My Lath has developed the wobbles

[A-Marks]

I'm not a real mechanically minded wood turner and havent been able to work out why my lath has developed the wobbles lately
It's only when I put a big bit of wood on it - over 100x100 - even when its perfectly trued it still vibrates and carries on!

There is a threaded insert that attaches to the threaded bit of the chuck could that wear out?

Allan

[Skew ChiDAMN!!]

I'm not a real mechanically minded wood turner and havent been able to work out why my lath has developed the wobbles lately
It's only when I put a big bit of wood on it - over 100x100 - even when its perfectly trued it still vibrates and carries on!

There is a threaded insert that attaches to the threaded bit of the chuck could that wear out?

It's not likely that the insert will wear out, unless you've been doing something extremely unusual and unsafe... but it is possible that the grub-screw that locks it in postion has come adrift. This is more likely to result in the chuck spinning off the spindle when turning the lathe off than creating a wobble though.

The basic wobble checklist:

ensure your belt is in good condition, no lumps or chunks missing. (unless you have direct drive, of course! :D )
similarly, check your pulleys are clean. (as above)
check the headstock is bolted down and/or locked securely in position.
check for wear in your headstock bearings! Both side-play and in-and-out. If you can eyeball any slop, they're worn.
ensure the drive spindle isn't bent: Spin the lathe up without the chuck and lightly place the flat of a skew chisel on the top of the thread near the end. If it chatters, well... bad news.
do the same with the chuck mounted, to ensure the chuck's body hasn't warped.
double-check that you have each jaw mounted on the correct slide!
If you're using the tailstock as well, insert a drivespur in lieu of the chuck and bring up the tailstock to touch, making sure it's correctly aligned.

I know the above's not specific to the problem you describe, but working through it really narrows down the possible causes...

...one thing that has me puzzled though; how can you tell if the blank's perfectly true while it's wobbling? :confused:

I had a similar problem not long ago and it turned out the problem was a micro-fracture in the chuck body, where the insert threads in. Working through the list didn't find it, but did enable me to work out where to look. So far as I know I'm the only person who's had this particular fault, but maybe not for long, eh?

[rsser]

Might try some of your tests myself SkewChidamn.

The Vicmarc has started a kind of thrumming when I'm pushing towards the headstock with a bowl gouge. Seems to happen with pretty much any bowl at any stage no matter how well mounted.

Tightening up all the mounting bolts made no difference.

Does anyone know whether the tapered roller bearings are adjustable? Any other things to look for?

TIA

[Woodturnerjosh]

Rsser,
To adjust the tapered roller bearings in a Vicmarc you need o adjust the "bearing adjustment nut" on the left hand side of the headstock. If your machine is like mine it will have a collar with three allen head grub screws that all have to be tightened up the same amount or if it is a newer model it will only have one grub screw to tighten up ( this is set-up like a clamp). As an owner of a VL200 who has replaced the bearings completely I can tell you this is a bugger of a job. If you pre-stress them too much they heat up and not enough they rattle. I would explore all other avenues before doing this. One way to test is to take everything of the left and right hand side of the headstock (leave the bearing adjusment nut where it is) so all you're left with is the spindle, start up the lathe and while holding a piece of cloth (old rag) put pressure against the inboard spindle shoulder. If it still makes the noise you are hearing then it is probably your bearings.
Good luck.
BJ

[rsser]

Thanks BJ.

It's a 175. Sounds like yours with a collar on the outboard side with three grub screws.

So it's the tension on these screws that adjusts the collar?

[Woodturnerjosh]

Sorry,
I did not explain that part properly.
To adjust the bearing tension you need to :
1. Loosen the three grub screws.
2. Thighten up the "bearing adjustment nut" or "collar" a degree or two.
3. Tighten up the three grub screws.

When you loosen the grub screws undo them by the same amount each, say a turn and a half, and retighten the same amount. If you tighten up one, more than the other it will actually cause the "adjustment nut" to bind up against the casting. Rotate the shaft by hand and you will be able to see the gap between the adjustment nut and the casting, this should remain as even as possible. You will also be able to feel if it is rubbing against the casting.
It's a trial and error sort of process. To check mine I would tighten the nut a little bit, tighten up the grub screws and then run the lathe on full speed for about 30 seconds. Feel the bearing " adjustment nut" and the inboard spindle shoulder, if they are hot to the touch loosen the "adjustment nut" a little bit. They can be warm but they should not be hot. The cooler the better!
I apologise in advance if this is still unclear. It would be easier to explain with pictures but I am not that technologically endowed.
Keep me posted if you need any help.
Your lathe user guide should touch on how the adjust the bearing tension (I think.)
Good luck
BJ

[Woodturnerjosh]

To address the original post.
If the timber you have put on is green but still trued it can have uneven levels of saturation. I once had a perfectly round piece of green wood (pear I think) 300 by 100mm that had to be roughed out at about 300 rpm because one side had about twice the amount of moisture as the other. I think this was due to some rather dramatic changes in the grain pattern and direction that was in about the center of the blank (one of the reasons I chose it).
If the vibration you are experiencing is all the time I would go to the belts first as Skew chidamn reccomends.
Good luck
BJ

[RETIRED]

Have you checked the speed?:)

[hughie]

Does anyone know whether the tapered roller bearings are adjustable? Any other things to look for?

TIA
[/QUOTE]

Ern,
Can you get your fingers any where near the bearings when its running. Worn or over tight bearings will run hot even when not loaded ie a great lump in the chuck. Or check the bearing area when its cold run it for 30min to an hour turn it off and check again it will most likely be warm but not hot to touch. Also see if the bearings are dry, dry or over greased bearings will run hot and flog them selves out.
hughie

[rsser]

Thanks Hughie and BJ. Clear now. Will do the checks.