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27th Apr 2018, 11:10 PM #1Golden Member
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metric Uk bridgeport - acme or trap leadscrews?
Hi all,
Just doing a cleanup and inspection on a 1981 UK metric BP. Screws are not tooo bad but nuts are not very good.
Anyone know if the leadscrews on a metric BP are 29deg acme form or 30deg trapezoidal form?
Many thanks,
Greg.
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28th Apr 2018, 08:46 PM #2Diamond Member
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No idea as to metric or imperial, but if you measure the pitch over 10 or more threads that should enable you to tell what variety you are dealing with.
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28th Apr 2018, 09:16 PM #3Most Valued Member
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Sorry bob, how would measuring the pitch tell you the flank angle, I think the issue is He doesnt know what the flank angle is.
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29th Apr 2018, 08:11 AM #4Diamond Member
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Metric has 30 degree flanks imperial has 29 degree.
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29th Apr 2018, 10:09 AM #5Golden Member
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Thanks Bob, I do know the pitch. It is 5mm vs the 5 tpi of an imperial BP. It is not a given that because it is a metric pitch it has a 30 degree angle. It could be a 5mm pitch cut using the 29deg acme form. I also asked this over on PM and a fellow from the UK says he measured it and it was 29, not 30. The reason I ask is that, depending of what else need fixing on this BP I may or may not have the budget to buy new nuts. I guess this is some research into 'if I made them myself ... etc'.
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29th Apr 2018, 10:51 AM #6Senior Member
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Greg,
If you have the screws out of the mill you are welcome to use my Optical Comparitor to check the thread angle.
Cheers Piers
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29th Apr 2018, 03:50 PM #7Golden Member
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How can I say no to that! Thank Piers that would be amazing. I do have the screws out. I'll PM you.
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30th May 2018, 07:36 PM #8Golden Member
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the "big reveal" ... the winner is:
First, a big thank you to Piers for spending time with me on his awesome optical comparator trying to discern 0.5deg on a worn leadscrew. Not easy. Although not conclusive, we felt it was more likely ACME than trap.
Thanks Piers, it was a great experience and I learned stuff. I owe you one.
BUT .... I contacted Hardinge .. who contacted their "UK friends" to see if we could get an answer. It took a couple of weeks of emails .. but ... dignitaries, ladies and gentlemen, boy and girls. It is ACME. Here is a snippet of their manufacturing spec.
leadscrew_spec.jpg
case closed. )
Greg.
Thanks again Piers.
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