Ideas for balancing 8520 drive pulleys

[JPigg55]

Doing a little milling today and found I have a small vibration issue at higher RPM's.
Any suggestions on ways to find the imbalance and fix the vibration ?

 

[Terrywerm]

First, remove both drive belts, also remove the drawbar and any tooling installed in the spindle. Run the motor by itself. Note any vibration. Inspect the belts for any damage, cracks, chunks missing etc.

Second, spin the intermediate pulley and the spindle by hand, one at a time. Note any roughness or ticks whatsoever in any of the bearings.

Third, install the primary drive belt between the motor and the intermediate pulley so that the intermediate pulley will run at maximum speed. Turn on the motor and note any vibration.

Fourth, install the secondary belt to run the spindle at its fastest speed. Remove the drawbar and any collets or drill chucks from the spindle. Turn on the motor and note any vibration.

Lastly, install the drawbar and a drill chuck, with a drill bit tightened in the chuck. Turn on the motor and note any vibration.

Simple process of elimination should help you narrow down the problem. If you are unsure of your findings, report back to us here and we'll see what we can come up with.

 

[JPigg55]

Thanks again Terry, you're probably getting tired of helping me out. LOL
Motor and pulley are fine. I know this since I ran it by itself when I replaced the motor. Belts are new as well. I replaced them when I replaced the motor.
I'll try the other two things you mentioned next although I don't suspect bearings since it runs smooth at lower RPM's just when I put the motor belt up to the high speed pulley.
Any tricks to figure out what side of the pulley would need a balance adjustment if I isolate it to either the spindle or intermediate pulley ?

 

[Terrywerm]

To be honest I don't think that it's a balance problem. The drawbar tends to rattle slightly in my 8520 when I do things at high speeds. I first thought that one of the spindle bearings was going bad, but removing the drawbar got rid of the noise and vibration. Odd, yes, but stranger things have happened!

When I got the new drawbar for my 8520, I hoped that the problem would be resolved. Not so, it still does it. I'm thinking some sort of harmonic problem. :noidea:

 

[wa5cab]

Terry,

If there is enough clearance, try pulling a length of shrink tubing over the unthreaded part of the drawbar and shrink it. Probably won't totally stop it but at least it won't be the sharp metal on metal sound.

Robert D.

 

[Bill Gruby]

I believe you are overlooking something that has not been mentioned yet. At least I didn't see it in this thread yet. Check the Vibration Dampners on the motor mount between the motor and mount. There is one on each bolt. If these are bad it will cause your problem. Make no mistake, they are there for a reason, as the vibration becomes greater as the speed is increased.

"Billy G"

 

[Terrywerm]

Terry,

If there is enough clearance, try pulling a length of shrink tubing over the unthreaded part of the drawbar and shrink it. Probably won't totally stop it but at least it won't be the sharp metal on metal sound.

Robert D.

Interesting thought, Robert, and not a bad idea. The old drawbar had room for some heat shrink along part of the shank, but the new one does not.

I believe you are overlooking something that has not been mentioned yet. At least I didn't see it in this thread yet. Check the Vibration Dampners on the motor mount between the motor and mount. There is one on each bolt. If these are bad it will cause your problem. Make no mistake, they are there for a reason, as the vibration becomes greater as the speed is increased.

"Billy G"

Interesting point, Bill, thanks for bringing it up. Since the motor runs at a constant speed, wouldn't the vibration be the same at all speeds if it were being caused by the motor?

The rubber vibration dampers on mine were hard and crusty and breaking apart when I got my mill so I ended up making new ones that are spacers made from Delrin with two pieces of old inner tube on each side. Not the best, but they seem to work, I don't get any vibration on my machine from the motor, or at least not that I can tell.

My machine only makes noise when I am cutting, and it is worse at higher speeds. It does not make noise when drilling, only when applying side pressure. It has a metallic chattering sound that I find hard to describe, but it sounds to me like the drawbar is hitting on the inside of the spindle. There was a thought that it might be one of the bearings, but the spindle feels fine when I turn it by hand with the belt removed. When I got a different drawbar for it I thought that the problem might go away. It is less of a problem now, but it does still occur, so I am leaning toward rebuilding the head on mine, putting in new bearings and having it over with.

I guess I will need to attack my machine one little problem at a time, and will probably start with purchasing some proper motor mount bushings or grommets, whatever their proper name is. The bearings for the intermediate pulley were both replaced when I bought the mill, as one of them was bad then, so I guess the next step would be to rebuild the head.

In Jimmy's case I thought it best to 'divide and conquer' and narrow down the source of the problem to see when it occurs. If you take a part of the machine out of the picture and the noise still occurs without change, then that removed part has nothing to do with it, or so one would think.

 

[Terrywerm]

Thanks again Terry, you're probably getting tired of helping me out. LOL
Motor and pulley are fine. I know this since I ran it by itself when I replaced the motor. Belts are new as well. I replaced them when I replaced the motor.
I'll try the other two things you mentioned next although I don't suspect bearings since it runs smooth at lower RPM's just when I put the motor belt up to the high speed pulley.
Any tricks to figure out what side of the pulley would need a balance adjustment if I isolate it to either the spindle or intermediate pulley ?

Nope, never get tired of helping people out.

I did have a new thought just now. If the vibration only occurs when one belt is in a certain position, in other words when a certain sheave on the pulley is in use, check to see if one of the sheave sides has a small bend in it. One that would make a tight pinch spot for the belt. Aluminum pulleys can be bent very easily, and a point that pinches on the belt would most certainly cause a heavy vibration in the machine.

 

[Bill Gruby]

Terry --- While the motor is at one constant speed The Spindle is never at that speed. Each speed has its own harmonics level thus it will have a different vibration level. One thing you mentioned I had forgotten, the bent rim will cause some vibration.


"Billy G"

 

[JPigg55]

Did a little testing on mine today, here's the results.
Motor alone has no vibrations except for a little when turned off while coasting down, connected to the intermediate pulley on high speed has some vibration. I took it off, cleaned it up and worked a little oil down in it and it seemed to help some. Bearings seem smooth, but I may replace them at some future time.
Put the spindle drive belt on for max speed and it uppedthe vibes a little more. Unchanged with drawbar in or out, I did notice some wobble in the belt though. I think it's tensioned plenty good enough and hopefully not too tight.
Any of you guys have a source for replacement rubber vibration dampers ? Mine are originals I think and replacing them can't hurt.