Thread: Cross slide graduations on a Metric Lathe

I have a 2.5mm pitch screw on the cross slide of my Chinese lathe.

Graduations are marked 0.04mm which is diameter.

The major graduations or numbering is from 0 to 125. Or 125 count of 0.04mm divisions.

I may be a bit on the thick side but I find this very confusing. As a result I tend to sneak up on finished size. Not really the right way to go.

As a consequence I am thinking of making a new dial that makes more sense to my old brain.

So my questions;

Is this graduation style normal for a metric lathe? Or is mine a bit odd?

It it is odd, what are the more common divisions?

If I am to remake it what divisions and numbering would make sense?

Question is NOT, what is the difference between a diametrically and radially graduated dial. I get that bit.

Thanks in advance

The graduation appears to be 1 rev at 5mm diam, hence the 0.04... which translates to about a thou on radius, which is what I have on my old Macson... it really depends on what increments work for you. I find counting in 0.05s easy to keep track of, but you will lose some resolution if you do. Going to .02 will get pretty noisy on your dial. You could make it 0.02 on radius and just relabel what you have...

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The graduations can be what ever you like (it's your lathe)

My previous lathes were graduated radially but the current one (which is imperial) is graduated diameterally. I've been told this is more common for larger industrial type lathes. It takes a little bit of getting useful but at the same time is handy - measure a diameter, work out what the difference is to the target and just dial up that number.

Anyway there is nothing stopping you graduating in 0.05mm divisions if it is easier to understand. I must admit 0.04mm would be a bit annoying.

Michael

Make a new collar with 100 graduations on the full circle and that will be .05 per grad. A mark every 3.6 degrees . However unless you have a dividing head to mark those graduations accurately it could end up less accurate than using it as it is. Sneaking up on a diameter is very normal as with back lash you can easily turn off too much by just going straight too a calculated final setting .
Without digital readouts and no backlash ball screws I sneak up on everything .

If you mean what I think you do, and what the picture seems to show, then the numbers on your dial do not represent millimetres. 10 divisions represents 0.4mm and a full turn represents 125 X 0.04mm, 5mm. That is weird in my book. I am no expert, but I would find that really hard to use. Your dial should be numbered in millimetres. I have a 3mm screw, my dial show shows diameter and it is numbered to 6mm with the smallest graduations being 0.02mm.

I had to make a new dial for my old Nuttall lathe as it did not have one (long story). I had no way to graduate it accurately so I made a disk with a 375mm circumference and slightly set in a 375mm length of stainless steel tape measure so it was flush. 3mm on the tape represented 0.001" for the 8tpi pitch. It worked, but it was confusing. The original dial came to me on my current "metric" lathe and was passed on to the new owner of the Nuttall. It was only used as a handle. My lathe has an excellent metric/imperial dial and was only missing the handle (3 ball) for the usual reason lathe cross slide dials are broken. The carriage wheel has a wobble. It was welded up. Nice job other than the wobble.

You should do something about your dial. I occasionally mess up when adjusting the mill boring head because that is graduated radially so having a dial that is different again is just asking for trouble.

Dean

Radially, diametrically? school me please! Always something new to learn!

Movement (cut) with respect to radius of part versus diameter.

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My lathe shows 6mm on the dial for a 3mm lead screw. When I dial in 1mm the work diameter reduces by 1mm. With most smaller lathes if you dial in 1mm the work diameter reduces by 2mm. As was previously mentioned by Michael, my lathe is an industrial machine.

Dean

I don't see what the problem is ? The screw pitch is 2.5 mm and you have 125 divisions on the collar .
2.5 mm divided by 125 = .02 mm movement per division . So a tool movement of .02 mm in would reduce the work diameter by .04 mm which is what the collar is telling you .
A full turn of the collar would advance the 2.5 mm pitch of the thread and reduce the work by 5 mm .

Originally Posted by Retromilling

I don't see what the problem is ?

Yeah, you are probably much smarter than me. 😃

Whether it takes a given measurement from the radius or diameter makes little difference. You quickly get used to that. I have used lathes with both.

When I advance the cross dial by a count of 15, it will move the cross slide 0.3mm. That does not make for quick mental arithmatic to my old brain. 😃

So I just wondered if this style of dial numbering was normal or common on metric lathes.

This thread reminds me why I put a DRO on my lathe

My lathe is marked in Imperial and metric and has Imperial lead screw and cross slide screw . That makes the imperial markings the most accurate and the Metric less so .
The .02 mm movement is = to .0008 so each graduation would reduce the work diameter .0016 .
Half graduation movement would reduce the work diameter .0008 . You could just stop thinking in metric and use those Imperial sizes .

I have inadvertently bought a machine with the same arrangement. You are correct it's very confusing. Having the dials marked in numbers that do not relate to a real world unit trivially is annoying.

As the machine is conceived moving from the graduation marked 10 to the graduation marked 20 will give 0.4mm taken of the diameter it would make more sense if the markings where 0.4 0.8 1.2 etc then at least they would be in millimeters.

What solution did you eventually find?

Originally Posted by Greolt

I have a 2.5mm pitch screw on the cross slide of my Chinese lathe.

Graduations are marked 0.04mm which is diameter.

The major graduations or numbering is from 0 to 125. Or 125 count of 0.04mm divisions.

I may be a bit on the thick side but I find this very confusing. As a result I tend to sneak up on finished size. Not really the right way to go.

As a consequence I am thinking of making a new dial that makes more sense to my old brain.

So my questions;

Is this graduation style normal for a metric lathe? Or is mine a bit odd?

It it is odd, what are the more common divisions?

If I am to remake it what divisions and numbering would make sense?

Question is NOT, what is the difference between a diametrically and radially graduated dial. I get that bit.

Thanks in advance

One of the hobbing machines at work has a dial with 0.0125mm per division Does my head in, I actually counted them 3 times to make sure it was really 8 lines between the 0.1mm marks.

It's an older English machine, so I assume it's a metric dial on an imperial screw where one division is actually half a thou and the leftover 0.2 microns can safely be ignored.

Originally Posted by lamestllama

As the machine is conceived moving from the graduation marked 10 to the graduation marked 20 will give 0.4mm taken of the diameter

My God, that’s appalling. I’d be remaking the graduations so they gave some non-confusing millimetre readout.