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Metric Thread On Imperial Lathe

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doubleboost:
That means the boxford hand book is wrong :( :( :( :( :(

Regards
John

BillTodd:

--- Quote from: Pete. on December 19, 2010, 12:04:13 PM ---I agree with Richard. It all depends on how the scale is marked up on the lathe. In the video, the compound is angled 30° off parallel to the spindle axis, where it should be 30° off perpendicular. My lathe is the same I have to set the scale to 60° (or actually 60.5) for a metric thread. The way it's set in the vid will give a 91° angle thread rather than a 60.

--- End quote ---

Yes, On my Hardinge it is 59°

doubleboost:
I am really confused now :doh: :doh: :doh: :doh:
Interesting stuff though
I would go and cut some threads if it were not below freezing in the shop :( :( :( :(

BillTodd:
I think the difference (and thus confusion) is down to how the trailing side of the thread form is to be cut.

If the top-slide angle is less-than the the thread angle ( i.e 29.5° for a 30° thread) then the trailing edge is cut by the back edge of the tool.

If the angle is greater than the thread angle then the trailing edge is cut by the tip of the tool, (as the back edge clears the face) and is thus defined by the angle of the slide.

If the slide is set to exactly the thread angle, then the cutter just scrapes the edge.


Bill

RichardShute:

--- Quote from: doubleboost on December 19, 2010, 12:12:32 PM ---That means the boxford hand book is wrong

Regards
John

--- End quote ---

Well it's not really 'wrong', just rather ambiguous. It says '...set at an angle of 29 deg...' which a legalese pedant would argue is not quite the same as saying 'set the compound slide so that the scale reads 29deg.'
It is very poorly worded, but at least we've got to the bottom of it.

Richard

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