Spindle cutting in and out

C

Cad cam man

Registered
Registered
Joined
Mar 5, 2021
Messages
55
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 ???
 
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
 
Last edited:
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
 
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.
 
Getting warm is to be expected, but hot to the touch could indicate a preload issue. I'd call PM.
 
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.
Click to expand...
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.

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

.
Click to expand...
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
Click to expand...
Yeah I had plans on upgrading to a better high speed bearing but I wasn't expecting to do it this soon
 
Last edited:
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.
 
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
 
You must log in or register to reply here.
Back
Top