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| Screw Cutting an ACME thread |
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| NickG:
Hello, I need some advice on cutting an internal 8tpi ACME thread on the lathe. This is to repair my milling vice which I recently found out had a part broken as some of you may have seen in my Poppin flame licker thread. My lathe has a screw cuttting gear box with full range of feeds and speeds so that isn't an issue, it's also easily man enough for the job. The real problem is, I don't really know how to grind the tool. I guess I could work it out from the thread geometry, probably on CAD but it would take a while. I need to know what clearances I need on the tool and what size cuts I should be taking etc, also whether it is critical to feed in and an angle etc. Please don't suggest any other options for repairing the vice, I know there are other ways to skin a cat and I have a few options but I want to have a go at repairing it the right way first. Thanks, Nick |
| sbwhart:
Nick You can use the bolt as a grinding gauge for the tool, don't worry too much about clearance angles as long as you've got some side clearance and some top rake it will be OK. From my Machinery hand book acme screw threads have an inclusive angle of 29 deg so I would rotate the compound over 14.5 deg and feed in at that, you may find it easyer to turn the tool upside down and turn on the far side of the job that way you can see what's happening better. Hope this helps and good luck Stew |
| Bernd:
Nick, Might need one of these to grind the cutting tool with. It's an Acme thread gage. Lower left notch is for grinding the proper angle. All the notches with numbers gages how wide the tip of the tool should be for your given tpi. So you should grind the nose of the tool to the 3 notch from the right on top, #8. Good luck. Bernd |
| No1_sonuk:
If you're not averse to getting a book: http://www.amazon.co.uk/Screw-cutting-Workshop-Practice-Martin-Cleeve/dp/0852428383 That has a lot of info, including tool geometry for "normal" and trapezoidal thread cutting. Is it actually Acme, or is it square? |
| Jasonb:
And if its a new machine it may have an ISO trapizoidal thread which has a 30deg angle not the 29deg of ACME but would likely be 3mm pitch. Jason PS you can buy ACME taps |
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