How to do fine threads

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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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".
 
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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I think I have opened a can of worm here!

On that we agree! o_O

Because you said this:
Yes I did receive quite a few gears for cutting threads, but no combinatons seems to arrive to 27 TPI.
....and this:
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. :confused 3:

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