Sheet metal fab question

[loose nut]

I need to roll a tube out of 16 gauge cold rolled sheet steel that is precise in the diam. dimension. The circumference calculation is πDbut to get it very accurate dimension do I use the OD or the ID diameter or for this thin a material does it matter?

For example - the tube needs to be 2.322" in diameter (finished) so the OD of the material would be 3.1415 x 2.322" or 7.294" in width but the ID would be 3.1415 x 2.197" or 6.901" in width. Obviously using the OD or ID matters. The math suggests it would be the OD dimensions but the little I know about sheet metal work tells me it is not that simple. Possibly you would split the difference.

[oxford]

In for answers but good luck with holding precise dimensions with the slip roll.

[JRouche]

Not too sure but I think tube is ID dependent where pipe is OD, or the opposite

I have worked extensively with 16ga. To get it to that dia is going to be difficult.

If I had to I would roll out a tube of slightly larger dia then wrap the tube over itself (overlap) to the final dia. Tack weld then cut through both sections where you would get your 2.322". Then weld the seam shut. JR

P.S.: One of the reasons I suggested the overlap deal is to get a correct radius at the cut edge. If you cut a sheet of 16ga to size and wrap it around a mandrel (great idea by the way) the cut edge will be impossible to get the same radius as the rest of the sheet. It will come to a "peak" at the edge and that will have to be hammered down.

I have made cylinders from 16ga and have had that happen to me.

I do like the mandrel though for wrapping the oversized sheet around. I have use strap hold downs for that before. JR

[The Artful Bodger]

I would need a mandrel for that so my suggestion: Turn the mandrel to ID and cut the material to size and wrap it around the mandrel. Weld the butt joint. Getting the finished tube off the mandrel can be the subject of another topic!

[Dan Dubeau]

I like JRouche's plan. Only I'd turn up a couple discs the final inside dia (maybe a hair small), and clamp round those as best I could while tacking along the length. I doubt you'll get it perfect, but pretty close is good enough for a lot of things....

[oxford]

What’s the length of the finished piece?

If the finished diameter is as important as you say, how important is keeping it perfectly round and what is the plan for that?

Honestly, it’s probably going to be both of the mentioned above. Mandrel and roll long and trim the ends.

[J Tiers]

If the sheet is wrapped, not in any way "forged" or modified in shape (as metalsmiths may do), then the OD and ID on the tube will be the same length. You have not stretched the metal, you just wrapped it around. If anything, the OD, which becomes longer, has been stretched to be less likely to "close up"

!6 ga is about 1/16" thick. so the diameter of the OD is 2x that, or 1/8" different. You seem to show that also, although I did not check the numbers.

If the ID is correct, and the edges of the material touch at the ID, then there will be an open V down the length where they come together.

Sounds like an opportunity to me..... Make it to size, using dimensions so that it comes out with the ID touching. Then weld down the V, and you have your tube to the needed dimension (once you grind down the weld)..

[strokersix]

I'd split the difference.

Actually, I'd find another way. Like buy some 2 3/8 inch OD then cut and reweld smaller. Or machine ID and OD of some heavy wall tube.

I think you are going to have quite a fight on your hands to curl 16 gage that tight. A lot will depend on how long it needs to be. Only an inch long a soft mallet over a piece of round stock will do it. 12 inches long is going to be more difficult. Material? Soft steel will be much easier than stainless for example.

[DR]

A customer brought me a piece of very expensive micro perforated stainless that had been cut to the calculated inside diameter. The material thickness was about equivalent to 18 ga steel. When it was rolled up it would come to around 3" ID. He'd shopped all the fab shops and was told there would be flats on the ends if done in a conventional 3 wheel slip roll. And those flats would have to be hand formed. But the material could not be hammered on since it would potentially damage the perforations. He said the ends would be laser welded.

This was the type job I'd hope somebody would bring me some day. I rolled it perfectly on my 2 roll slip roll. Actually not a 2 wheel slip roll, it's a 3 wheel Di Acro 12" slip roll with the third roll backed off. No modifications to the machine. Took all of ten minutes.

If the material had been substantially thicker (stiffer) I could have done it in my press brake, but that would have required a mandrel to be turned to the ID.

Think a bit about how I could do that and I'll tell you later.

[Bented]

4 decimal dimension sheet metal work?

The stock itself will not be within .0005" uniformity.

[chipmaker4130]

4 decimal dimension sheet metal work? The stock itself will not be within .0005" uniformity.

Right on! If it isn't long, turn/bore it from thicker wall material.

[chipmaker4130]

If roundness also matters, you're sunk already. You will never get a rolled and welded sheet steel to behave. We buy some pricey DOM stainless tube in 16ga and that isn't round either.

[boslab]

The neutral axis aka centre line would be a good choice imho, the od will be longer ID shorter leading to a slightly inclined or bevelled end
mark

[Richard P Wilson]

A customer brought me a piece of very expensive micro perforated stainless that had been cut to the calculated inside diameter. The material thickness was about equivalent to 18 ga steel. When it was rolled up it would come to around 3" ID. He'd shopped all the fab shops and was told there would be flats on the ends if done in a conventional 3 wheel slip roll. And those flats would have to be hand formed. But the material could not be hammered on since it would potentially damage the perforations. He said the ends would be laser welded.

This was the type job I'd hope somebody would bring me some day. I rolled it perfectly on my 2 roll slip roll. Actually not a 2 wheel slip roll, it's a 3 wheel Di Acro 12" slip roll with the third roll backed off. No modifications to the machine. Took all of ten minutes.

If the material had been substantially thicker (stiffer) I could have done it in my press brake, but that would have required a mandrel to be turned to the ID.

Think a bit about how I could do that and I'll tell you later.

Just tell us now!

[Bented]

A customer brought me a piece of very expensive micro perforated stainless that had been cut to the calculated inside diameter. The material thickness was about equivalent to 18 ga steel. When it was rolled up it would come to around 3" ID. He'd shopped all the fab shops and was told there would be flats on the ends if done in a conventional 3 wheel slip roll. And those flats would have to be hand formed. But the material could not be hammered on since it would potentially damage the perforations. He said the ends would be laser welded.

This was the type job I'd hope somebody would bring me some day. I rolled it perfectly on my 2 roll slip roll. Actually not a 2 wheel slip roll, it's a 3 wheel Di Acro 12" slip roll with the third roll backed off. No modifications to the machine. Took all of ten minutes.

If the material had been substantially thicker (stiffer) I could have done it in my press brake, but that would have required a mandrel to be turned to the ID.

Think a bit about how I could do that and I'll tell you later.

You held .0005" OD numbers? Please do tell.