Thomas Bending Rolls

[andrew winksParticipant @andrewwinks64215]

Construction of Thomas bending rolls well under way, I want to fit the gear set to the rolls as per some designs. Does any know of a supplier of spur gear stock in Aust? I also wonder about the complex design of the 4 gears to drive the top roll from the lower fixed roll. This is so designed so that gear mesh remains constant when the adjustable roll is set in different positions. But relatively small travel with the top roll, why not just fit a gear to the bottom and top roll, and put up with a bit of back lash when the top roll is set at the widest gap. Those who have scratch build this or constructed a Hemingway kit will know what I'm on about. Comments much appreciated.

Andrew

[andrew winksParticipant @andrewwinks64215]

[WorkshopPeteParticipant @workshoppete]

Hi Andrew

I built a set of these 35 years ago and they have been excellent I increased the roller length by 3". I believe I bought the gears from Neil Hemmingway. The four gears are far better than trying to get two gears to mesh as if you are rolling say a 1/16" strip the mesh will be very in adequate and may slip.

Best of luck

Peter

[andrew winksParticipant @andrewwinks64215]

Thanks Peter. I also increased the roller length to suit my boiler cladding length of 24" and also increased the Bearing journal size by an 1/8" to beef it up. I now regret not increasing the end plate width to 5/8" but will see how it goes.

[WorkshopPeteParticipant @workshoppete]

Hi Andrew

The drawback with making the rolls 24" is they will bend although on Cleating it should be ok. Even on my 13" length rollers there is a tendency to bend. Mind I use mine for all sorts of jobs from rolling up smoke boxes to rolling cab roofs and with the rear nip roller you can get rid of the flat at the end by turning the job 180 deg and re rolling a typical well thought out GHT design. In some way I wish I had made the rollers a larger diameter and from something like EN8 but that would had needed larger gears it has lasted me this long and it will not be changed now.

Regards

Peter

[andrew winksParticipant @andrewwinks64215]

Hi Peter, yes the possible deflection of the rolls was also a concern so I actually used larger diameter rolls as well. 35 mm diameter for the main rolls and 1" for the forming roll. Will lose out if trying to roll tight circles, will be interesting to see how it performs, cheers, Andrew

[duncan webster 1Participant @duncanwebster1]

Using EN8 won't make any difference to deflection, it has the same Young's modulus. Unless you're bending it so much that it yields of course, but then it would be permanently bent.

[WorkshopPeteParticipant @workshoppete]

Hi Duncan

I had not realised that I thought EN8 would be much better than EN1A.

Peter

[andrew winksParticipant @andrewwinks64215]

Duncan, I wonder if a there is a calculation to determine at what pressure will cause deflection at certain diameter rolls?

Or is this more a matter of trial and error beginning with optimum diameter of rolls? Cheers, Andrew

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