1st time thread cutting

Hi everyone. I have been enjoying my Smart and Brown Mk2 laithe which I have restored bit now I want to learn how to cut thread.

I just need a little bit of guidance. I do not understand the gear chart. Eg If I wanted to cut 1.5 mm threads it gives in the F gear 1 is 1.5 which I think is the thread I am wanting to cut. 2 is 0.75 no clue and 3 is .375 and i haven't a clue.

Any help explaining the gear chart would be much appreciated.

Thanks in advance.

Edited By mark novak on 26/08/2021 13:09:56

It sounds like your F gear position on the gearbox give s3 ratios. The middle one is 0.75mm pitch, one of the other positions doubles that yo by 2:1 so you get 1.5mm pitch and the other position halves it 1:2 so you get 0.375mm pitch.

Put F into the one that corresponds to 1.5

Assume you have any other levers or change gears positioned as required

EDIT Now you have posted the photo you will need to put the lever that has positions 1, 2 & 3 into the correct position and also make sure you use the gear train at the top of the chart section and finally move the lever under the chart to the 1.5 position(f).

<>Looking closer at the chart the upper set of gears use1, E Not F or the lower set of gears would allow 2B to be used. the 1-2-3 lever is likely to be bottom left of headstock

Edited By JasonB on 26/08/2021 13:42:43

Jason B So this photo is one I have in my album of my laithe which is at work and I am at home with a broken collar bone. So do I put the gear into 1 and the other leaver into E to get 1.5 mm thread? Sorry I am a real noob at this but very willing to learn. Thanks Mark

That's it 1E if the gears are as the top set of pitches, 2B if the second set of pitches

As a means of peace of mind, before cutting metal, it would be worth checking that rotating the chuck by hand for 1 or even 10 revolutions moves the Saddle by 1.5 mm or 15 mm.

Once you are happy withe set up, then you can cut metal.

My first attempt at thread cutting was a 1 mm pitch for the lens panel on a plate camera, done with much fear and trembling. At least if it had gone wrong, it would only have meant throwing away some Aluminium sheet, rather than hours of work on something more complex!

Once you succeed, you will have the confidence to do more in the future!

Howard

My usual trick is to sit there trying to work out if I'm about to accidentally cut a Left hand thread rather than a right hand thread.... I get it right almost 50% of the time.

Sharpie or other felt tip pen in the tool post and along bit of bar so you are well away from the chuck is a good way to try things out as you can just draw a helix around the bar and practice disengaging the leadscrew at a marked position. Just wipe it off and have another practice until you are happy to cut metal.

Remember, screw-cutting is not a race. Exactly the same amount of material is removed by the tool whether the work is rotating at 1 r.p.m. or 1000 r.pm (exaggeration to make the point). Go slower at first until you get into the 'rhythm' of releasing the half-nuts and withdrawing the cross-slide. I always use the set-over top-slide technique and you can also use this method on internal threads if you invert the tool and cut the thread on the rear of the bore. This means you avoid any confusion, or possible disaster, by inadvertently withdrawing the cross-slide instead of advancing it when cutting an internal thread. Alternatively, you don't withdraw the cross-slide at all in conjunction with releasing the half-nuts. Obviously, the tool will just cut a circular groove at the end of its travel and you can withdraw (or advance on internal threads) the cross-slide at leisure. This is perfectly acceptable and, in any event, always happens if you are using any sort of rapid threading attachment such as the Ainjest.

Thanks guys for all your wisdom and help, I will try your methods as soon as I get back to work. Thanks again