Jet 9X20 lead screw ?

I just got around to noticing a table for using the threading
indicator. The table
is the usual listing of indicator readings versus thread pitch.
However I just noticed that the thread pitch column is labeled TPI and
the threads
listed are all imperial threads.. I have reason to believe that the lead
screw is metric.
So my question is, where is the error? Is my lead screw wrong and I
should have
a Imperial or is the label wrong and no 9X20 was ever shipped with a
imperial
lead screw.
Confused
Bill K7NOM
Reply to
Bill Janssen
Loading thread data ...
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
Reply to
DeepDiver
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
Reply to
DeepDiver
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
Reply to
Jack Hayes
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:
Reply to
Grant Erwin
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.
Reply to
Dean
My Grizzly G0516 is listed as having a 3/4"x10 tpi leadscrew but it is 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
Reply to
Dennis Peterson
That reminds me, There is one flaky thing about using a metric pitch machine cutting inch threads (at least the Russian lathes) & it is that the half nut, on some pitches, can only be engaged on the exact same unique point on the thread dial or you might not be in sync with the previous cut. They make it tricky though by marking the dial like an inch machine so you think you can just drop it in whenever your number comes by. A colleague of mine ruined a leadscrew nut for a 5" HBM made from a cu$tom bronze ca$ting due to this.
Reply to
Dean
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
Reply to
DeepDiver
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
Reply to
Dave August
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
Reply to
Bill Janssen
Ok I get 16 or so for one inch.
Bill k7NOM
Reply to
Bill Janssen
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
Reply to
Eric R Snow
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
Reply to
Bill Janssen
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
Reply to
DeepDiver
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!"
Reply to
Keith Marshall
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:
Reply to
Bill Janssen
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.
Reply to
DoN. Nichols
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.
Reply to
DoN. Nichols
Yes Don, I caught that as soon as I posted the first response (and acknowledged my error in an immediate follow-up post).
- Michael
Reply to
DeepDiver

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.