Wobble with screw on chucks and plates

[BKind2Anmls]

I have a Turncrafter Pro VS Midi Lathe. When I screw on a chuck, a face plate, or a collet I get serious wobble which I meaured out to be 50/1000 near the screw and even more, of course, farther out.

However, when I measure runout on the shaft or on a morse taper center, I have hardly any problem. Why would things that I screw on have so much runout and what can I do about it?

Thanks.

 

[low_48]

Probably because the shoulder on the shaft is not perpendicular to the thread or taper.

 

[KenV]

Susan,

Are the appurtances threading up to and seating firmly against the head stock flat ?

There should be no gap there and there should be a solid engagement as the flat on the Chuck/faceplate meets the flat of the head stock.

Damaged or burred threads are one way this fit may not be happening.

 

[BKind2Anmls]

I wondered about that but not having a machinist-type mind I couldn't wrap my head around how that could be if the thing you screw on matches the threads.

If I put some sort of soft, thick washer on the spindle before I screw the chuck on should that help? I could gap where the chuck meets the round part of the spindle near the headstock and see if it is seating perfectly flat.

Do I need to re-cut the threads? Would a tap and die set do this? Or, do I need a new spindle?

 

[Charlie_W]

I wondered about that but not having a machinist-type mind I couldn't wrap my head around how that could be if the thing you screw on matches the threads.

If I put some sort of soft, thick washer on the spindle before I screw the chuck on should that help? I could gap where the chuck meets the round part of the spindle near the headstock and see if it is seating perfectly flat.

Do I need to re-cut the threads? Would a tap and die set do this? Or, do I need a new spindle?

Adding a washer just thick enough to remove any gap would be a good test to prove this theory. Some lathes have a longer spindle nose past the shoulder than others. I have seen this before.
No to a soft washer. A solid washer as in brass would be a better choice. Start by looking in plumbing fittings.
A flexible washer such as the plastic washers will take up space and are sold as a remedy to help remove a Chuck that is on tight.
At a recent woodturning workshop with an international woodturner, Nick Agar, He said a washer, especially plastic or fiber would introduce some flex and vibration when turning.
You could try making a washer from some tempered Masonite or plexiglass or even some 1/4" plywood as a test. In use, I would stay away from the plexiglass in case it shatters. The plywood will compress...and unevenly.

Good luck.

 

[low_48]

I wondered about that but not having a machinist-type mind I couldn't wrap my head around how that could be if the thing you screw on matches the threads.

If I put some sort of soft, thick washer on the spindle before I screw the chuck on should that help? I could gap where the chuck meets the round part of the spindle near the headstock and see if it is seating perfectly flat.

Do I need to re-cut the threads? Would a tap and die set do this? Or, do I need a new spindle?

Definitely no to die cutting the threads. You can't alter how the threads align on the shaft with a die. You would have to have them remachined on a metal lathe. The threads are surely not the problem. They are basically there to draw and hold the faceplate or chuck up against the shoulder. The shoulder and face on the holding device is what sets the runout. Both statements are correct unless the shaft was really messed up. Contact the company and talk to them about your problem, then talk to them about a replacement shaft.