Does anyone know the raito of the backgear on a Portass PD5 lathe? I know that I can count the teeth on the gears, but the lathe is out in the garage, and it's cold out there! And counting the teeth would be a pretty tedious process… So if someone knows the answer I'd be very grateful. If they don't, then gear tooth counting is coming up in the coming days, and I will report the results here…

Thank you – Rowan

All those are good suggestions thank you, but I think I will count the teeth. I am creating a wall chart showing what settings (i.e. which pulley and whether backgear or not) to use for various materials and various diameters, and I'd like the chart to be as correct as possible. I do have a tachometer, but I haven't yet made it work reliably, so measuring rpm is not as straightforward as it should be…

Thank you – Rowan

Edited By Rowan Sylvester-Bradley on 09/12/2022 13:07:55

Edited By Rowan Sylvester-Bradley on 09/12/2022 13:08:30

I braved the cold and counted the teeth. The large gears both have 65 teeth, and the small ones 25 teeth. This means (if I've got this right) that the ratio is (13/5)^2, or about 7:1 (more precisely 6.76:1).

This means that the speeds of the main shaft (in rpm) are:

Backgear Without With
Pulley 1 526 78
Pulley 2 292 43
Pulley 3 156 28

Now I can get on and make my wall chart!

Thank you – Rowan