Yet again a ring roller thread.....

[Spark plug]

a little while ago, well many a year or two I built a ring roller one weekend out of whatever I had lying arround.

Any way from this I have learned a lot about ring rollers and how they work, I have also found out how not to build a ring roller.

the probloems I found with mk1 where:

• The bottom rollers are too far apart, but due to the design this could not be improved
• Because I used a welded box section frame the moveable top roll isn't always square to the bottom rolls, this causes a twist in the material

Now that mk1 has proved usefull I can justify putting some money into building another.

I plan to follow a design similar to the commercially available rollers starting with a pice of thick plate for the main frame. I have a 3 phase gear motor in the shed that's been lying arround for a while and an VFD to match so this one looks like it will be powered.

There's going to be many probloems to solve along the way but one that's got my head spinning at the present is, if I decide to drive all 3 rollers (just to be awkward) how as the bend gets tighter do all 3 rollers run at the correct speed? As the roller on the inside of the bend will have to turn slower the the other two.

 

[rtbcomp]

Could you have different diameter rollers? - a larger diameter will have a faster peripheral speed for a given rpm than a smaller one.

 

[Spark plug]

If that where the case I would just stick with the 2 roll drive as it works well enough, I just would like to go 1 better if I could and it's annoying me as to how it works on a commercial machine.

 

[Spark plug]

Hear are some of the build pics of mk1

 

[rtbcomp]

If that where the case I would just stick with the 2 roll drive as it works well enough, I just would like to go 1 better if I could and it's annoying me as to how it works on a commercial machine.

Don't see what you mean - the 2 outside rolls would be slightly larger than the inner, otherwise you have to have different sized sprockets, so you may as well just have different rollers - cheaper and easier.

 

[rtbcomp]

You could drive the inner roller through a slipping clutch, so the clutch slips rather then the pulley to prevent marking the metal or wearing the pulley, but i don't think that would give much if any advantage over the two-roller drive.

 

[Spark plug]

Don't see what you mean - the 2 outside rolls would be slightly larger than the inner, otherwise you have to have different sized sprockets, so you may as well just have different rollers - cheaper and easier.

I see ware your coming from but It wouldn't be convenient and practical, as the speed ratio would change with each pass of the bend meaning the centre roll would need to be changed for each pass. Also the difference in ratio would increase with material thickness aswell.

You could drive the inner roller through a slipping clutch, so the clutch slips rather then the pulley to prevent marking the metal or wearing the pulley, but i don't think that would give much if any advantage over the two-roller drive.

That would be one way of doing it but as you say wouldn't give mutch advantage over a 2 roll drive system.

 

[rtbcomp]

... the speed ratio would change with each pass of the bend meaning the centre roll would need to be changed for each pass. ...
.

I wondered about that, but reckoned that as the thickness of the material remained the same, the ratio of pulley sizes would do so too, however after throwing some maths at it I now reckon

D2 / D1 = (ID + T) / ID

Where
D1 is the diameter of the inner roller
D2 is the diameter of the outer rollers
ID is the internal diameter of the ring (decreases with each pass)
T is the thickness of the material (remains constant)

The above assumes that all the rollers are driven at the same rpm.

Does anyone agree or disagree?

A conical belt drive may do the trick and could also function as a slipping clutch, but I think that's getting over complicated.

 

[Wendelspanswick]

I think your over thinking it as the tube is used as supplied so slightly oiled and the rollers are smooth and hardened so even with three driven rolls slippage will account for any difference in roller speed.

 

[Spark plug]

I think your over thinking it as the tube is used as supplied so slightly oiled and the rollers are smooth and hardened so even with three driven rolls slippage will account for any difference in roller speed.

Thinking about it more this might be why only the realy big section rollers have 3 driven rolls, the effect of the 3rd roll slipping may help in the bend sort of holding the top of the material back, but this will also mean a lot more force haas to be applied to drive the rolls.

 

[Kent]

Drive the top roll give it a light knurl for increased grip

Move the bottom rollers in and vertically to get your bend but make them very free running

Anyhow that's my plan still looking for that old mixer but had thoughts about a big starter motor from a decent size diesel and sprockets

I think a foot switch is a must then you just take your foot off in case of problems

Keep us up to date with your developments on this though

 

[wilbur]

Does anyone agree or disagree?

I agree, almost, though I think the thickness would add twice to the ID (because it's a diameter not a radius), so I think it's:

D2 / D1 = (ID + 2T) / ID

A way of thinking about it which makes it obvious that it's going to change with curvature is that if the metal was straight (i.e. when you're starting), there would be no difference in roller speed, so if there was is any difference once it's curved, then it must be a relationship between the speed-difference and the curvature.

If the ratio of the two roller speeds is 1 : (1-2T/D), then 3mm flat rolled into a 300mm circle (which sounds reasonably tight/ambitious to me - I'm not sure what the OP is planning) would have a 2% difference in speed.

Which puts me firmly in wendelspanswick's "don't over think it" camp. Perhaps down here in the South West we don't overthink stuff because it takes us so long :-)

 

[Spark plug]

Drive the top roll give it a light knurl for increased grip

Move the bottom rollers in and vertically to get your bend but make them very free running

Anyhow that's my plan still looking for that old mixer but had thoughts about a big starter motor from a decent size diesel and sprockets

I think a foot switch is a must then you just take your foot off in case of problems

Keep us up to date with your developments on this though

I like the idea to move both bottom rolls up and in but I think this will be a very tricky design to pull off right, defenatly more superior tho.

 

[Spark plug]

I'm not sure what the OP is planning

40x10mm flat on edge with a 750 o/d just for an example.

 

[wilbur]

40x10mm flat on edge with a 750 o/d just for an example.

That's less than 3% slip, so I can't see it being a big deal, personally. Though I'm definitely on intuition/******** here, not years of experience of rolling rings...

 

[Spark plug]

That's less than 3% slip, so I can't see it being a big deal, personally. Though I'm definitely on intuition/******** here, not years of experience of rolling rings...

Tell me about it, ware are all the ring rolling experts when you need them.

 

[rtbcomp]

I agree, almost, though I think the thickness would add twice to the ID (because it's a diameter not a radius), so I think it's:

..

Good point, I don't think I'll bother doing it again though.

One thought did occur to me - the diameter going into the rollers is greater than that exiting, where does the change take place and do all 3 rollers try to rotate at different speeds?

 

[Spark plug]

Good point, I don't think I'll bother doing it again though.

One thought did occur to me - the diameter going into the rollers is greater than that exiting, where does the change take place and do all 3 rollers try to rotate at different speeds?

My head is starting to hurt

 

[Kent]

I like the idea to move both bottom rolls up and in but I think this will be a very tricky design to pull off right, defenatly more superior tho.

It's still in my head at present but it sorts a few issues

Plate is Deffo the way thinking overkill on that one

 

[Spark plug]

It's still in my head at present but it sorts a few issues

Plate is Deffo the way thinking overkill on that one

Initial thorts are to get a pice of 80mm plate burnt out once I settle on design/dimensions. 40mm shafts mounted in 6008 bearings. But now you have me thinking about moveing the bottom rolls so all could change.