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[Keith MathesonParticipant @keithmatheson47708]

[Keith MathesonParticipant @keithmatheson47708]

Hi starting to use my lovely new Toolco 1130 (same sort of thing as the warco 290 etc etc). It has a 3mm lead screw and I was cutting a 1.5mm pitch thread. I know I have to engage and re engage on the same number but looking at a plate on the lathe some threads can go onto a few numbers. However, 1.5 is not on the list. Does that mean I can only engage and re engage in the same number I pick originally OR I can pick any? Plate photo should be below.

[Mick B1Participant @mickb1]

About 1000 years ago I learned that if the leadscrew pitch was divisible by the pitch to be cut, the halfnut could be engaged anywhere on the chasing dial. We were talking inches back then, but I think the principle is the same. Someone will be along to tell us if it's not.

I'd try it with the tool out of contact with the work, after cutting an initial 5 thou scratch. Engage at several random points on the dial, stop the spindle while engaged, and see whether your tool point is still coincident with the scratch.

I usually find it just as fast and safe to leave the halfnut permanently engaged while screwcutting, and reverse back with the tool retracted before taking the next pass.

[TSHParticipant @tsh73987]

Keith,

I'm assuming that Z=30T implies that there are 30 teeth on the worm wheel which meshes with the leadscrew. If that is correct then there are in total 30 possible places you can engage the half-nuts (only 6 are marked on the dial). To cut a thread of 1.5 mm pitch you can engage the half-nuts anywhere—that is, on any place on the dial, marked or unmarked. By the way, the same is true for a pitch of 3 mm and 1 mm (and lots of others) even though the table implies you need to engage on one of the marked lines (1 – 6).

I have sent Neil a short article giving the general rule for this; I presume it is awaiting its turn for publication.

Regards,

Trevor

[Thor 🇳🇴Participant @thor]

Hi Keith,

Congratulations with your new lathe. Trevor is right. On my metric 290 lathe you can engage the half-nuts at any of the numbers 1 – 6 when cutting 1.5mm pitch. A few pitches are missing from the chart, 0.7mm and 0.8mm for instance, to use the threading dial when cutting these I made a 28T worm wheel to replace the standard 30T.

Thor

Edited By Thor on 05/03/2018 05:32:24

[Neil WyattModerator @neilwyatt]

Hello Trevor,

When and how did you send me your article? I don't have any record of it.

If it was an email with a lot of or large attachments I would not have received it and I don't get a message to let me know.

Thanks

Neil

[Martin ConnellyParticipant @martinconnelly55370]

Kieth, have a look at this in my albums.

Martin C

**LINK**

[TSHParticipant @tsh73987]

Hi Neil,

I have sent you a personal message.

Regards,

Trevor

[Keith MathesonParticipant @keithmatheson47708]

Thank you all for your contributions to my question. Really useful information and guidance. I'm very very grateful

Keith MM

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