Info on thread dimensions.

[morrisman]

If you mean the spindle thread, yes that would be wise to read the wires on an unworn part of the thread, but this lathe is relatively new, the spindle is hardened, and it's not like I'm changing chucks every 5 minutes. The wear would be minimal.

Pete

Yes thats what I meant.. My sheraton 9 has a worn threaded spindle nose, the 1.5" threads taper down quite a bit. Being a ex school lathe, the chucks were changed around a lot

[Pete F]

Ok, in that case I'd either work off the part of the threads up by the bearing, or just use the calculated dimension over wires. I've retrieved my notes from the vertical filing system, and if I can understand my scrawl, the calculated dimensions over wires for this tolerance and size thread wire were 44.98 - 45.12 mm. I measured 44.075 by the looks of the photographs, and the final thread measured 44.058. If stuck, do what I did and aim for something in the middle of the range and you should be good.

I use Machinist Calc Pro for this type of thing, and mentioned it a while back. It's good as the dimensions can be mixed between imperial and metric without any real concern, and the output in a form that's useful for me. I always need to work from the booklet, as I'm not using it every day, but it's quite simple to use. I presume there would be some type of online equivalent. I do recall the thread wires I used were 0.072" as they're from the US. Not an issue and I wouldn't bother trying to decipher the table corrections, come up with an imperial solution and then convert that to metric. A recipe for disaster if ever there was one! I technically wouldn't have needed to measure the original spindle, but it's always good to confirm things and will save an embarrassing cluster %^&* if a mistake in calculations are made and the result is just taken as gospel. Measure twice, cut once.

[Old Croc]

Pete, just giving feedback on this. I got your instructions printed out and got a pro with better measuring gear than me to come and watch over me do the job. (XXXX Gold was cheap for this). 1st thing he found was the factory thread was machined quite accuratley (not bad for Chinese) so I then cut my dummy blank to match it and kept measuring and when close, tried the chuck insert that fitted onto the lathe spindle. Just crept up on it at .002 inch a cut, till the final trim and was happy at that. As I now have a dummy spindle, I can cut all the female threads to suit.
I really appreciate the trouble you and some of the other posters put into your replies as I learnt a lot from this exercise.

thanks and regards,
Crocy.

[Pete F]

Cool, thanks for the feedback. Here's something I made off my dummy spindle I posted about above, an ER32 collet chuck. After a little dicking around I was able to get the runout within 0.01 mm so that will do me. The ER32 collets tend to register ever so slightly differently and that can affect the runout. The collet holder itself has insignificant runout on the taper.

ER32 Collet Chuck.jpg ER32 Chuck with nut.jpg

Anyway I'm glad it all worked out for you and the information was of some use.