Screwcutting on WM180

[Phil SParticipant @phils66830]

I have screwcut BA threads on a mini lathe with the topslide set at 23.75 degrees so the tool cuts on one side only. As shown in the image the cross slide handle then just clears the topslide when the toolpost is in a good position for screwcutting. My question is can this be done on a WM180 or does the cross slide handle foul the topslide ? There may be two answers as I believe the cross slide handle and topslide positions changed on the later version of the WM180.

Edited By Phil S on 21/04/2021 11:41:17

Edited By Phil S on 21/04/2021 11:43:42

[Phil SParticipant @phils66830]

[JasonBModerator @jasonb]

Third answer is not to bother setting the top slide at an angle and just use the cross slide to feed straight in.

4th answer is to take one of the handles off and replace with a spacer then use an allen key or hex driver in the cap screw to turn the leadscrew.

[Anonymous]

Posted by JasonB on 21/04/2021 12:00:05:

……………..not to bother setting the top slide at an angle and just use the cross slide to feed straight in.

That's what I do, never bothered to set the top slide at an angle. Feeding from the cross slide allows depth of thread to be read directly.

Andrew

[Bo’sunParticipant @bosun58570]

Is this thread cutting with the compound slide at an angle a new thing? In 1972, I served a toolmaking apprenticeship with a well known car company, and no mention of it then. I think there may be some benefit with larger pitch threads, but that's about it.

[Phil SParticipant @phils66830]

Thank you for your replies. I would agree in many cases feeding in using only the cross slide is fine. However as I see it using the topslide maximises the unsupported length of thread that can be cut without chatter. The force from the deformation of the v shaped chip from cutting on both flanks is considerably more than double the force from cutting an almost flat chip from one flank for the same depth of cut. Also the tool can have some top rake to the leading flank again reducing the cutting forces. As for my original question, by estimation of dimensions I believe the answer is there is a clash for older WM180s and clearance for newer models, but only just ! If anyone with a WM180 can confirm here or by PM I would be grateful.

Edited By Phil S on 25/04/2021 19:14:11

[Nick WheelerParticipant @nickwheeler]

Posted by Bo'sun on 21/04/2021 13:26:03:

Is this thread cutting with the compound slide at an angle a new thing? In 1972, I served a toolmaking apprenticeship with a well known car company, and no mention of it then. I think there may be some benefit with larger pitch threads, but that's about it.

I don't do much screwcutting, and don't offset the top slide. I'd be more likely to do it for really fine pitches, to increase the amount of adjustment.

[John HaineParticipant @johnhaine32865]

Keep topside parallel but when you infeed say F on the x slide feed the topside F sin(thread angle) , or is it cosine? Gives the same effect as angling the topside as most of the trailing flank of the tool doesn't cut.

[Nigel Graham 2Participant @nigelgraham2]

Bo'sun –

No, it's by no means a new technique.

Probably, the workshops in which you were trained and employed did not need to use it. Were they cutting relatively fine threads on hefty lathes with lots of rigidity and inertia? Or using thread-chasers as well as single-point tools?

[egaParticipant @ega]

Posted by Bo'sun on 21/04/2021 13:26:03:

Is this thread cutting with the compound slide at an angle a new thing? In 1972, I served a toolmaking apprenticeship with a well known car company, and no mention of it then. I think there may be some benefit with larger pitch threads, but that's about it.

In his 1951 ME Lathe Manual ETW says that swivelling the top slide is "usual"; he no doubt had in mind the class of lathe used by the hobbyist of the day and either carbon steel or HSS tools.

The same work shows a 6TPI Acme thread being cut "straight in" but the text recommends narrowing the tool to allow for side to side adjustment of the cut when full depth has been reached.

[egaParticipant @ega]

PS The classic SB book How to Run a Lathe 1942 edition says that " in manufacturing plants, where maximum production is desired, it is customary to place the compound rest of the lathe at an angle of 29 degrees for cutting screw threads."

[Author]

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