# Spindle cutting in and out



## Cad cam man (Jun 21, 2021)

So this evening I was running some aluminum nothing aggressive on my pm727v converted to cnc with spindle control via kbsi240d board and acorn . After about 30 minutes into the run I noticed the rpms fluctuating just enough to hear i kept running and about 5 mins after hearing the rpm change the spindle dropped way low almost cutting off . I slapped feed hold maybe thinking I needed to give the tool time to catch up although I was not hogging . After letting it catch up I felt of the spindle motor and it was hot too hot to touch knowing better I kept on running and soon after the spindle shut off . Has anyone had this happen ? I have not changed the bearings (yet) and it is the factory variable speed motor that comes on the pm727v . Does anyone have any suggestions on what I need to start checking ??? Could this be from the kbsi240d board not being spot on ???


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## markba633csi (Jun 21, 2021)

Maybe a bearing seized up?  Too hot to touch is usually not desirable for motors.  Will the motor still turn when cold?
How long have you had the unit?  Is the temp usually within reason?   A bad bearing might run for a while then die


-Mark


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## Cad cam man (Jun 22, 2021)

Just a quick back story this machine does not have any hours on the spindle it just now got 30 minutes on its 1st run so the bearing are brand new . That does not mean they are not bad but just saying..... The motor was hot to the touch as well as the side of the head stock . I was running at 2100 rpm's in high, 3 . the machine is rated for 3k so I didnt think was a problem . I shut everything down waited 10 mins and fired it back up and no problem everything came back on so I just turned it off for the night. Do you think I should check the spindle bearings? How would I go about doing that without tearing down the headstock


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## Tipton1965 (Jun 22, 2021)

There was another member with a brand new PM-833 and his spindle on that machine was getting pretty hot at higher RPM.  He called PM support and they walked him through taking the spindle apart so he could loosen the bearings.  PM thought they were a little too tight.  PM said it's a fine balance between too loose where you have spindle runout, and too tight where you have excessive friction/heat.


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## Christianstark (Jun 22, 2021)

Getting warm is to be expected, but hot to the touch could indicate a preload issue. I'd call PM.


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## Bi11Hudson (Jun 22, 2021)

Tipton1965 said:


> There was another member with a brand new PM-833 and his spindle on that machine was getting pretty hot at higher RPM.  He called PM support and they walked him through taking the spindle apart so he could loosen the bearings.  PM thought they were a little too tight.  PM said it's a fine balance between too loose where you have spindle runout, and too tight where you have excessive friction/heat.


The "rule of thumb" that I was taught 55 odd years ago was to lay your hand on the motor for half a minute. If it was so hot that it couldn't be stood for that time, it was too hot.  It will vary somewhat as every person has a different tolerance for the heat. But *as a rule*, high temperature comes from high current in an overload condition.

On a lathe, as with any machine, a mechanical overload can come from several sources. The most likely for a lathe being spindle bearings. Taking off the belts and spinning the spindle by hand feeling the bearings takes considerable experience to feel something "not right". The easiest adjustment is essentially the same as a front wheel bearing on a car. Run it down until it drags, then back off 1 flat (1/6 turn) and lock it. That allows the bearing room to expand as it heats up running. Mounting it cold, leave a little more. If it's already hot, leave a little less. In either case, just "how much" is a matter of experience. And the only way to gain that experience is to try an adjustment, observe and learn from it, and then try again. Early in the learning curve, one is less concerned with half a thou tolerance. Concern is more for steady and smooth work. As experience is gained, tolerances will become tighter, almost on their own.

.


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## markba633csi (Jun 22, 2021)

The stock bearings are probably not the best.  I would install something decent like SKF.  Buy once cry once
-M


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## Cad cam man (Jun 22, 2021)

Bi11Hudson said:


> The "rule of thumb" that I was taught 55 odd years ago was to lay your hand on the motor for half a minute. If it was so hot that it couldn't be stood for that time, it was too hot.  It will vary somewhat as every person has a different tolerance for the heat. But *as a rule*, high temperature comes from high current in an overload condition.
> 
> On a lathe, as with any machine, a mechanical overload can come from several sources. The most likely for a lathe being spindle bearings. Taking off the belts and spinning the spindle by hand feeling the bearings takes considerable experience to feel something "not right". The easiest adjustment is essentially the same as a front wheel bearing on a car. Run it down until it drags, then back off 1 flat (1/6 turn) and lock it. That allows the bearing room to expand as it heats up running. Mounting it cold, leave a little more. If it's already hot, leave a little less. In either case, just "how much" is a matter of experience. And the only way to gain that experience is to try an adjustment, observe and learn from it, and then try again. Early in the learning curve, one is less concerned with half a thou tolerance. Concern is more for steady and smooth work. As experience is gained, tolerances will become tighter, almost on their own.
> 
> .


I have been taught the same way that's how I was able to notice that there was a problem, I know a little heat is normal but after about 15 seconds I had to pull my hand off, i just didn't know if that may have been a part of a break in deal or something I'm gonna go ahead a contact pm and see what they say


markba633csi said:


> The stock bearings are probably not the best.  I would install something decent like SKF.  Buy once cry once
> -M


Yeah I had plans on upgrading to a better high speed bearing but I wasn't expecting to do it this soon


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## Shootymacshootface (Jun 22, 2021)

As Bill Hudson said, bearings need clearance for running while warm. I remember some chat on here about a shop that would turn on their surface grinder first thing and it would run at temperature all day until they went home.


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## Cad cam man (Jun 22, 2021)

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


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## markba633csi (Jun 22, 2021)

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


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## Ken226 (Jun 22, 2021)

Cad cam man said:


> 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.


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## Ischgl99 (Jun 22, 2021)

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.


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## Cad cam man (Jun 22, 2021)

markba633csi said:


> 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


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## Cad cam man (Jun 22, 2021)

Ken226 said:


> 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
> 
> ...


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


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## Ken226 (Jun 22, 2021)

Cad cam man said:


> 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.


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## brino (Jun 22, 2021)

Ischgl99 said:


> 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


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## Ken226 (Jun 22, 2021)

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.


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## Cad cam man (Jun 22, 2021)

Ken226 said:


> 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.
> 
> ...


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


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## Cad cam man (Jun 22, 2021)

Ken226 said:


> 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.
> 
> ...


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??


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## Ken226 (Jun 22, 2021)

Cad cam man said:


> 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??



I'm not familiar with the kdsi-240d,  but I looked up it's specs.   It appears to be an isolator,  not a motor controller, unless I read it wrong.    

I'll read up on that kdsi240 some more.

So your stock board converts 120v ac wall power to DC power,   which then provides input power to your kdsi-240d board?

So,  is your stock motor controller still providing the dc power for the motor?  

If so,  that stock board can't handle running the stock motor full-speed for long.


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## Cad cam man (Jun 22, 2021)

A small update I was out in the garage poking around and if you are looking up at the bottom of the tool where you can see thru the spindle there is a spanner nut it was less than hand tight so I unscrewed it and found the bottom taper roller bearing . After inspecting the bearing while looking upside down in the spindle it has very little grease but this maybe normal maybe .... but the sign of the spanner nut not even being hand tight ??? Does this mean the preload is gone ?? I will upload a picture


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## Cad cam man (Jun 22, 2021)

Yes your right it is an isolation board the factory board is running the motor


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## Cad cam man (Jun 22, 2021)

I see what your saying kind of like my truck can do 120 mph but running it at 120 to the store and back all day long with blow it out


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## Cad cam man (Jun 22, 2021)

What did you do to make your G0704 run like it does ? You said you upgraded your motor ??


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## Ken226 (Jun 22, 2021)

Cad cam man said:


> A small update I was out in the garage poking around and if you are looking up at the bottom of the tool where you can see thru the spindle there is a spanner nut it was less than hand tight so I unscrewed it and found the bottom taper roller bearing . After inspecting the bearing while looking upside down in the spindle it has very little grease but this maybe normal maybe .... but the sign of the spanner nut not even being hand tight ??? Does this mean the preload is gone ?? I will upload a picture



I doubt it.  If your spindle is like mine, the only preload adjuster is way, way up inside the spindle.   The bottom bearing presses in, both the inner and outer race.

A properly greased spindle bearing won't show alot of visible grease. Though I could be mistaken,  I doubt this is your problem.


BTW, the kdsi-240d boards manual lists it's maximum output as 10v 10 milliamps.
     It's definitely not powering a 90vdc motor.  It's just a signal isolator that's letting your computer control your DC motor controller.

Go through those checks I mentioned. Start isolating variables.

Does it still cut out when the spindle is dis-engaged from the motor?

Immediately after it starts cutting out,  does the spindle turn freely?

What is the temp of the motor controller heatsink when the problem starts occurring?


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## Ken226 (Jun 22, 2021)

I used a 2hp BLDC motor kit from GlockCNC.   I bought 2 motors from them,  a 6000 rpm motor,  and a silver 5000rpm motor as a backup.

The BLDC driver works very similar to a 3 phase ac motors and VFD.

The pc controls the BLDC driver via a c7 spindle board,  using the BLDC drivers onboard user control terminals.

I'll upload a video in about 15 minutes. So I don't get carpal tunnel typing.


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## Ischgl99 (Jun 22, 2021)

I haven’t looked at the manual for your mill, but on my Millrite, the nut on the bottom holds the spindle in the quill by providing tension on the outer rings.  If that is loose, the spindle could be floating around a bit, but you should still have preload on the bearing set.

There should not be much grease in there, the proper amount depends on bearing size and speed, but typically it only gets filled at most to 30% of the free space in a bearing of the size used in hobby mills.  Here is a good article that goes into detail on it.



			https://www.klueber.com/ecomaXL/get_blob.php?name=klu5896-1BearLubAllWP-A12b.pdf


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## Cad cam man (Jun 22, 2021)

Ken226 said:


> I doubt it.  If your spindle is like mine, the only preload adjuster is way, way up inside the spindle.   The bottom bearing presses in, both the inner and outer race.
> 
> A properly greased spindle bearing won't show alot of visible grease. Though I could be mistaken,  I doubt this is your problem.
> 
> ...


Ok im gonna do these checks and get back on here tomorrow and give an update . I really do appreciate the help Ken you have already done more than the company that sold the machine to me


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## Ken226 (Jun 22, 2021)

Cad cam man said:


> Ok im gonna do these checks and get back on here tomorrow and give an update . I really do appreciate the help Ken you have already done more than the company that sold the machine to me



No problem.   

In case you start thinking about upgrading your motor/controller setup, here's my setup.  It's not the best, but it's been working for me:


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## Cad cam man (Jun 23, 2021)

Ken226 said:


> No problem.
> 
> In case you start thinking about upgrading your motor/controller setup, here's my setup.  It's not the best, but it's been working for me:


WOW man that is a very sweet setup , and the manual pm mill and lathe in the back ground are bad a@#.... I have a 2.2 kw vfd from a router build I am not going to use anymore it went to the fleabay water cooled spindle and vfd kit but I really like the idea of using the servo for complete closed loop that would be perfect . Thanks for showing me your setup it has given me alot of ideas on where I need to go with my build


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