Sharing a few tidbids of knowledge regarding the VMS70

[opcode66]

Over the past year that I've had my lathe I've run into a few little problems. I've managed to determine the source of these problems and decided to share my findings. Seasoned VMS owners will likely know all of this. But, new VMS owners might find this information helpful.

1. I spent a lot of time cutting unmodulated grooves and playing them back through headphones at very high amplification. I had various sources of background noise that I was trying to pin down. When I cut 12" Reference dubs I could hear a sort of sucking noise or sound of air rushing (a breeze if you will). At first I thought it was the suction tube on the bottom of the cutterhead. I tried repositioning it a million times. I did notice that some sound would translate to the unmodulated groove if the tube was touching the black disc like piece of metal it is next to where it curves in toward the stylus. Angling the tube so it doesn't touch any of the parts of the cutterhead helped. Also, installing a Variac (very large potentiometer) on the ac line going to my vacuum allowed me to control the air flow and that also helped.

2. When cutting a 12" dub I was setting my chuck table to the 12" setting. WRONG!!!!! Don't do it! Set it to 10". With my chuck table, if set at 12", then the holes at the outer edge suck air in around the edge of the dub and that acts like the edge of an airplane wing. The air rushes past the edge and makes a sound that is audible in an unmodulated groove if played back at high amplification monitored on headphones. Setting the chuck table to 10" solved this problem entirely.

3. I highly suggest adjusting your dashpot! Such a simple thing to do. What fantastic results I now have. This was not really an issue when cutting master lacquers. They tend to be very flat on the preferred side. But, when cutting both sides of a dub I would sometimes get a whooshing background noise on the B side (non-preferred side)

To adjust the settings I suggest using the B side of a dub. The non-preferred side with the numbered stamp. I have almost universally noticed that the non-preferred sides are not entirely flat. Since it is uneven it is a great way to test your dashpot settings. I took the top off the suspension. Turned the stylus heat off. Started the pitch motor. Lowered the cutterhead. Slowly turned the shield ring at the top of the dashpot until it came off. Moved the ring out of the way. Turned the knurled knob for the dashpot all the way counter clock-wise. That is no damping at all. You'll notice the head will move completely freely up and down. If you were to cut you would notice the head would appear to be moving up and down a lot. I dialed the knurled knob clockwise a little and did some test cuts. I repeated the process until I had proper head damping and I did not hear anything in an unmodulated groove. When there is too much damping you can actually hear sort of a whooshing sound once per revolution (wherever the bulge was on the surface of the disc). I could watch my playback arm when playing test cuts. Whenever it moved up I could hear the whooshing sound. That meant the knurled knob was dialed too far clock-wise. You have to do a few test cuts to get it dialed just right. But, when you do you will get proper damping and no noise! Mine is set about 3/4 of one revolution from fully closed (fully counter clock-wise).

4. Sometimes I would notice that under the scope the grooves appeared to jump. There was a smooth progression of the grooves and then suddenly one seemed to make a jump or very sudden movement laterally. It almost seemed like there was some resistance to the movement of the carriage and then suddenly the resistance was overcome and the carriage moved a lot at once. I determined that this was due to not oiling the SIDES of the track. I was always mindful of having proper lubrication on the top of the track. But, I wasn't as regular about oiling the sides. Once I stripped my track and re-oiled both the top and the sides it worked like a dream. No more jumping grooves. On playback, you could hear a sort of pop sound where the groove makes a lateral jump.

Well I hope this helps someone now or in the future. Again, I'm sure for a lot of you this is already common knowledge.

Happy Cutting!!!!!

[concretecowboy71]

I have had many of the same issues and wish there had been more info around when it was happening.

I think having this all compiled into one post is a good idea.

You can also get groove "skipping" if the lock nut is worn or out of adjustment.

Had that happen to me also.

Nice job.

[opcode66]

I think we collectively need to have a quantity of half nuts manufactured. That is the one piece on the lathe that worries me to no end. Without a working one the lathe is not functional. And, with absolutely no replacements currently available, that is a bad scenario. I would be willing to invest to have a quantity made. Anybody else interested?

[concretecowboy71]

I am certainly interested.

I have a friend that owns a machine shop and he has offered to do this for me.

He made me new helium nipples for the back of the lexan regulator block when I broke mine.

In fact, opcode, you might have one on your machine.

I sent a few to Al because he needed some spares.

Does anybody have a mechanical drawing for the part? Or would we need to produce one?

[cohearent]

Yep. Good stuff!
I have found that the chip tube wants to be as close as possible to the lacquer without touching. That means allowing for about a 5 mil-wide groove.
I usually back the suction pump down to 60 volts. You were running flat out?
Neumann used to sell a variac for this purpose with the lathe. In addition to making way less noise it will increase the life of the pump considerably!!! BTW I put the pump in another room and punched a hole through the wall behind the lathe. WAAAAAAAAAAAY quieter in the room when cutting. I could never go back to having it in the room with the lathe.
I have a couple spare half nuts, I have never had one wear out. I believe I have a drawing somewhere, I will check.
There is a vacuum cleaner belt that works perfectly for the Fast motor. There are a few belts that work for pitch, but none that I am completely happy with. The best I have found so far is a toothed belt that you can use inside out. Lets keep this going!

Best,

Kev

[opcode66]

I am interested. I am in.

I have no technical drawing or specifications whatsoever. Therein lies the first hurdle.

Short of removing a working halfnut from someone's VMS system how do we make a copy of them?

If I have a helium nipple you supplied then Thank You! I appreciate it!

Anybody have the specs on the halfnuts? I think there were two kinds. Squared and rounded. Not sure if the shape was the only difference. Any Trolls have any information?