Help! Anyone got a 31/32 UNF tap?

[evildrome]

Hi All,

I need to buy a 31/32 UNF bottoming (3rd) tap for a camera body I'm making. Its an underwater camera that mates to a proprietory cable (which has the 31/32 UNF male fitting).

I'd like to buy a tap from someone. If the worst comes to the worst I'll attempt to make one out of steel (the camera body is Alu) but buying one would be better. I could go $100 if you've got one to sell.

Sorry to post this here but I did look in the Classifieds section and I didn't find a 'Wanteds' section only 'For Sale'.

Thanks for looking.

Wilson Logan.

wilson.logan (at) ntlworld.com

[Mcgyver]

is 31/32 in a unf series? I know you can make a un profile any dia you want, but never seen a series in 32nd's....i'm sure there are places that'll make it if you don't want the bother, but in this largish dia can;t you just just cut it in the lathe for a one of?

[Geof]

KBC Tools supplies an enormous range of taps, different diameters different threads but that doesn't help someone in Scotland. Also I seem to recall the prices for the larger ones are multiple hundreds.

I suggest figuring out a fixture to hold it in a lathe to screw cut or get it done by thread milling which is what I would use having access to CNC.

Another thought is to find the fitting that the cable end is supposed to screw into and see if that could be epoxied into your aluminum housing. It will likely have a flange for surface mounting with little screws so you would need to turn the OD.

EDIT: I looked at a catalogue; no 31/32", 15/16" all the way up to 32 TPI, 1" all the way up to 48 TPI. And the price is better than I remembered at less than $50.

[evildrome]

Hi Guys,

Thanks for the replies.

31/32 UNF is a non-standard thread. Its been made that way by the manufacturer specifically to stop people doing what I'm doing. They want you to buy their camera shell for X hundred dollars rather than turn one up out of $10 worth of aluminium.

A company has offered to make me a 31/32 tap but the price for one is.... wait for it... $1460. If I took a dozen the price would be $200 each but I don't need a dozen.

I've recently acquired a small industrial lathe (Colchester Student) but it has no screw cutting gearbox & the change gears have been lost a long time ago. Its a good lathe for $400 but the lack of a gear box is a PITA.

I can make a tap on my friends lathe but if someone just happened to have the right tap laying around it'd be easier. If you don't ask you don't get!

Cheers,

Wilson.

[HuFlungDung]

Are you certain that it is not a 25mm metric thread? I would suspect this because there is no specs for 31/32 UNF, so we cannot even tell what the pitch is. What is the pitch?

[evildrome]

Hi,

IIRC its 20tpi 31/32 UNF 2B.

The company that offered to sell me some sent it away to their tap manufacturer for identification.

Additionally, as a test, I made a 20 tpi 31/32 UNF bolt on my friends lathe as a test piece and it fits. Sadly, I made it a bit of a rattling fit otherwise I could have turned the bolt into a tap.

Cheers,

Wilson.

[Mcgyver]

$1460!!! outrageous i say. I do it for a mere 1300

Geof's idea is a good one, outsource thread milling if you can't fit it on a lathe

[Geof]

I think put in a bit of time looking for the mating piece. If you are double lucky; first luck is finding it, which should be the case; second luck is finding it is made out of brass not pot metal, which is questionable; then you can do as I suggest, set it into your housing.

You do not rely on the epoxy for either the water seal or adhesion. Incorporate a small section O-ring for the seal and have ridges or some form of roughness to get a mechanical interlock with the epoxy. If you use aluminum filled epoxy your thermal expansions will be close. This sort of thing can work, I have done it.

[evildrome]

Hi Geof,

Good plan. Excellent plan in fact. Finding the 31/32 UNF threaded item is going to be the hard part... errr... I just remembered when I was looking for 31/32 UNF taps I found that 31/32 UNF is the standard fitting for an Italian brand of radiator TRV. Hmmmm.... If they do an adapator collar that might be the very thing...

Thanks for that.

Wilson.

[evildrome]

Nope. I was wrong. I checked back and 31/32 is the height of threaded part, not the diameter.

Still, not a bad idea. I will continue to look.

Cheers,

Wilson.

[Geof]

Here is another approach.

You have the 31/32 thread on the end of a cable. Do the epoxy trick int wo places: Find something that has a fine thread 1" diameter both male and female. Bore out the male thread and bond it to your cable end and bond the female thread into your housing

[evildrome]

Not a bad idea at all Geof.

BTW I notice that 20 tpi is not a million miles from 1.25 metric (20.4 tpi). There are only about 4 full threads in the camera housing. Would it be possible to find something with a 1.25 pitch thread and have it go on 4 threads before binding up?

Cheers,

Wilson.