groove stability whith neumann vms 70

[finalstep]

HI all Trolls,

i' ve a problem for the third time.

obviously the turntable is not stable.
under the plate of the vms 70, we have 3 screw to fix it.

First and second time we have sold the problem but now it's impossible to solve the problem.

Our measurements after replacement are 90μm - 115μm - 115μm...
Nice just turn the main screw up (small quarter round) and after our measurements are 90μm-130μm-100μm. If i go back, it's impossible to return at the same measurements.

Who can help me ?

Thanks

Olivier

[andybee]

yes, I had the same problem on my AM32, still not perfect,
I have no idea, why this happens, maybe the laquers have
not a very stable thickness?
Normally, the spring compensates this issue?
Maybe, your turntable is not flat, or there is some dust
between the aluminium table and the iron table?

any inspiration welcome

[concretecowboy71]

There is an easy way to make sure your platter is level.

I was taught this as I was driving myself crazy doing exactly what you are doing.

1) Focus the microscope on the grain of the metal of the platter when the section of the platter with the screw is under the scope. Move to the other screw and tighten or loosen the screw until the grain is in focus. Repeat with the other screw and the platter should be level. There is one screw that is not supposed to be moved.

If the top of the platter with the vacuum holes moves when you spin the whole platter, you have lowered all of the screws too much and they are not engaging with the top part of the platter and you need reset all of the screws to get back to a "zero" point.

This method was suggested on this forum to me and Chris Muth walked me through it over the phone one afternoon.

If you are sure that the platter is level, there are other factors that can cause your problem:

1)Dashpot -- mine was very tight at one point and was not allowing the head to follow the natural imperfections of the lacquers causing wide spots in my cuts.

2)Vacuum Tube -- Make sure the tube that comes off the back of the head is not touching the secondary tube that it extends into. If it does, it can interfere with the head dropping all the way down and you will get a problem with your gooves.

I feel your pain. I wore holes in my fingers one time adjusting and re-adjusting my platter before figuring some of this stuff out.

If anybody else can add more to my platter leveling explanation, jump in. I am not sure if the way I explained it is clear enough.

[gold]

I prefer to use a dial gauge to check turntable flatness. I think it's easier and more precise than focusing on the grain. If you are sure the turntable is flat then the problem lies elsewhere.

1. Make sure the slide is oiled.
2. Play with the dashpot and see if the instability improves.
3. Check the suspension box spring. The general rule is to adjust the head suspension spring so the pivoting plate is flush with the face of the box when the head is resting on the lacquer.
4. Sometimes the lubricant in the ball bearings in the head suspension dries out. A squirt of WD40 loosens it up.

[finalstep]

ANDYBEE : between the aluminium table it's cleaned and under the aluminium table we have scratch (around center where screws are placed) but we have scratch since the beginning.
I have tested with Transco & app. it's the same.
If my turntable is not flat how is it that ok at a time and other time is not ?

CONTRECOWBOY : no tube touch other, i have chek it. I don't understand about the grain. If i made focus on the metal on the red point after the point A - B & C are focused and the grain appears.
About the tree screew, i have removed the plate and down all.
After replacement and test we have 50-80-100...

Stop for today i'm not ok to continue test.

Thanks for all supports, i come back home on saturday. Have nice w-e.

Olivier

[finalstep]

Gold :

What did you mean for slide in the first point ?
The suspension box is good.
How long time for replacement the oil in the turntable ? have you idea.
I have a dial gauge but i have not a good system to fix it.
I think the mesurement is not good with my system.
Necessary i need good system to view if my turntable is flat.

Olivier

[gold]

Gold :

What did you mean for slide in the first point ?

The dovetail that arm that holds the suspension moves along. The main part that slides to move the cutter head across the disc surface.

How long time for replacement the oil in the turntable ? have you idea.

The heavy oil never needs to be replaced as long as there is enough. To check the heavy oil remove the vacuum turntable. Only the aluminum top. There is threaded insert that can be removed with a coin as a screwdriver. There is a dip stick attached to it. If the oil is near the line it's okay.

You should put a few drops of light oil in the tube that is under the turntable assembly every six months or so.

I have a dial gauge but i have not a good system to fix it.

I use one with a magnetic base. It wasn't expensive. Any machine tool supply should have them.


You need to know whether the problem follows the machine or the lacquer. When you run into a problem mark the orientation of the lacquer with a scribe. Cut it again to make sure the problem is repeatable. Then rotate the lacquer while keeping the turntable stationary. Then recut. Does the problem follow the lacquer or the turntable? If it follows the lacquer you probably need adjust the suspension.

[finalstep]

Sorry Mr Gold for the slide... but my english is not the best.

The slide is oiled and i'll chek for sure the heavy oil but you confirm about that, i have the good info.
I want to find a magnetic base to test it but i think the laquers is ok.

Olivier

[gold]

One more thought. Check the rod between the turntable and the turntable motor. Make sure both screws that hold the rod to the turntable are tight. It's hard to get to that.

[concretecowboy71]

If the grain stays in focus from A to B to C (or your dial gauge indicates no movement) then your platter is level and you have to start looking for other problems.

Paul's suggestion that you look to see if the problem follows a lacquer or the machine is key. It took me two days to figure that out on my own. No lacquer is perfectly flat. When you are cutting tests, look at the lacquer and note darker areas and lighter areas.

If the problem happens in the same spot on the same lacquer, I would start looking in other areas (suspension box/dashpot) for the problem.

[finalstep]

I'm not at the studio today.
I'll come back on saturday for the next of the history.

Thanks to all for the support

Olivier

[Serif]

If the grain stays in focus from A to B to C (or your dial gauge indicates no movement) then your platter is level and you have to start looking for other problems.

Paul's suggestion that you look to see if the problem follows a lacquer or the machine is key. It took me two days to figure that out on my own. No lacquer is perfectly flat. When you are cutting tests, look at the lacquer and note darker areas and lighter areas.

If the problem happens in the same spot on the same lacquer, I would start looking in other areas (suspension box/dashpot) for the problem.

In the case of the LS-76, although it's possibly only of academic interest, here, and I have no access to a real-deal Georg Neumann, but the microscope focus on The Lathe can not be trusted to set the tt run out. Au contraire. It is, rather, whether or not the inside grooves look blurry, even though there is good focus at the outside grooves, which determines the need for adjusting the tightness of the adjusting screws for the base of the microscope. As Paul says, the best way for adjusting tt run out, after using a spirit level on the frame and tt, is to fine tune the tt's flatness with a 1 mil dial indicator. I, too, sprung for the magnet base kind, although I got my Mitutoyo on eBay. I noticed the same one on a milling machine down the street which can do 3600 rpm. (They were fixing some microscope parts for me, although much more slowly than that.)


- Doug Intuit

[gold]

[quote="concretecowboy71"
In the case of the LS-76, although it's possibly only of academic interest, here, and I have no access to a real-deal Georg Neumann, but the microscope focus on The Lathe can not be trusted to set the tt run out.

He's not talking about run out. He's talking about turntable flatness. My understanding of the term run out would mean the turntable is not centered around the rotating axis. I think looking at the grain is fine for measuring flatness although seeing the dial gauge meter move gives me a sense of security.

[Serif]

[quote="concretecowboy71"
In the case of the LS-76, although it's possibly only of academic interest, here, and I have no access to a real-deal Georg Neumann, but the microscope focus on The Lathe can not be trusted to set the tt run out.

He's not talking about run out. He's talking about turntable flatness. My understanding of the term run out would mean the turntable is not centered around the rotating axis. I think looking at the grain is fine for measuring flatness although seeing the dial gauge meter move gives me a sense of security.

Turntable flatness is not correctable in the studio. But the turntable's maximum perpendicularity to Earth's gravitation _is_ its minimum "run out."

Same concept as for a disc brake, although the brake is trying to be perpendicular to the shoe.

http://www.sobjoy.com/disc-brake-run-out.html

Using a dial indicator on the surface of the turntable, at about the 15" diameter (for a 17" tt), is how Larry wants me to check the "run out" on his turntable. If it runs up and then runs down, it's not flat and can be adjusted with the tightness of three screws that hold the tt onto the hub. There is no leeway for minimizing the eccentricity of rotation. But the "flatness" can be made correct as possible, as far as regards perpendicularity to the modulus of gravitation. (I just wanted to say modulus.)

When I see the dial indicator needle _not_ move (even though it is pushing against the rotating platter) I have a sense of security in the setup.


Andrew

[gold]

Turntable flatness is not correctable in the studio. But the turntable's maximum perpendicularity to Earth's gravitation _is_ its minimum "run out."

Flatness is the wrong word. I looked up a definition for runout and I found "The radial variation from a true circle."

I think "true" would be the right word for leveling the turntable. I think true generally refers to parallel surfaces.

[Serif]

From the L. J. Scully manual for the LS-76, under the heading Turntable Runout Test and Adjustment:

"...Move dial indicator and its "feeler" to a diameter of approximately 15 inches on the top surface of the turntable. ...Slowly rotate turntable to see what runout (vertical variation) occurs. If total indicated variation exceeds 0.001 inch, one or more turntable flatness adjustments are needed."


So, I guess you get to say, "flat," but I get to say, "runout." (;


As I was trying to say, the turntable may be warped for whatever reason, and the adjustment screws for this "flatness" can not remedy _that_. They _can_ however make the distances between arbitrary points on the platter's surface and the virtual floor closer in value.



- Chip Swarf

[gold]

"...Move dial indicator and its "feeler" to a diameter of approximately 15 inches on the top surface of the turntable. ...Slowly rotate turntable to see what runout (vertical variation) occurs. If total indicated variation exceeds

Well, there you go! Let's have the machinists weigh in.

[finalstep]

Hi

After some tests....

Here's step was done for my problem :

1. i removed two elements of the turntable and it's was cleaned with
isopropyl alcohol.
2. I removed vacuum and replace all connection to the lathe. Also the rear side : RS 132- RS 131, vacuum tube and the connection to the floating box.
3. Repleced all screw to flatness (for me the point of "O" is under the level of the first turntable ?)
4. cleaning vacuum tube.
5. cleaning and oiled slide
6. put back 2 elements on the lathe.
7. place sx 74
8. Turn down the floating box
8. first test with no signal : 90-110-100
9. Turning up the screw B for adjusting groove... check on the microscope
10. After 10 test with the same point 9. i'have 109-110-110... was nice with dubplate APL - TRANS master disk 14" at differents points.
11. Last step : set up the wheel (left of the floating box) and test it for reference 70-70-70
12. 70-130-100.
13. AGAIN SHIT.

I'm waiting for the arm to test the flatness turntable but i think we haven't problem with it.

Is it possible have trouble on the slide or the floating box ?

Thanks to all the the reply.

Olivier

[concretecowboy71]

I would look at the suspension (floating box).

Like Paul suggested, the bearing could be gummed up or need lubrication.

Try opening up the dashpot all the way and see if you get a change also.

[mossboss]

Watching this thread with great interest
Ok here is my 2 bits worth
It seems to me that the spring is the culprit and nothing more
Look there is the screw at the back of the suspension box that is used to take up the weight of different heads as an example a 45 is a lot lighter than a 68 or a 74
It is a simple enough part and it has a further adjustment on it so as to provide more tension as an example when mounting a westrex head on it which is quite heavy
If I where you I take the spring out and check it so as to make sure it has not lost its tension which would be most unusual as it does not do much
Now if you look at the way it is mounted you will see that it is possible that it could have slipped off the stud from the section on the front where you can adjust the coarse tension
The nut in the back is for finer adjustment
Check it carefully or better still pull it off make sure it is still OK and remount the whole thing
Lubricate it as well as the threads on the nut at the back with a bit of WD40 before you remount it
Place the head on the normal place and adjust the whole thing so as to take the weight all as per manual
I would have thought that would be the first place one looks when issues like that arise as the platter rarely goes out
Any way this is a 5 minute job and I somehow feel after having read what you have done it points to the spring
I would be surprised if it is anything else
Check it out and please look at the manual for the correct setting
The correct setting just in case it is the face plate being perfectly flat and parallel with the outer casing of the suspension box without any current to it and with the head mounted
I am sure you know the other steps
I use the little alluminium block that comes with the cutting head so as to check that it is parallel to the TT
Place it against the outer case on the wide side and slide it down if the face plate moves it needs adjustment from the nut in the back if it does not it is fine
sincerely hope this helps
Cheers