Your question, exactly, was:
What is the margin of error we are willing to tolerate?
To which the answer could well be something unachievable. But +/- 50µm seems a fair answer and a good target. Put another way that would be tolerable from a test perspective, and any better than that seems unnecessary to ask for.A recent run of a small 7" pressing some colleagues and I had done recently has a slightly undersize hole which is centred +/-60um on one side and +/-40 on the other side by measurement, without asking for anything special. Could just be luck, but they are consistent across copies.
An undersize hole helps a lot.
At the end of the day we might well have to compromise, certainly against standard specs. But it's well worth pursuing to get as good as possible, and worth paying a premium for if necessary. Knowing what is 'tolerable' can only help, especially from being excessive with requirements. All IMHO, of course.
LD
Last edited:
I imagine that at least one product has appeared in the last 67 years, which accurately centers an LP record upon a spindle-less turntable platter, and then reliably clamps it in place via weight or vacuum or both. Why not resurrect this product and use it as step 1 of a two step process, in which we drill a spindle hole ourselves, with great accuracy?
Yes, I have not looked in a while but the the cheap sound I/O's for it are perfectly sufficient for our purposes and it runs Python natively. I'm sure a savvy member could create a turnkey SD card image that runs the entire set of tests.
Give me some time. Moving in the next few days, but working on a solution to this.
Probably a week or so at least till I'm back to "normal".
Have you an example or suggestion of such a tool? It sounds really neat if there is one!
This technology must exist, laser machining equipment exists that can drill holes far beyond the accuracy we need. A problem I see is that the outside edge of the LP after stamping is probably not a good measure for finding the exact center so I can't see a perfect solution without some custom tooling which IME blows the budget.
I might be able to help with this part, feel free to pm me about it.
Well, the variance on the stamper centering should more or less set the possible variance. The more off this is, the variance compounds.
I think the precision of the stamper is the key, as the errors seem to be very similar within the same pressing from my experience.
What is interesting is some discussion I had with a plant technician which I'll reproduce below. He suggested a "book mold" process which I have never heard of until now, which he suggests will provide better results from an automatic machine.
----- his response below ------
There are a few parts to the equation of how centered a record is. The first is the stamper. As you likely know, this is a manual step using optics. Have you discussed your tolerance range with any plating facilities?
The next part is the pressing machine. On any automatic pressing machine, one mold is stationary. So, the centering on this side is fixed based upon the stamper on that side. Again, on automatic pressing machines, the other mold is not stationary – it moves, both laterally and horizontally. So, there will be a very slight variance in terms of centering on whichever stamper is mounted to that mold. When you refer to “guaranteeing” a set variance, that would not be possible. Based upon my experience, I would not think any pressing plant using automatic pressing machines would be able to candidly/honestly provide such a guarantee.
Conversely, on manual pressing machines, a “bookmold” is used. There is no horizontal movement on either side of a bookmold. So, it sounds like this type of mold would be best for your project. We do have a single manual press. But, again, the centering of each side will depend heavily upon who (and where) the plating is happening, or more specifically, the stamper centering.
That last part of the equation is how exactly you are measuring the tolerance. Are you referring to a reticle measurement that is independent of groove spacing (for example, if I measure my lock groove in this manner, it would provide a repeatable and quantifiable figure regardless of whether the side was cut at 400LPI or 100LPI). Is this how you came up with your measurements?
Last edited:
Also, anyone ever poke around in here?
The Secret Society of Lathe Trolls • Index page
Some very interesting stuff.
The Secret Society of Lathe Trolls • Index page
Some very interesting stuff.
I added a folder for Software in the Test LP repo.
It can be found here.
If Scott wants to pop it in there temporarily until we find a more permanent home, may help others from digging around in the dark-thread.
Like the dark-web, only weirdos, deviants and criminals go more than 30 pages back. ;-)
For now the work we've done is in the turntable speed stability thread, my 93 yr. old mother has had a bit of a downturn so I might be a while with updates.
Basically we used Python to read .wav's of the tracks on the LP and then have essentially the entire open source signal processing library at our disposal. Right now only the radial display of turntable speed stability is implemented but IMO this is by far the most difficult.
Last edited:
How about a magnetic platter, and using a (strong) magnet to fix the record in place once it is prfectly centered (no spindle, obviously)? Or, use a screw-on clamp with a oversized center hole?
The next question is - how to center it perfectly? Here , Scott had a IMHO brilliant (if somewhat unnoticed) idea in this thread: using a closed track (no lateral movement of the cutter head) and a USB microscope, one could assess eccentricity by turning the platter by hand and shifting the record until it is centered. Now, how to shift a record on the platter by e.g. 10um steps is another question......
Thoughts?
I've been looking at microscope options on and off. Obviously a lathe microscope with reticule is the ideal solution, but could be pricey. USB microscope is cheaper and takes up less space, but the you need either a TV or laptop to plug it into and they don't come with reticules from my searches.
This is so cheap it can't possibly work, so of course I will have to buy it to test
Digital Portable HD 1-600X 3.6MP Microscope Continuous Magnifier 4.3Inch Display | eBay
The nudging part for me is easy at least on one of my tables.
This is so cheap it can't possibly work, so of course I will have to buy it to test
Digital Portable HD 1-600X 3.6MP Microscope Continuous Magnifier 4.3Inch Display | eBay
The nudging part for me is easy at least on one of my tables.
Print a stick on reticle with a labeler and special characters and put it on the top of the cart. There is a USB microscope with a good solid mount now sold through Elector.
Maybe talk to this guy, he is a hobbyist who just happens to have access to an electron microscope. He made a video (which is actually a series of stills) of a stylus "playing" a groove.
The video goes into detail as to how he made the stills, and it's quite interesting but really all you need for this project is to view the brief video at the beginning. Maybe one of the images (they are all quite similar) would be appropriate.
The reason I think this might be a good option is I think, due to the nature of his work, that he might be open to a license to use the image(s) at no cost to us.
We don't necessarily have to have such an image as the front cover; it could appear anywhere at any size. But such images are "neat" and appropriate for the project.
YouTube