[kestreltom]

I looked at a nice older VMC-15 with the 7500 rpm spindle today. I think that this spindle is the single speed, single belt version. The spindle was perfectly quiet until it hit about 3600 rpm and then it set up a howl-like harmonic that sounded like a siren. The sound would change in pitch and get louder or softer as we raised the rpms. Below 3500 rpm it was absolutely quiet. Above 5000 rpm it got a little scary.
I did not pull the spindle head cover off, so I do not know the condition of the belt or if the tension is correct. Could the belt tension have been the cause of the howling sound?

[arc8d-drmn]

Out of balance, no corks in the balancing weight holes, belt, bad spindle.... Doubt it is electronic, but you can check by running the spindle to 7500 rpm and then hit the disconnect. The spindle will now coast. If it still makes the same sound it is definitely mechanical. The poly chain belts were always louder than the pozi drive belts... What you can also do is isolate the spindle from the motor by taking the belt off and turning the spindle on. You will have to turn the spindle byhand to makethe halls effect switch on the pully to "fake" out the control. It timesout after a few seconds. So if you turn it at 1 rpm your fine. If no noise at high rpm then you have eliminated the spindle motor... Just ideas.... Good luck.

[kestreltom]

Ok then, we will go back, pull the spindle head cover and check the belts, corks, alignment, etc... I also doubt that the problem is electronic, but that "hit the disconnect" test sounds easy, if not harsh...
The machine was used almost exclusively to cut plastic, so the screws and linear bearings are all in great shape. The downside is that this machine will not take well to heavy cutting... but I am sure that you can adjust feeds and speeds to ensure that it does not chatter even while cutting tool steel or Ti - just have to run within the machine's limits.
My dream would be to find a Mori MVJr or MV35 nearby... but that's a long shot.

[arc8d-drmn]

Ok then, we will go back, pull the spindle head cover and check the belts, corks, alignment, etc... I also doubt that the problem is electronic, but that "hit the disconnect" test sounds easy, if not harsh...
The machine was used almost exclusively to cut plastic, so the screws and linear bearings are all in great shape. The downside is that this machine will not take well to heavy cutting... but I am sure that you can adjust feeds and speeds to ensure that it does not chatter even while cutting tool steel or Ti - just have to run within the machine's limits.
My dream would be to find a Mori MVJr or MV35 nearby... but that's a long shot.

I know the hitting the disconnect seems harsh but that is what we did when I was in Service at Fadal.... Drives are okay you just do not want to hot shot them. That is power on and off a bunch of times within a short period of time.... When cutting steel the box way machines were better. More rigid... One thing to look at is the belt. The old style was a v groove type belt that was much quiter but it could slip in heavy cuts. Especially if there was coolant contamination on the belt. (Get a spindle motor filter and torit for that issue) so if you pull the cover see if it is a v groove or a poly chain type. The poly chain is louder but will not slip like the v groove.. Also thought of one other issue that cause noise. Check the tool in out assy and make sure the piston is not touching the knock out cap on the spindle. The tool in out spring breaks and instead of the cylinder being pulled up it will rest on the knock out cap causing a loud noise until it welds to it...