# PM 12x36 capable of more than 52 TPI ?



## slingshot (Mar 13, 2013)

I have been researching info on the pm 12x36 and from what I have found it appears to me that the pm 12x36 is capable of cutting 105 threads per inch.If any one is having a problem with figuring out which z gear you need to cut different tpi this will also be useful to you. I am going to attempt to paste it here in a pdf file format I don't know if it will work or not.
	

		
			
		

		
	

View attachment All_Pitches.pdf
View attachment Common_Pitches.pdf

	

		
			
		

		
	
 thanks..J.B


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## Ray C (Mar 13, 2013)

That's good to know.  Thank you very much.

I still wonder though, what in the world needs a thread much finer than the 48-56 range?  Sure, I'm certain there are applications but I would probably be using an American Turnmaster style lathe (assuming I could scrounge up 30 grand give/take a little).

BTW:  When you start cutting threads much finer than the 60 TPI range, you'll soon find-out how good your leadscrew is.  I'll bet dollars to donuts that most of the lathes that advertise ultra-fine thread capability do indeed have gear ratios that theoretically achieve that ratio but, the leadscrews need to be ultra-precision.   For anything much beyond 60 TPI, you're talking about a bit tip not much wider than a sewing needle.

Ra


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## slingshot (Mar 13, 2013)

Sure thing Ray, I have a job coming up on a couple of 70's JD hydraulic cylinders the threads are super fine I don't know how fine but I will be finding out soon.There was a lot of issues with those because of the fine threads.Thanks J.B


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## GaryK (Mar 13, 2013)

I have been meaning to do that ever since I got the lathe but you have saved me the trouble!

Thanks!

Gary


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## darkzero (Mar 16, 2013)

IIRC, when I bought my lathe, Matt did mention that there were a few optional gears available that would allow additional threads to be cut. That was quite a while ago & I could be mistaken but I do remember something about keeping it in mind but I never needed them yet.


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## trukker (Mar 18, 2013)

Does the 1236 come with gears to cut threads greater than 52 tpi?  How many?  If not included how much is it to get a set?  Thanks!


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## george wilson (Apr 3, 2013)

I made a teeny little tap with my 12" Sears back in the 70's. something like #000 120. No problem with the lead screw.

For my 16" Grizzly,I just looked around and found some extra gears(I'm a gear pig!) that I can add to the end of the QC box to halve or double the indicated TPI.


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## Ray C (Apr 3, 2013)

Hi...

This is like DeJavu...  I'd swear I answered this question already.  I think the reply was lost in one of the database crashes.

Anyhow, I checked with Matt about this and he's not aware of any gears available from the factory.  This is not condemnation that finer threads are not possible.  As George implied, home made gears can be attached to the bottom-most sprocket that drives the leadscrew to perform any ratio you want.

Matter of fact, I'm going to need to do this soon to make a 1 TPI oil groove (or possibly 2, 1/2 TPI grooves) for a high-speed turbine shaft.  I looked it over last night and really did not see any major obstacles.  -Then again, it was 1:00AM and I probably wasn't seeing anything too clearly.  I digress...

Anyhow, after recently looking at threading inserts to tackle a couple jobs that need to be perfect.  I saw very few standard inserts finer than 48 TPI.  I saw a couple inserts that were 72 TPI -costing just under $100 each!  I measured my Starret and B&S micrometer barrels -and they are 40 TPI.

I really have some questions...  Who the heck needs threads that small and how do you make them?  I see it as a 1-pass operation quite literally using the tip of a sewing needle as a bit.  What are the practical applications for such fine threads?  LOL... the little screws that hold your eyeglasses together are 56 TPI.  ... A thread twice as fine???  Really?

Ray




trukker said:


> Does the 1236 come with gears to cut threads greater than 52 tpi? How many? If not included how much is it to get a set? Thanks!


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## trukker (Apr 16, 2013)

Yes, Ray, you answered some of my question and I hated to ask you to do it again when the page got lost.  I thought you said that the pm12x36 could thread up to 60 tpi.  I am assuming that would be without using a change gear.   I have looked at the new Grizzly G0750G which looks very similar to the PM12x36.  The specs say   4 to 56 tpi but, it comes with 6 change gears.   Both thread metric 0.4 - 7.0 mm.  It looks like the PM machine can do the same threads plus a few extra tpi but, does not include extra change gears.  Something don't seem right?


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