[Heka81]

Hi,

I have a few yers old BF30 bench top milling machine (label of the machine says HBM, but same Chinese as many others)

The problem is that the machine accelerates when loaded heavily.. This happens with bigger drill bits etc. Has anyone had such an issue? And even better if someone would have a solution for this? Is it just that I should adjust the IR compensation potentiometer (I assume that there is one on the circuit board)? Anything that might go wrong because of this adjustment?

Thanks

[photomankc]

It's a bit of a dance. There should be an IR Comp pot on the spindle driver board that lets you adjust that. You want to set that so it maintains speed or maybe a bit over when you really clamp down on it. I use some work gloves and squeeze the spindle nose to load it up and test the setting. But realize it's tough to get perfection without a spindle encoder for feedback. It's likely that if you drop it enough that a big drill chugs on perfectly that it will not react to smaller loads and they may lag behind the commanded RPM.

For instance mine is set pretty good for most medium loads and tracks within 10 to 50 RPM of commanded but will over-rev by about 250 RPM on a heavy cut with the TTS super-fly. I just set my RPM accordingly knowing that. If I adjusted IR Comp to eliminate that, I would see the speed sag in more of the normal cuts.

It is worse and harder to eliminate in my experience at really slow speeds (hundreds of RPM). Nature of the beast with a DC PWM control.

[Heka81]

Thanks photomanck for you answer.

From your text I can see that it could be hard to make the machine to work as desired with original drive&motor combination. The over-rev in my case is most undesired when using big drill bits or hole-saws with very low RPM (100-300). With heavy load the RPM can increase to 500-600 RPM. That is a lot if you command 150 RPM.. This can cause blades or bits to burn. I have no problem with any milling operation. The rpm is steady as rock in every other case.

Do you think that I can help this over-rev with lower IR-setting or is it better just to do heavy drilling on other machines?

Thanks a lot!

[RCaffin]

You need to reduce the IR compensation a bit.
Setting it to 0 will do no harm but speed will drop under load. Setting it too high will cause the revs to increase under load.
So tweak away for a bit, with a load, to find the right spot in between.

What driver are you using, just out of interest? I am using a KBWT-26, and it too has IR compensation.

Cheers
Roger

[photomankc]

Definitely give it a shot with adjusting. I'm just pointing out that you may see the speed drop under load in normal milling at over 1000 RPM if you eliminate the over-rev at very low speeds under 500 RPM. I sacrificed the really low end on mine anyway because of the belt drive speeds. Big hole saws and slotting blades are not in my bag of tricks. As mentioned, turn it down to 0 and then start working your way up from there.

[Fastest1]

Doesnt that machine have multiple pulleys?