1958 Powermatic 90 lathe spindle threads

[kreck]

I recently purchased a PM 90 lathe on an auction. This didn't come with a faceplate (have one on the way) and I don't have a Chuck that will direct thread on it given the not common size (1 1/2 X 8). Upon inspection of the threading it seems that the first couple threads have been flattened. Is this going to be an issue for threading a Chuck or faceplate?

https://goo.gl/photos/togiYFqx9gy5Sp1a8

 

[Duker]

I recently purchased a PM 90 lathe on an auction. This didn't come with a faceplate (have one on the way) and I don't have a Chuck that will direct thread on it given the not common size (1 1/2 X 8). Upon inspection of the threading it seems that the first couple threads have been flattened. Is this going to be an issue for threading a Chuck or faceplate?

https://goo.gl/photos/togiYFqx9gy5Sp1a8

Kreck those threads are pretty rolled which will be an issue in getting a face plate on the lathe. I have restored a couple 90's and one of them I had to find a replacement headstock and the other I was able to use a thread restorer which was enough to be able to run a die across to fix the issue. You appear to have enough material there to be able to restore the threads.

*

 

[aircommuter]

I have used several of those. It looks like someone was letting their sandpaper get over there. It should not prevent you from using it, if it won't go on you could use a thread file and clean it up a bit.

 

[Milton Shaw]

The 4 sided double end thread restore files are what it's going to take to fix them. The three piece set with two SAE files and one metric will handle just about every messed up external thread you come across. If you don't have them, get them they are worth there weight in gold every time you run across messed up threads. Amazon has them ranging from $41 on down. They show a 4 piece set but I have only three pieces and have not run into any thread they won't fix.

 

[kreck]

I guess when the face plate arrives I'll gingerly try to see if it will thread on and if not set about doing some repair. Thanks for the tips.

 

[ttpete]

You could probably clean it up with a threading tool in the toolpost. Set up for 8 threads or whatever it is, get the tool lined up with the threads, put the lathe in back gear and take it slow back and forth while feeding slowly until the face plate will screw on.

 

[454ragtop]

You could probably clean it up with a threading tool in the toolpost. Set up for 8 threads or whatever it is, get the tool lined up with the threads, put the lathe in back gear and take it slow back and forth while feeding slowly until the face plate will screw on.

Pretty sure that's a wood lathe, without threading capability.

 

[EricP]

Kreck

Some good advice so far. If you are not able to repair the threads you could have a machinist turn the spindle down to a smaller and common size. The headstock is morse taper 2 so on that spindle nose there is a lot of meat. If you need to do this you will want to take your chuck along with the spindle. The base of the threads needs to be precisely machined so as to seat with repeatability on the chuck to prevent runout if you remount the chuck with work piece.

 

[larry_g]

I have used several of those. It looks like someone was letting their sandpaper get over there. It should not prevent you from using it, if it won't go on you could use a thread file and clean it up a bit.

I would agree with the above. Those threads look to have had the crests removed, not smashed down. In your favor, faceplates and chucks locate on the register not the threads. I don't think your going to have a problem unless the threads on the faceplate are shallow and the registering diameter is to long preventing the faceplate from grabbing the good threads. One solution to that is to turn the faceplate registering surface back to allow more threads to come into play.

good luck

lg
no neat sig line

 

[kreck]

The faceplates arrived and both fit without issue. I also got a spindle adapter to go from 1.5 to 1.25, which I thought was needed to direct thread on my Nova G3 Chuck, but it appears that may be 1.5x8? I used an insert with my old lathe (Harbor freight 10x18) I can't seem to find confirmation of that fact (that the nova inserts were threaded to convert TO 1.5) in the documentation from teknatool.

 

[larry_g]

Did you check the amount of thread engagement? How many turns of the faceplate did you have to make to get it to seat? The number of turns tell you how many threads are engaged. It looks like you have ~8 threads on the spindle of which 3-4 are compromised. If it were mine I would want at least 6 turns of engagement to make sure the faceplate is grabbing 3 good threads.

lg
no neat sig line

 

[Duker]

Did you check the amount of thread engagement? How many turns of the faceplate did you have to make to get it to seat? The number of turns tell you how many threads are engaged. It looks like you have ~8 threads on the spindle of which 3-4 are compromised. If it were mine I would want at least 6 turns of engagement to make sure the faceplate is grabbing 3 good threads.

lg
no neat sig line

^^^^ This was my concern when looking at the threads and the reason for suggesting repairing the threads earlier. If there wasn't any wobble when you rolled past the first few turns then you may never have an issue. However, if you do and you mount a large, off balanced piece even at low rpm....things may become very interesting ....don't ask me how I know!



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[kreck]

I observed 5 full turns of engagement

 

[kreck]

Actually it seems to vary, I assume due to differences in threading on accessories. My smaller faceplate is just over 5, the larger faceplate and adapter exceed 6.

 

[larry_g]

Actually it seems to vary, I assume due to differences in threading on accessories. My smaller faceplate is just over 5, the larger faceplate and adapter exceed 6.

If you measure from the register surface to the first thread inside the face plate and then transfer this measure mentto the spindle you can see where the threads in the faceplate stop on the spindle. Look to see if you have enough room in the hole lengthwise to turn off part of the register surface allowing more thread engagement.

This page might help http://www.lathes.co.uk/latheparts/page7.html

They also refer to the register as spindle abutment surface.

Another write up http://www.practicalmachinist.com/vb/south-bend-lathes/machining-chuck-adapter-130129/

lg
no neat sigline