Internal thread & taper in same hole

[Dell]

Happy new year one & all I have a conundrum, I have a small four jaw chuck that I want to make a backplate to be able to fit it to my Pultra lathe , the end of the Pultra spindle has a taper & a 7/8” 26tpi thread , has anyone got any suggestions as to the best way to proceed?, I have some 55mm cast iron .
I have added a picture of a carrier for between centre turning because that is the sort of thing I need to make, just a shame I haven’t got 2 of them then I could re purpose one.
Thanks Dell

 

[Kram]

I'm assuming you have another lathe to do it on?

Chuck up the carrier and set the compound slide by indicating off the taper.

While your doing it, make two, or several as 90% of it is getting the setup done.

 

[Agroshield]

The picture looks just like the inner race of a taper roller bearing pressed into a housing. Would a similar design work for the backplate?

You would need to measure the minor diameter of the thread, the largest diameter of the taper, deduct the first from the second and divide by two to see what minimum wall thickness the "bearing race" would have.

Leave the threaded boss plenty long and tune its length once the tapered piece is fitted so everything snugs up as it should (or the gap between backplate and headstock matches a factory item).

 

[Dell]

I'm assuming you have another lathe to do it on?

Chuck up the carrier and set the compound slide by indicating off the taper.

While your doing it, make two, or several as 90% of it is getting the setup done.

Yes have another lathe but never thought of chucking up carrier and indicating thanks,
Just got to find out if 7/8” 26tpi 60 or 55deg probably the latter as lathe is 80 plus years old.

 

[RichardM]

Check that it is 26 tpi as bscy 7/8 is 24 tpi @ 60'

 

[Dell]

Check that it is 26 tpi as bscy 7/8 is 24 tpi @ 60'

According to Tony’s website it is that thread but I was going to check anyway & BSB has a 7/8”26tpi all be it for brass

 

[Agroshield]

I think it could be risky making the assumption that a lathe spindle thread would fall within _any_ defined thread series. What is it about this specific application that justifies the assumption (why should a spindle nose have a standard thread)? If the correlation is common, what other metalwork lathes have spindle threads that fall within a defined thread series? Myford, Boxford, Raglan? No, no, no. As an observation, standard threads are more often seen in wood lathes.

As you are doing, identify major diameter, pitch, and flank angle. If they happen to co-incide with standard thread series, it is exactly that - coincidence. The one advantage you gain _if_ it is a standard thread is that you will not have to calculate dimensions (screwcutting infeed) from first principles.

 

[Dell]

I measured spindle today 22.219 so seems to be 7/8” and a 26tpi gauge is best fit to the thread so next job is to make a dummy spindle front but the taper is that small it will be a job to measure accurately, it of trial & error probably.
Dell

 

[Kram]

Joe Pie has some good videos for accurately measuring and setting angles on lathe, worth watching.

 

[Misterg]

next job is to make a dummy spindle front but the taper is that small it will be a job to measure accurately, it of trial & error probably.

You've got the between centres drive dog with the taper on it, so (assuming that fits the spindle taper OK) set that up in your lathe, get it true, and indicate off its taper to set your top slide (no need to measure anything).