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Post by bookworm on Dec 19, 2008 18:05:03 GMT
In the latest edition of Model Engineers Workshop magazine, Tracy Tools are selling a Coventry Die Head Thread Chaser mounted in a simple holder. They say you can cut new threads by screwcutting in a lathe by just using this one chaser in its holder.
Has anyone done this and what are the results?
Peter
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Post by spug103 on Dec 19, 2008 19:46:29 GMT
i have used coventry die heads, they are good, but with certain limitations, we have now put our sets aside and upgraded to a Rigid threading machine (although the parts are very expensive),
if you are looking to invest in coventry die sets i could see if my boss is willing to part with them.
regards
Ben
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Post by jonkett on Dec 19, 2008 23:13:00 GMT
Coventry Dieheads are very mach technology of the Capstan Lathe era. They are used mainly for the production of large batch quantities of bolt or threaded fasteners. The dies themselves are very expensive, with very few british suppliers.
Dies for a 1" diehead are going to cost in the region of about £40 a set and you need a set for every size of thread. Imported Japanese dies have gone up in price by nearly 40% recently, actually they want to stop production so may increase even more in the near future.
For model engineering purposes I would have thought that a tailstock dieholder is more than adequate, easy to make and the dies are more reasonably priced.
Unless of course you are thinking of going in to mass production.
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Post by alanstepney on Dec 20, 2008 1:55:23 GMT
All true, but when making a batch of something, arent they superb!
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Post by spug103 on Dec 20, 2008 2:03:38 GMT
as you said jonkett, the coventry die heads are old technology now, hence machine shops / factories have stopped using them and second hand items becoming available all the time, and they are adjustable to get a nicely fitting and repeated thread size.
although as with all proffessional quality tools they are expensive new, as mentioned.
regards
Ben
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Post by bookworm on Dec 20, 2008 14:50:03 GMT
The point I was trying to get across was that they were not advocating using a coventry die head, but just using one of the chasers held in a simple holder and used freehand or in the lathetool holder, for both cleaning old threads and making new threads.
Peter
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Post by jonkett on Dec 20, 2008 14:57:29 GMT
ok nothing wrong with that idea, remember that many secondhand chaser dies are more than well used.
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Post by alanstepney on Dec 20, 2008 18:31:49 GMT
You used to be able to buy hand thread chasers, and all they were was one die, with a handle attached. Or, to be accurate, were made from one piece of metal that had a handle one end, and the other formed into a die.
Same idea, new method.
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Post by spug103 on Dec 20, 2008 19:10:27 GMT
We have those aswell, im not a fan as they can tend to rip a thread slightly, could just be me as im not really willing to give them that much of a chance,
i prefer the rigid machine or split dies depending on purpose, but it is down to preferance really.
regards
Ben
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redmog
Part of the e-furniture
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Posts: 461 
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Post by redmog on Dec 20, 2008 21:15:42 GMT
In the latest edition of Model Engineers Workshop magazine, Tracy Tools are selling a Coventry Die Head Thread Chaser mounted in a simple holder. They say you can cut new threads by screwcutting in a lathe by just using this one chaser in its holder. Has anyone done this and what are the results? Peter Peter - I think your question has been misunderstood ! Yes - I have done this. But I cut the thread as normal with a tool and the leadscrew first and chean up with the chaser to get the crests to form. Three tools for doing this are shown below. 1. An internal thread chaser fitted to a file handle and chased by hand,(not that I'd fancy doing it !) or put in the toolpost and chased with the leadscrew. 2. An external chaser for in the toolpost and chased with the leadscrew. 3. Or find a Tap with the required threadform and use that chased with the leadscrew as shown. Can be used for internal or external threads, just make sure the flute cutting edge is at centre height. All are successful to clean up the thread crest but I would'nt fancy cutting a full thread form with them from scratch. A Coventry Diehead with 4 dies is a differnt tool to just a chaser ! Chris. 1.  2.  3.  |
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Post by Deleted on Dec 20, 2008 23:57:48 GMT
Absolutely spot on Chris, you beat me to it! I have finished threads with a hand chaser, and provided the centre height is right, good results are forthcoming. I have also used a Coventry chaser to do the same thing, mounted in the tool post, as advocated by Tracy Tools: works quite well.
jb
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Post by bookworm on Dec 23, 2008 9:41:00 GMT
Many thanks for answering my question.
I need to cut a thread 3/16 x 40 up to a shoulder but my die set isn't up to it (can't get close enough). I will have to find someone who can grind the die down for me.
Cheers,
Peter
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Post by Deleted on Dec 23, 2008 10:44:45 GMT
Peter. I hope this is not a daft question, but can't you get away with an undercut at the end of the thread, thus allowing the nut to go up to the shoulder ? This is how I've always got over the problem.
Regards
JB
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Post by bookworm on Dec 24, 2008 12:08:51 GMT
I tried that but the undercut was too large for the size of the thread.
Iv'e now taken to making it in two parts and silver soldering them together
Best wishes
Peter
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Post by Chris Kelland on Dec 24, 2008 18:04:48 GMT
Hi,
There is a little bit in Harold Hall's book 'Lathework, a complete course' about using individual chasers held in a holder. I have just had this same problem making some caps for a steam chest oiler. In the end I undercut the thread using a very thin hacksaw blade in a holder. On larger threads I have used a thin parting tool, but ther thinest I have is 1.5 mm. would it be possible to make a suitable tool from a hardened hacksaw blade suitable ground?
Chris.
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