The Secret Society of Lathe Trolls

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

Has anyone mounted a stereo cutterhead to a presto 8N I have a grampian head works well but would like to upgrade to a stereo head soon but I read on presto history site that large heads will not mount to the carrage so before I buy a stereo head would like to know if it will fit??
Would like somthing like a SC-99 or ortofon dss So has any one tied or using one of these on a presto carrage????
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JayDC · Posted: Fri Nov 23, 2007 10:34 pm Post subject:

Flo did this mod to a 6N a while back. He used the vinylium sc-99. I think the overheads are similar so it should be possible, and awesome!.. Lucky you!

How much will you want for the grampain?

audiocarver · Joined: 23 Mar 2006 Posts: 12

I currently have the exact same rig. Let me know how you've done it too!! I thought about this but with a Haeco stereo head instead. But the Vinylium head would be awsome!!

Now to figure out that variable pitch problem....

AC

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

My 8N has vari pitch from one lead screw 83 to 302 lines per inch it was converted by Mr john d harmer prestident and chief engineer of capital city sound recording co. and he even sent me the write up which he published in broadcast engineering detailing how the mod was done using the 8N overhead and a 6N overhead and steped pullys I can sent you details if you know a good engineer. Im just getting into recording as Im a dj and some old dance records are hard to find. so it looks as if I will sorce a sc99 head and mount it. the grampian is not for sale as it cut loud tracks ideal for dance tracks. Can send you pics of overhead if you are intrested PM me...
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flozki · Joined: 19 May 2006 Posts: 38 Location: switzerland

yes it is definitely possible with sc-99.
i can measure out the dimensions and put on my website if that helps.
although i have to say that this is a quick and dirty solution. as always. i needed instantly and didnt had time for great solutions...
i did a completly new suspension block with new toe-bearing? i mean the pointed screws that act as bearing.
you dont have too much space for the cutterhead and for nice lateral and vertical adjustment during cut i think there is not enough space.
also oil damper is missing

for the ones havent seen yet. here again
http://www.floka.com/lofi/portable_lathe.html

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

On my 8N overhead i have oil damper and also there is a ajustable mounting for where you want the head to sit I dont know if this is standard or someone made it as my lathe has lots of mods on the overhead.the carrage is made of a 8N on the front and a 6N is fitted to the rear and steped pullys conect them together. I have looked a pics of a 8N overhead and the one I have seems to be diffeerent where the head is fitted. if you post pics it would help me as I have never seen a SC99 close up and I dont know how it conects to the overhead.Thanks flozi.....
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Karl Welty · Joined: 12 Nov 2007 Posts: 22

Heya,

It was said:

"My 8N has vari pitch from one lead screw 83 to 302 lines per inch"

Now this is something that I've been thinking about for a few weeks. The Neumann Lathe had a computer which based variable pitch off of a preview head. as the amplitude or low end content changed, the computer modified the pitch to allow more room.

In theory... couldnt this be done using our marvels of current computer technology ? A file could be read prior to being fed to the cutter, and the pitch of the cut adjusted ? Shouldnt be a tough program to write ?

CNC machines are run by computer all the time. Could a lathe have its "Y" axis so controlled ? "X" isnt an issue, constant velocity feed. "Z" isnt as much of an issue, cutter depth is based on the presumption that one has *flat* blanks and perhaps vacuum assist to hold it that way... though if the "Z" axis could be responsive to the same preview approach, would that be of benefit ?

Could a servo based motor with position sensing be used to drive the lead screw ? Increase its speed based on an analysis of amplitude and frequency ? Steppers might be easier to implement, but would they induce mechanical vibrations from the "ticks" ?

Or has this already been done ?

Karl

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

my pitch is set prior to cutting using belts and pullys. i have thourght about a stepper motor and circuit but I dont know enough about record cutting yet to do the mod but would be a nice addon when i get a stereo head. if the motor was mounted properly the ticks shouldnt be a problem the circuit should be easy and just a delay in the signal to cutter amp so the motor can do its stuff? not sure how the neumann setup works out how far to "push the width" seem that it sees a louder signal and pushes the goorve width and a quite signal pulls it back to the preset amount.A pic chip could handle the motor and a a to d converter to give it a signal level from the program sorce but dont quote me on this. Im a electronic engineer just learning about record cutting it seems that the more you learn the more you dont know. so its alway intresting...look now you got me thinking !!!!!!!!!
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Karl Welty · Joined: 12 Nov 2007 Posts: 22

Heya,

"just a delay in the signal to cutter amp so the motor can do its stuff?"

Guessing here, purely speculative... while the rpm remains constant, the linear distance the cutter travels per revolution decreases as the cutter nears the center. A static delay would work, but it seems to me that position sensing of the carrriage on the lead screw would allow maximum use of the available surface area of vinyl.

Just "scooching it over" a touch would accomplish something... but by the cutter knowing where it is in the revolution of the disc, the pitch variation could be optimized. That makes it more complicated, and requires analysis of an adaptable program... or does it ?

Mechanical engineer I am NOT. Simply musing.

Karl

audiocarver · Joined: 23 Mar 2006 Posts: 12

I think a stepper motor would work, as long as the resolution was high enough.

Personally, I would try using an AC servo motor with high resolution absolute encoder. With this, it would solve the 'ticking' problem but the computer would still know the exact position of the motor shaft. All the rest could be done in software on the fly. I think that is how the Neumann lathes do it anyway, but in a more or less earlier design approch. I am not sure how to set up such software though. Programmer I'm NOT!!!

The other issue though is cost. A good servo motor with a high resolution encoder would be very expensive. Then to have a motor amplifier to drive it.

AC

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

The lines per inch remain constant all the way a 1KHz signal cut at begining has just as wide groove as at the center or on playback the level of signal would drop as the stylus reches the center.
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Karl Welty · Joined: 12 Nov 2007 Posts: 22

Yup. LPI for 1k is the same out or in, but doesnt the "land" between grooves need to change for amplitude or frequency ? To avoid cutting over ? That was kind of where I was thinking, as the Neumann system seemed to optimize the available total time on the disk by compacting or expanding the LPI as appropriate/needed.

Quite grooves with little low end, compact them. Loud grooves with lots of low end, expand them. Kind of the audio equivilent of "defragging".

Karl

JayDC · Posted: Sun Nov 25, 2007 7:09 pm Post subject:

kewl. I was thinking of building a similar system for my 6N, so I could at least adjust the pitch via a motor, so I didn't have to find a bunch of lead screws.

I was thinking of something a lot simpler, ie: motor, speed control, knob for adjustment.

I know VB programming, and if provided with the proper hardware I could develop such a software as discussed earlier.

Electrical Engineer I am not.

I have seen some electronic "kits" that are stepper motors, and a controller board, I'm sure we could fingure out a way to have a computer tell it what to do.

What would be neeto is a solenoid or servo that can raise the head, then we could add a lead out switch.

Karl Welty · Joined: 12 Nov 2007 Posts: 22

Heya,

I "have this friend" who has built two CNC machines from scratch. He used the first machine to build higher quality parts for the second. The whole affair is run from a somewhat clunky bit of software on a PC, it was a shareware thing. His brain can be picked.

Automating the cutter dropping and raising would be control of the "Z" axis, as this is what drops the router down onto the material and then lifts it at the end of the run. For cutting metal, you cut shallow and then program it to do consecutive passes... each slightly deeper. A single depth command would be "easy" to implement.

Driver cards are somewhat common fodder, for either steppers or servos. Common drive voltages fed to them, and they interpret commands regarding position and speed.

I see no reason these ideas couldnt be implemented, though thats easy for me to say having never tried to implement them.

Over the next few days, I will see what I can find out.

Karl

JayDC · Posted: Mon Nov 26, 2007 4:57 pm Post subject:

okay what I'm thinking is:

Use Pulse Width Modulation to control the lead screw motor.
Use TTL +-5v to control a relay to a soleniod to raise the cutter.

What would be keen is some sort of position detection. Then via the software, we could totally automate the cutting process using waveform analysis.

It would drop the head at the proper spot on the plate, record the sound, run out the groove, and raise the head. Every aspect could be calculated before pressing start, with no delays.

Karl Welty · Joined: 12 Nov 2007 Posts: 22

Heya,

Via my very limited understanding of such things...

A stepper motor receives a series of pulses to run. Feed it 1000 pulses and it has moved a certain amount in its rotation. If for some reason it skips over some of these pulses, it will not correct. A servo system senses the position of the rotation of the motor through active feedback. It will correct, and know where it is in respect to rotation. That rotation then translates into cutter position via the lead screw ?

Upscale CNC's use servo's, so that if there is drift of the tool due to torque requirements (I am freely using mechanical terms, not sure if they are correct). With servo's... the tool path is consistent because the machine knows where it is.

A position sensing servo system, based on a known pitch of lead screw, could be told at what feed rate it needed to travel to allow enough land between tracks on an adaptive basis... using waveform analysis as suggested.

A solenoid on the cutter would be an "up" or "down" proposition. A smaller lead screw assembly for the "Z" axis would allow for the cutter to be gracefully lowered and gracefully raised... and also automated.

And yes... the Neumann system had presets for the lead-in/lock groove... auto spacing for bands between tracks, and the repeat groove at the end of the disc. Each of those could be subroutines which the program could run... sort of like track ID's on a CDR.

1) programmed lead in lock groove
2) track one, with pitch adjusted for optimum land between grooves
3) programmed silence band between tracks, corse cut
4) track
5) silence
...etc... etc... etc...
6) final track
7) programmed lead out and repeat groove

Oh what fun... and yet again, easy for me to speculate about having not implemented it... though having seen my friends homebrew CNC's do such things, I see no reason the techniques couldnt be adapted. I will inquire, and report back to class.

Karl

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

how about mounting a slotted or toothed gead onto the lead screw and a hall effect devive to pick up the pulses as long as the carrage always starts a the same point you could work out the distance traveled by the pulses just like a car ecu knows the cam position of the cam from a toothed gear and sensor and is very accurate +/- 0.1 degree.a simple micro switch at each end of the carrage and the software whould know the exact position of the carrage by always working from the outer stop microswitch to the inner and back on swich on so it would know where it is to start with what do you think????
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JayDC · Posted: Mon Nov 26, 2007 6:15 pm Post subject:

I think this all sounds good, and with some help with the math I'm confident I could make said software. I even have a IO card from one of my show lasers that would be able to drive the motors.

These principals are similar to how I can control a laser beam via the computer, for laser shows.

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

the head lift could be done with a 12V solanoid and a simple damper when you want to lift the head ramp the voltage to 12v slowly so it dont go with a clang and ramp it back to 0v to drop it this should give a nice smooth steady lift and drop movment. if this was fitted to a lathe all you would have to do is get computer to scan the audio file and work out the optimum groove widths. My 8N already has a 50W DC servo motor driving the platter so the computer could even control the speed and start and stop. all you would have to do is tell it the blanks size 7 10 12 16inch and what speed you would like it to cut at. the computer would control everything even the riaa as a plugin. all you would need is a very good sound card and a IO card in a PC and a good power amp. would doaway with all the outboard kit. Dont sound bad. The electronics would be easy to make just simple interface to the io card. The servo motor I have has a control board with it start stop speed brake are all 5V ttl level so would not even need any electronics to interface it most io cards are ttl compatable there is a speed output on the controler so the computer can keep the platter and the exact speed.I using a vexta AXHM450KC motor and control found on ebay for £17. The only thing that I cant do is the programing but a friend is a programmer Il try to talk to him nicely would be a real good setup. You could then cut inside out and locked grooves with ease and the risk of messing up a cut is a lot less all you would do is make sure the chip is sucked away.Even the sucktion would be controled by computer.1960 mechanics and 2007 electronics in harmony!!!!!!!!!!!
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Karl Welty · Joined: 12 Nov 2007 Posts: 22

Heya,

Here's my first guess at how a system could be pulled together to accomplish whats been discussed so far. G code is normally used to run a CNC, and I am trying to avoid that by using more garden variety ideas.

1) Preview capability
2) Variable pitch based on amplitude
3) Automation assist of cutter lower/raise

1) Use a sound card or breakout box which will support 4 channel playback (2 channel for mono cutting). Software suited for multitrack applications. Create a sequence of files (playlist), in order and with appropriate gaps between songs. Dual monos, or interleaved stereo. Copy this whole sequence and paste to a secondary parallel track(s) (stereo1/stereo2 or L1-R1/L2-R2). This technique will allow a time offset to be introduced between 1 (preview) and 2 (cutter feed). The offset time would need to be determined.

Using an analog tape deck (ala Neumann) for program source, a playback head would be mounted at some point ahead of the main playback head feeding the cutter amplifier.

2) The preview source feeds an RMS detector such as a DBX chip, or a circuit similar to the detector of a compressor. It would need adjustment for attack and release. Timing capacitors could suffice, or the offchip components as appropriate. Preview is needed so that the cutter can have allowed enough land before its needed. Adjustable attack so that the pitch transition isnt abrupt, and adjustable release for the same.

<insert magic unknown bridge section here>

The goal of the RMS detector is to create a DC voltage which varies in accord with the RMS level of the program material. Greater low end content would generate a higher RMS level, and though not fully frequency based it would accomplish a similar result. Perhaps a filter network for the preview signal.

The DC voltage feeds a servo motor directly. In a sense the RMS to DC convertor/processor *is* the driver card. The DC voltage would need to be biased for a maximum GPI, with the swing range of the detector causing the grooves to be cut with more space as the amplitude increases.

The preview time offset would need to be fixed so that the pitch will have been changed at the conclusion of a single rotation of the disc. A global preset, based on general cutting speed (78, 33.3, etc). This might need to be averaged, or set for the inner groove spacing by default.

The attack/release controls would allow this to be fine tuned. Perhaps a change in biased voltage to the motor as the cutter moved from outer grooves to inner grooves... the pitch equivilent of diameter EQ.

Space bands between cut tracks could be inserted manually by use of an A/B toggle or push button. Have a preset DC voltage which replaces whatever amount was being sent to the motor.

The Neumann system depended on an optical sensor, which could identify white or transparent leader between songs on a reel of tape. This switch to coarse groove spacing could be automated from the playback medium in a variety of ways. A MIDI event could be placed at the appropriate timing locations which could trigger a relay to switch between the fixed voltage (band) and preview voltage (adaptive pitch).

3) Infact a solenoid could be employed for the cutter lower/raise function. A dashpot could be installed for a gentle lowering. Another used to cushion the cutter on lift, so that the solenoid doesnt "bash" the head. Once again, these commands could be MIDI events appropriately placed driving a relay. A smaller motor and lead screw might be more elegant, though not required.

The only two presets I havent figured out yet are the lead in groove, and the playout to lock groove at the end. A pair of chips/circuits which could generate ADSR (attack/decay/sustain/release) to DC voltage which would also replace the normal pitch driving voltage. Each as a button... depress LI, then lower the head. It runs its course and then is switched to the RMS/DC drive. At conclusion of disc, depressing LO runs the playout to lock groove subroutine... and lift the cutter. These two could once again be automated... MIDI commands and relays.

Now wouldnt that be a neat thing to have. Wink

The RMS/DC detector could be omitted, DC run manually by a knob... observing the grooves with a microscope as they are cut, and simply using the other subroutines as manual operations.

Karl