Help with 1/4-40? thread with .272 diameter

[Bill in PA]

Hello,

Need to machine custom collet with the same thread as sample (see photo). Checked the thread pitch under a microscope and it is exactly .025". However, the diameter is .272".

I don't know the machine/device that the sample fits. It is used in the electronic industry. The collet bore gets a sharp thread to bite into a cable jacket.

The sample has a different taper than the one I am making. The customer spec.'d the wrong thread on the drawing for the one I already made. He sent me this sample to match the thread.

I normally use a threaded fixture to hold the end of the collet to saw the slits. However, a .272"-40 isn't going to go in a 1/4-40 tapped hole.

Any ideas what this thread might be?

Thanks,

Bill

 

[Monarchist]

I normally use a threaded fixture to hold the end of the collet to saw the slits. However, a .272"-40 isn't going to go in a 1/4-40 tapped hole.

It could do.... if you but slit the FIXTURE across that tapped hole, first. Four-way, reasonably certain, three ... or but two...mebbe not so good.

2J "emergency" collet? Simple vise-tooling?

 

[Bill in PA]

It could do.... if you but slit the FIXTURE across that tapped hole, first. Four-way, reasonably certain, three ... or but two...mebbe not so good.

2J "emergency" collet? Simple vise-tooling?

I also have a fixture that the sawed collet goes in for final boring, so that it will spring open when released. The collet is drawn in with a nut.

Figuring out how to fixture with this odd thread is not the issue. I can single-point the thread in the fixtures with whatever diameters I desire. Just simpler to thread with an off-the-shelf tap. Especially for a one piece order.

More or less wondering if anyone has run across this size before.

Thanks,

Bill

 

[Bobw]

You don't have a #16-1/2 - 40 tap laying around???

Bastardized metric american hybrid.. 7mm by 40 pitch??

I wonder.. IF 1/4-40 was a standard helicoil/STI size, if that would be it.

Maybe you can find somebody that has a 1/4-40 H44 tap in stock???


THIS is why you get paid the big bucks.

It is on a collet, so I would assume they made their own thread "standard" so that everything worked.

Just a thought. IF you had rigid tapping, you could get a 7mm x 1.25 tap (not common, but not
hard to find). And tap your hole twice, offsetting the start point by .0125". That would be
damn close, and might just work.

EDIT: NO IT WOULDN'T.. That would be a 2 start thread. but everything else would be damn close.

Edit #2. Get out the thread wires... 9/32"-4 HSS Bottoming Tap (2 Pcs.): Amazon.com: Industrial & Scientific

 

[Illinoyance]

It sounds like one of the common threads for an 8mm collet for a watchmaker's lathe. If I remember correctly I have seen taps and dies for that thread but I'm damned if I can remember where. getting old, can't remember shit.

 

[Illinoyance]

Here is a collet drawbar to fit your collet. One end is .275-40. The other is metric. I don't know if this helps. This vendor does sell taps for the 6mm drawbar. I did not spend time searching for the 8mm version

 

[Bill in PA]

It sounds like one of the common threads for an 8mm collet for a watchmaker's lathe. If I remember correctly I have seen taps and dies for that thread but I'm damned if I can remember where. getting old, can't remember shit.

Yeah, the shank is about .3135".

Bill

 

[Bill in PA]

Here is a collet drawbar to fit your collet. One end is .275-40. The other is metric. I don't know if this helps. This vendor does sell taps for the 6mm drawbar. I did not spend time searching for the 8mm version

Do you have a link?

Bill

 

[Illinoyance]

Bingo!
WW Size .275 - 4 Tap for Bergeon Levin Etc Watchmaker Lathe Drawbar - Threading Taps - Amazon.com

.275 x 4 tap | eBay

 

[Bill in PA]

Bingo!
WW Size .275 - 4 Tap for Bergeon Levin Etc Watchmaker Lathe Drawbar - Threading Taps - Amazon.com

.275 x 4 tap | eBay

Thanks.

I just found the specs. for a WW collet too.

Might be possible to modify an off-the-shelf collet if it is soft, but it will be just as easy to make a new one. I can charge a little more for this one since I will have to buy the goofy tap.

Here is a photo of the one I made to the faulty print:



Thanks,

Bill

 

[EPAIII]

0.275 x 40 Tap?

All you have to do is search for that.

WW Size �.275 - 4� Tap for Bergeon Levin Etc Watchmaker Lathe Drawbar - Threading Taps - Amazon.com

New BSW .275 x 4� British Standard Whitworth Thread Tap �.275''-4� | eBay

New BSW .275 x 4� British Standard Whitworth thread tap �.275”-4� | TIMESHOPPING

Many, many more returns. Jeesh, it wasn't even hard. Apparently it is a standard for WW collets. I am not sure if it is a 60 degree Vee thread or a Whitworth.

 

[Bill in PA]

0.275 x 40 Tap?

All you have to do is search for that.

WW Size �.275 - 4� Tap for Bergeon Levin Etc Watchmaker Lathe Drawbar - Threading Taps - Amazon.com

New BSW .275 x 4� British Standard Whitworth Thread Tap �.275''-4� | eBay

New BSW .275 x 4� British Standard Whitworth thread tap �.275”-4� | TIMESHOPPING

Many, many more returns. Jeesh, it wasn't even hard. Apparently it is a standard for WW collets. I am not sure if it is a 60 degree Vee thread or a Whitworth.

Yup, had I known that this was a .275 thread or a WW collet, I would have Googled that and not bothered everyone with this thread. I am not a watchmaker and this is not a hobby shop. I am not familiar with these collets (or had seen them before). I did not consider that this was some sort of lathe collet considering I normally make molds for over-molding cables and connectors for this customer.

Anyway, the sample collet has a 60 degree thread and I did not find any taps readily available in the States. No big deal, I'll single-point what I need. Now I know what it "officially" is.

Thanks to all who kindly replied.

Bill