Tapered spindle thread

[morrisman]

hi An observation : On both of the threaded spindles I have , the thread is actually tapered . If this is due to wear over the years or , if it was made like that, I dont know . As the backing plate threads up the spindle it becomes tighter , until it reaches the shoulder, where the larger diameter thread on the spindle effects a wobble free fit . This is evident on both the Sheraton and the PREMO lathes. MIKE

[pipeclay]

Have you been able to measure the amount of taper?

[morrisman]

Have you been able to measure the amount of taper?

Yes I measured it many times . On the Sheraton the taper is 20 thou over the length from where the threads begin at the tip to where the threads end at the shoulder . The bush I made screws on to about 2/3rds , then goes tight . I made a gauge that is exactly 1.5" OD along its whole length , this screws into the bush OK .

The spindle diameter at the shoulder where the threads end is actually 1.510 , and it is 1.490 at the tip where the thread begins "

MIKE

[Metmachmad]

I would imagine that the taper is due to wear 'n tear over the years. Whenever I replace chucks, faceplate etc, always support the parts weight being screwed on or off, so the weight of the heavy chuck is not hanging on the last few turns of the spindle thread. Also keep the threads (external and internal) very clean with a light oiling to help stop wear and rusting.

[pipeclay]

Did you measure only the threads or did you measure the shoulder as well?

It would take a lot of on/off fitting of spindle adaptors to wear the Spindle threads that much.

Most but not all fittings screwing onto the Spindle threads are Cast Iron,a material which is softer than the Spindle threads.

I would of thought if anything,the adaptors that may of come with the lathe would of been worn.

Do you happen to have any original spindle adaptors that came with the lathe?

If so measure the diameter of the relief cut into them and see if this diameter is greater than 1.510".

What diameter did you cut your relief too?

[morrisman]

Did you measure only the threads or did you measure the shoulder as well?

It would take a lot of on/off fitting of spindle adaptors to wear the Spindle threads that much.

Most but not all fittings screwing onto the Spindle threads are Cast Iron,a material which is softer than the Spindle threads.

I would of thought if anything,the adaptors that may of come with the lathe would of been worn.

Do you happen to have any original spindle adaptors that came with the lathe?

If so measure the diameter of the relief cut into them and see if this diameter is greater than 1.510".

What diameter did you cut your relief too?

Yes I have the three original chucks ( one 4" 3 jaw and two 5 " 4 jaw Burnerd ) that I am certain were supplied for this lathe from when it was new ... I have measured the minor diameter of the chuck threads and it comes up as 1.363" . The shoulder diameter on the spindle is 1.510" . I am not sure how to measure the relief cut in the chucks ( major diameter ) MIKE

[pipeclay]

Try a vernier or inside calipers and outside micrometer.

So does the thread up near the shoulder measure the same as the shoulder or less?

What size relief have you given in the one you made?

[morrisman]

So does the thread up near the shoulder measure the same as the shoulder or less?

What size relief have you given in the one you made?

Yes the shoulder measures up as having the same diameter e.g., the thread major diameter at the point where the thread meets the shoulder . I obviously didnt give it enough relief .. the next bush I make will have more relief MIKE

[pipeclay]

Seems more of a problem than that if the 1.500" thread is really measuring 1.510",that would appear to be a manufacturing defect.
Possably all Sheratons may be like this,not very good.
Seem Hercus and Southbend were able to turn to correct tolerances,makes you wonder who the Sheraton company was employing.