Quote Originally Posted by Neale View Post
There have been (and still are, for all I know) plenty of lathes around with "dual-system" dials - the dial has two sets of graduations and sometimes a sliding cover so that only one shows at a time. However, given that you are not changing the feedscrew pitch, one of these is always going to be an approximation. I don't know what the feedscrew pitch of your machine is, but let's say that it is 0.1", and there are 100 dial graduations corresponding to 1 thou each. You could make up a new dial with 125 graduations, think of the feedscrew pitch as 2.5mm, and then each graduation corresponds to 0.02mm. Obviously, there is going to be a slight error. After one full turn, you will be out by 0.04mm (about 1.6thou). However, you will have just made a cut of 2.5mm depth, which is actually fairly large for a machine of this size and you wouldn't expect a cut of that depth to be a finishing-to-size cut.

In practice, then, this kind of thing can work. What you are often doing with a machine of this size is measuring, working out how much you need to take off, and machining. Then you re-measure and repeat the process. It is rare that you would, for example, measure your workpiece as 1" and take it down to 0.5" (in a series of passes) without a few intermediate measurements anyway to check progress, so the ability to wind the cross-slide by exactly 0.25" isn't too important when the last few cuts are going to be just a few thou and the error too small to matter. Actually, I realise that those measurement should have been metric equivalents but you get the point. The dial error when you are just doing the final few light cuts almost certainly isn't going to be big enough to make any real difference.

I'll probably bring down the wrath of all the professional machinists of the forum (I am, after all, only an amateur so what do I know?) and suggest that you try this idea, using a strip of heavy paper wrapped around the existing dial, mark the overlap, take it off and divide into whatever number of graduations makes sense on your machine, and "install" the new dial with a bit of sellotape around it for temporary protection. Use that for a little while and see if the concept works for you. If so, then making a proper dial would be an interesting little project and probably not too difficult and much, much easier than making a new leadscrew and nut (even if that is, undoubtedly, the better long-term solution).

Or you could do what I did for years on my imperial machine which was to take a copy of the drawing with metric measurements and just write on the imperial equivalents. It isn't actually that much more difficult to work to 0.197" instead of 5mm!

Actually, from what I have seen the Hobbymat lathes generally came with metric feedscrews, so if yours really is imperial, maybe there are replacement metric spares around that would fit?
Thank you for the information. I have only recently got the lathe and it came with plenty of spares so maybe there are some spare indicators.

I do like the idea of using digital read outs and I'm not looking for precision accuracy at this stage. Some of the parts I intend to make don't need to be spot on.

I did consider converting the measurements but at the moment I don't even know how to read the current dial indicators.

If I knew what metric dials would fit the machine I could look on ebay. I could make one I do have a cnc with a 4th axis to engrave the metric readouts but that's something else I'm still trying to get right.



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