Optomechanical hybrid lathe

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skynext
Posts: 2
Joined: Mon May 22, 2017 9:35 am

Optomechanical hybrid lathe

Post: # 46933Unread post skynext
Mon May 22, 2017 4:27 pm

Hello, as a first message on the forum, I had the following design in mind for an edgy tech...

Basically it comes down to an hybrid mechanical cutting head mount where the needle is replaced by a laser.
However, the design is hybrid because there is still a couple of audio transducers on the head mount at a conventional orthogonal setup.

Hybrid because cutting is divided into an optical domain and mechanical domain.

mechanical domain : only for L/R stereo image reproduction : the laser is driven through sideways vibrations and cuts a groove with excursions normal to the groove direction.

optical domain : for signal amplitude only : since the laser would deviate vertically of a ridiculous amount compared to the inverse square law of light propagation power, this setup would not do any good for signal amplitude (groove depth)

So the basic idea would be to : attach a feedback sensor (magnetic pickup like a guitar ?) to the laser mount that would pickup the vertical deviations, amplify, and modulate the laser output based on that drive. laser closer to the vinyl, increase power, laser further, decrease power.

So now, question time :
Was this design already discussed before ?
Does this seem doable / sensible to cutting experts ?

Thank you.

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markrob
Posts: 1623
Joined: Wed Nov 28, 2007 1:14 am
Location: Philadelphia Area

Re: Optomechanical hybrid lathe

Post: # 46936Unread post markrob
Mon May 22, 2017 5:33 pm

Hi,

As you describe it, I don't think so. Do you understand the the geometry required for a proper groove to be cut? How will the laser create this? Is your system vertical/lateral with matrix to encode the 45/45 system in use? Have you considered the small size of the groove wall features that need to be cut so that high frequency information 50-70 db below operating level are recorded? I'm not sure I follow the feedback system you are describing. Is its purpose to control the power level of the laser due to warps in the recording blank? I think more details are needed to evaluate this.

Mark

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skynext
Posts: 2
Joined: Mon May 22, 2017 9:35 am

Re: Optomechanical hybrid lathe

Post: # 46940Unread post skynext
Mon May 22, 2017 6:53 pm

Yes, i understand some of the issues...
first the laser beam geometry, lensing may be required to focus the beam if it is too divergent. I may even have to make an adaptative lensing to control the precise laser beam geometry.

And of course, there is the fact that a laser uses radiated energy that will "melt" the acetate instead of carving it.
Ideally the energy and focus should be adjusted so as it sublimates the media instead of burning/melting it on place where it would re-solidify.

So basically i think of two issues :

beam geometry : stable or adaptative
average beam energy (and laser wavelength - shorter wavelength - greater details)

For the capture of mechanical amplitude excursion with an analog device I think you're right it is a recipe for a lot of distorsion, but would be a "simple" method...
The other approach would be to modulate the beam with a processed image of the signal to extract the amplitude information (it may be more complicated than that I am certainly not an expert sound engineer), but I am sure that complex algorithms will probably be necessary and could induce delays if not well compensated)

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markrob
Posts: 1623
Joined: Wed Nov 28, 2007 1:14 am
Location: Philadelphia Area

Re: Optomechanical hybrid lathe

Post: # 46942Unread post markrob
Mon May 22, 2017 6:58 pm

Hi,

I just don't think the resolution can be obtained by melting with a laser. I say get to work and build up a prototype to demonstrate proof of concept. FYI, the details that must be cut are on the order of a wavelength of visible light in size. If you run the numbers, you'll see.

Mark

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SRSanford10
Posts: 7
Joined: Fri Aug 14, 2009 9:26 pm
Location: Long Beach, California

Re: Optomechanical hybrid lathe

Post: # 47026Unread post SRSanford10
Fri Jun 02, 2017 4:07 pm

You might want to take a look at "RCA Review" in the period of 1979 to about 1984 (I don't have the exact issue in front of me). In one of these there was a detailed description of a laser based mastering system for the RCA CED videodisc. The recording medium was photoresist on a metal substrate. It was capable of making shallow groves and modulating them with an FM TV signal. They had the same problem which Markrob pointed out wherein the recorded signals needed to be smaller than the wavelength of the laser recording them. They had an interesting way of solving this. You can find "RCA Review" in any large university engineering library.SRSanford10
SRSanford10

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JJZL
Posts: 25
Joined: Wed Mar 04, 2015 5:05 pm

Re: Optomechanical hybrid lathe

Post: # 47033Unread post JJZL
Sat Jun 03, 2017 8:02 am

E. O. Keizer, "VideoDisc Mastering," RCA Review, vol. 39, No. 1, Mar. 1978, pp. 60-86.

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Gridlock
Posts: 286
Joined: Tue Jun 21, 2011 6:41 pm
Location: eugene oregon

Re: Optomechanical hybrid lathe

Post: # 47035Unread post Gridlock
Sat Jun 03, 2017 11:53 pm

Good luck experimenting and innovating while getting toxic fumes everywhere lol. "giant later" I vote against lasers dude ALL THE WAY.
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Recordette Sr.......Presto K-8

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