Left hand thread

[ShedBoy]

Will it work if I mount my tool on centre upside down, run the spindle backwards and feed in the normal direction. My mate wants to make a largish size wood lathe (he is cheaper than me). He wants to turn large bowls so to the left of the head I was thinking of threading the spindle lefty so it doesn't loosen when he digs in. Not a fan of wood. He is talking 700mm bowls here. Suggestions

 

[mzetati]

You can start a thread at either end of the workpiece: in case of a LH thread, I'd take advantage of the 'towards the TS' direction, especially when turning to a shoulder.
Chuck a short lenght of PVC tubing and practice a bit, if You're new to threading on the lathe.
Marcello

 

[ShedBoy]

Yep new to threading. Hand ground a bit once and threaded some acetal going into steel. It tightenened up but didn't feel the best. It should just be a straight shaft the thread is the most common one for wood lathe 1inch x 8tpi. I realy don't like imperial. I was doing some doodling on the aeroplane on the way home ffrom work and my idea should work. I could always post pictures in the ****oo section if it goes pear shaped. I have been reading the tafe machining bible and I think I know wht is happening. Good idea though trying it on some pvc. I will post it if I have to do it. Has anyone done a post on threading for beginners with lots of pictures. The disengaging the leadscrew and then starting in the same spot again for the next cut has got me thinking. I just stoppped the machine last time and reversed it out never took the half nuts off the screw which I am sure is not the way to do it but I figured not too bad on acetal with a ground up bolt for a tool.

 

[mzetati]

Cutting all the thread without disengaging the leadscrew is common practice on 'mini' sized machines, especially when it comes to cutting imperial threads on a metric leadscrew or viceversa.
Just note the reading of the dial and retract the tool on back passages. I suppose that could do for larger ones too, especially when no thread dial is available.
Have the tool overhanging from the post as little as You can.
Use slow speeds as the carriage would travel quite fast at 8TPI.
When possible, a discharging groove at the end of the thread helps a lot.
Apply oil.

Marcello

 

[Ken I]

Just 2c worth

Wood lathes obviously use a RH thread at the spindle and a LH thread on the outboard end of the spindle.

Here's the interesting bit - attatchements such as faceplates are often screw cut both left and right hand (ie deliberately cross threaded) so they will fit both ends.

From a metal machininsts point of view this is barbaric - but commonplace on woodturning lathes.

You can turn a LH thread with the tool in the normal orientation with the feed in reverse - ie going away from the chuck. You then start near the shoulder / undercut and work out.

Ken

 

[ShedBoy]

Thnks for the info on double threaded faceplates. I may end up making them for him aswell. The upside down set up still intrigues me

 

[Stan]

This may sound ill informed or just stupid but if you are going to work on the outboard end why not just run the lathe in reverse and then all the attachments would fit both ends with right hand thread.

 

[ShedBoy]

Good idea Stan. Thanks

 

[Ken I]

Unlike metal working lathes - I've yet to see a reversible woodworking lathe (single phase motors and all).

Good idea though.

Ken

 

[Groomengineering]

Well if you think about it there's no practical need to run a wood lathe in reverse. ???

When I turn LH threads I just reverse the leadscrew and turn towards the tailstock. It actually is less stressful to me than threading towards the chuck. :

Oh, and having a 9" SB with a screw on chuck I can't run in reverse anyway...

Cheers

Jeff

 

[imagineering]

This may sound ill informed or just stupid but if you are going to work on the outboard end why not just run the lathe in reverse and then all the attachments would fit both ends with right hand thread.

Hi Stan, ill-informed, but not stupid.
Most Wood Lathes have provisions to mount an outboard ToolRest on the Front of the Machine.
Reversing the direction of rotation would not be advisable as the work would then lift the Gouge up off the ToolRest. Remember that Wood Turning is done with Gouges which are HandHeld, not clamped down.
The professional Lathe that I used for many years was constructed with Left & Right Handed Threads and had 'Handed' Faceplates and Chuck Adaptors.

Murray.

 

[Stan]

The only wood lathe project that I have seen on the outboard end was about three feet in diameter and the operator was working with a floor mounted tool rest that was longer than the workpiece. I guess he did bigger pieces than the one I saw.

With that type of tool rest, you could just work behind the center with the lathe running in reverse.

 

[bezalel2000]

Hay Murray


For a brief moment I thought someone had been taking photos in my shed

Ken

Unlike metal working lathes - I've yet to see a reversible woodworking lathe (single phase motors and all).

Good idea though.

now you have!

This lathe has a 2hp single phase reversable motor - reason for it being reversable is for sanding and sealing.

With the motor rotating normal direction you have to hold the sandpaper underneath which has a tendency to throw the dust up into the air.
When reversed the sand paper is on top and the sawdust is mostly thrown away from the operator and downward.

The benefits when sealing with buffing oils are similar. If the motor is running forward you have two choices, 1. hold the oil applicator on the top where gravity draws the oil down onto the job while at the same time spraying the operator with any surplus oil.
2. the other way which is to hold the applicator underneath. This reduces the oil shower affect but gravity is pulling the oil away from the job and between the fingers.

In my humble opinion a reversable wood lathe motor is more a "must have" than a could have.

If you are interested in how to wire a single phase induction motor with a reverse switch,
I'll start another thread just on that.

Just to bring us back towards the the original topic of thread cutting
The yellow lathe has succefully cut a 10 TPI thread in wood before, alas can't find any photos

Bez

 

[bezalel2000]

Hi Shedboy

I don't see anything technically wrong with your proposal.
The conventional way to cut a LH thread with change wheels is to add an idler gear to the banjo to reverse the direction of the leadscrew
Doing this with the tool post in normal position with motor running forward you are naturally cutting towards the tailstock

I Cut this LH worm gear last week same way I just described

Bez

 

[Ned Ludd]

Hi Guys,
I don't think that both left and right handed threads in wood lathe attachments is that common, I have only come across it on Graduate (1 1/2" by 6TPI) lathe, first available this side of the pond I seem to recall, from APTC on their self centring four jaw.
It seems to work quite well on such a large coarse thread, but if tried on a finer thread would not leave much metal to screw the chuck onto.
Ned

 

[ShedBoy]

Well I am going to give my idea a go on something soft, Just got to get a valiant car motor out of my shed.
Thanx all for the comments and suggestions. I will post the outcome.

 

[Ken I]

Ned is right - the double handed thread is only possible on a large diameter - coarse thread.

I mentioned it more as a curiosity - personally I think its a terrible idea.

Ken

 

[Ned Ludd]

Hi Ken,
I agree a terrible idea, not sound engineering practice at all, but you know these woodworker types and it does work.
Ned

 

[Ken I]

Ooh Ned - now you've done it - you are going to get tarred and feathered (with wood shavings). :big:

 

[Ned Ludd]

Bring it on! I need some excitement.
Ned