Help identifying X2 spindle wobble

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shooter123456

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Thank you in advance for any help anyone can offer.

I have an X2 mill with a belt drive from LMS that I have been using for about a year now. Recently with my CNC conversion, I have been able to use the high end of the 4300 RPM range the belt drive has and that has directed me to some spindle problems. At high speeds, the entire head vibrates too much for comfort.

When looking closer, I found that the pulleys are both wobbly and the draw bar is not even close to running true. The inside of the spindle is only out about .0005" and with a collet and endmill tightened in, the tool is out .0015" directly below the collet. This is consistent across 3 different collets and several tools each. All are out almost exactly .0015" according to my indicator. You can also hear a sort of gritiness when the mill is running at low speeds that reminds me a little of the gears from before and not nearly as quiet as I remember it being when I first put the belt drive on. The spindle and head also get very hot at 4300. I tested when I first put the belt drive on and after 15 minutes, it was only slightly warm. Now it is activate burn reflex hot. After about 10 minutes.

Additionally, the spindle pulley isn't a sliding fit anymore. I specifically remember it being a darn near perfect fit when it was initially installed. The motor pulley can't be trued up with the key in, but it will run pretty true using only the set screw.

Last, when looking down through the spindle, you can see that something is way out. I have a video because its hard to explain but it is substantially more than .0005" out like the spindle itself. I took the whole belt drive assembly apart and cleaned it up and didn't find anything out of place in the spindle. What should I be looking for to solve these issues?

Here is a video of the assembly running at low speeds then higher speeds and I put the camera next to the head to try to capture the sound a little better.

Here is the wobble in the motor pulley.

Here is the view down the spindle. You can hear the rough grinding sound here.

Once again, I appreciate everyones help. This forum has been instrumental in my growth as a wannabe home machinist.
 
Did you upgrade the spindle bearings when you did the belt drive?
 
Just a thought but the spindle bore is not a critical surface and might not be made to run true.
At least that is the case with my lathe where the spindle bore wobbles but the other critical surfaces run true.
The spindle bore is off by a visual amount but it is of no consequence.
IMG_1493.JPG
 
Tozguy said:
Just a thought but the spindle bore is not a critical surface and might not be made to run true.
At least that is the case with my lathe where the spindle bore wobbles but the other critical surfaces run true.
The spindle bore is off by a visual amount but it is of no consequence.
View attachment 227599
Click to expand...
Do you think the vibrating could be caused by the unbalanced weight as it rotates?
 
shooter123456 said:
Do you think the vibrating could be caused by the unbalanced weight as it rotates?
Click to expand...

Thats a good question, at your high speeds it might very well cause vibration.

Since my lathe usually is run below 1000 rpm the imbalance does not cause significant vibration.
I do get vibration at certain speeds when spinning my 6'' and 8'' chucks. But there is no objectionable vibration at any speed with the spindle bare.

Hopefully someone who has a mill like yours will be of more help than I am. The heat build up that you mentioned in the original post is not normal. At 4300 rpm nothing should wobble or heat up that much. I suspect bearings are complaining.
 
Tozguy said:
Thats a good question, at your high speeds it might very well cause vibration.

Since my lathe usually is run below 1000 rpm the imbalance does not cause significant vibration.
I do get vibration at certain speeds when spinning my 6'' and 8'' chucks. But there is no objectionable vibration at any speed with the spindle bare.

Hopefully someone who has a mill like yours will be of more help than I am. The heat build up that you mentioned in the original post is not normal. At 4300 rpm nothing should wobble or heat up that much. I suspect bearings are complaining.
Click to expand...
Is there any way to determine if the bearings are bad besides just replacing them? I have nothing against getting new ones, but I would prefer to diagnose the ailment before I start treatment.
 
Tozguy said:
One of the first things I do to diagnose a bad bearing is to listen to it with a stethoscope.
https://www.kmstools.com/neiko-mechanics-stethoscope-4060
I can't always tell even with that. So if you are upgrading your mill, better bearings might be called for anyway and would strengthen the heart of your mill.
Click to expand...
I will go ahead and look into replacing them. That will be helpful if I get a larger motor and increase spindle speed anyway. I appreciate your advice.
 
shooter123456 said:
Is there any way to determine if the bearings are bad besides just replacing them? I have nothing against getting new ones, but I would prefer to diagnose the ailment before I start treatment.
Click to expand...

I would suggest taking careful readings for run out at the spindle. Un-do the belt from the spindle up top and turn the pulley by hand. Put the tip of a good DTI inside the spindle taper and first check concentricity by marking the pulley with a Sharpie. Make one full revolution and note the run out. Then push and pull the pulley in all directions, looking for movement of the indicator needle. If you see excessive run out, either with the static concentricity check or with pushing/pulling on the pulley then your bearings are likely the issue.

Just looking at the upper spindle running at low speed, you can see it wobbling. To me, this suggests that the bearings are shot or the spindle, if it is one piece, is bent. The grinding sounds and high temps also suggest the bearings are shot.

If your bearings are original Chinese bearings then getting more than a year or two out of them is about all you can expect. I suggest replacing them with high quality angular contact bearings or deep groove ball bearings. It is also a good idea to use sealed bearings that are lubricated for life and typically require no run in time. It might be a good idea to consider using ABEC-5 or equivalent bearings in your spindle; they cost more but will last longer at the speeds you're running. Going for more precision in a bearing might not be cost effective on a mini-mill.
 
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