ratchet system for pole lathe

[dervishcarving]

Any ideas?

I am trying to turn some larger bowl (the small ones seem to come out real nice and people have asked for some large ones) but the problem is that large bit of wood have momentum and so turning it on a normal pole-lathe is difficult (and hard work). I have heard about the possibility of a ratchet-type system you could adapt a pole-lathe with to make it turn only 1-way and you add momentum as you pump your leg. Anyone got any ideas where i might get plans for such a thing?

Ta

d

[slack ma girdle]

I have seen it demostrated with a flat piece of leather wrapped around the bowl, so that the momentum of the bowl carried on spinning when the man liffted his leg and the tension released. As soon as the peddle was pressed and the tension re-applied the bowl was spun again. Judging by the sweat dripping of his nose it is still hard work.

[fergusonforestry]

what about adapting a bicycle rear hub?

[dervishcarving]

Now thats not a bad idea, i can try that Sunday. Any one else have any ideas? or a link to a page where it is discussed or even a pic/video?

[dervishcarving]

adding a wheel-hub is ok but we try to only use traditional green-wood methods/equipment so metal wheels and bearings is kind of 'against the grain' (pardon the pun)

[fergusonforestry]

any use?

[dervishcarving]

wow, thats nice work by somebody Im amazed at the wood skills of some people. i am more of a chainsa-carving or bowl-turning type

[agg221]

I think the problem with a true ratchet system on a pole lathe is that you can no longer directly drive the workpiece.

 

If you are running a conventional pole lathe with the drive string from pole straight to wrapped around the workpiece there is nowhere to insert a ratchet. If you're turning between centres it could be done by pushing a drum ratchet piece onto the workpiece, but I suspect you're not turning large bowls between centres. If you're hanging the bowl one side of the headstock, fixed to a runner through the headstock, you could apply a ratchet drive through a drum mounted on the other side of the headstock. Otherwise, you'd need indirect drive, with string to ratchet drum on what is effectively a layshaft, with a second drive from layshaft to workpiece (probably with an additional idler for tensioning) but that's quite complicated.

 

The ratchet drum itself could be quite simple - you want a free running drum mounted on the shaft, with a set of ratchet teeth around one end. You then have a fixed wheel on the shaft, with a click mounted on it to engage with the ratchet teeth. Drum and wheel (disk) can be turned, the ratchet teeth are just cut square to the radial lines around the centre and sloped back towards the next one (think handsaw teeth, rip pattern). The click could be carved up and pegged on to the wheel. The drive string goes around the ratchet drum. This is basically a simplified version of a weight driven clock drive drum and ratchet wheel configuration (without the gear teeth), a design which hasn't changed since the middle ages, so pretty straightforward.

 

Slack ma girdle's approach is much simpler though!

 

Alec

[Baggy]

Have you tried a larger mandrel?

 

Or ask Robin Wood for advice, he turns huge bowls

Robin Wood :: wooden bowls & plates :: traditional turning :: spoon carving :: countryside furniture

 

or ask on the bowl turning forum

http://www.bodgers.org.uk

[dervishcarving]

Thanks for the input there lads, excellent engineering-viewpoint Alec. I dont have any desire to go to that length for it! i dotn think i have anywhere near the skill needed. I run direct drive to the bowl via a mandrel so there is nowhere to fit a true ratchet-system, i would have to go the route you suggest which would, i suspect, be a horribly complicated build.

I think the leather idea is worth a short, i contacted Ben Orford (he made the tools i use, lovely chap and very helpful) and he said a similar thing but suggested dogfish skin as it has barbs so it would grip one-way and run smooth the other. Now i just need to find some dogfish skin

I will ask on the bodgers site once the administrator gets back from holiday and activates my account. This is a more long-term project. My small bowls are now coming out lovely and people are buying them they are also asking for larger ones, hence the 'ratchet' question. I will post the results here if anyone is interested

Dave