Lathes With Threaded Spindles

[talvare]

I am just throwing out a general question/idea concerning lathes with threaded spindles. Over the past years I have read numerous comments about the caution required when reversing rotation of the spindle on these lathes. I'm curious if anyone has considered making a modification to their chucks to help prevent unscrewing when running in reverse. I was thinking that if I had one of the smaller lathes with the threaded spindle, I would consider drilling and tapping the chuck hub radially in probably three locations and using some of the soft tipped set screws available on the market to help prevent unscrewing of the chuck. This method may not work well on larger chucks just because of the inertia of the spinning chuck, but it seems that it may work for smaller chucks. Is this a bad idea or are there other better remedies ? The link below shows the type of set screws I was thinking of.

http://www.ondrivesus.com/precision-fasteners/tipped-set-screws?gclid=CPG9tInjic8CFZSPfgodvxsH1w

Just some food for thought.

Ted

 

[Bob Korves]

That is a good idea, Ted. I suppose the only place you really could put them on conventional spindle lathes is to the OD side of the register. Your SAG 14 has a D1-5 spindle, so not needed there. Are you thinking about getting another lathe?

 

[talvare]

Hi Bob,

Nope, not looking for another lathe. I've just seen and heard this caution about threaded spindles for many years and I was reading one of the threads on this forum this morning where this issue was mentioned again. So, since there is very little else occupying my little mind, it just got me to thinking and wondering if anyone has addressed the problem. If I had a lathe with a threaded spindle (actually my first lathe many years ago did), I would certainly want to be able to safely use it in reverse. Anyway, I'll stop thinking now before I start smelling burning wood

Ted

 

[T Bredehoft]

On my Clausing Mk2 I cut a .100 groove in the spindle, inboard of the threads, and modified the chuck backing plate to accept a clamp which would interact with the groove. There is possible movement if the chuck loosens, but it won't unscrew. No images, computer/camera interface problems.

 

[MozamPete]

I have a threaded spindle but I have to say I have never found a need to run the spindle in reverse. The one use I know of is to use an upside down parting tool, but I made a rear parting tool post for that so the spindle still runs in the normal direction.

Out of interest when else would you want to run the spindle in reverse?

 

[RJSakowski]

On my Clausing Mk2 I cut a .100 groove in the spindle, inboard of the threads, and modified the chuck backing plate to accept a clamp which would interact with the groove. There is possible movement if the chuck loosens, but it won't unscrew. No images, computer/camera interface problems.

The Grizzly 602 lathe uses a similar approach with two dog clamps which engage a V groove in the spindle. The clamps are tightened by means of two socket head cap screws threaded into the adapter plate hub which will pull the clamps down and tend to draw the adapter plate tight to the spindle shoulder.

 

[T Bredehoft]

Yah, that's about what I did, wish I'd thought of the taper....

The MK2 has no possibility of a rear mounted tool, without making a new cross slide.

 

[RJSakowski]

On my Grizzly 602, I machined a secondary position for my compound. It involved boring a second hole for the compound pivot, drilling and tapping six new holes for the compound clamp, and moving the location of the lead screw oiler to be accessible when the compound was in the alternate location.

The modification added almost 5" to the travel of the compound/cross feed and gives me full accessibility from the rear of the lathe. Machining was done while I had the cross feed table off for machining for the DRO scale.

The pivot hole and clamp holes not being used are filled with a plug and setscrews, respectively, to prevent swarf from entering.

 

[talvare]

Out of interest when else would you want to run the spindle in reverse?

Well, there are a few situations that I use the spindle in reverse. When machining an internal thread into a blind hole, it's really nice to thread away from the headstock. Also, I have machined external threads many times from left to right (tool upside down) when the threads have to go up to a shoulder. Also used reverse machining a left hand thread. And, I frequently touch up a machined surface with a file and I prefer to have the machine pulling the file away from me rather than it trying to push it back at me. I'm sure there are other good applications but those are what come to mind.

Ted

 

[David S]

My Atlas 618 is threaded. When I run it in reverse I take the tension off the jack shaft and let the motor come up to speed and then just slowly engage the jack shaft tension. Yes it slips on the belts a bit but have been doing this for at least 20 years with the same belt.

I use reverse direction when I am using my tool post grinder.

David