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Thread: ARM compound screw
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18th Aug 2019, 12:23 AM #1Intermediate Member
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ARM compound screw
Finally getting around to doing something about the slightly bent screw on my metric Hercus. Can anyone confirm whether the screw is trapezoidal or acme?
The dials say 2mm per revolution.
And a source for threaded rod, or am I going to have to make it?
Cheers, Martin
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18th Aug 2019, 06:01 AM #2
Hi Martin,
You could try to straighten it. A flat plate, a few shims and a copper hammer usually works.Best Regards:
Baron J.
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18th Aug 2019, 09:18 AM #3Most Valued Member
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Why not buy one?
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18th Aug 2019, 10:25 AM #4Intermediate Member
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Thanks for the suggestions. Can anyone answer the question I asked?
I have tried straightening it, but I can't get it completely flat.
I could buy one of course, but this is an opportunity to learn. I haven't turned square thread before.
Martin
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18th Aug 2019, 11:21 AM #5Member
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18th Aug 2019, 11:22 AM #6Intermediate Member
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Yep, I've checked the pitch. It's the form that I'm asking about.
Martin
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18th Aug 2019, 02:42 PM #7Intermediate Member
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I'm sorry but I do not know what the form is either.
Here is a link to a "Tubalcain" video on Youtube about cutting Acme threads:
MACHINE SHOP TIPS #24 Acme Threading Part 1 tubalcain - YouTube
I regret that often you will find that members of forums either have a problem with reading comprehension, or respond to a question by asking a new question. (Who would have guessed that so many lawyers were active posters on metalworking and other forums ?)
You could try locating someone with both types of 2mm nut and see which nut fits your screw and which nut does not fit your screw. Always hoping that at least one nut does not fit. Maybe both nuts would fit one form of thread, and only one nut would fit the remaining form of thread. Then you would start looking for something like a set go / no go nuts to eliminate doubt !
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18th Aug 2019, 03:50 PM #8Most Valued Member
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Seeing you have been able to workout that it's a square thread just make a new one, I thought you weren't sure what shape the thread was.
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18th Aug 2019, 04:17 PM #9Philomath in training
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A trapizoidal thread is 30 degrees, an ACME 29 degrees. The difference between the two is probably almost indistinguishable from wear that may have taken place over the years. I can't think of any fastener shop that would have a nut like that on the shelf either.
For the OP -
Short of knowing someone with a profile projector that can check the angle for you, I don't know anyway of definitively knowing that. I would lean towards ACME, simply because the imperial lathes that were made would have been ACME.
I don't know whether due to the closeness of the thread profiles for the size of screw you are talking about, whether you would notice the difference with either angle.
Michael
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18th Aug 2019, 08:57 PM #10Senior Member
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I think Hercus used Acme.
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18th Aug 2019, 09:23 PM #11Intermediate Member
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Thanks Michael, I think I'll hone the acme hss tool I have and give it a run.
Obviously it's a 2mm pitch given the feed dial.
I turned up a blank this afternoon. Hopefully I'll get some shed time tomorrow to finish it off.
I'll post up my attempt.
Martin
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18th Aug 2019, 09:29 PM #12Philomath in training
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Your choice, but but I've just noticed your location as AU. If you change it to a suburb or area you may find there are members near by who can help with repairs like this.
Michael
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19th Aug 2019, 08:41 AM #13Most Valued Member
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I'm pretty sure that if it is an imperial pitch it will be acme and if it is a metric pitch then it will be trapezoidal.
I'm open to correction but am nearly certain that is the case.
Phil
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19th Aug 2019, 08:02 PM #14Philomath in training
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I recently cut a couple of nuts for metric pitch leadscrews and I thought they were trapezoidal at the time. With hindsight, I have my doubts...
Michael
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19th Aug 2019, 08:57 PM #15Senior Member
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Hercus seemed to put metric pitches on imperial shafts so if the original shaft measures up as an imperial size then don't be too surprised, it was probably easier doing that than changing all of the machines for different size material
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