The Secret Society of Lathe Trolls

Doug 6N · Joined: 21 May 2007 Posts: 66 Location: Washington

Hello everyone:

So the deal is this. I've done pretty good at cutting 78's. Now I've tackled 33Rpm microgroove.

I've now this same problem 3 times with damage to stylus each time. After anywhere from 1 to 3 sortoff successful cuts. The stylus has then started to bounce on disc. Cutting through and wrecking stylus. I'm using Transco 462 heated. New Apollo 10" Dub. 224LPI leadscrew.

I've tried cutting angle and depth of cut adjustments. What am I overlooking here? I've varied the curent on the stylus from 150 to 400 MA. I'm a bit of a loss as to what to look for now.

Funny how the 78's are really quite decent. Shiny groove good sound all seams well.

Any input is greatly appreciated Smile

Doug

cuttercollector · Joined: 11 Jun 2006 Posts: 286 Location: San Jose, CA

Somewhat out of my league here but if this is only happening at slow speeds (only 33 or 45 too?) perhaps there is some sort of very low frequency (5-10Hz) resonance induced by cutting at that speed and it takes a while to "run away". Is it that you can cut for a while as in time on the same disc or after several discs it starts to happen when you touch down? Is everything mechanically tight? No extra play?
It sounds as if you are eventually "going deep". Have you looked at your test cuts under a microscope to see if the depth of cut is increasing somehow till it hits bottom and starts to bounce?
Perhaps adjust everything as best as possible with zero heat if you can achieve a quiet groove at the lower speeds or as nearly optimal as you can get it, then start with as little hjeat as possible to get it the rest of the way always watching to see if your cuts are going deeper as you go along. Is it possible the stylus is "burnishing in" so to speak as you cut?
One other possibility is that your lathe to turntable height is not consistant from outside to inside and thus everything about angle and cutting pressure changes slightly throughout a given cut. I would say that all problems and errors are magnified with slower speeds.

Doug 6N · Joined: 21 May 2007 Posts: 66 Location: Washington

Hi Cuttercollector:

Just reading over your thoughts.

I have gone over the turntable height to angle by putting thin paper under the disc that drives the cutter carriage and making sure the fit was even all way around. Seamed ok. However I'll check that again. What your saying makes a lot of sense to me. Sure something to recheck.

I've thought about the resonance thing. Hmmm. I seam to get this problem after the cutting is going on for a period of time which varies. It seams worst toward the middle of the disc although it can happen anywhere randomly. I do know my 33RPM drive tire is very tired. I currently am having a set of tires rebuilt. So will not try this again until I do get the new tires on.

In the microscope the cut appears to get very ragged looking on the edges just prior to all hell breaking lose. This has happened with new and old blanks but only at 33 RPM. I wonder when the raggedness starts showing up if that is where some wierd vibration is starting?

I'm going to go over all again before the next trial. As I've now killed two stylus.

Thanks for your imput. Back to the drawing board as the saying goes. Smile

Doug

cuttercollector · Joined: 11 Jun 2006 Posts: 286 Location: San Jose, CA

One other thing with the resonance/vibration, if you can catch it before it starts to run away and bottom out would increasing the speed back to 78 cause the problem to stop? Similarly, would slowing the table to a stop cause the problem to happen?
Again, I would make sure that you are cutting as shallow and quiet of groove as possible with no heat (as a baseline) then dial it up from there.
It is unclear whether the depth is beginning to break through causing the "scud" or the vibration happens causing the breakthrough.
Perhaps it is just a combination of the proper angle - not too steep - plus very low stylus heat and not too deep. The actual stylus temp might be changing at low heat as more time passes after you turn it on. The material is also going by more slowly. As I said, all problems tend to become more of an issue at the slower speeds.
It might be just on the edge with the combo that works fine @ 78.

Also see my other post about listening to your cutter as you try and cut a quiet groove.

Doug 6N · Joined: 21 May 2007 Posts: 66 Location: Washington

Hi Cuttercollector:

Thanks for the input. I doubt I can cut anymore with the present damaged stylus. But I'll go through all we have discussed to this point.

I'll have to watch this thing very close. As the times it's given me problems all has been proceeding nicely. Then bam. The sound off the cut before problems has been ok. Not great but ok. Probably turn out to be 90% human error and 10% the equipment. Very Happy

Or maybe it's all the drive wheel? I'm go to check all this over very carefully once again. Taking you suggestions into account. And when I get the next new stylus. I'm going to take a listen to it. I do know about that and how it's done. Something I just have'nt done yet.

Doug

Doug 6N · Joined: 21 May 2007 Posts: 66 Location: Washington

Hi Cuttercollector.

Back again. Well tonight I went through all the adjustments once again. Very meticulously.

After doing all this I was able to cut a 10" 33rpm with no issues. The stylus is damaged so grooves aren't shiny. But I had no cutter head bounce problems. The other thing I did was to fill the dashpot. I had'nt used it yet. it was an option so I just kindof ignored it.

I also hooked the cutter head up the pickup input and adjusted for quietest groove which is'nt all that quiet do the damaged stylus. However I did the best I could. Then turned on the heat very low current. I watched the grooves in the microscope. I noticed a change with heat. As I brought the heat up to where I had it before I noticed a change in the sound. I backed the depth off a little. And tried again. The reduction in noise is phenomenal. From low heat to the higher level. So once I a get another new stylus. I should have a real quiet groove. Smile

I was running the current at up 500ma with no problems. The highest current yielded the quiest groove.

The disc I cut tonight plays good even with the dull grooves. So I just cut a worn record. Save the time of wearing it out. Very Happy

Doug

JayDC · Posted: Thu Feb 07, 2008 4:35 am Post subject:

doug-
are you using the microgroove advance ball?.. I think thats what it's for.
Please send me the plans for the dash pot assembly, if you get a chance..

Doug 6N · Joined: 21 May 2007 Posts: 66 Location: Washington

Hi:

Last night I found the problem. This is just insidious. The very end of the stylus clamping screw is bent when I tightened the screw the stylus would twist a few degrees. So no matter what I did the angle and cut was wrong. I had gone over the whole carriage and finally took the head off and apart. Then I saw what was happening when I tightened the stylus. No way to see that with the everything assembled. I took the setscrew from my K8 and put that in. Reset everything and it works just fine now. I have now been cutting 33Rpm with 224 LPI leadscrew and no issues. Plus one heck of a lot better sound.

Thanks sincerely for all the suggestions. I used them all. Smile

Doug

JayDC · Posted: Fri Feb 08, 2008 1:52 am Post subject:

It's funny how the littlest things can make this process go to poop Laughing