Charts...Disc cutting timing per LPI at 3 speeds

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Charts...Disc cutting timing per LPI at 3 speeds

Unread postby Steve E. » Sun Jul 13, 2008 7:57 pm

UPDATE: A significant revision of this chart appears later in the thread. As always, room for improvement. I think there should be an even more conservative version:

viewtopic.php?f=9&t=824&start=20#p30702

I am leaving all versions up as tastes vary.

******

I am trying to figure out my max possible cutting time using various lines per inch (LPI), as I figure this will help me make certain decisions about which new feed screws I want manufactured.

I came up with this data based on theory (and one research source) as opposed to experience. I am using the Presto 6N as my guide. In the case of the Presto, the absolute max inner cutting diameter seems to be 4 1/8 inches (or 10.5 cm). I am unclear as to whether the run-off groove can extend beyond this point because the lathe is not yet fully functional. (anyone know?) (EDIT: It appears that on the Presto 6N, That's IT.)

I have a xerox of a "Disc Cutting Timing Chart" circa 1964 or so, from the long- departed *Impact Sound Recording Studio of 7102 1/2 Castor Ave in Philadelphia, Pennsylvania, 19149 USA. Their data looked pretty close to this chart (I've evened out the seconds so they make strictly consistent mathematical sense):

Image

I prepared three other versions of the chart based on extreme and "safer" estimates of the potential running times at each feed screw size. Can anyone confirm which of these (if any) is most accurate? Thanks.

Notice that on this next chart, recording a 12 inch 33 1/3 rpm record gives you LPIs that are numerically related to the running time in minutes. (120 LPI gives you slightly over 12.0 minutes running time, etc.)
Image

Image

Image

EDIT: By the way....here is the original sheet I based this on. In both its unaltered form, and with my scribbles:

http://www.steveespinola.com/lathetrolls/resources/Impact-Sound-Disc-Cutting-Timing-Chart.pdf

EDIT: Charts were updated October 10, 2012.
My original charts can be found here, in case anyone prefers them:
http://www.steveespinola.com/presto6n/lpi1.gif
http://www.steveespinola.com/presto6n/lpi2.gif
http://www.steveespinola.com/presto6n/lpi3.gif
http://www.steveespinola.com/presto6n/lpi4.gif


* Impact Sound was owned by an engineer named Tony Schmidt, who operated it out of a basement underneath a (his?) shoe store. It is now known in soul music record collecting circles for Phil Gaber's productions, from perhaps 1964 to 1971.
Last edited by Steve E. on Wed Oct 10, 2012 7:58 pm, edited 3 times in total.
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Unread postby Doug6N » Mon Jul 21, 2008 11:31 pm

Hi Steve:

I have a Presto 6N and it can only cut to around 4" on the diameter so your 4 1/8 is right. I just never precisely measured it.

Now to drive you nuts. How about a chart taking that into consideration for us 6N users, :) :)

No! You really don't have to do it. But ya got to admit it would be kindof handy.

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Unread postby Steve E. » Tue Jul 22, 2008 6:23 pm

After the first of the four sections, this chart _is_ for Presto users! :) On my unit at least, 4 1/8 is the innermost groove, not 4 inches.

I am hoping that someone who has one o these units that is fully functional can corroborate some of my timings. Thank goodness I finally got a response. ;) more, more!
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minimum recording diameter on a 6N

Unread postby Charles Bork » Wed Jul 23, 2008 10:15 pm

Steve wrote:

> I am unclear as to whether the run-off groove can extend beyond this point because the lathe is not yet fully functional. (anyone know?) (EDIT: It appears that on the Presto 6N, That's IT.)

There are two ways to extend the travel of the cutterhead on a 6N so that lock grooves as small as 3.5" in diameter are possible.

The problem is that most standard 6N lead screws have a thread just long enough for a 12-inch lp lead-out/lock-groove. But not long enough for a 7-inch 45 with its smaller diameter label and lock groove. However, I have two that are long enough (a 120 and a 160). I would guess these were introduced in the 50s when 45s became popular.

So, one way to solve the problem is to get or make lead screws with an extended thread range.

The other is a little clunky, but works quite well. Just attach the head to the left of the normal mounting slots. About half and inch to the left. The next slot over, as it were. This will cause the head to hang off in space to the left the standard position. But it works if you use longer mounting screws and a metal brace behind the mount--just a straight piece of metal with two holes for the head mounting screws--which functions as a clamp. Perhaps not the most elegant solution, but an easy one.

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Unread postby Steve E. » Thu Jul 24, 2008 2:11 pm

Charles, both of these sound potentially excellent. Even the extended thread screw idea is in the realm of possibility when we find a machinist and get the feed screws made.

The problem I predict is the cutting head bumping into the flange. (The flange is the 2 1/2 inch piece that fits over the label and drives the worm gear that drives the feed screw.) First, I picture the bottom of the head scraping the flat part of the flange. Does the head clear that when correctly mounted? Mine, as mounted when I received it, definitely wouldn't.

In the case of moving the head over, I also see a risk of it crashing into the sticking-up part of the flange if one is not careful. I could imagine damage to the feed screw, or to the thin blade which travels on it, if this happens. Were you simply careful or is there a safety measure to protect from this happening?
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minimum recording diameter on a 6N

Unread postby Charles Bork » Thu Jul 24, 2008 3:02 pm

> The problem I predict is the cutting head bumping into the flange. (The flange is the 2 1/2 inch piece that fits over the label and drives the worm gear that drives the feed screw.) First, I picture the bottom of the head scraping the flat part of the flange. Does the head clear that when correctly mounted?

Yes. Presto 1-C and 1-D heads with long-shank styli and Grampian Type C and Type D heads with short-shank styli will clear the stock 6N flange. I have also conducted some experiments with Presto heads using short-shanked styli. A modified or substitute flange of with a diameter of less than two inches (or a height of .1") is required because of the low-clearance of this configuration. I have had my local 6N-friendly machinist make one of these.

> In the case of moving the head over, I also see a risk of it crashing into the sticking-up part of the flange if one is not careful. I could imagine damage to the feed screw, or to the thin blade which travels on it, if this happens. Were you simply careful or is there a safety measure to protect from this happening?

One does need to be careful. But that is true of record cutting in general. If your ruler is correctly marked you won't have a problem. I have never run the carriage into the spindle. I think I have at least 30 seconds (depending on pitch) to spare beyond the placement of the the lock groove. Also, if you make lead screws, you can have the thread end just before a collision would occur. But I probably wouldn't bother with that. As I say, I have never had a problem.

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Re: minimum recording diameter on a 6N

Unread postby Steve E. » Thu Jul 24, 2008 7:51 pm

Charles Bork wrote:>
I have had my local 6N-friendly machinist make one of these.


Tell me more about this "local 6N-friendly machinist'. ;) I have not settled on a machinist yet.
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Unread postby JayDC » Thu Feb 24, 2011 4:19 pm

Can some one help me with some math.. I want to take the 45 chart, and make a tube insert for the presto.. I want to find out how long in inches is a minute based on the lpi? Then i can design the tube insert in photoshop, and post it here..
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Unread postby markrob » Thu Feb 24, 2011 8:17 pm

Hi,

RPM / LPI = Distance_minute

For example, if you you run 45 rpm, then there will be 45 revolutions of the platter in one minute. If the lead screw pitch is 45 LPI, then you just moved 1 inch in one minute.

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Unread postby cymbalism » Thu Feb 24, 2011 8:58 pm

markrob wrote:Hi,

RPM / LPI = Distance_minute

For example, if you you run 45 rpm, then there will be 45 revolutions of the platter in one minute. If the lead screw pitch is 45 LPI, then you just moved 1 inch in one minute.

Mark


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Unread postby JayDC » Thu Feb 24, 2011 9:32 pm

cymbalism wrote:
Check out the big brain on Mark :) as Samuel L would say hehe


I know, it's pretty awesome to have access to people smarter then yourself.. Thanks mark..
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Unread postby Steve E. » Mon Jun 25, 2012 3:27 pm

Hey, I'm about to upgrade these charts. A few more LPIs on each end. Better subdivisions so it is easier to read.

I'm adding 24, 48, 264, 272 and 296 LPI. (24 and 48 for puzzle records/parallel grooves.)

Also, I wonder about the amount of cutting space I'm claiming for 7" records. I think the "Extreme" version should allow for more time. Requests? I have records that use at least 1 1/4 inch, so I'm thinking 1 1/8", 1 3/16", 1 1/4".
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Unread postby tragwag » Mon Jun 25, 2012 4:06 pm

Steve E. wrote:Hey, I'm about to upgrade these charts. A few more LPIs on each end. Better subdivisions so it is easier to read.

Also, I wonder about the amount of cutting space I'm claiming for 7" records. I think the "Extreme" version should allow for more time. Requests? I have records that use at least 1 1/4 inch.

i'm not super up on the math with any of this,
but today I was cutting over 7 min on a 7in with a 224 lpi
I'm thinking it was because there was more cutting space?
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Unread postby opcode66 » Mon Jun 25, 2012 4:16 pm

I've cut 6 minute projects on 10" Master Lacquers for a 7" pressed release. It all has to do with the levels and the depth of cut. If you want to cut loud (0 VU to +2 VU or in the red) then you obviously will eat up lateral disc space quickly. On a fixed pitch system, loud cuts with LPI set too high will produce overcuts. Without a scope on the lathe you wouldn't be able to tell if you are overcutting or not (unless you hear distotion/pops/skips on playback). For sure you can cut at higher LPI and but, if the audio is loud enough, on a fixed pitch system, you will have overcuts.

So, saying you cut 7 minutes to a 7" doesn't tell the whole story. Where were your peaks on the meters? What depth of cut (width of groove) were you cutting at? Certainly you can't get 3 mil grooves and peaks around 0 VU and cut 6 or 7 minutes on a 45. The best I've ever got at hot volume and deeper cut was 4 minutes. But, -3 to -4 VU peaks and 2 mil groove I can get 6 to 7 minutes. But, I do have a variable pitch system as well.
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Unread postby Steve E. » Mon Jun 25, 2012 5:32 pm

I just looked at my 45 of the Beatles' "Hey Jude", which was a famously long 45 in its day. 7:11 mono taking up 1 1/8 " of the surface. But I also have Mad Magazine's "A Super Spectacular Day" flexi which uses 1 1/4" of the surface.
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Unread postby Steve E. » Thu Oct 11, 2012 11:21 am

Note that the charts have been updated (at top).
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Unread postby tragwag » Thu Oct 11, 2012 11:33 am

I'm going to print and frame these charts soon.
I look at them every day!
Thanks Steve :)
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Unread postby Steve E. » Thu Oct 11, 2012 4:21 pm

You are welcome. Again, I'd love ongoing feedback on which of these charts seems experientially most useful and accurate, and on any further recommended tweaks.
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Unread postby opcode66 » Thu Oct 11, 2012 4:45 pm

For me, with variable pitch and cutting loud so 3 to 3.5 mil grooves, the chart work with some modification. I look at the chart for length of time, diameter and rpm. That gives me an initial lpi. I then move up the chart two or three lines depending on how loud I need to cut. That gives me a great estimate of my base pitch. From there I do dry runs and tweak it just so.
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Unread postby Steve E. » Tue Oct 16, 2012 8:20 am

opcode, which of the 4 do you do this with? and cool!

If I made the "effective cutting space" on the 12" 3 1/3 inches, then the running times for a 12" record would exactly match the LPI. 120lpi = 12 minutes, etc.
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