Bridgeport spindle balance problem

[wierdscience]

Got something going on with my Bridgeport.Mid 80's VS head has developed a vibration in the high speed range.Most prevalent in the 550-1200 rpm range.Mill had a new belt set and top cover bearing installed about two years ago and has been running fine since.The head runs quiet,with no abnormal noise or change in tone.

So that has me wondering why all of the sudden it should decide to start making the DRO look like it's a paint shaker.VS pulley bushing going out????

[lakeside53]

Maybe, or the belt is shredding on one edge. That range puts the most stress on the sheaves as the belt is running on the outer portions of the disks.

Bushings and the key are cheap and easy to change. If ignored they wear the motor shaft.

[wierdscience]

Sigh,think I will be tearing into the belt drive soon.If it is the culprit it may just be time for a VFD and a few mods.

[lakeside53]

I use mine with a VFD and get the best of both worlds.

[wierdscience]

I never was a big fan of VS belt drives.Too much mass to spin up,too many parts to wear out.Gotta go on fleabay and do some motor shopping.

[lakeside53]

I was using it today to engrave at 6000 rpm.. No issues at all. Also ran my 2.5 inch face mill in steel - I wound the VS down to 1200rpm and kept my VFD at 60hz; for that I needed the gearing.

If you do do direct drive and no belts (or belt and no changing), consider 5+hp to get decent hp at the spindle at less than 1000rpm. Top end is easy. Changing to back gear can help but not much in the 1000 rpm range..

Most VS drives last many decades... and most complaint are from guys that have never maintained them and run them into the ground.

[wierdscience]

I've ran and worked on more than a few,I just never was a big fan of reeves drives.

A friend has one of these Grizzly mills with the EVS drive on it.Nice machine,quiet,plenty of power and basically the factory took their stock belt drive VS head,removed the the movable half of the spindle pulley and the spring loaded motor pulley and replaced them with a cog belt drive.

http://cdn0.grizzly.com/partslists/g0667x_pl.pdf

That one runs a 3hp motor on a 5hp inverter for single phase operation.More than enough power on the 60 rpm bottom.I think I may do just the same on this mill,assuming it's not an easy fix,except I will use a double 3v belt instead of the cog belt drive.

[lakeside53]

60 rpm puts it in low gear so no issues. The problem area is the lower portion of the high range which is direct drive. As I use carbide EM or inserts, 99% of my mill machining is 500 rpm and above. Back gear is typically for larger drill bits. Your needs may of course be quite different.