Changed mini lathe to metric

[Neale]

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?

[Doddy]

A very convincingly argued point from Neale... perhaps I'm being blinkered.

[Neale]

I used to use an imperial-only machine. About a year ago I bought an ex-toolroom lathe which is just a little better built - the bed looks like the deck of an aircraft carrier and the whole thing weighs about a ton and a quarter. The "imperial" version of this lathe actually came with dual-system dials but for inexplicable reasons my metric version is metric only. Little bit of a shame as I do a fair bit with old designs with imperial measurements. The saving grace, though, is that the machine came with a DRO already fitted, and I have barely looked at a dial since I started using it. I can take an initial cut, measure with imperial micrometer, punch in the diameter on the DRO in imperial, switch to metric at the push of a button, and start cutting to a final metric dimension. After 40 years without, I hadn't realised just how useful a DRO could be on a lathe until I started using one. However, I doubt that any of the usual commercial DRO kits would comfortably fit in the space available on the Hobbymat machines. A bit of a shame, perhaps, but it shouldn't change the quality or accuracy of the work - it just takes a bit more cut-and-measure and mental arithmetic to get there. Never be wihout a scrap of paper and pencil by the machine to do the odd sum or make notes of dimensions as you go!

It's not a quesion of being blinkered - a Bentley Continental might get you there more quickly, more quietly, and more comfortably but the Ford Escort will get you to the same destination in the end! Although it's difficult to go back to a Ford Escort after driving a Bentley (I would imagine...)

[dfox1787]

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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[Doddy]

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.

That's what all the time-off around Christmas is for :-)

[mekanik]

I think you need to measure the cross slide pitch,as Neale has stated i also was of the opinion that the Hobbymat series where metric. do you have a Dial Test Indicator ? if so set the zero on your dial(cross slide) and zero the DTI then do one complete revolution of the dial and read the displacement on the DTI

[dfox1787]

I think you need to measure the cross slide pitch,as Neale has stated i also was of the opinion that the Hobbymat series where metric. do you have a Dial Test Indicator ? if so set the zero on your dial(cross slide) and zero the DTI then do one complete revolution of the dial and read the displacement on the DTI

I do have a dial indicator but at the moment no way to mount it.

So do the values on the image I sent not tell you if it's metric or imperial?

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[mekanik]

treat yourself to a magnetic base, you will be needing it for setting up work in your 4 jaw
https://www.yourspares.co.uk/parts/y...yABEgLsl_D_BwE
The image you show of the dial is exactly the same as mine 0.1mm between the numbered sections 10 to one complete revolution therefore 1mm pitch leadscrew ie metric

[spluppit]

Am i missing something here?

Why don't you just learn English decimal..... It's kind of very, very simple to do basic conversions in your head.

In the trade we use 40 thou (.040) = 1 mm its a tad over but more than adequate as long as you know very basic times tables (and if you don't and you have bought a lathe, something is wrong) its as easy as it gets.

So lets say your machine cross slide lead screws/ dial work as most lathes do (not all) and it removes double the amount you put on the screw.

You need to remove 2mm from a diameter, you touch the job or turn a diam to clean up the stock material.. this means you need 1 mm on the dial because when you turn, you machine both sides of the part because its rotating (a basic thing that a lot of newbies don't get) so 1 mm is 40 thou so you put a cut on of 40 thou... there is your 2 mm cut.

1 mm 40 thou
2 mm 80 thou
3 mm 120 thou and so on its a the 4 times table... it cant get much simpler.

Now to go in the other direction.
.75 mm 30 thou
.5 mm 20 thou
.25mm 10 thou
.10mm 4 thou
.05mm 2 thou

These are the rules we use in the trade and it really is simple to follow. I expect a lot of here will also use these rules it's not really rocket science to grasp.

If a dim has to be a good size or has tight tolerance then you never normally say, oh 3 mm cut and hope you have the thing within a thou or less. You always, cut measure, cut measure, cut measure. Always make that cut smaller than the dimension you need so you gradually get nearer the size you need. Experience will speed up this process.

There is nothing wrong with the advice you have been given its all sound.... but to me, learning how to use the machine is the answer not making the machine learn how to work to you.

Really is no need to alter anything on the machine, the lathe isn't really the problem, its about you learning to use it This is a much cheaper solution.

[dfox1787]

treat yourself to a magnetic base, you will be needing it for setting up work in your 4 jaw
https://www.yourspares.co.uk/parts/y...yABEgLsl_D_BwE
The image you show of the dial is exactly the same as mine 0.1mm between the numbered sections 10 to one complete revolution therefore 1mm pitch leadscrew ie metric

That has been added to my xmas list to my wife so fingers crossed.

Appreciate all the advice guys

I just made this which is the first thing I've ever made on my lathe.



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