New bowl lathe and poppet question

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New bowl lathe and poppet question

Postby Steve Byrne » Tue Aug 25, 2009 10:28 pm

I've just built myself a bowl lathe, using an old telegraph pole for the headstock, tailstock and supports. Its all pegged together with a mixture of applewood and ash pegs (I thought I'd experiment), and is so heavy it took two of us to shift it once it was put together. It's a beast of a thing.
Image
Initially I used a lump of oak as a poppet, but it wasn't really wide enough and so I've substituted that for a great bit ash one.
Here it is with the original poppet. I've used 15mm threaded bar for the points, and just taken the thread off on the exposed bits.
Image
and its new poppet, with my first test bowl on -
Image
While I was at it, I made a new mandrel with a bit of oak, and I've tried grooving it to see if that helps with grip.

I'm using 2 wedges to secure the poppet, but however hard I try, I'm getting movement in the bowl after a very short period. Is there some knack to using 2 wedges, or a particular way to shape them that works best?
If thats no good I'll try with a single wedge and see if it holds. I'm missing the ability to just turn the handle and keep the work tightly held already..
Suggestions please as I'm dying to get some bowls turned, and this is the only thing left to solve..
Cheers
Steve
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Re: New bowl lathe and poppet question

Postby robin wood » Tue Aug 25, 2009 11:27 pm

Looking at your set up I don't think the poppit has moved so your centre has worn into the bowl . This happens more quickly if your centres are not perfect cones so start by checking they are as near perfect as possible then get some abrasive paste, valve grinding paste, t cut or whatever smear it in the centre hole and spin away for a while to grind and polish it to a perfect cone.

That is one of the best looking bowl lathes I have seen on here.
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Re: New bowl lathe and poppet question

Postby Steve Byrne » Wed Aug 26, 2009 8:39 am

Cheers Robin, I'll give that a try - looking at the points they are a bit one sided, and the point on the poppit has dug in a bit. I'll have a go at them and see what happens.
Glad you like the lathe - I've had that telegraph pole sitting in the yard for years and its amazing how solid it still is. All the pegs I used are a good inch in diameter, so it should last well.
One question - are the points better off being 'flatter', with a shallower angle, or more pointy? Any preferences out there?
cheers
Steve
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Re: New bowl lathe and poppet question

Postby paul atkin » Wed Aug 26, 2009 9:04 am

Thats a great looking lathe twisty, look forward to seeing some bowl pics
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Re: New bowl lathe and poppet question

Postby Robin Fawcett » Wed Aug 26, 2009 10:34 am

twisty wrote:One question - are the points better off being 'flatter', with a shallower angle, or more pointy? Any preferences out there?


I reckon a 60 degree angle is the one to aim for.
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Re: New bowl lathe and poppet question

Postby gavin » Wed Aug 26, 2009 2:32 pm

twisty wrote:I'm using 2 wedges to secure the poppet, but however hard I try, I'm getting movement in the bowl after a very short period. Is there some knack to using 2 wedges, or a particular way to shape them that works best?

If you get someone else to pump your treadle and set a billet of say 4 or 6 inch diameter between your centres, you can watch your lathe at work, and often spot any wobbles or loosening. Do check if your wedges press over all of the mortice of the poppet head - you don't want the pressure on on one spot.
twisty wrote:
I'm missing the ability to just turn the handle and keep the work tightly held

Yes, something like these T-handled centres (which I sell ). You can make them yourself from 20 cm of 20 mm threaded bar if you have a metal-working lathe and a welder to fix the T-handle. As I fear the T-handle may be cut off below, do look here )
Image

twisty wrote:I
One question - are the points better off being 'flatter', with a shallower angle, or more pointy? Any preferences out there?

I am with Robin F here: 60 degrees and ideally get them turned in a metal working lathe. For bowls I suggest you want at least 15 mm diameter centres, and I use 20 mm.

Abrasive paste?
I have tried Robin Wood's suggestion to grind the points symmetrical with some abrasive valve-grinding paste on either end of a billet of wood, but after 15 minutes treadling I gave up as I was not removing anything that I could see. The points were mild steel. Did I miss something? Has any one used this method successfully?
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Re: New bowl lathe and poppet question

Postby Steve Byrne » Wed Aug 26, 2009 2:55 pm

Thanks for the suggestions - I've just had a go at them with a fine-ish file, and then put a blank bit of oak on with some honing paste either end and thats polished them up well. Seems that when I took the grinder to them I'd left a bit of a flat spot on the undersides and that must have been causing it.
Half turned a bowl there and its still tight, so this was obviously the culprit. Just goes to show how something seemingly minor can have such an effect.
Gavin, I'd put a handle on my original lathe, and its definitely handy to have that adjustment, but for the bowl lathe I thought that I'd do without (and it does tap up really tight, I'm surprised at how well).
All the big bowl lathes I've seen don't seem to have the adjuster, I don't know whether that's just because its one less thing to have to make, and it is simpler and as effective to just have 2 fixed points; or whether there is some other reason I haven't worked out.
So often the simplest solution is the one that stands the test of time.

cheers
Steve
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Re: New bowl lathe and poppet question

Postby gavin » Wed Aug 26, 2009 3:45 pm

Have you fixed the short 'T' sections of telegraph pole seen on the floor to the vertical members? If so how? or are they just held by their own weight?
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Re: New bowl lathe and poppet question

Postby Steve Byrne » Wed Aug 26, 2009 4:25 pm

They are jointed very simply - just cut half way through and then cleaned up with an axe to give 2 flat surfaces, and then drilled right through with a 1 1/4" bit. I had a lump of pretty well seasoned apple wood here, so made oversize pegs (2 just shaved down to size, and 2 on the lathe to see if it made any difference).
Image
Then just drove them home and its solid as anything. No movement at all in them. The only problem I had was that the pegs were quite long , and getting them large enough to be a tight fit but not so large they went nearly all the way in and then split. Only one did, and it was so nearly in it doesn't matter.
The bed is attached the same way, although I'd already made the joints there intentionally tight, so its not going to move. It's pegs go in from each side though, rather than being one that goes all the way through.
cheers
Steve
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Re: New bowl lathe and poppet question

Postby gavin » Wed Aug 26, 2009 5:34 pm

Would you have considered fixing the lathe-bed to the uprights with threaded bar - say m12 or m10?
If authenticity was not needed, I'd be wary of the wooden pegs potentially loosening on the lathe-bed. I think you'll be fine with the 'T' feet and their pegs.
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Re: New bowl lathe and poppet question

Postby Steve Byrne » Wed Aug 26, 2009 5:54 pm

Yep, I did consider it, and to be honest it would have been a lot quicker than doing it with the pegs but it was something I wanted to try, and I didn't have enough threaded bar about, so pegs it was.
Really though, they are so tight, I can't see it moving, and I still have the option of putting little wedges in the ends of the pegs to tighten them further. I'd meant to do that, but haven't got round to it yet.
The other factor is that I wanted to use what was around the place, and I had just enough 3/4" bar to make the points, and everything else is what I had here. BT changed the poles on our boundary a couple of years ago and were happy to leave the old poles here. I get a few from them when they are in the area - they make very good gateposts for field gates.
cheers
Steve
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Re: New bowl lathe and poppet question

Postby robin wood » Thu Aug 27, 2009 12:16 am

twisty wrote:Thanks for the suggestions - I've just had a go at them with a fine-ish file, and then put a blank bit of oak on with some honing paste either end and thats polished them up well. Seems that when I took the grinder to them I'd left a bit of a flat spot on the undersides and that must have been causing it.
Half turned a bowl there and its still tight, so this was obviously the culprit. Just goes to show how something seemingly minor can have such an effect.
Gavin, I'd put a handle on my original lathe, and its definitely handy to have that adjustment, but for the bowl lathe I thought that I'd do without (and it does tap up really tight, I'm surprised at how well).
All the big bowl lathes I've seen don't seem to have the adjuster, I don't know whether that's just because its one less thing to have to make, and it is simpler and as effective to just have 2 fixed points; or whether there is some other reason I haven't worked out.
So often the simplest solution is the one that stands the test of time.

cheers
Steve


Glad that sorted it, thought it might. I find screw threads slow, if my poppit is loose I give it one whack on the side to drive it in and tighten up then a whack on the wedge to hold it firm.
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Re: New bowl lathe and poppet question

Postby Donald Todd » Wed Sep 02, 2009 9:12 pm

You can grind in the points more aggressively by using emery (Carborundum) grit mixed with spit. Generate the grit by scrunching up emery paper and collecting what breaks away. Even fairly coarse grit gets ground up fairly fast. I've done this for spindle turning points, and found it helped to turn the points themselves about 1/4 turn every few minutes, which you may not be able to do. Use a soft wood billet and make a deep hole with a gimlet, so the points are "swallowed". If you can't turn the points try to keep the cord tension as low as possible.
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