The farmer and his plow - When I set out to build a record cutter

[farmersplow]

Heating FP-9 (part2)
09/2023

To improve the temperature measurement not only visually, but also technically, I have installed an additional automation system. Previously, I had to swivel the measuring arm (which was made of plastic) over the turntable by hand (and turn it away again by hand at the end of the cutting process). I always had to pay close attention to the position of the IR temperature sensor, because the temperature sensor has a measuring cone, i.e. an area that is measured.
To improve the measurements, the arm should be positioned according to the size of the blank (12", 10", 7"). And because I generally hate monotonous, repetitive tasks (and am too lazy for them), I prefer to take the trouble to automate things.
So I thought I would control the Swivel arm with a servo motor. I first had to learn how to control a servo motor with Arduino, but that wasn't difficult.
It was more difficult to design the construction because I wanted the arm to be quiet, precise and durable. Therefore, friction surfaces such as aluminium on aluminium must be avoided. I therefore produced Teflon bushes at the friction points, which have low friction and are easy to machine. The cable routing through the whole part was a little more complicated, but I was able to manage that too.
The following two pictures show the construction of my moving element.
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I then fitted the servo motor to the moving disc drive and connected the two parts with a lever:
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I then fitted all the cover plates and started a first test run. It didn't immediately work as planned! I connected the 5V servo motor to the 5V "on-board power supply", which also supplies the Arduino microcontroller, the touch display and many other things. During the first test, all the displays started flashing and the relays clicked in an uncoordinated manner. The problem was that at the first moment the current consumption of the servo was so high that the voltage on one of the supply contacts collapsed. It was a bad contact there. And as I have a lot of plug contacts on my makeshift "grand-mother-board", troubleshooting was the first order of business. But after an extensive search, I was able to find and rectify the fault. I'll have to be even more careful with the crimp connections in future.
But it worked on the second attempt! As a test, I moved the arm back and forth twice at maximum speed. You can see this clearly in the following video.
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vid 55.mp4

VIDEO: MOVING ARM
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The first hurdle has now been overcome. But more needs to be done to ensure that it ultimately delivers good measurement results and controls the heating lamp properly.
So far, my control/regulation system has been quite simple:

• I set the desired temperature in the touch panel.

• The microcontroller took the setpoint and compared it with the actual value.

• If the turntable was rotating, then it continued (heating should not take place when the turntable is stationary, because then there is no even heating and the blank is deformed). In addition, my heating lamp is not centred for various reasons.

• If the actual value was too low (with a tolerance of one degree), the lamp was switched on via a relay.

• If the actual value was too high (with a tolerance of one degree), the lamp was switched off again via a relay.

The lamp switched on and off regularly. It always worked very well, but!
But once a cutting thread formed on the plate (unfortunately this happens from time to time) and I had to remove it with a brush or cloth while cutting. I briefly created a shadow with my hand. What happened next was an interesting experience. The cooled area came to the measuring sensor and it said: "too cold". The lamp switched on immediately. With a warm-up time of around 0.5 seconds, it became really warm after 0.9 seconds.
And for all those who want to think along now: At 33.3 rpm, 0.9 seconds is half a revolution!
So it was the warm spot near the lamp and sensor and was warmed up even more. Of course, the sensor said "too hot" and the lamp switched off again. After a further 0.9 seconds (half a turn), the further cooled spot came to the measuring sensor (it was not heated). The game continued until one half to heat up and the other half continued to cool down, causing the blank to deform.

I'll explain how I managed to solve this problem in the next post.

Greetings from Austria
Thomas

[farmersplow]

Heating FP-9 (Part 3)
09/2023

To solve the heating control problem, I changed two things. Firstly, instead of a permanent measurement, I carried out a time-controlled measurement of the surface temperature. And secondly, I developed a controlled lamp heater instead of a "brutal" on/off switch.
First the measurement. Instead of permanent measurement, I distributed ten measuring points per revolution. The measuring interval thus changes depending on the plate speed. Then I took an average value of the measuring points (taking into account the maximum and minimum values) as the control variable and thus calculated an actual value.
The controlled lamp heating was a little more difficult to solve. The basic idea is that the heating lamp is now dimmed (instead of being switched on and off) and therefore lights up more or less intensively. I had thought of this before, but then forgot the idea again.
But a very nice latte troll from England (master cutter) had visited me in June and we had tested the lathe back then and made cuts (at that time still on the old lathe). And he gave me the idea of controlling the lamp continuously. He also gave me the idea of a midi control. - Thank you Philipp!

So I took a small breadboard and experimented with an Arduino Nano to carry out the measurement.

For those who know a little about Arduino: To repeat the measurements at regular intervals in a "loop", the delay() function is usually used. However, this does not work here and micros() was used. Micros() means that an Arduino internal counter is used, which permanently counts in microseconds (micros) and milliseconds (millis). To execute an action after a certain period of time (e.g. 5000µs), a time is saved [micros(x)] and then checked in the loop to see whether the actual [micros(Y)] is 5000 higher. The big advantage over the delay function is that the program continues to run and the Arduino can do something else during the 5000µs. With delay(5), the program stops for 5ms (5000µs) and only then continues in the text.

For those who are not familiar with Arduino: It does not work in a simple way, but complicated it works then.

A first test has shown that the measuring function basically works. I can only do the final test on the rotating turntable. Here is the breadboard structure, which already contains parts of the control area.
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Controlling the heating lamp is somewhat more complicated than measuring it. It must also be taken into account that mains voltage (EU 230V 50Hz; US 120V 60Hz) is used here. The best way to control a mains voltage for a heating lamp is with a TRIAC. Experts will say "of course". For those who do not know the part, a brief explanation. A triac looks similar to a transistor and also has three connections. The function is similar to a FET transistor (actually two pieces of FET). The TRIAC can switch between two of the connections (in both directions +-, which is important if you want to control an AC voltage). The third connection is the G (gate). When an "ignition voltage" is applied there, the triac starts to work. The ignition voltage (at G) is only an initial ignition and is switched off again immediately, while the triac lets current through until the voltage applied goes to zero. Then it must be re-ignited. This is very practical for mains voltages because the output power is no longer 100%, but is throttled - i.e. the lamp shines less brightly. I have taken the liberty of making a drawing to explain the principle.

Example1: no ignition voltage and therefore no output voltage.

Example2: 2.5ms (2500µs) after each voltage zero crossing (positive or negative), an initial voltage is applied to the gate (for about 1ms). The triac then lets voltage through and the output is about 85% of the power (the lamp lights up very brightly).

Example3: 5ms (5000µs) after each voltage zero crossing, an initial voltage is applied to the gate (for about 1ms). The triac then lets voltage through and the output is about 50% of the power (the lamp is medium bright).
Example4: 7.5ms (7500µs) after each voltage zero crossing, an initial voltage is applied to the gate (for about 1ms). The triac then lets voltage through and about 15% of the power is obtained at the output (the lamp lights up very dimly).

Note the mains frequency. In Europe the mains supplies 50Hz and in the USA 60Hz. The times must be adjusted accordingly, which can be done by a further measurement process.
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Now it is only necessary to determine where the "zero crossing" is so that you have a starting point from which to ignite. An LTV-817C optocoupler is used to measure the zero crossings. In order not to damage it, 2x 100kOhm series resistors are used. The output of the LTV-817C goes to the Arduino as a trigger signal. The second optocoupler (MOC3020) is used to control the TRIAC and again galvanically isolates the circuits. It receives the triac control signal from the Arduino. The triac then does the rest and switches the mains voltage through accordingly.
The Arduino also has a low/high input to know whether heating is required at all. Only when this information reaches the Arduino is the main relay (via optocoupler (PC817) and transistor Q1) switched on via another low/high output.
Here is a picture of the mains voltage side:
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Attention for all those who want to build something like this! Working with mains voltages (e.g. AC 230V or AC 120V) can be life-threatening and should only be carried out if you know what you are doing!

The entire Grand Motherboard is also getting bigger and bigger. But a first test run shows that it works once; even if I make a shadow with my hand!
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Perhaps it will be clearer what I have done if I show the circuit diagram:
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The circuit diagram also shows three LED outputs. The Arduino therefore provides additional information as to whether the actual temperature is too high (red), appropriate (green) or too cold (blue).
A connection via SDA & SCL to the SDA&SCL of the OLED display and to the SDA&SCL of the IR temperature probe is also shown. These are simply connected in parallel.


Greetings from Austria
Thomas

[markrob]

Hi Thomas,

A better approach to doing the phase control is to use an unused hardware timer setup to cause an software interrupt after it reaches the required delay time. In the interrupt handler, you fire off the triac with a short pulse and then do any setup the for the next line cycle or half cycle. I assume you are are using D9 to trigger an interrupt to sync to the AC mains zero crossing to establish a timing reference point rather than polling. Polling, even using the micros hardware counter not a great way to implement this. Using interrupts as a background task leaves the standard foreground Arduino loop() open to running completely independently. You will need to dive into the datasheet for Atmel ATmega328P processor to learn how to program the timers. The Arduino c++ complier allows you to directly reference all of the CPU hardware registers. For example, the line:

OCR1A = 100;

sets timer 1 output compare register A to the value of 100. '

You can create an interrupt handler with code like this:

ISR(TIMER1_COMPA_vect)
{
// your code here
}

If you master this aspect of Arduino hardware programming, you can do some amazing things.

Hope you find that helpful.

Mark

[farmersplow]

Hi Thomas,

A better approach to doing the phase control is to use an unused hardware timer setup ... will need to dive into the datasheet for Atmel ATmega328P processor to learn how to program the timers. The Arduino c++ complier allows you to directly reference all of the CPU hardware registers. For example, the line:
If you master this aspect of Arduino hardware programming, you can do some amazing things.
Hope you find that helpful.
Mark

Hello Mark,

Thanks for your suggestion for improvement. I get the trigger signal via D9 (correct). And you also correctly recognized the way of my programming (superficial Arduino knowledge). Your suggestion to improve the programming is excellent and a new world of programming at a higher level. A level that I have not yet mastered. I know what a c++ compiler is and I know a little about the CPU hardware register, but not enough to achieve an elegant solution. (I was already happy that I could measure and control temperature measurement, mains frequency, zero point and triac ignition point at the same time).
But it is a very good suggestion that I should look deeper into it. I will do it and if I can then I will implement it as you suggested. It will also help me to program the variable pitch better than I have so far. And I can actually think of a few other things.
Thanks Mark, that was helpful!

[markrob]

Hi Thomas,

I'm glad you found this helpful. If you need some help sorting this out, feel free to ask. Based on your abilities, I'm sure you will be able to dive in. The Arduino timers are a bit complicated, but they can be made to operate in several different modes. The Nano and Uno have very few timers open. But the Mega is not that much more costly and offers many more timers and I/O. Here is a little blurb I found on the web that I find helpful when deciding what timers to use:

The Atmel AVR ATMega 168 or ATmega328 have 3 timers, called timer0, timer1 and timer2. Timer0 and timer2 are 8bit timers and timer1 is a 16bit timer. On a Mega (AVR ATmega1280 or the ATmega2560) you have 6 timers, Timer 0, timer1 and timer2 are identical to the ATmega168/328 and timer3, timer4 and timer5 are all 16bit timers.

All timers depend on the system clock - most often 16MHz

On your Arduino :

- timer0 is been used for the software Sketch timing functions, such as delay(), millis() and micros() ==> if you change timer0 registers, you influence the Arduino timing function.

- timer1 on Arduino Uno or timer5 on Arduino Mega is used for the servo library

- timer2 is used by the tone() function ==> to make your life easy you can use that function to achieve what you want to do with less work

Timer 3,4,5 are only available on Arduino Mega boards if you don't use PWM

if you want to use PWM

On a UNO as we only have 3 timers but 6 PWM pins, they go in pairs and the relation between timers and PWM outputs is as follow:

- timer0 = Pins 5, 6
- timer1 = Pins 9, 10
- timer2 = Pins 11, 3

On a MEGA you have 6 timers but 15 PWM pins (PWM: 2 to 13 and 44 to 46) , they also go in pair or triples

- timer0 = Pins 4, 13
- timer1 = Pins 11,12
- timer2 = Pins 9, 10
- timer3 = Pin 2, 3, 5
- timer4 = Pin 6, 7, 8
- timer5 = Pin 44, 45, 46


if you want to explore timer you can change the Timer behavior (different clock sources can be selected for each timer independently) through the timer register values (prescaler, Timer/Counter Register, Interrupt Mask Register, ...) and timers can be configured in different modes such as PWM or CTC.

[farmersplow]

Hi Thomas,

I'm glad you found this helpful....

Hi Mark, thanks for the support. It's helpful again. I have started to study these three pages since the last letter. But I still need some time before I can apply it (at least until the end of the week).
https://www.schaerens.ch/iot-arduino-timer/
https://forum.digikey.com/t/mastering-non-blocking-delays-and-timers-from-arduinos-c-to-the-opta-plc-s-ladder-logic/35742
https://emalliab.wordpress.com/2022/01/23/arduino-nano-every-timers-and-pwm/#:~:text=For%20the%20ATmega328%20as%20used,B%2C%20OC2A%2FB).
Thanks Mark!

Greetings from Austria
Thomas

[farmersplow]

Neuer Schneidekopf CH-9 (Teil 2)
09/2023

The housing parts of the CH-9 cutting head are ready from anodizing. The wait was worth it. I chose a slightly more elaborate grey anodization and deliberately did not sandblast the parts as I did with the previous models. Because I love the slightly more technical look.
Just holding it in my hand makes me a little proud of the result.
I can not only notice the difference in size, but also the reduction in weight.
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This is also very clear on the scales. The CH-6 case weighed 550 grams and the CH-9 only 194 grams.
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To check whether the main parts fit together properly, I fitted the covers and the 15-pin connector plug.
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A direct comparison clearly shows the difference in size compared to the "old" cutterhead.
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Of course, the reduction in weight and size has more than just visual advantages. It can be cut further towards the center and the counterweight can be lower (or the spring for weight compensation can be weaker). As a result, the vertically moving masses are lower. This also has further consequences for the dashpot and the contact force control.

Now that the good piece makes a good first impression (for me), I can get on with finishing the remaining cutterhead parts.

Greetings from Austria
Thomas

[urieldeveaud]

nice design for the head! it goes very small in size. great job!
did you change the type of aluminium from last time?

[farmersplow]

nice design for the head! it goes very small in size. great job!
did you change the type of aluminium from last time?

I'm glad you like it.
The aluminum is (in principle) the same material: EN 5083 (ALU AlMg 4.5Mn).
However, with a small defect that was only recognized by the electroplater. The aluminum blanks were made of cast aluminum. Only the middle top cover was made of rolled aluminum. No difference could be seen before and after CNC machining. But when anodizing, the materials behave differently. If you anodize clear or black, it makes no difference. But with grey anodizing you get slightly different colors because of the different reaction times during anodizing. It doesn't bother me too much, but I will pay attention to it in future.
It's hard to believe all the things you have to consider when building something like this. But what I always say: you learn so much from mistakes!

[farmersplow]

Hi Thomas,

I'm glad you found this helpful. ...

Hi Mark, I've done it with the timers & PWMs! - Thanks for the tip, it's much more elegant to program.
I also took the opportunity to reprogram the turntable lighting. Previously I only had blue or red light (LED strips) to indicate the status. (Blue = Ready & Temp. cool; Red = CUT! & hot). But I never liked it. I also wanted alternating colors to indicate the warm-up phase, for example. But the flashing was awful and "pulsating" with (millis) was too complex.
But with the PWM programming it was great.
Here are two examples:

Video blue pulsing:

vid 56 a.mp4

Video blue&red alternating pulsing.

vid 56 b.mp4

Thanks again Mark and
Greetings from Austria
Thomas

[markrob]

Hey Thomas,

Nice work! I knew you would dive right in and get that sorted.

Mark

[farmersplow]

New CH-9 cutting head (part 3)
10/2023

I had to play a bit with the programming, because Mark distracted me with it and I spent days on these things again instead of continuing! Thanks Mark! (I get distracted so easily ). But now I have found a little time to continue writing the report

I also need a new torsion tube for the new cutting head. Firstly, I have set the VCA (vertical cutting angle) to the exact angle of 20° in my design. I still don't know exactly how this angle is measured! Why is that and why do I only "estimate" what I am doing?
The problem for me lies in the detail:
I have already addressed the topic of VTA (Vertical Tracking Angle) and VCA and Rake Angle in another treat (https://www.lathetrolls.com/viewtopic.php?p=63307#p63307).

But I didn't go into a specific detail in the topic, namely how the VCA is measured exactly. I have made another drawing for this and ask the question: Which is the correct VCA?
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I admit that the maximum difference is only +/-0.5 degrees, which supposedly doesn't matter, but I'm interested in the principle.
Do I measure (example A) from the tip of the needle to the V-spring, because there is a point around which the torsion tube can move up and down by one point for the first time?
Or example C, from the tip of the needle to the holding point where the wire is firmly connected as an extension of the torsion tube by the holder? Or should the center (example B) simply be taken?

If anyone knows, please let us know. And if you have an opinion on this, please comment on how you see it!

Without any brakes and without this detail, I set to work on the torsion tube. As always, it's a laborious precision job. This time I decided to drill the hole for the diamond graver in such a way that I get a rake angle of 5°. That is far more than I have had so far. I'm hoping for a quieter "silent cut" because the plow travels flatter through the field. However, there is also a risk that I will need too much cutting force, which in turn can push my disk drive beyond its limits with 12" blanks. This can lead to synchronization fluctuations. But I'll give it a try.
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The tube turned out well and weighs 0.78 grams. Maybe I can think of another way to save even more weight. If I make the tube thinner (outer diameter), I'm afraid that the wires of the drive rods can no longer be anchored properly and I'll have a new problem.
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Then I'll mill small holders out of aluminum to hold the piano wires at the end of the torsion tube. These little things will then be glued to the end of the torsion tube.
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Greetings from Austria
Thomas

[Thelatheofus]

Nice work !

Instinctively I would say answer C is the right one, but I have 0 experience in the subject. If your plan is to cut PVC I've read Jesus say that the VCA should be higher than the usual one we see for lacquers, to compensate for the spring back effect of pvc. Then again I don't have any source to back this apart from a facebook comment.

I found on their website that the default rake angle of the sillitoe machine is +7°for lacquers, if that info can help. From that other thread you mentionned it seems that the VR has an even higher rake angle.

I have one question about your design, how do you chose the angle between the torque tube and the push rods ? I guess they are perpendicular ? I have seen many angles discussions but I don't remember seeing infos about this.

[Thelatheofus]

I can't edit the message, by push rod I mean what you called the drive bar in that other thread. I've seen examples where they are perpendicular to the record, and others where they are perpendicular to the torque tube. If anyone has infos about this that would be appreciated !

[farmersplow]

I can't edit the message, by push rod I mean what you called the drive bar in that other thread. I've seen examples where they are perpendicular to the record, and others where they are perpendicular to the torque tube. If anyone has infos about this that would be appreciated !

In my case, they are perpendicular to the torsion tube

[farmersplow]

If your plan is to cut PVC I've read Jesus say that the VCA should be higher than the usual one we see for lacquers, to compensate for the spring back effect of pvc. Then again I don't have any source to back this apart from a facebook comment.
I found on their website that the default rake angle of the sillitoe machine is +7°for lacquers, if that info can help. From that other thread you mentionned it seems that the VR has an even higher rake angle.

You have to be very careful with the angles that are given in different ranges. There is a big difference between cutting and embedding when it comes to the rake angle and this must be taken into account depending on the report. The rake angle is often confused with other angles. There is the VCA (vertical cutting angle - VTA), the angle of the graver in the torsion tube, the angle of the torsion tube itself and the angle by which the head is inclined. The rake angle is ultimately the sum of different angles (head inclination plus torsion tube angle (in the head) minus the angle of the graver in the torsion tube).

[Thelatheofus]

Yes I was going to say that, they speak about this angle when speaking about the "Stylus Rake Angle Adjustment stage" which tilts the whole cutter head. So I guess the angle they talk about is not the angle between the stylus and the torque tube but the overall angle in relation to the disc (so in this case I guess 90+7°)

Thanks for the answer btw !

[farmersplow]

... but the overall angle in relation to the disc (so in this case I guess 90+7°)

Correct. About 90+7°. (in this case the rake angle is +7°).
As far as I could find out, this angle is almost 0° or slightly more for DMM on copper.
For cuts in lacquer at 1° to 2°.
For cuts in PetG or PVC over 2°. Sometimes values from 7° to allegedly 15° are given. But I think that is too much. I have already achieved very good results with 2° in PetG. With 10° the results were much worse. What the ideal angle is depends on many factors. As far as my setup is concerned, I am still experimenting.

[farmersplow]

An excellent article on the subject of rake angle and VTA by J.I. Agnew:

Vertical Tracking Angle Meets Stylus Rake Angle
https://www.psaudio.com/blogs/copper/vertical-tracking-angle-meets-stylus-rake-angle-part-one

Accordingly, the rake angle should not exceed the 2° mark and must be taken into account in the head design in advance.

I would also like to point out that the back angle of the recording stylus is about 40°. This is the angle at the back of the cutting surface. With a vertical graver (0°), this residual angle of 50° (90°-40°) is sufficient to prevent you from getting caught in your own shaft when the graver moves up and down due to the audio. With a rake angle of 15°, only 35° would remain at the rear (50°-15°). There would already be a risk of the graver sitting in its own cutting track at the back - I suspect.

Supplementary images from patent specifications:

Bild1.png

Bild2.png

Greetings from Austria
Thomas

[farmersplow]

New CH-9 cutting head (part 4)
10/2023


The "old" cutting head had lighting, but it was not satisfactory. We would call it "glowworms". That's why I planned really bright lighting for the CH-9 and incorporated it into the design. As the head is a lot smaller, it was a bit of a challenge because the light had to shine on the stylus and the torsion tube couldn't cast a shadow. But in the end I found a way.

To make the light body, I first created a pattern shape out of wood.
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This was to fit perfectly into the planned recess on the cutting head:
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I took the matching white LEDs and SMD series resistors from a 12V LED strip as a test.
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For testing, I cut a strip PCB to size and soldered the LEDs and resistors.
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I then coated the package with epoxy resin to avoid air pockets when casting later.
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As with the last lamp productions, I again created a mold, inserted the lamp and filled it with epoxy resin:
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After the drying time, I drilled the mounting holes and sanded the surfaces a little.

Finally, a function test:
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Voilà - fits, is appropriate and lights up. - With love and heart, another small step closer to the goal.


Greetings from Austria
Thomas