# Metric threads on a Powermatic?



## Happycamper (Jan 8, 2018)

Anyone cut any metric threads on a Powermatic 11” lathe?


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## Nogoingback (Jan 9, 2018)

http://lathe.com/faq/index.html#_Toc95180297

This link from Logan provides information on cutting metric threads on Logan lathes.  Assuming your Powermatic has a gear train
the same as a Logan, it should be possible.  I would call Logan directly and ask for Scott Logan: he can help you out.


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## bfd (Jan 9, 2018)

as long as you have the right gears 127 tooth or there are more combinations that will do it. I don't know what they are at this time. what you need to do on most lathes in to engage the half nut and not release it until your thread is done use forward and reverse, take a cut reverse the lathe back out the tool and run the tool bit back. take other cuts until thread is finished  then you can release the halfnut. this is how you cut a metric thread with an sea leadscrew. my old lathe manual had this information.  bill


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## rambin (Jan 9, 2018)

when I bought the instruction book for my log/wards 700 series there was  a page talking aobut the ability to do metric threads with a certain gear that you would have to buy im guessing...and it said you had to leave the half nut engaged to do them.. Id have to look up the page again if you wanted more details...what model do you have?


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## bfd (Jan 9, 2018)

10" wards model which was made by  same company bill


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## eeler1 (Jan 9, 2018)

Short answer; no, nobody has done it.  But there’s a lot of Logan/Wards/Powermatic owners that have investigated it.  I believe that Logan sells the transposing gears, but it’s a 37t/47t combo that comes close to metric threads but misses slightly in terms of precision.  Actually, there’s lots of metric threads you can cut with your imperial gearbox, not exact but will work fine on short threads.


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## bfd (Jan 9, 2018)

there are 25.4 mm per inch. the first gear that works evenly is5 times 25.4 which equals 127 tooth gear if you can find that gear in your pitch then you can cut accurate metric gears  you just need to work out the ratio of headstock spindle to leadscrew rotation. I never studied this but I'm sure the machinerys handbook has how you figure it out bill


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## RandyM (Jan 10, 2018)

Nogoingback said:


> http://lathe.com/faq/index.html#_Toc95180297
> 
> This link from Logan provides information on cutting metric threads on Logan lathes.  Assuming your Powermatic has a gear train
> the same as a Logan, it should be possible.  I would call Logan directly and ask for Scott Logan: he can help you out.



Yup, all is explained in Section 4.1. How can I cut metric threads on a Logan lathe?


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## rambin (Jan 10, 2018)

my mong wards was sold as a powr-kraft  what is the diff between that and a power matic?   the paper I haveon metric threading tells the exact same information as the link above so its of no help to the original poster


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## Nogoingback (Jan 10, 2018)

Powermatic bought out Logan and produced their lathes for a period of time, but only in the larger sizes.  The older machines like the 
Model 200 and your Wards lathes had been dropped from the line.  But, I just looked at a copy of a 1980 Powermatic/Logan catalog
and it indicates that transposing gears were available as an accessory for cutting metric threads.


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## wa5cab (Jan 12, 2018)

The problem with the 127T gear is that on most lathes, it is much larger than the largest standard gear furnished.  I haven't looked at the Logans with this in mind but on the Atlas machines made 1938 and later, the largest gear is 64T.  Running a 127T may result in having to run the machine with the change gear cover open.  Which is a safety no-no.  

The compound gear set sold by Atlas for the purpose was 52T/44T.  This results in an M1.0 being M1.0006.  This isn't good enough to make precision lead or positioning screws but it's certainly close enough for normal lengths of engagement.  As the thread pitch grows coarser, the absolute error increases so M7.5 nominal is actually M7.50450000.  Which is where I cut off the threading chart (modified copy of the metal chart rivetted to the QCGB) that I made up for the QCGB equipped Atlas 10" and 12".

A man named Conrad Hoffman wrote a treatise on cutting metric threads on an Imperial lathe (specifically a 1947 Model 211 Logan).  I have the document as a PDF but although the document isn't so marked, the home page of his web site says contents copyright 2016.  So I'll merely give here the URL for the document.  You can get back to the rest of his site by clicking the HOME button on the last page of the document.

www.conradhoffman.com/metricthreading.htm

The main reason that I am mentioning it here is that he describes a method whereby you can cut metric threads with an inch lead screw _WITHOUT_ having to leave the half nuts engaged throughout the entire process.


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## eeler1 (Jan 12, 2018)

I figured up the OD for the 127 tooth gear, planning to make one for my 11” Logan 957, and the OD was over 8”.  I haven’t pursued it since, and rarely (never?) have to make threads that can’t be made with a tap or die.


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## whitmore (Jan 12, 2018)

eeler1 said:


> I figured up the OD for the 127 tooth gear, planning to make one for my 11” Logan 957, and the OD was over 8”.



That's the dimension for a 16 diametral pitch gear (14.5 degree), so if you want
something in the 4" size, you want 32 diametral pitch.  That won't mesh with
other gears from the box, so you'd need TWO 32 pitch gears (possibly pinned to
some* standard gearing, but only meshing with each other).*

*Seems like the 'correct' gearing is not impossible, but the 'close' gear solutions
of 37/47 or 44/56 are easier to make fit?  Is 44/52 really used?  How?
For exact conversion, the ratio has to include the prime factor 127*
100/127 = 0.78740157...  (exact conversion to metric)
37/47 =     0.78723
44/56 =     0.78571
44/52 =    0.84615
and 44 /52 *(13/14) = 0.78571
       44/52 * (27/29) = 0.78779  
       44/52 * (40/43) = 0.787119 is the closest match I see
       44/52 * (53/57) = 0.78677


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## wa5cab (Jan 13, 2018)

Here's how you use a 52T & 44T compound gear:

The 52/44 compound gear converts an Imperial QCGB that's made to cut tpi to a metric one for at least a useful range.  Starting with the gear box set for cutting 30 tpi: 

30 tpi converted to mm pitch is 25.4/30 = 0.84666667 mm (same thing as 1/30 = 0.03333333 inch pitch, and that times 25.4 is 
0.8466666667 mm pitch).

0.84666667 * 52/44 = 1.0006060606 mm pitch

as I said before.  

If one were to use 127/100 as the speed-up compound gear, you would end up with 1.07526666667 mm pitch insted of 1.0006060606... .  The difference is in whether you use the conversion gear set  to slow down the lead  relative to the spindle or speed it up.  Your solution slows it down.  Carvel's solution speeds it up.  There is usually more than one way to skin a cat (and no, I do not know why anyone would want to skin a cat).  The disadvantage is that apparently a lot of Imperial GB's do not do 30 tpi nor 60 tpi (for M0.5).  I have not investigated fully whether or not there is an exact conversion.


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## rambin (Jan 15, 2018)

just something too consider..... as its been pointed out to buy these special tooth count gears aint gonna be cheap...  mrpete222 's  latest video he shows making gears for an atlas using a 3d plastic printer.. if someone had the ability to draw these oddball gears up then printed them they would be fairly cheap and there not going to get used often anyhow?  actually if you go to makerspace and do a search there are a few logan gear drawings already done...of course not these oddball ones but maybe if you searched a bit harder it might something may show..


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## Nogoingback (Dec 4, 2018)

I know this an old thread, but came across these links and thought I'd add them.  This is the official word from Logan on
metric threading.

http://www.loganact.com/tips/met-thd.htm
http://www.loganact.com/tips/metric_threading.pdf
http://www.loganact.com/tips/metric_thread_charts/1mm.htm
http://www.loganact.com/tips/metric_thread_charts/1mm.htm


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## middle.road (Dec 4, 2018)

Nogoingback said:


> I know this an old thread, but came across these links and thought I'd add them.  This is the official word from Logan on
> metric threading.
> 
> http://www.loganact.com/tips/met-thd.htm
> ...



Not that old. Thanks for resurrecting it, I missed it somehow. I need to figure out how to get metric either on my Logan or my Birmingham.
I didn't get all the gears required with the Birm.


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## Nogoingback (Dec 4, 2018)

I think Logan sells them, but they aren't cheap.


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## middle.road (Dec 4, 2018)

3D Printing should be the way to go. The types of materials available should fit the bill.
Just don't leave the gear installed for more time than is necessary to accomplish the task.
Now for the engineering. . .


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## Nogoingback (Dec 4, 2018)

I just noticed someone selling printed metric transposing gears for Logans on eBay, but they want a lot
for them.  You could print same extras and undercut their price...


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## RonRock (Apr 10, 2020)

I'm in need of doing some metric threads on my Logan 1937. 

Not enough to justify the price of the ebay printed ones. But I do have a 3D printer. I searched and could not find the files needed to print my own. Anybody here figure this out and care to share?


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## brino (Apr 10, 2020)

RonRock said:


> I'm in need of doing some metric threads on my Logan 1937. Not enough to justify the price of the ebay printed ones. But I do have a 3D printer. I searched and could not find the files needed to print my own. Anybody here figure this out and care to share?



Hi @RonRock,

See here:
https://www.hobby-machinist.com/threads/gears-for-my-oldtimer-lathe.82245/post-718054

It can be done for free!
Feel free to PM* me if you need help.

-brino

*PM = Private Message. Just hover your mouse cursor over my user name and then hit "Start conversation" on the pop-up.


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## RonRock (Apr 28, 2020)

So I broke down and bought a pair of 37/47 gears. I have read many many threads on how to do metric threads on a Logan. For the life of me I just can't get it sorted how to set up my lathe for metric.

Many different thoughts and suggestions, just not one that I can wrap my head around. So I will ask if someone can point me in the right direction.

Here's what I have,


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## RonRock (Apr 28, 2020)

Those are a little big. Sorry I thought that the forum would format.

I should have added that I have a Logan 1937 with quick change gearbox.

1.5 mm pitch is what I'm after this time around.

The 37/47 gears fit the shaft where the 36 tooth Stud Gear is. The shaft that holds the 72/64 is smaller. I would have to make a bushing for the 37/47. Can be done easy enough if needed.

The 72 tooth "Safety Gear" drives the QCGbox. Part of what is throwing me off is that I am seeing that that 72 tooth is often shown as a 60 tooth.


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## ErichKeane (Apr 28, 2020)

As you've got it setup, ONLY the final 72 tooth and the 36 tooth gear matters.  The 72/64 pair are doing nothing.  SO, you've got a 2 to 1 ratio from spindle to gearbox.

What you need to do is put the 37 and 47 gear on the same axle (where the 72/64 is!).  Drive the 47 tooth gear with the 36, and have the 37 be the output of the conversion (going to the 72 tooth gear).

As far as selecting a metric value, that would depend on the gear ratio in your gearbox.


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## RonRock (Apr 28, 2020)

Thank You ErichKeane. 

Looks like I need to make a axle that will hold the 37/47 as well as "pin" them together. 

Very helpful.


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## ErichKeane (Apr 28, 2020)

RonRock said:


> Thank You ErichKeane.
> 
> Looks like I need to make a axle that will hold the 37/47 as well as "pin" them together.
> 
> Very helpful.



You SHOULD be able to replace your 72/64 pack there, there should be a keyway on the shaft that you can use to put those together.


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## RonRock (Apr 28, 2020)

My 72/64 had a keyed bushing that holds them together. 

I pressed it out. It might fit the 37/47 but would be a very tight press fit. I think that I'll be best off to either buy or make one. Then I can put them together and leave them. Not have to worry about fouling the fit going in and out with the bushing.

Is the bushing a piece I can buy?

Mine measures .437 id. .625 od.
	

	
	
		
		

		
			





Sent from my SM-G930V using Tapatalk


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## ErichKeane (Apr 28, 2020)

Looks like they are a bit expensive to buy, its probably easier to just turn one


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## ErichKeane (Apr 28, 2020)

(Whoops, double post!)  

As it likely wasn't your fault, I'll leave you with credit for the post.  This is at least the third maybe fourth instance of this that I have seen since the server upgrade.  Most of the time the "Save" action is quick.  But sometimes it takes several seconds and it appears also that if you click Save again while the fluctuating gray boxes are appearing under the right end of the main toolbar at top of screen, sometimes the Save command gets saved in a que somewhere and saves the same post twice.

WA5CAB/Robert D.


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## RonRock (Apr 28, 2020)

It is a pretty tight fit. I'm going to try heating up the aluminum gears and see if it fits then. Hopefully it will come out with the same method. Not sure how the steel bushing will heat when I try to heat the aluminum for removal. 

I sure do appreciate the help.


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