 10mm square section rings 303mm in dia from aluminium.
If I build a small ring roller that works do I roll extra to account for the straight ends and then cut the overlap off each end?
Or is it possible to roll the rings to the exact size knowing the circumference required?
Thanks
 
The work I have seen done uses stock longer than needed to be able to completely finish accurately rounded rings. The ends will not be bent properly and you can stop and cut off the overlapping ends when you reach the correct diameter. The stock needs to stay engaged by all three rollers all the time you are bending to avoid problems.
 
I would agree with Bob. Two factors come into play. Roller engagement as Bob discussed and the material thickness. While you can calculate the theoretical length of material based on ID or OD you still need to allow for the additional material to create the type of joint specified for the part


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It will just be a butt joint, no welding, the complete ring will be bolted to a plate.
The only criteria is that it must be perfectly circular and dead flat.
 
It will just be a butt joint, no welding, the complete ring will be bolted to a plate.
The only criteria is that it must be perfectly circular and dead flat.
You often need to persuade them into dead flat after rolling them round and cutting to length.
 
I worked (as an electrical contractor) in a heavy fab shop. They would roll pressure vessels out of up to ~9" thick plate. They would use a brake to start the curvature before placing the plate into the roller. After it was rolled, it was welded. Then it was put on a rotary table and cut square with a stationary torch while the table was rotated.


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That is only 11.929" in diameter, if you require high accuracy rough mill it from plate or round and finish in a lathe.
Ah ha, hadnt thought of that, I had got as far as designing a pattern for casting the ring on the support plate but then worried about the weight when flipping the mold.
There will be a 10mm square cushion of very firm foam rubber sitting on the ring then the mirror sits of that then the mirror is pulled from its centre down onto the foam under pressure to distort it from a sphere into a parabola.
Any discrepancy in the supporting structure results in aberrations showing on the mirror surface.
The major problem from my perspective is that I would have to get a shop to do the job and that hurts:p
 
Ah ha, hadnt thought of that, I had got as far as designing a pattern for casting the ring on the support plate but then worried about the weight when flipping the mold.
There will be a 10mm square cushion of very firm foam rubber sitting on the ring then the mirror sits of that then the mirror is pulled from its centre down onto the foam under pressure to distort it from a sphere into a parabola.
Any discrepancy in the supporting structure results in aberrations showing on the mirror surface.
The major problem from my perspective is that I would have to get a shop to do the job and that hurts:p
A telescope mirror support (if that is what it is) needs to be pretty accurate to not induce aberrations when the mirror is pulled and is purposefully distorted. I am not sure a ring roller is accurate enough for that work, and I also have no idea how you can keep the foam in the accurately correct place (perfect average pressure circle) all the way around the circle while pulling down on the center. I personally would plan on multiple prototypes before success...
 
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