Harrison l5 lathe

Hi all I have a harrison l5 lathe. I have been trying to screw cut on the lathe for the first time. I have the right combination set up for the gear train but it will not thread to the correct pitch. I tried to cut 7tpi and it cut the thread at around 10tpi and I stripped the gearbox to check it and was OK has anyone got any idea what could be the problem thanks Ronnie

Yes it will and I have! That, with the stated error, tells me you have been caught out in the same way as me.

Nowt wrong with the machine, but its trap for the unwary is that the inoffensive little 3-position feed-shaft gear box below the headstock, also controls the lead-screw!

The 1:1 ratio that relays the true change-wheel setting to the lead-screw, is given by the lever's middle position; assuming your lathe is close enough in details to mine.

The other two positions give lower ratios, for extra-fine feeds (though you could also use them deliberately for screw-cutting if you know those ratios).

I suggest you try again, on some spare material - it needn't be the right diameter for this test - on the same change-wheel combination, but noting the effect of the gear-lever positions.

+++

Another point to note. The manual, or at least the edition I bought in photocopy form from Tony Griffiths, has change-wheel tables based on a 40T primary pinion. That on my L5 has 20 teeth - though it could have been some owner's modification, I suggest seeing if your lathe's fitting does match any tables you have for it.