Ian beat me to it, but here's a link anyway

32tpi would be so close to a point that thinking of a tip radius of 0.0037" produced by hand is mind boggling.

I would get er11 carbide tooling for that job, especially as the diameter is so nice and big.

I'd grind it as close as I could to a 55 degree point set in a Vernier protractor or one of those digital angle gauges from Lidl, then stone the tip rad by hand with a medium/fine India oilstone. If it's 32 TPI on a 60mm diameter it's not gonna matter much if the tip rad is too small and the root's a thou or two deeper than it would be if the tip rad's crack -on size, unless the thread's on an extremely thin-walled tube. So my stoned rad would do little more than break the sharp edge.

After roughing out the tool use double sided tape to attach a wooden angle template to the tool that you can align with the side of the grinding wheel, Then do the other side so you have a true angle and a dead sharp point.
Next attach a toolmaker's clamp to the tool using paper for grip just to establish a reference position. measure the distance from this reference to the absolute tip with a height gauge or equivalent. Calculate the amount to be removed from the tip to bring it to the flat top or peak of the modified tool. Remove a little from the tip with a slip stone and measure until the calculated height is achieved. Then for rounded thread types round off by guessing how much is needed from the effort required to take off that tip in the previous stage.

I use hand grinding method with my 60 years year old Moore and Wright thread gauge,and is sufficiently accurate for most jobs. Another method not mentioned above is to use high speed steel internal and external machine thread chasers, these are not just for finishing off threads correct to form as the old tech books say , they can be used from start to finish cutting threads, and they produce very accurate thread forms.Back in the 1990s when there were a number of recessions a lot of chasers became available on the second hand market quite cheapl,nowadays their price has risen a lot ,I have a lot and cut a lot of threads with them,mainly BSP for full size steam,The chasers must be the machine type where the shank is flat and parallel,the older shape hand chasers which are shaped to take file handle are not recomended, as supplied they do not have top rake but are ok like this for steel if speed is reduced.The skill is that at the end of the thread a very quick two haded operation is required to disengage the half nuts and at the same time withdraw the tool by a quick wind of the cross slide handle, If you look at a box of used chasers you will find that some have had the row of teeth reduced at the L H side reduced to two this allows the chaser to run into a relieving groove,without the quick action required with a multi tooth chaser. For internal threads the chser shape allows the threading teeth to run through the bore,,blind bores are tricky and not for the novice. I have a good english made set of tool holders and imperial and metric carbide inserts but I rarely use them I much prefer the chasers particularly on commercial jobs.In my early working life the thread angle gauge was used for most jobs,there was just one job where the acme thread cutting tool was checked on the optical projector,not available to the amateur. one tip a tool dealer told me if you buy second hand chasers check that they are for right hand thread,he occasionally came across left hand chasers.

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As Andrew has noted : The Whitworth thread form was very clearly specified: **LINK**

https://en.wikipedia.org/wiki/British_Standard_Whitworth#Thread_form

But producing an accurately formed tool for 32tpi is likely to require an optical comparator to check your progress.

MichaelG.

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Edit: That said … I am inclined to agree that the C-mount thread is likely to be 60°, as I believe it was first specified by Bell & Howell.

Update: … admittedly not definite proof, but quoted from a respected source:

”The C-mount connection is described in the specification 1-32UN-2A. It is an imperial thread with a diameter of one inch and a pitch of 32 threads per inch.”

Ref. https://www.stemmer-imaging.com/en-gb/knowledge-base/lens-mounts/

Edited By Michael Gilligan on 02/02/2020 23:40:36

You're overthinking things a bit (a lot) with magnifying glasses and vernier protractors and exact tip radiuses..

Machinists have been cutting fine threads like that for over a century by using a standard, good quality screwcutting gauge (eg M&W), the little sheet metal one with the V notches cut in it.

Yes, for small threads, the very very tip of the tool is in the straight clearance slot in the gauge. But that's no problem at all. If the rest of the side matches the gauge, and the side is straight, the tip must be the same angle.

Secret is to finish the tool off by rubbing it on a bench oil stone, the type used to sharpen kitchen knives etc. Rub both sides of the V on the tool bit on the stone to get it nice and flat and smooth.

And agonising over exact tip radiuses (or radii if you are one of those pedantic types) is the realm of pedantic armchair engineers and what Martin Cleeve describes as "over-zealous amateurs". All you need to do is rub the tip on the bench oil stone a few times with a nice rolling motion, just enough to take the sharp point off. The main reason for doing this is not for thread form — it really does not matter as the point will cut a handy clearance at the root of the thread — but to stop the sharp tip from tearing off under cutting load. No need to measure the exact radius. Just feel it with your finger.

This is the way threads much finer than yours (32tpi is run of the mill average really) have been cut countless millions of times in machine shops since the days of Mr Whitworth and James Watt etc through to the late 20th Century when carbide inserts started to take over. Somehow since then, people have come to think there is something exotic about the shape of a thread cutting tool for general work.

There isn't.

Edited By Hopper on 03/02/2020 01:33:52

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Just to show solidarity with Hopper … Permit me to amend that statement, for clarity

”But producing an accurately formed tool for 32tpi is likely to require an optical comparator to check your progress.”

Would probably better read:

”But producing an accurately formed tool for 32tpi would be likely to require an optical comparator to check your progress,; and, for a C-mount thread, such detail is probably unnecessary.” [*]

Incidentally, however: Whitworth’s own test gauges are a joy to behold !

MichaelG.

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[*] and would be irrelevant, if the information in my update is confirmed.

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I suppose it might be wise to ask whether the proposed mount is for an exotic camera/lens, before deciding that this is ‘general work’. The cost of recovering jammed or worn components could be high.

MichaelG.