It must be a metric lathe? Metric thread pitches are not necessarily simple multiples of the leadscrew pitch. So a metric thread dial indicator has a choice of gears, five on the metric version of my lathe (Harrison M300), to simplify the maths. The chart on the indicator should list the gear to be used for a given pitch as well as the numbers at which the half nuts should be engaged.

Andrew

As a corollary to Andrew's post, and something which will simplify your life considerably, any thread which _is_ a factor of the leadscrew pitch does not need a thread dial at all. You can engage the half nut wherever it drops in.

I am guessing that the Student has a 6mm pitch leadscrew, so this means that the following pitches do not need the indicator dial:

0.2 ,0.25, 0.3, 0.4, 0.5, 0.6, 0.75, 1, 1.5, 2, 3, 6.

He did say in the post that his lathe is a Student. I am assuming he means a Colchester Student.

The principle holds for any pitch leadscrew, imperial or metric and the calculation is not difficult (far easier than working out change gear combinations, for example). Divide your leadcrew pitch by the thread pitch and if the answer is a whole number (integer), the dial is not needed.

With a typical imperial leadscrew of 8tpi, the indicator is not needed for 8, 16, 24, 32 or 40 tpi (I wonder if this is why the ME threads were chosen with these pitches).

If you were to be doing batch work, Martin Cleeve was very big on choosing a leadscrew pitch to suit the thread being cut. If you had a load of M12 stuff to make, there would be a good case for a 3.5mm pitch leadscrew.

geoff

When you have the thread dial operation data figured out I suggest you make up a data plate giving the threading dial drive gear and number of divisions between engagements for the various pitches. Either attach it to the lathe or somewhere else where it can easily be found and read when using the machine.

My metric Smart & Brown 1024 has a factory made one screwed directly to the apron. Frankly I'd be lost without it.

The S&B has a 4 mm pitch screw with 12 division dial so, unfortunately, you can't just copy mine. The relevant data for your machine will be in a manual and so should be findable via the internet if you don't have the right book.

I find the cheap laminators, mine is from LiDL, work well for making decently durable machine data labels from simple printouts. Stick or screw to the machine as needed. I've yet to replace one in over a decade of making them. Roller type paper cutter, LiDL cheapy again, makes a neat job of cutting to size.

Clive