[thisthat]

I have a somewhat basic question, my machine specs state its speed range to be 12000 to 24000 rpm at max torque. Can I run it lower than 12000? why the low value? I sometimes run it at 5000 rpm for drilling ops, it seems to been spinning at the correct speed. Does it simply mean that below 12000 it won't be at max torque, if so what exactly does that entail?

[awerby]

High-speed spindles like that usually need to run at a high percentage of their maximum speed, or they'll overheat, since the internal fan isn't running fast enough to cool it down. If you've got a water-cooled spindle this isn't as much of an issue, but yes - you'll find that it doesn't have much torque at the lower-than-recommended speed.

[joeavaerage]

Hi,
if your spindle is air cooled then its bad practice to run it at low speeds.

You are correct it will spin at low speeds but if the cooling fan is mounted on the same shaft then it too will be spinning slowly with
dramatic loss of cooling and you risk 'cooking' your spindle.

To a very close approximation torque is proportional to current so if you supply 5A at 24000 rpm to have 1Nm torque then if you supply
5A but at 5000 rpm you will have the same 1Nm torque.

Spindle heating is caused by current so the heating effect is the same at 5000 rpm at 5A as at 24000 rpm at 5A but the fan cooling
varies inversely proportional to the square of the speed. The cooling effect will be (5000/24000)²=0.043, ie only 4%
of the cooling. You might get away with running it at 5000 rpm for low power ops and for very brief periods but thats all.

Craig

[thisthat]

The spindle is liquid cooled but I gather then that either way it is probably best not to run it under the indicated speed range. Although as I said I do run some drilling operations below that range, usually at 5000 rpm, I work strictly in wood, and its usually fairly shallow 1/4in holes with a 1/4in drill bit, is that fine? I could switch to boring operations with a 1/8in bit but it's slightly less efficient.