Position of tool rest on a bowl lathe

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Position of tool rest on a bowl lathe

Postby Stanleythecat » Mon Sep 06, 2010 9:10 am

Hi All

I'm not sure if this will spur on huge debate or whether there is a clear answer to this but what is your preference for the position of the tool rest?

The reason I ask is that I was taught on a lathe that had its tool rest in line with the centres, a friend of mine who is self taught and learnt in parallel sets his tool rest much lower and tends to do all of his turning bellow the centre. He found my lathe very hard work too so I am wondering if I have set mine up correctly.

On another note, we also differ in that I use bungees (firstly because we do not have any coppice in our wood so no poles! and secondly from a safety persepctive; space is limited and as a mental health project the pole was both a trip hazard and had potential to bang someone on the head... some people can trip over a flat surface!) and Nick uses a pole. Nick found the bungee hard going, eapecially as the return was slow and there was some lag at the bottom of the cycle before the return. I wouldn't notice this as I haven't used a pole but for those of you who do use a bungee do you have any hints or tips please?

Many thanks

Leo
Last edited by Stanleythecat on Mon Sep 06, 2010 10:27 am, edited 1 time in total.
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Re: Position of tool rest

Postby Robin Fawcett » Mon Sep 06, 2010 10:02 am

I have my tool rest at the same height as the centres, using it below centres sounds like a power lathe technique for scraping.

Try using a longer piece of bungee set up as in the diagram below...
Image
It has more the feeling of using a pole and doesn't snatch as much as when you just have it stretched between the top of the uprights. Also I use a shock cord from boat chandlers - much stronger and more resilient than the stuff you get at B&Q.

You could have a go at making the pulleys from turned wooden discs held in place with a cut-off nail.
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Re: Position of tool rest on a bowl lathe

Postby Stanleythecat » Mon Sep 06, 2010 10:31 am

Hi Robin

Thanks for your reply. I use some fairly good bungee I bought online, does this setup work for bowl turning? I haven't turned for a few months (we had a baby in May and life kind of took over!) but yesterday it seemed really hard work to pedal, I'm pretty sure its not my fitness, it just seemed a real labour compared to before. Hmm!

Leo
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Re: Position of tool rest on a bowl lathe

Postby jrccaim » Tue Sep 07, 2010 3:38 am

If your lathe is hard to treadle ( I speak from bitter experience) it is due to friction above and beyond the allowable. it may be due to a number of factors. (1) your centers are misaligned. This is very easy to achieve when you are building the lathe -- just get careless for 30 seconds! (2) your centers are not 90 deg. to the poppets. (3) you drilled the holes in the workpiece or mandrel too deep. This causes undue friction. (4) you did not oil (or wax) the centers. (5) your centers are ground to a too-sharp or too-shallow angle. Sharp worse than shallow; the centers act like nails and dig into the wood. Ugly friction again. The "canonical" angle is 60 deg from centerline. I am quite sure 55 would work, but 45 is too shallow and 70 is too sharp. Make a template out of a beer can and check. (6) you screwed in the tailstock too tight. It should go in enough so as to have no end play, but no more than that. (7) You are turning soft wood. The centers want to dig in and slow you down. I got around this problem by drilling a hole in the workpiece and sticking in a hardwood insert.

I think I had every one of these problems when I built my lathe, and some rebuilding was in order! In my opinion, you seldom if ever need a heavier bungee; you need to remove sources of friction. One of the items on my overloaded agenda is to make a 60 deg. center drill. Machinists use this to make sure item (3) above does not happen.

Oh yes! Tool rest height. The book says put the rest at center height. The thing is, the gouge or whatever tool you are using must have the bevel just rubbing on the work. That way the thing will cut (shave) and not scrape. I do not know from where the people that make turning tools get their bevel angles. I wound up making an adjustable (within reason) tool rest. I find it much more comfortable when the rest is ohhh 50-100 mm below the centers. With a hook tool (I found out today) you have a lot more flexibility than with a gouge, but still: shave at a tangent!
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Re: Position of tool rest on a bowl lathe

Postby paul atkin » Sat Sep 11, 2010 6:46 pm

for what its worth my rest is set at about an inch below centre, i tend to take off a cut below above and on centre depending on which part of the bowl i am turning
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