Imperial/Metric micrometer dials

[Colin LLoydParticipant @colinlloyd53450]

My Chester Multi-Mini Lathe/Milling machine has micrometer dials on all movements (cross-slide, tail stock, Lead screw and top slide) marked with 0-25 divisions. In assessing backlash (and thanks to a MEW forum discussion _ I know a lot more about that), it became obvious that this machine probably has Imperial travel threads (25 divisions = 0.05in). I have metric dial clocks and for Top slide, Tail stock and cross slide 0-20 movement on the dials = 1mm. The lead screw is different at 0-20 =1.25 mm (why?).

Ever since I began work in 1965, I have always used metric – so am not going to change now. I'm guessing there is nothing I can do except place alongside the machine, a reminder that 0-20 on the dials = 1mm, as the screw threads themselves are imperial. I suppose I could replace the dials themselves with ones marked in millimeters – but is this what experts would do? – or just run with the knowledge that 0-20 = 1mm or 1 division = 0.05mm.

[Colin LLoydParticipant @colinlloyd53450]

[Howard LewisParticipant @howardlewis46836]

It is unlikely that Imperial and metric leadscrews would be mixed on a machine.

My impression is that Chester only sell Metric machines.

Are there no markings on each dial to indicate what each division represents?

There is no reason why a 20 (or even a 25) division dial should not be used on a Metric leadscrew.

20 divisions would give 0.05mm per division , 25 would give 0.04mm per division.

Why not use one of your Metric clocks to check the travel for one turn of each dial?

You may be pleasantly surprised.

Howard

[Neil WyattModerator @neilwyatt]

The mini-multi is a SEIG machine, as far as I know. SEIG happily mix and match on small machines so check with a digital calliper braced against something.

Neil

[Neil WyattModerator @neilwyatt]

Colin,

Not sure how useful this manual is – it doesn't answer your question but may help in other ways:

chestermachinetools.forumchitchat.com/file?id=2070433

Neil

[Colin LLoydParticipant @colinlloyd53450]

Thanks for the input:

Howard – that is exactly what I did – below are my results.

These are the readings from my metric clocks on each of the screws. (x-x) = dial division movement followed by the clock reading (mm).

Top Slide: (0-5) = 0.24; (0-10)=0.54; (0-15)=0.76; (0-20)=0.99; (0-25)=1.25

Tail Stock: (0-5)=0.23; (0-10)=0.49; (0-15)=0.75; (0-20)=1.02; (0-25)=1.25

Cross Slide: (0-5)=0.25; (0-10)=0.49; (0-15)=0.75; (0-20)=0.99; (0-25)=1.23

Lead Screw: (0-5)=0.3; (0-10)=0.59; (0-15)=0.92; (0-20)=1.28; (0.25)=1.60

These readings were repeated at least twice and in both directions as I was also trying to measure bashlash. As you can see the lead screw is the odd one out.

[BazyleParticipant @bazyle]

Well 1.25 mm is a standard metric pitch so a logical change to reduce the amount of twiddling relative to a 1mm pitch. Divisions of .05 are also a reasonable small increment if you stop trying to convert to thou. It might have been that they used a bit of M8 threaded rod for the prototype so it seemed to fit the bill or they were converting from a 20 TPI prototype.

The leadscrew is close to 16 TPI which might be used on a small imperial lathe whose general concept they were following. As a metric equivalent 1.6mm pitch is convenient as it is very easy to use for metric screw cutting with simple ratios though 1.25 and 1.5 would also be fine. The dial is a throw away gesture as you have a topslide for fine increments.

The off-kilter choice though does illustrate the pitfalls of having a product deigned on paper (or rather 3D CAD) and never field testing it before production. More and more desk bound designers think their CAD is so perfect it doesn't even need a trial run. When the first ones rush off the production line any corrections are vetoed by managers who never use the product and are only interested on the bottom line.

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