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Wood lathe runout

JoshNZ

Aluminum
Joined
Jan 16, 2018
I recently got hold of an old union graduate lathe for a pretty good price. Here in NZ I couldn't find anything to fit the 6TPI thread. I didn't like the idea of an adapter so I knocked the spindle out and took it down to a friends shop and got him to machine a new thread so that one of the nova inserts would screw onto it.

I don't know what's gone wrong but I seem to have a bit of runout after getting it back together. I've attached a video showing a ~3mm flathead screwdriver up next to the spindle shoulder, no dial indicator sorry. The flange and the taper (MT3 to MT2 sleeve) are both still running true but the whole thread and shoulder seem to be off centre.

What's gone wrong here? Is it too much for wood turning?

There's not enough meat left to turn to a smaller thread. Starting from scratch will double the price of the lathe. Building up and trying again is an option I suppose but I've read it's not a good idea. Do I have any other options?

 
The position of the thread is what matters, not the shoulder. It does look like the job got fouled up but if you spin on a face plate and it runs true then ignore it. If the face plate does not run true than it can be a issue if you want to be able to remove work and then reattach like in a jaw chuck. But if you screw on a block of wood to a faceplate to make a bowl then it won't matter. I use a precision backup washer behind the the faceplate so that the faceplate always stops in the same position.

Screw on a faceplate and do the same check.
 
I don't have any face plates right now I was planning to just use faceplate rings and chuck them with the supernova2 chuck. The chuck exhibits the same wobble when snugged up tight. So the thread and shoulder are off center obviously.

Even the nova insert by itself which is like a tiny faceplate, exhibits the same wobble.

I do quite often reverse and rechuck stock. I've dealt with worse tolerances in crappy lathes while I was learning so I know it is workable but this was going to be my last lathe ideally, hence why I spent the money on getting the thread right. Next was going to be a VFD and motor to suit etc. I'm pretty dissapointed to see it.
 
Also that isn't the shoulder, the chuck insert has a relief cut inside it so it screws down right over that piece and squares up against the big flange which I had machined square.
 
I recently got hold of an old union graduate lathe for a pretty good price. Here in NZ I couldn't find anything to fit the 6TPI thread. I didn't like the idea of an adapter so I knocked the spindle out and took it down to a friends shop and got him to machine a new thread so that one of the nova inserts would screw onto it.

You should complain to your friend about the work.

I have seen what happens to those Nova chucks. The holes for the handle bars get elongated because the chuck is made from aluminium.
 
I think the chuck is nickel plated steel.

I will mention it but I don't think there's any use complaining there's not much that can be done about it now. What would a machinist charge roughly to start from scratch? A photo of the original spindle is below. The flange is a real pain surely you wouldn't start with a chunk of steel that thick and turn down the rest of the shaft? It must be welded on is it?

http://www.gandmtools.co.uk/wp-content/uploads/2017/04/DSCN8560.jpg
 
I would (and have) started with thick chunks of steel.

My wood lathe spindle has a backup collar that has a large hex head. It screws onto the spindle over and past the thread for the face plates. I had to make a replacement and I was glad that it was not one piece.

A friend bought one of those early Nova chucks and complained about the lever action holes used to tighten and loosen the jaws. The holes looked like ovals.
 
It might be one of novas first chucks you're talking about, I think I know the one. They have come a long way since then. Not using holes any more this one is a geared chuck you tighten it with torque from a hex tool. Heavy as hell. I wouldn't think it had any alu in it.

If you're going to start again then you have to start with a bar the size of that flange then huh. Story gets worse and worse =/. How many hours machining to get through all of that...
 
QT [I don't know what's gone wrong] you machinist ran it out of his chuck and put lathe chuck run-put into that part..
Had you come here first the guys would have told the correct method..run between centers.
If you should have your friend cut another have him/her turn and thread it between centers...
But your friend only tuned the end ..Making new is a big job for a one up..likely $100 USD or more. Your face plate can register and be trued in place so run out will be no problem..Needing a chuck and thinking the .020 or so a problem.. if so you might get a Independent 4 jaw check..

Having a hole through for a draw bar screw you might make a stub arbor that goes to the ID taper for holding a 3 jaw chuck..Yes the check would stand out perhaps an inch.
 
Also if the stock wasn't supported by tail stock the chuck could fly out of the taper at any moment haha.

I don't want to piss around with truing faceplates to match etc the whole point of this was to make it an easy machine to use so that I did use it. It's a lost cause I think this spindle will have to go in the bin. I'll shift it to the back of the shed and keep my eye out for a second hand spindle I think.
 
QT:[Also if the stock wasn't supported by tail stock the chuck could fly out of the taper at any moment haha.]
A draw bar screw would be a long thread going through the whole head stock pulling the stub arbor that holds the chuck so about as secure as secure could be...
 
Ah yes I understand sorry my eyes skipped over the bit about the draw bar.

It still sounds like more trouble than it's worth for me. The whole point of having it machined was so that it would be simple and easy to use, and decent quality. I've had several lathes, one I built myself, and I'm at the point where I'm sick of compromising so I'll just do it right this time I think.

Thanks for all the comments.
 
The hole through the spindle is probably not true to the shaft so turning it between centers is not right. Holding the spindle on the outside bearing surface like in a chuck is right. The error was probably introduced because they turned between centers. If I was doing the work I would have machined the inside hole perfect to the outside before turning between centers.

The last guy who used your center could have done a lot of work using spur centers. He bangs it in to hold the wood. Then bangs it outfrom the other side. Over time the center hole gets screwed up. The a revolution or two of thread on the end can break off over time. Happened to me.
 
Certainly the hole should be tested first..I Think it would be true at the out end so if nothing less that could have been put to the tail center and Yes tested for true.. putting between centers and testing it even with a screw driver if not having an indicator..A decent machinist would/should never make such a part with having run out..

Off the bearing would be fine if tested for true...+-.002 or less would be my target. likely I would get +-.0005
 
There's not enough meat left to turn to a smaller thread. Starting from scratch will double the price of the lathe. Building up and trying again is an option I suppose but I've read it's not a good idea. Do I have any other options?

The thread looks pretty. Was it done on a machine tool or a manual pipe threading contraption used for running drain pipes. I bad idea I had was to weld a stub onto the tip and start over but that would be a real hack.
 
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I think he would have been ok turning between centers. Maybe not the best way, but the center is turning true to my eye so it would have been close enough. But yes, I should have marked on the shaft where the bearings sit so that he knew where to chuck. Realistically though, anywhere on the shaft is true enough I can see the spindle inside the head stock and none of it has the wobble that the two cut threads have. There's obviously been a chucking error. Maybe he used a 3 jaw chuck or maybe he used a 4 jaw and just eyeballed it without a dial indicator.

It was a CNC lathe with standard cutter as far as I'm aware.

What do you guys think of building weld up over threads and re machining? Waste of time? Same as welding a stub right. Asking for trouble?
 
Because the center is true justifies it would have the best way to turn it ..but done is done.. you can figure a smaller thread if that would do for holding something ..or make the stub arbor to hols the chuck off the ID taper and held tight with a draw bar screw from the back of spindle head..

To save the existing spindle.. with still having enough meat at the out end one might turn it down to a smaller size and thread.. make a part to thread over, that has a desired nose OD to support the desired thread.. wrench it on tight.. pin it with a taper dowel.. peen the out end (small) of the taper dowel so making the nose fixed part.. turn the desired thread off the nose ID tape between centers.

Yes the added nose could be pressed on..pinned and threaded
 
I'd agree with Michiganbuck; seems you could design a part to press onto/into the existing spindle, if you take note of where the bearings fit onto the spindle, and design accordingly for a part that would avoid deforming or changing the size of bearing journals. Make that part with extra material for post-machining, then press into place, drill/pin, and finally remachine to the correct profile for the spindle nose you want. The remachining should be done so as to be concentric to the bearing journals.
 
likely you could draw the spindle nose you want.. than take it to a local machine shop and get a quote...
likely bid two hours and the steel..
Having the hand drawing will save a lot of wasted talking time.

likely the guy the guy who turned the part in error could turn a nose piece..press it on ..pint it.and then turn it correctly..

It is a very nice lathe and worth fixing IMHO.

I Should add that if taper pinning the added nose part, the pin would be off to the side so fixing it to be a non come apart unit , but not crossing the taper ID.
 
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What do you guys think of building weld up over threads and re machining? Waste of time? Same as welding a stub right. Asking for trouble?

I think now is the time to ask what wood lathe you have? The color is green, General? Powermatic? Is the thread a 1" 8 TPI.

I once filled a taped hole on a custom handle and turned it down, then relocated the hole. The weld spot disappeared. But that was in stainless and the handle only had a 1/4 20 hole. For you situation I would not do it.
 








 
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