Mandrel RPM.....Likely?

Having measured the diameters of the pulleys on the Myford ML4 I have used an online calculator to find the mandrel RPM in each of the 3 'gears' available. RPM range appears to be from approx 500 to 200 RPM. Does that sound like the likely range for this machine ?

Sounds about right given that this machine was designed in the days when carbon steel rather than HSS tooling would have been the norm for the impecunious. With modern oils and proper attention to regular lubrication it should be quite safe to up the speed to perhaps 750 - 800 rpm top if you so desire. Which might get things done a bit faster and will be generally more in keeping with the HSS book..

But sharp, really sharp, tools are what a machine like that loves.

Clive.

Thanks Clive. I would have to do something with the countershaft pulley gearing to get up to 800 RPM but it is doable as there is easily room on the countershaft for another pulley.

200 to 500 is about right but the bit missing is power/torque

With backgear these older machines like the drummond M can munch hard stuff all day at 60 rpm which would blunt a cutting tool at faster RPMs

Then finish off at a higher rpm with a sharp carbide tool

Edited By Ady1 on 24/08/2017 00:49:41

Thanks Ady1: doing the calculations I can get 800 rpm if I put a 6.8 inch pulley on the countershaft. Have to work out how I would either change belts or tension the existing belt that would be too long on the smaller countershaft pulley. The motor pulley is a twin so moving the belt across and tensioning is likely to be easier.

Bear in mind that the Headstock bearings may not have been designed for higher speeds. Correct and adequate lubrication is a necessity for any bearing, but becomes more important as speed is increased.

As already said, a higher spindle speed will mean that less torque is available for cutting. Another reason, if needed, for keeping tools sharp. (And replaceable carbide tips are not sharp in the way in which HSS tools are, or should be).

Howard

I agree with Howard and that you are going to exceed the design speed for the bearings and fail. Older plain bearings need to maintain an oil wedge for good lubrication which will breakdown at higher RPM.

Clivve

Mmm, I hadn't considered that the design might not stand up to the increase in speed. Ill stick to sharp tools