The minimum diameter will depend on the material you wish to bend. Working in a jobbing shop we rolled everything from Armour Plate a total pig to anything less than 5 times the roll diameter to soft brass that was 1.25 the roll diameter was quite easy to achieve.

For up to 8 mm round stock you can use the spring makers method and wrap the on a mandrel in the lathe with snubber block in the toolpost.

Eric

That would depend on thickness of material, how far you can close up the rollers and roller diameter. One would hope they quote for same case but giving the smaller size will sell more tools.

eg if rollers are 1" dia and will only close up to leave a 1/4" gap you could in theory roll 1/4" material to a 1" dia but 16" material could not be rolled as tight, some calculation would be needed to determine actual bend which I can't be bothered to do.

Well that is what the OP is asking.

Interestingly both RDG and Chronos sell these and throw a third anomoly into the works with a 3" ring diameter and 1" bend radius. may be worth contacting them.

I can also see that you would get different bends on round stock to flat as the ring groove cut into the rollers would affect what is possible so maybe they twist sizes quoted what sounds the best

How can something with a minimum bend radius of 7cm produce a ring of 1” diameter ?

Perhaps there might be “optional extras’ of smaller diameter wheels available, if the machine has sufficient adjustment for the rollers?

One, at least quotes the diameter of the wheels as 7cm. One shows a pic of a 180 degree bend (of 7cm diameter inside diameter if flat bar) – but that would not be the minimum radius of a complete ring. So I expect their claims are about right in that a ring in max diameter (of material) is not possible at the roller diameter of 7cm. Thin stuff (not much thicker than we might term ‘wire&rsquo might be a different matter.

The jargon/detail used is basic, and likely worded that way to befuddle dim purchasers?

Probably a badly translated specification regarding inside diameter, outside diameter and centre line diameter. In reality what can be achieved depends on material spring back and physical size together with the size of the rollers and their relative positions. These given values will change if the rollers are replaced with something of different size. Does it come with interchangeable tolling to suit different material sections? If so the given sizes may be minimums for two different sets of tooling. Here are some rolls I made for aluminium tube.

Martin C

If you are looking for fabricating equipment I'd have no qualms buying from "our" regular suppliers though it's other tools I have bought from them.

For sheet-metal handling though, you could also try WNS, in Rochford, Essex. They make a range of sheet- tube- and bar- rollforming tools from small manual up to big industrial machines. They sell some 2nd-hand machines, too, though it's not their main business.

I write just as a satisfied customer, once for a second-hand Warco bench-drill, second time for one of their own, new, manual, swaging machines (a form of tin-man's jenny).

And no, I am not their on-line "influencer"!