Grizzly G0678 8x30 mill belt noise

[bhusted]

I recently purchased a G0678 that is almost new. PO bought and kept in his garage for about a year before selling it to me. Most of the machine still had the cosmoline coating on it when I got it home. After cleaning it up, everything seems to work well, but the spindle is noisy. This machine has a 3ph motor with VFD and a single belt to the spindle.

Running the motor without the belt installed is silent until it gets up to the max speed when I think there is a vibration caused by imbalance in the fan. Turning the spindle by hand feels silky smooth. With the belt installed, there seems to be more vibration/noise than there should be. Running the spindle with the cover open revealed a lot of movement in the belt and I can visually see the motor pulley wobble. The indicator shows .020-.030" of run out in the motor pulley with the shaft running dead true. Thinking I had located the issue, I turned a close fitting mandrel tonight so that I could true up the pulley. To my surprise, the pulley ran true on the mandrel. More inspection revealed that the motor shaft is .748" and the bore of the pulley is .756". With the key installed and set screw tightened, the clearance gives the pulley a major wobble. I *think* this wobble is causing the vibration in the belt that is leading to the noise I'm hearing.

I'm looking for options, ideas, opinions on how to proceed.

1. Leave the pulley alone and look elsewhere for the cause of the noise.
2. Machine or buy a new pulley.
3. Somehow true up the existing pulley as installed.

Thanks in advance for any ideas, suggestions, or comments.

 

[markba633csi]

I would re-bush the pulley and re-bore
You should be able to get it within a thou or so.
8 thou is definitely too much

 

[bhusted]

I would re-bush the pulley and re-bore
You should be able to get it within a thou or so.
8 thou is definitely too much

Thank you for your thoughts. Do you think it's better to bore out the existing pulley, press in a sleeve, re-bore, broach a new keyway, and set screw hole or to just start from scratch? As far as I can tell, the original is cast iron. Do you think the pulley wobble is the source of the noise/vibration?

 

[markba633csi]

The pulley runout will certainly cause vibration, but there can also be issues with the motor's rotor being not well balanced at the factory
You could try buying a new Grizzly pulley but it may be just as sloppy; if you repair the original you have control over the final fit

 

[bhusted]

The pulley runout will certainly cause vibration, but there can also be issues with the motor's rotor being not well balanced at the factory
You could try buying a new Grizzly pulley but it may be just as sloppy; if you repair the original you have control over the final fit

Running the motor with nothing attached is smooth and silent until I get close to 2200rpm. I suspect this vibration is from the balance of the rotor and fan. I did look up a replacement pulley from Grizzly, which comes in at $146.75! Unfortunatly 19mm bore doesn't seem to be an industry standard that McMaster-Carr sells for their pulleys.

 

[markba633csi]

Instead of repair, consider taking up the slop with a strip of shim stock (perhaps even a piece of tin can, provided it's the right thickness)
Easy to do and cheap. If it works well it might even be a permanent fix

 

[Road_Clam]

Ive had to do several "re-shims" and modifying component spacers to gain better belt, change gears and my lead screw alignment. These lathes are obviously just frantically slapped together at the factory in china with zero attention to alignment correctness. Its definately worth your time. My lathe had all kinds of misalignment bind noises and now it functions perfect.

 

[bhusted]

Thanks! My plan is to try to add a shim to see if I can get it to run more true and see what impact that has on the noise/vibration. In the long run, I'll make a new pulley to make it run as true as possible assuming that it improves the situation with the shims.

 

[bhusted]

Just to follow up on this. No amount of shimming that I tried could get the wobble out of the original pulley. I could not source one from McMaster and elsewhere of the proper dimensions, so I made a replacement.

This reduced the noise and vibration drastically, but there was still some. The original belt was not very smooth and was leaving rubber dust in the top cover, so I decided to replace the belt with one made by Gates. This removed all of the remaining noise and vibration. The mill is as quiet as I would expect now. Thanks for your help and suggestions.