Hi or Low

On a WM14 mill is it preferable to run 620 rpm in the high ratio or 620 in the low ratio?

I allways tend to always run in a LOW ratio unless needing the higher speeds for tiny cutters / non ferrous etc. Generally because this puts less load on the motor - they aren't particularly powerful or hefty, and get hot quite quickly (there have been numerous posts here in the past about cooling issues with these models) and I learned the hard way by burning one out.

regards Mike

Hi Eric,

I too run my small milling machine in the low ratio, you get a bit more torque and as Mike says, less load for the motor.

Thor

I know what you mean I did the same as I used a slitting saw for the first time.

I'm the opposite and run mine (X3) in high almost all the time. Only shift to low for big diameter tools such as slitting saws and the boring head.

Though the lathe tends to stay in low

Like Jason, I almost mostly run my mill in high speed and use slow for large diameter cutting.

To answer Eric's question about the same speed in High or Low, speed in low gear is best because the mechanical gears or belts provide best torque ('turning power'. In high-gear, the same RPM has less turning power. It's because motors produce best torque, power output and efficiency at one particular combination of load and speed. The operator should try to run motors in their comfort zone. Gears preserve torque whilst electronic speed control tends to lose it.

My mill has an 1100W motor and it's torque in high gear, low speed is adequate for most of my purposes. Not needing to change gear can be handy, if lazy. My mill makes changing gear easy with a knob. I'm more likely to be lazy on my lathe because changing it's speed range involves opening the headstock and shifting belts.

However, in principle it's always best to use the lowest gear or belt combination that provides the required speed.

Dave

It is worth thinking about the heat. Most motors will be happier at a higher speed when their fan can shift some air. Speed controllers are also prone to overheating at low speed/high current. On the other hand always using the gears introduces noise, wear, and sometimes less smooth drive (more noticed on a lathe than mill).

Speed is also only half the story as it will depend on what you are running at that speed as to what load is being put on the machine.

A 12mm dia HSS cutter could be happily run at 680rpm as that's about 25m/min surface speed

You could also be running a 40mm carbide insert facemill at 680rpm as the tips will be happy with the 85m/min cutting speed

One will load up the machine a lot more than the other so you would be better off using low ratio on the carbide but hi should be OK for the HSS unless taking a very deep cut.