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Kleftiwallah
Joined: 27 Oct 2016 Posts: 222 Location: North Wiltshire
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Posted: Fri Nov 10, 2017 1:14 pm Post subject: Thread cutting phenomenon |
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I'm in the shed making a new brake rod from 5/16 th mild steel cutting a B.S.F. thread 5 inches long. The first two inches are spot on, but then the thread seems to form a long amplitude helix (although the threads along the whole length are acceptable).
Now, why is this happening (or has happened)?
Over to you knowledgeable people. Cheers, Tony. _________________ It may work in practice, but not necessarily in theory!
Last edited by Kleftiwallah on Fri Nov 10, 2017 1:27 pm; edited 1 time in total |
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peter scott
Joined: 18 Dec 2007 Posts: 7120 Location: Edinburgh
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Kleftiwallah
Joined: 27 Oct 2016 Posts: 222 Location: North Wiltshire
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Posted: Fri Nov 10, 2017 1:26 pm Post subject: |
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Nope, not stretched. Still the original length.
Cheers, Tony. _________________ It may work in practice, but not necessarily in theory! |
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47Jag
Joined: 26 Jun 2008 Posts: 1480 Location: Bothwell, Scotland
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Posted: Fri Nov 10, 2017 1:45 pm Post subject: |
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Could it be that the rod is twisting due to the resistance to the die cutting and in so doing reduces in diameter slightly
Art |
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alastairq
Joined: 14 Oct 2016 Posts: 1954 Location: East Yorkshire
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Posted: Fri Nov 10, 2017 3:41 pm Post subject: |
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Whilst I admit to inexperience when it comes to thread-cutting, a chum has suggested the thread form has 'stretched' because the thread itself was being cut, 'too quickly'...the die apparently can march down the rod improperly if turned too fast? |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4105 Location: South Cheshire
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Posted: Fri Nov 10, 2017 6:19 pm Post subject: |
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alastairq wrote: | Whilst I admit to inexperience when it comes to thread-cutting, a chum has suggested the thread form has 'stretched' because the thread itself was being cut, 'too quickly'...the die apparently can march down the rod improperly if turned too fast? |
When I cut male threads on the lathe with a die I turn everything by hand, I'm sure someone will correct me , but I cut male threads with the die open wide, and them mak a couple of passes with it closed.
Dave |
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Uncle Alec
Joined: 14 Jan 2008 Posts: 734 Location: Manchester
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Posted: Fri Nov 10, 2017 10:03 pm Post subject: |
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Me too Dave. I convert surplus Riley RM radiator steady rods into clutch rods by doing just what you say; expand the die as far as by sending the V-pointed grub screw way in, then another run with it out and the locating grub screws tight in. |
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Kenham
Joined: 12 Mar 2012 Posts: 209 Location: Kent
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Posted: Sat Nov 11, 2017 9:00 am Post subject: |
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I find it easier to turn threads with the lathe , quite a satisfying job I find. All well and good if you have a lathe of course. As to the original question yes to much too soon I suspect and turning the rod instead of cutting properly. |
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Kleftiwallah
Joined: 27 Oct 2016 Posts: 222 Location: North Wiltshire
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Posted: Sat Nov 11, 2017 11:10 am Post subject: |
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Thanks to all your knowledgeable answers,
I think 47jag has hit the nail on the head. I did have the rod projecting quite a way up from the vice jaws. I cut another length with only 1 1/2 " out of the vice at any time dieing down until I barked my knuckles only then lifting the rod higher by the same amount and the thread is spot on all the way down..
Take a sweety out of the jar 47jag!
Cheers, Tony _________________ It may work in practice, but not necessarily in theory! |
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Ray White
Joined: 02 Dec 2014 Posts: 6320 Location: Derby
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Posted: Sun Dec 24, 2017 6:16 pm Post subject: |
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Forgive me for casting aspersions but you say you are making up brake rods? . That sounds like you are using some pretty crummy steel to me. I would want something a bit tougher if it was my life depending on it. |
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