Whats the most efficient cutting speed?

Anything goes! Inventors! Artists! Cutting edge solutions to old problems. But also non-commercial usage of record cutting. Cost- effective, cost-ineffective, nutso, brilliant, terribly fabulous and sometimes fabulously terrible ideas.

Moderators: piaptk, tragwag, Steve E., Aussie0zborn

Post Reply
User avatar
evildrome
Posts: 59
Joined: Wed Jun 21, 2017 6:55 am

Whats the most efficient cutting speed?

Post: # 47797Unread post evildrome
Mon Sep 11, 2017 6:35 am

I come from a metal turning background.

If you're cutting metal on a lathe there is usually a sweet spot speed for a particular metal with a particular amount of tool infeed.

Modern CNC lathes speed the job up as the diameter reduces to stay on this optimised "surface speed".

As cutting records is a similar process, one imagines there will be an optimum cutting speed which produces the best surface finish but which may not be any of the recognised standard playback speeds.

I know that older record lathes have very accurate main motors which hold one speed very well.

It seems to me that (nowadays) this is unnecessary. All that is necessary is to accurately know the speed of the motor and then control the lathe leadscrew appropriately.

This would mean that you could optimise the cutting process to suit the material and the music.

Thoughts?


Wilson.

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

Re: Whats the most efficient cutting speed?

Post: # 47798Unread post markrob
Mon Sep 11, 2017 10:04 am

Hi,

All of that goes out the window in this realm. Since we are cutting a spiral at a constant angular velocity, the linear cutting velocity changes quite markedly as you move from the outside diameter to the inside and over different platter RPM settings. In a professional setup, the cutting spiral pitch is variable based on the loudness of the program material. This is done to maximize the recording time of a cut (soft sections can be spaced closer together). In a stereo cutting setup, the depth of cut is also controlled to keep loud out of phase (vertical) information from cutting too deep or narrow. So the cutting process has to be (and is) tolerant of these variables. The feeds and speeds calculations done in the machining world are done to optimize not only surface finish, but also provide for maximum production throughput and tool life. In this application, the production rate is fixed (the cutting time of the side) and the tool life is what it is as long as the results are a good low noise cut with proper geometry.

One other thing that might not be apparent is the extreme fineness and quality of the surface details that are being cut. If you do the math, you will find that the system must cut surface details that are measured in distances of 100's of nano meters. That is in the order of light wavelengths.

Mark

User avatar
evildrome
Posts: 59
Joined: Wed Jun 21, 2017 6:55 am

Re: Whats the most efficient cutting speed?

Post: # 47813Unread post evildrome
Wed Sep 13, 2017 8:12 am

Thanks Mark,

I found this which was illuminating...

https://www.alchemymastering.com/half-speed-vinyl-mastering

It appears there are advantages and disadvantages to different speeds although the reasons are as you explained them and not as I thought ! :)

Cheers,

Wilson.

User avatar
fredbissnette
Posts: 383
Joined: Tue Oct 11, 2016 5:38 pm

Re: Whats the most efficient cutting speed?

Post: # 48209Unread post fredbissnette
Tue Oct 24, 2017 1:08 pm

it depends on your lathe

i have a diy with a rim drive deck and i can cut in real time but if i want perfect wow free audio i cut at 33 with the audio slowed to -26 % to play back at 45 and i get really high quality audio.


cheers
Instagram @styluspressurerecords

User avatar
karl hungus
Posts: 19
Joined: Sun May 03, 2020 5:54 am

Re: Whats the most efficient cutting speed?

Post: # 57759Unread post karl hungus
Tue Feb 09, 2021 1:24 pm

@fredbissnette
Just curious, how is dropping to 33 giving you less wow and flutter? Is there something particular to 45 on your machine, or is this a universal issue that 45 rpm introduces more w&f from mechanics/physics?
I’ve been thinking about this option vs 1/2 speed, to not lose as much bass info on the pitch down, and it’s encouraging to hear that its working well for you.

User avatar
dmills
Posts: 190
Joined: Sun Jun 16, 2019 3:33 pm
Location: Uk

Re: Whats the most efficient cutting speed?

Post: # 57767Unread post dmills
Wed Feb 10, 2021 11:13 am

Torque limitations I would expect.

The major reason to cut at low speed is to limit the amount of power needed to cut high frequency, and hence cutter head heating.

The force produced on the cutting head my the modulation is linear with current, and acceleration is linear with force, but for a given velocity acceleration required is proportional to frequency, which means that for a constant amplitude grove the required current rises at 6dB/Octave.

Trouble is the heat goes as current squared! So for a constant groove amplitude, cutter head power dissipation rises at 12dB/octave (6dB/octave faster then the IRIAA boost).

While this is not usually a problem unless cutting something daft like CD4 it does impose a limitation.

There are also the obvious geometric limits that apply irrespective of cutter speed, the 45 degree angle at the back of the cutting stylus means that you cannot have a peak radial velocity greater then the cutter linear velocity or you wind up destroying the groove you just cut, and the replay stylus osculating circle can impose a tracking limit depending on what people are using.

I suspect the major thing with the half speed cutting back in the day was that it made the head bump from the tape replay appear to be an octave up! The head bump being an effect of the replay head on the tape transport integrating the flux in the gap, it probably made a 30IPS master tape cut sounding like a 15IPS one (15 IPS was preferred for some material).

User avatar
SONARC
Posts: 56
Joined: Fri May 20, 2016 2:06 pm
Location: Land Of Port, Borough Of Hills, USA
Contact:

Re: Whats the most efficient cutting speed?

Post: # 58506Unread post SONARC
Mon May 03, 2021 5:41 pm

Hi there - I've read some other posts relating to this approach, but as the board has behaving a bit wonky lately, I'm having a bit of trouble tracking down exactly what I'd seen previously. In the meantime, though, if I'm understanding this, doesn't this suggest something like a ballpark bump of around 6dB (more or less) across the board applied to the RIAA curve being applied to the signal, in order to maintain a somewhat relative EQ in the end?
dmills wrote:
Wed Feb 10, 2021 11:13 am
[ - snip - ]

The major reason to cut at low speed is to limit the amount of power needed to cut high frequency, and hence cutter head heating.

The force produced on the cutting head my the modulation is linear with current, and acceleration is linear with force, but for a given velocity acceleration required is proportional to frequency, which means that for a constant amplitude grove the required current rises at 6dB/Octave.

Trouble is the heat goes as current squared! So for a constant groove amplitude, cutter head power dissipation rises at 12dB/octave (6dB/octave faster then the IRIAA boost).

[ - snip - ]

User avatar
dmills
Posts: 190
Joined: Sun Jun 16, 2019 3:33 pm
Location: Uk

Re: Whats the most efficient cutting speed?

Post: # 58508Unread post dmills
Tue May 04, 2021 11:18 am

For half speed you need to move the breakpoints down by a factor of two, most easily done by just doubling the capacitances in most cases, but you ALSO need to drop the level by 6dB, because the output of the IRIAA network is velocity and so to maintain groove amplitude you need to lower the level (amplitude is the time integral of velocity).

Post Reply