# How to do fine threads



## blue_luke (Feb 11, 2018)

Hello all!
The things I intend to fabricate are audio microphones accessories. (I am a sound engineer)

This pose a few problems.... I own a Precision Matthews PM1127 lathe. This is a nice machine and I am happy with it, but the most standard thread size for mounting microphone bracket is 5/8"-27tpi  On the charts given on the machine, there is no gear combination to cut this thread!
Also, I build my own microphones and I would like to learn how to cut fine threads like the ones used in photography lenses and filters.
This way I can use some nice capsules I have (Schoeps, AKG etc) to preamps and contraptions of my design or design accessories circuits like pads and low-frequancy roll-offs...
For those who don't understand this giberish,,, it all boils down to be able to thread fine threads on thin tubular brass or aluminium tube.
Right now I have no specifications to give, it is more the technique of holding the parts in a chuck, what geometry the cutting tool should have, how to avoid distortion in the finished parts...

Sincerely, Luc


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## mikey (Feb 11, 2018)

Did your lathe come with a change gear set? If so, you can calculate the gears needed and hopefully find the right gears in the set.

As for geometry, if you use a HSS tool then a standard 60 degree tool should suffice. 

Holding the stock depends on the size. A collet will hold it without distorting or damaging the tubular stock. A 6 jaw chuck will work better than a 4 jaw will but that gets expensive.


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## Ray C (Feb 11, 2018)

Fine threads are easy unless you are trying to put threads on really small diameter rods.  Putting fine threads on larger diameter pieces is no different than any other threading operation.   If you need a refresher on threading, I'm almost certain there's info about threading here:  https://www.hobby-machinist.com/forums/noteworthy-threads-info.290/ 

If you are trying to put threads on really small diameter rods (say, 1 mm or less), let me know when you get the process perfected... 

Ray


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## epanzella (Feb 11, 2018)

On my Grizzly G4003G I take the setting for 18 tpi and slow it down 50% to get to 27 tpi.  That is my gears for 18 tpi (with the QCGB set @ 18) are 40/86/40.  Switching to 40/86/60 (with the QCGB  set @ 18) gives me 27 tpi.


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## benmychree (Feb 11, 2018)

If you set your quick change for 30 TPI and have a 30 T gear on the stud gear and a 27T gear on the change box,  and any number of teeth on an idler, you should get 27 TPI; I did a post on this a couple of days ago.


epanzella said:


> On my Grizzly G4003G I take the setting for 18 tpi and slow it down 50% to get to 27 tpi.  That is my gears for 18 tpi (with the QCGB set @ 18) are 40/86/40.  Switching to 40/86/60 (with the QCGB  set @ 18) gives me 27 tpi.


Are you sure? I do not see how dealing with even numbered change gears can result in an odd numbered thread.


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## blue_luke (Feb 11, 2018)

Hmmmm! I think I have opened a can of worm here! :-D

For the 27 TPI threads, Yes I did receive quite a few gears for cutting threads, but no combinatons seems to arrive to 27 TPI. If memory is right, I can get 26 or 28 tpi but no 27!

For Ray C, no the diameter I have to thread, both inside and outside obviously, are more in the 0.750 and over up to about 2"
The threads are fine pitch and metric for sure, but again, I have no specs as of yet.

Usualy, a microphone (modular) is made of a tube shaped thing that contains an electronic circuit and at one end, the output connector, and at the other end, a single pin connector. This end  of the tube is threaded with a fine pitch and is meant to receive the capsule element mounted in a special housing. This housing is threaded internally to match the receiving threads on the tube.
The idea behind this approach is that, using the same électronics in the tube, we can insert different pickup patterns  capsules like omnidirectional that picks sound from everywhere, cardioid, that picks mostly up front, and many other types for different purposes.
Then using the same system, we can also insert modifying signal elements, such as 'pads' that will make the microphone less sensitive, when you record things that are very loud, like a huge concert bass drum, or a canon!, or filters that can eliminates very low frequencies that add nothing to the music but creates mud... like a big heating system fan, or nearby trafic rumble.
Here is a link to one microphone kit I currently own...  https://www.oktavausa.com/mics/product/mk-012-msp6-factory-matched-stereo-pair-microphones
The diameter is 27mm, the thread is unknown but I can fin out...
Anyway you see where I am heading. 
Another question, Usually, north american threads are cut at 60°, is it the same for metric threading?


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## Ray C (Feb 11, 2018)

Yes, metric threads are 60 degree... 

I cut a lot of threads but am not familiar with your machine.  The theory is the same on all modern manual lathes that are designed to cut both SAE and metric threads.  FWIW, the finest pitch I've ever cut is 32 TPI.  I can certainly see how anything finer than that would present some different challenges.  There's not much room for error...


Ray


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## benmychree (Feb 11, 2018)

Yes metric threads are also 60 degree; whitworth are 55 degree and there are a few other threads with other (odd) angles.  You would need a 27 tooth change gears to accomplish 27 threads.


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## blue_luke (Feb 11, 2018)

Thank you Ray and Benmy, obviously I will have to dig more into th subject.
For the time being I found taps and dies for 5/8-27tpi threads (these are a bit rare). This might get me by for a while, but I foresee some cases where it would rather cut the threads on the lathe.
Thank you, Luc


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## Chipper5783 (Feb 11, 2018)

Yes, I think if you dig into it a bit, you should be able to sort out what gears are needed to get you 27 tpi.  I have two pretty standard machines - one has the option to select 27 tpi (with the standard end gears), the other does not - just needs some different change gears (the change gear set is made up of 20 gears - added to the selections in the Norton box, that's a lot of thread pitch options).

No holding the tube is another issue.  If it is not too soft / thin - then Mikey's suggestions of a 6J or collet will be fine.  Be gentle and it will work out.

You may have to turn a close fitting plug to slip inside the bore (and then you'd have no trouble with using the 3J or 4J).


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## markba633csi (Feb 11, 2018)

I've found 27 tpi in a few places:  Microphone stands, 1/8" pipe threads, and also the threads on some bathroom sink faucets are all 27 tpi.
Not many lathes do it natively; the South Bend 10L, Atlas, some Sheldons.   Epanzella's technique is a good approach: 18 tpi + 50%


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## blue_luke (Feb 12, 2018)

Digging more into this subject, I just found this _VERY_ interesting on line calculator!  
http://bilar.co.uk/cgi-bin/change-gear-calculator.pl

(I am on my lunch break) I just tried it and entered some gears type and the thing seems to work quite well.
Thcickidout!  :-D


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## benmychree (Feb 12, 2018)

benmychree said:


> If you set your quick change for 30 TPI and have a 30 T gear on the stud gear and a 27T gear on the change box,  and any number of teeth on an idler, you should get 27 TPI; I did a post on this a couple of days ago.
> 
> Are you sure? I do not see how dealing with even numbered change gears can result in an odd numbered thread.


It took me a little time and figuring to discover that what EPANZELLA suggested does indeed make sense; "whatever works".


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## Wreck™Wreck (Feb 12, 2018)

I do this for a living, every bloody day.

I never use TPI only lead when threading, for a single start 27 TPI thread the lead is 1/27 or .037" per revolution or .03703". If one were to go about calculating gear ratios using a fixed number of choices it may be truly difficult to arrive at a lead in tenths. TPI takes a good deal of the angst out of the picture. Measuring the actual lead of a thread is difficult at best. Try it.


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## brino (Feb 12, 2018)

blue_luke said:


> I think I have opened a can of worm here!



On that we agree! 

Because you said this:


blue_luke said:


> Yes I did receive quite a few gears for cutting threads, but no combinatons seems to arrive to 27 TPI.


....and this:


blue_luke said:


> The threads are fine pitch and metric for sure, but again, I have no specs as of yet.



So are we talking 27 TPI or are we talking metric?
Did you mean metric pitch or the diameters are metric?
I'm confused. 

-brino


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## blue_luke (Feb 13, 2018)

Oooops! Brino, I am making things a bit confusing for sure! 
the 27 tpi I need is only because this is a standard thread used on microphone stands and want to build accessories that will fit on this thread.

The other thing I need to build are modular microphones accessories. _THESE_ can use any type of threading and they are mostly metric. A good example of what I am talking about is here: AKG C-460  You will see a good picture of an accessory called a 'pad 10db' that depict exactly what I am after. These threads are metric for sure, and very fine, made of a thin walled piece of brass tubing!
Luc


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## HarryJM (Feb 17, 2018)

blue_luke said:


> Hello all!
> The things I intend to fabricate are audio microphones accessories. (I am a sound engineer)
> 
> This pose a few problems.... I own a Precision Matthews PM1127 lathe. This is a nice machine and I am happy with it, but the most standard thread size for mounting microphone bracket is 5/8"-27tpi  On the charts given on the machine, there is no gear combination to cut this thread!
> ...


Just finished reading my introductory Jan/Feb 2018 copy of “The Home Shop Machinist” and they had a part two article titled “Any Thread: A Parallel-linked, Adjustable Sine Bar Threading Attachment”. The author mentioned making attachments for digital cameras, etc. He made it for his Logan lathe and mentioned that it could me altered for other brands of lathes.


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## KBeitz (Sep 10, 2018)

If you hook up a Zero-Max up to your lathe you can cut any thread you want.


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## benmychree (Sep 10, 2018)

KBeitz said:


> If you hook up a Zero-Max up to your lathe you can cut any thread you want.


And how would that work?  Zero max does not do definite ratios and the motion is choppy, being driven by a series of eccentrics and one way clutches, at least all of them that I have ever seen.
I posted a detail on how to cut odd pitches, all that would be necessary (likely) is a 27 tooth change gear;  if your lathe has a 24 tooth gear on the end of the change box, set the QC for 24 TPI, and substitute a 27 tooth gear for the 24 tooth gear, the lathe will then cut 27 TPI.  If the lathe has some different number of teeth on the change box, set the QC up for that number of teeth and exchange the 27 tooth gear for that gear.
The QC box may also be set for multiples or halves of the change gear number by manipulating the other levers on the QC box.


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## epanzella (Sep 10, 2018)

You can use different combinations of change gear in concert with your QC gearbox to cut many threads not on your chart. As you slow the feed the thread pitch gets finer. For example, my G4003G chart lists 18 tpi thread with the QCGB set @ 18tpi and a gear train of 40/86/40.  But off the chart, leaving the QCGB on 18tpi, gears of 40/86/80 = 36 tpi.  Using 40/86/60 (I use this a lot) yields 27 tpi. Using 40/86/20 yields 9 tpi. There are virtually endless variations on this theme depending on what gears you have available.


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## BaronJ (Sep 11, 2018)

Hi Luc,

The standard way to cut any thread on a tube, is to use a mandrel !  5/8" 27 should be easy.
Turn up a piece of bar long enough to hold in the three jaw plus the length of your work.
Turn to suit your tube. Make it a good fit for your tube without it binding.
Drill and thread the free end, any convenient size.
Countersink the threaded end.
Mark the mandrel so that you can put it back into the three jaw in exactly the same place it came from.
I use a pop mark to indicate jaw 1 and a scribed line to indicate the face of that jaw.
Now slit the mandrel at the threaded end, down its length about 2/3 of the length of the workpiece.
Make a cone that will fit on your screw and fit the countersink that you made in the mandrel.
Using a screw with the cone on it, screw it into your mandrel.
Now when you put your tube onto the mandrel, tightening the screw will cause the mandrel to expand gripping your workpiece.
If your tube is very long, make the mandrel longer and use a hex head bolt with a center drilled in the head.  Then support it with a live center in the tailstock.


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## Video_man (Sep 11, 2018)

I found this chart on line for the PM1127, if it is the same as yours, I figure the closest I could come to 27tpi is this:

H  60   (Z1 - Z2)
30 50  (Z4 - Z3)
80  H   ( L )
position A  = 26.6667 tpi, which I think is as close as it will come with the gears the manual indicates are provided.  This is with a top gear fixed at 40T and assumes you have the inch lathe.
	

		
			
		

		
	




If your chart is different, perhaps you can post a copy.


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## KBeitz (Sep 11, 2018)

Quote...  And how would that work? Zero max does not do definite ratios and the motion is choppy, 

I think you got it backwards... A Zero-max is made to do constant precision movements 
if run at designed speeds. Just put a digital RPM meter on one and watch...
The output shaft is regulated precisely .Accurate speed holding.  
I have one on my mill lathe for making twisted octagons... You would waste some rods
until you got it set for the threads you want, but then you could go to town....


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## P. Waller (Sep 12, 2018)

Just like coarse threads only less coarse?


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