Jet 9X20 lead screw ?

Based on what?

Btw, it might help if you told us the vendor of your particular 9x20.

I have yet to come across a 9x20 with anything but Imperial leadscrew & threading dial (at least in the US market). I would love to have a true metric leadscrew (and metric threading dials) on my 9x20 lathe. If you really do have a metric set-up, perhaps we could trade parts?

Regards, Michael

Oops, I guess I get the "reading-impaired award" for the day. Missed the brand name "Jet" in the subject line.

Jet 9x20 lathes definitely have Imperial leadscrews & threading dials.

- Michael

I have one that is called a CT-918 it may be the same as your 920. My manual provides tables to allow cutting of both imperial and metric threads by making some gear changes. Metric threads are from 0.5 to 3 mm, inch are from

8 to 56 threads per inch. Do you have a manual and the change gears?

Jack

It isn't too hard, Bill. You hold up a ruler next to your lead screw and count the threads per inch and see if you get e.g. 8 for 1" 16 for 2",

96 for 12" .. GWE

Bill Janssen wrote:

According to the manual the model BD-920N has a 9/16" x 16 TPI leadscrew. Usually though there is a metric/inch change gear, or on fancy machines just a selector. I believe the magic gear is a 127 tooth gear (25.4*5 = 127 = zero conversion error). I have used Russian made all metric machines that cut beautiful inch pitch threads, and vice versa. It doesn't really matter whether the lead screw is inch or metric as long as the gear ratio is correct you can cut any pitch you want. - where it matters is in the cross slide, if you have a metric dial that sucks.

20mm and 12 tpi. So much for the manual. I had to sort this out so I can build a thread dial for it.

dp

That last statement is a matter of personal perspective, is it not? For me, I work almost exclusively in metric, so having an Imperial cross slide (and compound, and leadscrew/threading dial) is what sucks for me.

- Michael

As has been pointed out in this group before, same goes for doing metric on an imperial machine. When you have the 127 gear on (or it's counterpart on a metric machine doing inch work) there is only ONE place you can engage the nut. Google the archives and you'll find a few tricks to *try* and make it eaaser but in the long run they are all a PITA.

Dave

I tried cutting a 8 TPI thread using the 1 on the dial and got three diferent start positions. Just counted the threads and it 16 or nearlu 16 per inch

Bill K7NOM

Ok I get 16 or so for one inch.

Bill k7NOM

Greetings Dave, I've been trying to figure out how to do this threading electronically. I looked at the Frog? controllers and they say you can do threading with them but they only drive steppers AND they only have one pulse per chuck revolution. The threading I do needs to be more accurate than that. I do have Gecko drives that take step and direction input and drive servo motors with encoder feedback. But I can't find software that's cheap enough. I do have BIG CNC lathes (21 inch swing) but for one or two parts it's usually faster to put that damn 127 tooth gear in place. If I can find the right software I'll put a ballscrew in the lathe and use it for all my threading. Eric

Ok then the trouble I had must be the wrong change gear arrangement. I cut a 8 TPI thread and after having trouble I kept the nut engaged in the same place and cut my thread. It works but may be off slightly but not enough to not work.

Bill k7NOM

Without seeing or knowing what you are actually doing (and without knowing your background or experience), it is hard to tell what the problem is. But I suspect it's a procedural error. If I'm wrong, I apologize.

I have an Enco 9x20, which is essentially identical to the Jet in every way except for the spindle nose threads (for mounting chucks) and the paint scheme. While I rarely cut Imperial threads, I have done so successfully by disengaging the halfnuts and using the threading dial. It worked exactly as advertised.

Regards, Michael

I have a JET 9x20 and I successfully threaded a new back plate on it for a

4-jaw chuck without any problems. The spindle is 1 1/2 x 8TPI.

Have you checked to be sure the gear on the end of the thread dial is snug up against the lead screw? It could be skipping if it's loose.

Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com

"I'm not grown up enough to be so old!"

Thanks for all the comments. I must have used the wrong combination of gears even though my threads were close enough to be usable. So I will try again but this time I will double check the gear combination.

Bill k7NOM

Keith Marshall wrote:

He did -- but only in the "Subject: " header, not in the body. I know that it is typically quite a while between the time I select subjects to read and the time a given article pops up, so I sometimes have to remember to look back at the headers.

As for the original question -- others know the machines better than I -- but I think that all in the US have Imperial leadscrews -- at least the longitudinal one used for threading.

The cross-feed and compound ones may be a near fit metric, especially if you wind up with weird counts on the dial for a full turn, like 127 or 63-1/2. Precise counts of 200 or 100 or 50 are more likely to be true imperial screws.

Enjoy, DoN.

Did you by any chance touch the reverse tumbler while doing the thread? That has to remain engaged until the thread is done, or you get as many different start positions as you have teeth in the tumbler gears.

Good Luck, DoN.

Yes Don, I caught that as soon as I posted the first response (and acknowledged my error in an immediate follow-up post).

- Michael