Looking for some information

This is where record cutters raise questions about cutting, and trade wisdom and experiment results. We love Scully, Neumann, Presto, & Rek-O-Kut lathes and Wilcox-Gay Recordios (among others). We are excited by the various modern pro and semi-pro systems, too, in production and development. We use strange, extinct disc-based dictation machines. And other stuff, too.

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grooveguy
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Looking for some information

Post: # 46056Unread post grooveguy
Fri Feb 10, 2017 3:37 pm

Greetings, guys,

In building a new, 'from scratch' lathe, I'm looking for information on how best to locate the cutterhead pivot. In his book, The Recording and Reproduction of Sound, Oliver Read goes into some detail on this, coming up with numbers (for a particular head) for best vertical stability; that is, the least tendency for the head to go into a bouncing oscillation. In his book, the head was pivoted one inch off the disc surface and two inches behind the stylus.

My own Rek-O-Kut M5S lathe pivots the head 1-1/4 inches off the disc surface and four inches behind the stylus. My recollection is that the smaller, M12S had a similar vertical pivot point, but the pivot was closer to the stylus. The M12S used a counterweight, but the larger M5S uses a spring, only, to set the depth of cut.

Anyway, I wonder if I could ask what YOUR lathe does in this regard? I'm particularly interested in the pivot location for the Presto 6N, as it seems to be the benchmark, so to speak, for 'semi-pro' (as opposed to 'mastering') overhead types. But I'd be grateful for numbers from other Presto, Fairchild, ROK, RCA, etc., all of which were probably designed around cutterheads that were similar in size and weight to Presto 1Ds.

Many thanks!

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rsimms3
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Re: Looking for some information

Post: # 46083Unread post rsimms3
Sat Feb 11, 2017 10:30 pm

For the Presto 8N and similar the pivot point above the disc varies since you can adjust the height to best match your needs for angle, etc. based on the head you are using. The distance from the stylus to the pivot point on my Presto Recorder overhead (early version of 8N style) is 2 1/4". This is with a Grampian Type C head.

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grooveguy
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Re: Looking for some information

Post: # 46084Unread post grooveguy
Sat Feb 11, 2017 10:39 pm

Thanks, rsimms3!

I recall that at least the Presto 8DG had a wide vertical 'position' adjustment range so that it could accommodate thick wax masters, which were still in use by some mastering houses when that lathe came out. Out of curiosity, however, when your Grampian head is adjusted for a near-vertical relationship to the disc, where is the pivot re: the disc surface? Thanks!

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jesusfwrl
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Re: Looking for some information

Post: # 46109Unread post jesusfwrl
Tue Feb 14, 2017 11:42 am

Good question, but the answer would be very long and complicated.

If you are considering mono heads only, then the important difference between them would be the mass. Stereoheads will have a certain degree of vertical compliance, which further complicates the calculation.
In practise, mono heads will have a vertical compliance as well due to the stylus shank and other parts of the head not having infinite rigidity, but this is a small part of the calculation. The rest is simply a matter of applying the physics for a mechanical oscillation, for which the important factors are the mass of the head, the spring rate, assuming that you are using a spring, and the distance from the pivot point to the centre of mass, which in many cases of mono heads, can be approximated as the pivot to stylus distance. You also need to factor in gravity, of course.
This will give you the frequency of oscillation, which all such systems exhibit. While these parameters could be fine tuned to achieve a low tendency of oscillation when cutting, in practise you can only cut very soft materials without further radical measures to prevent oscillation. To keep it short and simple, there are many other factors that should influence the correct placement of the pivot point relative to the stylus, which are far more important than the tendency to oscillate, if you are aiming for the ultimate fidelity.

When designing a professional lathe for high quality work, the pivot to stylus distance is defined by all the other considerations, and then the relevant calculations are made to design an adequate means of damping to actually control the oscillation. In most cases, of more modern lathes, this takes the form of an oil dashpot.

It is not necessarily a good idea to look at other lathes for inspiration on this, even the pro lathes could be made a lot better in this respect. I have experimented a lot with suspension units but I need to find some time for more experiments to reach reliable conclusions. In the meantime, I would direct you to literature regarding machine tools, in particular the cutting operations used in metal working. Most of these factors have never been discussed in disk recording literature.

In the end of the day, a disk recording lathe is simply a machine tool cutting a spiral groove at the desired pitch with extreme levels of accuracy.
~~~ Precision Mechanical Engineering, Analog Disk Mastering ~~~
Agnew Analog Reference Instruments: http://www.agnewanalog.com

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grooveguy
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Re: Looking for some information

Post: # 46110Unread post grooveguy
Tue Feb 14, 2017 12:10 pm

Many thanks, Jesus,

Indeed. The deeper I look into this, the deeper the understanding needs to be. Nothing is ever simple.

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markrob
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Re: Looking for some information

Post: # 46111Unread post markrob
Tue Feb 14, 2017 1:30 pm

Hi,

Have you read the H. Davies paper, "The Design of Hi-Fidelity Disk Recording Equipment"? He does a nice job discussing the tradeoffs. If you don't have a copy PM me with your email and I'll send it along.

Mark

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Fela Borbone
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Re: Looking for some information

Post: # 46114Unread post Fela Borbone
Tue Feb 14, 2017 4:50 pm

Hi,
In the AES anthology on disc recording, theres an article about the Hidrofeed lathe and comments a few words about the pivot placement...
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grooveguy
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Re: Looking for some information

Post: # 46115Unread post grooveguy
Tue Feb 14, 2017 5:16 pm

Thanks for that, Fela,

Deviating somewhat from the original question, I also have wondered over the years whatever happened with the "Hydrofeed" lathe idea. I have a 1950s-vintage Popular Science test record that was ostensibly recorded on one of these, with a very brief explanation on the jacket of how it worked. Simplicity itself, it seems, and might be worth some study. There are all manner of aircraft-grade hydraulic cylinders to be had on eBay, and feeding oil under pressure in on one side of the piston, and letting oil bleed out the other side through a needle valve surely seems easy. A small reservoir of oil under compressed air pressure with a manual pump to push the piston the other way would be how I'd do it, but I don't know enough about hydraulics, valves, check-valves and the physics of all this to undertake it. Should be quiet, though.

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Bahndahn
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Re: Looking for some information

Post: # 46116Unread post Bahndahn
Tue Feb 14, 2017 6:23 pm

Hello,

Cool question about the pivot point. Seems like you are on your way to designing a nice machine. Looks like the suggestions and literature above have you covered on this question for the most part.

Now for the other:
grooveguy wrote:Deviating somewhat from the original question, I also have wondered over the years whatever happened with the "Hydrofeed" lathe idea. I have a 1950s-vintage Popular Science test record that was ostensibly recorded on one of these, with a very brief explanation on the jacket of how it worked. Simplicity itself, it seems, and might be worth some study. There are all manner of aircraft-grade hydraulic cylinders to be had on eBay, and feeding oil under pressure in on one side of the piston, and letting oil bleed out the other side through a needle valve surely seems easy. A small reservoir of oil under compressed air pressure with a manual pump to push the piston the other way would be how I'd do it, but I don't know enough about hydraulics, valves, check-valves and the physics of all this to undertake it. Should be quiet, though.
The main trouble with this idea is that suddenly you need a whole other system– a hydraulic one. This means pumps, tubes, oil, fancy regulators, and so on. Positioning accuracy? Looks like you need a feedback system in there. Things are getting complicated fast here. I always appreciate the suggestion of uncommon techniques for doing things, but this one seems to be more work than it's worth. Yes, it could be done, like anything, but I don't think it's the best use of your R&D time.

I'm not going to shut down your idea without providing an alternative:

In my mind, the best possible record lathe cross-feed system is known as the "voice coil linear actuator" or something of that sort. To my knowledge, this hasn't been used where we are talking about using it, however, it is almost present in the electronic depth actuator on high-end auto depth systems yet those are said to be solenoids.

To give you a visual reference:
Screen Shot 2017-02-14 at 6.17.30 PM.png
These puppies can be made as a closed loop system. One of their strong points is that there is no physical contact–no sliding, rolling parts that are responsible for the force. Yes, they can be made PLENTY strong, and with a closed loop system your accuracy can be tuned to a resolution superior to most other linear actuation mechanisms. I can't offer you much more information as I leave that up to the EEs.

Best wishes on your design.
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grooveguy
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Re: Looking for some information

Post: # 46118Unread post grooveguy
Tue Feb 14, 2017 7:27 pm

Thanks, Bahndahn,

I'm sure you're right about jumping the fence into hydraulics.

Actually, I'd thought about using one of those linear actuators to lift the head off the disc. For me it is probably easier than figuring out some sort of lever and cam arrangement, and it can be automated with the spiral-out/lockgroove command. Probably doesn't need to be closed-loop, just ramp the voltage up and down. I'm having parts made by various machinists for this project, but the "little stuff" (miscellaneous leftovers) will be hacksaw and drill press items, maybe to be replaced later with pretty ones.

This is a "bucket list" project, and I'm spending money like the proverbial drunken sailor to make it happen. I've been cutting records for more than 60 years and have always wanted to build a lathe from scratch. We'll see if it works.

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Bahndahn
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Re: Looking for some information

Post: # 46119Unread post Bahndahn
Tue Feb 14, 2017 9:48 pm

grooveguy wrote:This is a "bucket list" project, and I'm spending money like the proverbial drunken sailor to make it happen. I've been cutting records for more than 60 years and have always wanted to build a lathe from scratch. We'll see if it works.
Wow! This is an exciting project. If you feel inclined to, be sure to document it here as I'm sure many people will be totally enthused.

I guess I'm left with wondering what sort of 'innovation' you aspire for in your build, for its clear that you are willing to entertain some out-there ideas like the hydraulic system. There are many ways of building a great lathe that works wonderfully, yet there are just as many ways you could alter the norm.

If I may add a couple random ideas about building machines they are:

-Don't forget about composites: Resins and fillers [epoxy granite!], ceramic and stone-like sorts [polymer concrete!], etc. that are casted.

-Consider unusual sources for manufacture: Need some granite for a solid base? Go to your local tombstone factory. The average polished tombstone is easily within 0.005". Countertop manufacturers also should be considered– they have perfect little pieces of precise stone from cutting out sink openings and the like.

-Consider picking up a copy of Machinery's Handbook if you don't already have one.

Attached are some course notes from one of my favourite [mechanical,in my case] engineering educators. Some fun ideas within :!:
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jesusfwrl
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Re: Looking for some information

Post: # 46125Unread post jesusfwrl
Wed Feb 15, 2017 10:37 am

Wasn't the Cybersonics advertising literature mentioning a linear actuator being employed for the feed?
The hydraulic system concept is a most excellent idea, although if used to increase performance, it is bound to also increase cost and complexity.
I am personally a very big fan of the idea of using a hydraulic system for a super silent feed, although it would certainly be a bit tricky to implement. The hydrofeed lathe description sounded a bit too basic, there are many other ways of implementing hydraulic actuators, with or without feedback systems, for very controlled and very accurate motion. You would still need a very precise bed and guide system though. This is the hardest part to make.
~~~ Precision Mechanical Engineering, Analog Disk Mastering ~~~
Agnew Analog Reference Instruments: http://www.agnewanalog.com

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grooveguy
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Re: Looking for some information

Post: # 46126Unread post grooveguy
Wed Feb 15, 2017 1:52 pm

I just now took a look, and that Popular Science test record is dated 1957, 'Recordio days' for me. I was nonetheless enthralled with the presumed simplicity of a hydraulic feed, and even had thoughts of using a common rotary hydraulic door-closer to make a 'swing-arm' recorder of some sort, which never happened. Although the concept of cylinders and oil is intriguing, with the plethora of linear-feed mechanisms available on eBay for DIY CNC projects, it would appear to be cheaper and faster to put something together based on the traditional lead screw, I think. Nevertheless, if someone wants to proceed along the lines of the Hydrofeed, my hat is certainly off to them, and I eagerly await news of their success.

Looking at the oversimplified 'concept sketch' of the 1956 system description, it's easy to see how an enthusiastic teenager might have been wooed in this direction.
Snap1.jpg
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