Spindle cutting in and out

[markba633csi]

I'm losing faith in PM hearing that. They should be a bit more specific about the bearing limitations I think. If they are dog poop they should say so
maybe in not those exact words but still...
-Mark

 

[Ken226]

Well I'm on my own on this 1 Mike at precision matthews said that running this machine at 2100 rpms for 45 mins is its limit "remember its a hobby machine" are his exact words . He did recommend changing the bearings to a "better" bearing so I guess the ones that come on in the machine really can't handle the 3000 rpms for very long . So having said that does any one have any recommendation for bearings ...I guess I'm fixing to do a bearing job

I used abec7 rated angular contact bearings from NSK in the spindle of my G0704 CNC conversion.

I've run it @ 6000+ rpm for 8+ hours at a time, many times over the last 5 years. The headstock casting at the bearing races run about 145° f

Runout is still well under a ten thousandth of an inch after 5 years of use.

Using a 2hp brushless DC motor.

 

[Ischgl99]

Any of the major brands would have something suitable, NSK, FAG, SKF. The higher the ABEC number, the higher the precision of the bearings, and the cost. I don’t know what bearings your mill uses, but expect at least several hundred each for ABEC 7. I would suggest avoiding unknown sources for the bearings, there is a lot of counterfeiting in the bearing world and the only way to know you have genuine bearings is to buy from an authorized distributor.

Before going through a bearing overhaul, you might want to take the spindle out and clean out the grease and regrease with the appropriate type and amount. Too much grease, or the incorrect viscosity, will cause excessive heat too.

 

[Cad cam man]

I'm losing faith in PM hearing that. They should be a bit more specific about the bearing limitations I think. If they are dog poop they should say so
maybe in not those exact words but still...
-Mark

Yes I agree . I chose to email rather than call so I would have record it seems that Mike is not too quick to offer help , now Matt on the other hand is a bit more helpful. Never the less I guess I will take on this job sooner ( a lot sooner ) than later

 

[Cad cam man]

I used abec7 rated angular contact bearings from NSK in the spindle of my G0704 CNC conversion.

I've run it @ 6000+ rpm for 8+ hours at a time, many times over the last 5 years. The headstock casting at the bearing races run about 145° f

Runout is still well under a ten thousandth of an inch after 5 years of use.

Using a 2hp brushless DC motor.

Does the motor ever seem to cut out or bog down while running?

 

[Ken226]

Does the motor ever seem to cut out or bog down while running?

No, it doesn't cut out or bog down.

There is a slight change in RPM when entering and exiting a cut with larger diameter end-mills. End mills above 1/2" ish. Maybe a 20-50 rpm change, for about a half second. There's a slight lag time between the encoder sensing the speed change and the BLDC driver adding power to maintain speed.

It kinda sounds like your motor may be ****ting the bed rather than a bearing issue. Have you tried running the motor without the belt/gearing engaged to isolate the problem to either the bearings or motor?

Personally, I suck pretty bad at guessing. Every time I try it, I end up being wrong. I like to treat these issues like algebra, and isolate the variables, then test them.



Maybe run it until it starts cutting out, then isolate the motor from the spindle by some means. Neutral gear, remove a belt, etc.

Run the hot motor without the spindle engaged and see if it still cuts out.

Turn the spindle by hand and see if the bearings are binding.

 

[brino]

Before going through a bearing overhaul, you might want to take the spindle out and clean out the grease and regrease with the appropriate type and amount. Too much grease, or the incorrect viscosity, will cause excessive heat too.

Agreed. Even adjusting the preload could help here.
-brino

 

[Ken226]

I looked up the specs on the pm727v. It appears identical to the g0704, other than the paint and logos.

That being the case, your stock motor is a 90v brushed dc motor.

My stock g0704 motor had a warning sticker on it advising not to run the motor at full speed very long. I don't remember exactly what it said, I scrapped that motor many years ago.

Could it be that you are overheating the board that converts the 120v wall power to 90vdc for the motor? I believe most of these mills use a Chinese knockoff of the KB120 motor controller.

You could pull the panel, and run the mill till it starts cutting-out, then check the temp of the heatsink attached to the stock board.

Shoot it with a laser thermometer.

In this pic, the spot to check the temp is on the left, near the screw slot. Where the transistors are attached directly to the aluminum sink.

 

[Cad cam man]

No, it doesn't cut out or bog down.

There is a slight change in RPM when entering and exiting a cut with larger diameter end-mills. End mills above 1/2" ish. Maybe a 20-50 rpm change, for about a half second. There's a slight lag time between the encoder sensing the speed change and the BLDC driver adding power to maintain speed.

It kinda sounds like your motor may be ****ting the bed rather than a bearing issue. Have you tried running the motor without the belt/gearing engaged to isolate the problem to either the bearings or motor?

Personally, I suck pretty bad at guessing. Every time I try it, I end up being wrong. I like to treat these issues like algebra, and isolate the variables, then test them.



Maybe run it until it starts cutting out, then isolate the motor from the spindle by some means. Neutral gear, remove a belt, etc.

Run the hot motor without the spindle engaged and see if it still cuts out.

Turn the spindle by hand and see if the bearings are binding.

No I haven't tried that yet I just assumed it was the bearing due to the heat it was putting off

 

[Cad cam man]

I looked up the specs on the pm727v. It appears identical to the g0704, other than the paint and logos.

That being the case, your stock motor is a 90v brushed dc motor.

My stock g0704 motor had a warning sticker on it advising not to run the motor at full speed very long. I don't remember exactly what it said, I scrapped that motor many years ago.

Could it be that you are overheating the board that converts the 120v wall power to 90vdc for the motor? I believe most of these mills use a Chinese knockoff of the KB120 motor controller.

You could pull the panel, and run the mill till it starts cutting-out, then check the temp of the heatsink attached to the stock board.

Shoot it with a laser thermometer.

In this pic, the spot to check the temp is on the left, near the screw slot. Where the transistors are attached directly to the aluminum sink.

Well thats it i have went around their board and I'm using the kdsi-240d board to gain control using the Acorn so u think maybe the kdsi-240d is overheating??