collet thread

[colin beightonParticipant @colinbeighton45883]

[colin beightonParticipant @colinbeighton45883]

My old south bend lathe arrived with a set of 3C collets.Some of them have obviously never been used because they are too fat to screw into the drawbar. I need to take 2-4 thou off. My experience so far with single point thread cutting has not been good. Is there are a better/easier way to slim down a fat thread? I cannot find a die for this size-0.0645×26.

[John Stevenson 1Participant @johnstevenson1]

http://www.webbikeworld.com/motorcycle-tools/thread-file/

John S.

[colin beightonParticipant @colinbeighton45883]

Thanks John, I have now purchased a thread file.

[Patrick Carnegy 1Participant @patrickcarnegy1]

Hello Colin,

In my experience 3C collets are a bit of a mystery. With my Boxford AUD 5″ lathe (1978 vintage) came a drawbar and eight 3C imperial collets. I had trouble in getting them all to hold properly, eventually discovering that four of the collets had a 26tpi thread c. 0.626 diam, while the other four had a 26tpi thread c. 0.644″ diam. No wonder some were sloppy in the drawbar and others tight! I got into serious trouble when one of the collets jammed through over-tightening, the pin in the collet chuck shearing. Took a lot of headache to discover how to release the spinning collet – but that’s another story!

I have therefore made two new drawbars, using a 0.625 x 26 tap to cut the thread in the smaller one, and screwcutting the 0.650 x 26 one (not easy, but satisfying to do!).

Boxford describe the correct thread as 0.647/650 x 26

Rotagrip supplies new ‘3C’ collets threaded 0.640″ x 26

In all cases we’re talking about the 26tpi Brass Gas Thread.

Not sure you should try to reduce the diameter of your collet threads. You could try using a 26tpi chaser (as available from, say, Tracy Tools).

Very interested to hear how you get on.

Best wishes,

Patrick Carnegy

[colin beightonParticipant @colinbeighton45883]

Hello Patrick, nice to meet you.My collet threads only need 1-2 thou off and so far the thread file is coping. But in view of your cautionary tale I will make sure they screw in freely. My particular drawtube needs 0.638in. for full engagement. My lathe dates back to the last war and I had thought the size variation was due to poor quality control at that time, but perhaps not so in view of your remarks. Thanks for the info re suppliers. Regards, Colin.

[mgjParticipant @mgj]

Well if its brass gas, its a plain whitworth 26 tpi form.. Set that up on changewheels or the gearbox and you’ll have it cut or cleaned up in no time. On an 8 tpi lead screw you can engage on any 2 opposite marks on hte TDI. Use topslide movement along the bed to position the tool for first engagement (so the helices overlap truly) and away you go.

 

There is a choice – have faith and learn to screwcut (I learnned myself! from Allan Bradleys book and if I can do it anyone can). Or pay the money and get the taps and dies from Tracy Tools.

 

If I could just make  two points:

 

1. It ain’t that difficult.

2. You are going to have to learn sometime – so now is as good a time as any!

 

 

[colin beightonParticipant @colinbeighton45883]

Good evening Meyrick. Thank you for your encouragement.  I shall take your advice, abandon the cerebral approach and start cutting actual metal. Best wishes, Colin.

[mgjParticipant @mgj]

Might be wise to start on a blank,  – get it cut to size, and set so it fits. Then munch the real thing.

 

Start getting into multi – start coarse helices (worms) and its easy to find it gets very interesting. So interesting that its probably worth buying the worm from the specialists. But a common or garden thread – and its dead simple.

 

Its like all these things – once you have done it once, you wondered where the problem was.

 

All the best – M>

 

 

 

[colin beightonParticipant @colinbeighton45883]

This job is now finished, using a v cutter followed by the thread file. I also had to fettle the back end of several collets in order to get them into the nose adaptor and now have a set of usable collets.Hurray! Thank you each.

[Patrick Carnegy 1Participant @patrickcarnegy1]

Delighted, Colin, all has worked out well for you.

Glad you’re enjoying to screw-cut.

The one sure thing is that older collet threads (3c, etc) are a problematic area in which nothing can be taken for granted.

A comprehensive review article in ME or MEW would be very valuable.

Best wishes, Patrick

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