[digits]

I was trying to cut some aluminium last night, but my mill's been stalling recently, and it did it again last night scrapping the part

I was cutting 12mm wide (0.5") and 1.5mm deep (0.06") with a rougher, and with my mist coolant soaking everything nicely. It started an almost full-width cut on the edge of the part (I reckon 10mm wide) and about half way along, the motor just started to bog down and stalled out after about 2s while I was scrambling towards the mill to hit the E-stop. I didn't get there in time, and the axes kept going, so the head got knocked out of alignment

I looked at the tool - thinking it might have galled up, but apart from the big chips it was trying to scrape out at 0 rpm, all the flutes were clean. The cut was at the edge anyway, so there was somewhere for the chips to go...

According to G-wizard, this should only need about 0.2kW - the mill claims to have 1.1kW so this should have been trivial, but I have a nasty feeling that either the motor or the controller are on their way out

Apart from some audible speed fluctuation at zero load, it all sounds OK, but randomly it will just bog down very gently and stall - it takes a few seconds to stall, and it will spin gently up again if you stop the axes. I've had it while drilling, as well as milling, but I'd been assuming it was just bad cut-parameters. I'm not so sure now though...

This is my 2nd motor on this machine - I'm getting tempted to bin the DC-motor and controller and try something with AC in the title...

Has anyone else had these issues on a BF30 class mill?

[LongRat]

Well, mine junked as well, although different failure mode. How much arcing are you seeing on the brushes? I was getting loads, shortly followed by a lot of smoke. From that point on I went AC.

[wizard]

Seriously DC motors are used in industry running full load 24/7. Of course these are quality industrial motors.

I was trying to cut some aluminium last night, but my mill's been stalling recently, and it did it again last night scrapping the part

I was cutting 12mm wide (0.5") and 1.5mm deep (0.06") with a rougher, and with my mist coolant soaking everything nicely.

That should be a piece of cake.

It started an almost full-width cut on the edge of the part (I reckon 10mm wide) and about half way along, the motor just started to bog down and stalled out after about 2s while I was scrambling towards the mill to hit the E-stop. I didn't get there in time, and the axes kept going, so the head got knocked out of alignment

Interesting that you heard the motor bog down. This could be a motor / controller issue but don't dismiss something happening with the bearings.

I looked at the tool - thinking it might have galled up, but apart from the big chips it was trying to scrape out at 0 rpm, all the flutes were clean. The cut was at the edge anyway, so there was somewhere for the chips to go...

According to G-wizard, this should only need about 0.2kW - the mill claims to have 1.1kW so this should have been trivial, but I have a nasty feeling that either the motor or the controller are on their way out

The load on the motor should be trivial.
Even then well designed motors don't die suddenly from minor overloads. I'm not sure who's version you have, but some of these machines aren't even using DC motors but rather Universal motors which are proving themselves to be crap. The controllers aren't all that great either. So given this there is a high probability that one or the other is going bad on your machine.

Apart from some audible speed fluctuation at zero load, it all sounds OK, but randomly it will just bog down very gently and stall - it takes a few seconds to stall, and it will spin gently up again if you stop the axes. I've had it while drilling, as well as milling, but I'd been assuming it was just bad cut-parameters. I'm not so sure now though...

Baring issues with the bearings that sounds like it is possibly brushes not seated correctly or worn out. Well that would be what you would look for on quality hardware.

This is my 2nd motor on this machine - I'm getting tempted to bin the DC-motor and controller and try something with AC in the title...

Well do realize that some of these machines run universal motors. Beyond that a quality DC motor will give you a very long life. AC motors are simpler and more reliable but in the home shop a proper DC motor should last a very long time. I'd also suggest that when combined with a good controller a DC motor offers a very useful speed range for many metal working machines.

Has anyone else had these issues on a BF30 class mill?

Don't own a BF30. However it is pretty clear from reading the various forums that these mills do have motor / controller issues. I'd check your brushes and go from there.

[digits]

Well, mine junked as well, although different failure mode. How much arcing are you seeing on the brushes? I was getting loads, shortly followed by a lot of smoke. From that point on I went AC.

Yeah, I remember that - the thing is I don't have any smoke or nasty noise, so I don't think my motor is the issue this time.

This is actually the 2nd motor I've had on this mill - originally the speed controller would ramp UP the speed by 10% when it started a heavy cut. My dodgy efforts to adjust the pots on the controller resulted in a overloaded motor which did burn out and die.

This motor though has been fine for 12 months plus - I made sure I set the current limit as per the board's instructions and the max-speed pot is about 10% lower than factory, so it should never see over-voltage either.

[digits]

Seriously DC motors are used in industry running full load 24/7. Of course these are quality industrial motors.


That should be a piece of cake.

Interesting that you heard the motor bog down. This could be a motor / controller issue but don't dismiss something happening with the bearings.

The load on the motor should be trivial.
Even then well designed motors don't die suddenly from minor overloads. I'm not sure who's version you have, but some of these machines aren't even using DC motors but rather Universal motors which are proving themselves to be crap. The controllers aren't all that great either. So given this there is a high probability that one or the other is going bad on your machine.

Baring issues with the bearings that sounds like it is possibly brushes not seated correctly or worn out. Well that would be what you would look for on quality hardware.

Well do realize that some of these machines run universal motors. Beyond that a quality DC motor will give you a very long life. AC motors are simpler and more reliable but in the home shop a proper DC motor should last a very long time. I'd also suggest that when combined with a good controller a DC motor offers a very useful speed range for many metal working machines.


Don't own a BF30. However it is pretty clear from reading the various forums that these mills do have motor / controller issues. I'd check your brushes and go from there.

I don't have anything against DC motors, but as you say, there are motors and there are good quality DC motors...

I suspect this is a controller board issue - but I really don't want to have to open it up and play with the trim-pots again. I have already killed one motor that way, and it also seems like a good way to get fried as you have to run it live to set the max current and speed etc.

I am leaning towards an AC servo system as it is not much more expensive than a decent vector-drive and it might let me do rigid tapping.

[LongRat]

I think my motor failure was caused by a dodgy controller too. I agree with what Wizard said, a quality DC motor and controller should last a long time. Thing is, these (controllers especially) are not that. It's much easier to find a quality AC set up. The controllers on the BF-type mills seem to be a copy of the KBIC type. From reading the forum and my friend's experience with KBICs, they seem to be quite well respected. You could simply replace your controller with one of those. My opinion on the matter was that an AC motor and VFD were cheap enough not to justify that and the extra hassle of wiring it all up and testing it, plus I would have had to have a new motor anyway. I just wanted to make parts.

[digits]

Yeah, I'm not going to bin that motor if there's life in it, but as you say, right now I just need to make some parts!

The unreliability of this machine at the moment is driving me mad - when it cuts it's awesome, but I can't risk kicking off another multi-hour job if I can't trust it not to stall randomly.

[Al_The_Man]

Try the motor on an automotive battery, let it run for a while then put some resistance on the shaft to test the torque, you should have a problem stopping it, carefull to not do this for long however as the current (torque) will go up without limit, if on the otherhand it goes 'soft' with resistance, it most likely is the motor.
The torque on a DC motor is normally flat up to the rated rpm, putting resistance on the shaft should cause it to go up to the rated torque and continuing the pressure puts it in to the intermittent torque range which is OK for a couple of seconds.
Al.

[wizard]

I don't have anything against DC motors, but as you say, there are motors and there are good quality DC motors...

I suspect this is a controller board issue - but I really don't want to have to open it up and play with the trim-pots again. I have already killed one motor that way, and it also seems like a good way to get fried as you have to run it live to set the max current and speed etc.

I am leaning towards an AC servo system as it is not much more expensive than a decent vector-drive and it might let me do rigid tapping.

I have a feeling this leading to a complete rebuild of your mill.

[digits]

Try the motor on an automotive battery, let it run for a while then put some resistance on the shaft to test the torque, you should have a problem stopping it, carefull to not do this for long however as the current (torque) will go up without limit, if on the otherhand it goes 'soft' with resistance, it most likely is the motor.
The torque on a DC motor is normally flat up to the rated rpm, putting resistance on the shaft should cause it to go up to the rated torque and continuing the pressure puts it in to the intermittent torque range which is OK for a couple of seconds.
Al.

Thanks - that's a good idea. I've actually got a current limited bench supply that I can use to test the motor. The thing is, even if the motor turns out to be fine, I then have to look at replacing the controller and I really don't want to replace it like for like. As LongRat suggested, I suppose I could look for a better quality KBIC one.

[digits]

I have a feeling this leading to a complete rebuild of your mill.

I hope not - but then again I hadn't planned to CNC this mill at all when I bought it

I can think of plenty of improvements to this machine, but for now at least, I want a decent spindle, and then I can start thinking about an ATC

[FastFarmer]

This happened to me today while facing with a 50mm cutter. The stepper motor just kept driving the table breaking a tooth and damaging the work. It was just luck I was close and managed to hit reset on Mach 3.

This is a SERIOUS fault in this machine... and buyers beware. I still don't believe this happened!

I have had the BF30 for 2 years now and CNC'd it as soon as it arrived. Although the work size limitation really annoys me, it's been a great mill.. but stallings is unacceptable and dangerous.

Any ideas on how I setup an input to monitor if the spindle stops would be appreciated?

Thanks

[SCzEngrgGroup]

It would not be difficult to add a spindle speed sensor, and create a Mach3 brain or macro-pump to monitor actual RPM compared to commanded RPM, and throw an E-Stop if actual RPM drops below some threshold, like 80% of commanded speed. Though a better solution would be to figure out WHY it's happening in the first place....

Regards,
Ray L.

[digits]

A spindle speed sensor sounds like a good idea - it might even let you do rigid tapping if you do it right

I replaced my stock motor a while back with a 1.5kW servo - which is way, way better. I have it setup so that LinuxCNC will just E-stop if the spindle alarms for any reason.

[FastFarmer]

Even if I find out why this happened, it makes me nervous it did happen.. I think a spindle sensor is now a must have. I often leave the mill cutting away while I do something else.

Does anyone know about the Optimum BF-30. Does the motor have thermal protection? What would cause DC system to reset?

Thanks
Stephen

[FastFarmer]

OK, after much experimentation and investigation, here's what happened... I plunged the face mill into the aluminium deeper than it can cut, causing the cutter to bind to material which in turn stopped the motor dead. After about a second of being stalled the motor will reset the DC system.

So I'm back to totally loving the BF-30 and BF-46 mill. I also discovered if you run your e-stop through pins 1 and 3 on block X9, it will estop on spindle stop. The only issue is you have to have the spindle running to move the axis, but given what happened, I'll live with that.

[mr_ping]

I got a BF30 and I've burned two motors on that one. Both of them burned all plastics inside. Now I use a 1.5kw VFD controlled motor which is much bigger. I disconnected the gear box too.

[Fastest1]

FF, Glad you appear to have it resolved however what did you do? Why does the system shut down on a motor failure?

Btw I hate those highlighted words that never link to the products the conversation is in regards to. Ray's link to an automotive wheel speed sensor (that could possibly be used somehow and I would be glad to know how), yours links to the whole hub and spindle assembly. Probably not what either of you were intending. Oh and the "block X9" leads to a floral foam. You arent proofing on that are you? It would be cheap and harmless during a crash, probably wouldnt overload the spindle either (jk) ;-)

[digits]

Electric motors aren't designed to be stalled! They will just overheat if they're consuming power but not spinning. There is nothing to limit how hot they can get except for how well they are passively cooled, so a stalled motor is a fire risk - 1.5kW is a half decent fan heater 's worth...

I really wouldn't run unattended unless I was sure a stall would cause the motor to trip out AND the CNC to stop - you don't want it snapping tools or trying to push a stationary tool through stock!

[Al_The_Man]

A motor has a continuous stall torque (current) rating and a peak rating, in the continuous torque mode the motor can be operated right down to zero rpm, the peak zone should only occur for a very brief time or damage can occur, most drives have a current setting that prevents continuous overload.
Al.