Record Lathe - Cutterhead V3

Around 2015/2016 I started building a new cutterhead. Looking for stuff at I found some inexpensive tweeters: Hochton-Lautsprecher 19104-041.71

With the goald to reduce the overall size of the cutterhead and to minimize the length of the cutting needle I started building a new case. The holes have a diameter of 30mm on which the tweeters are going to be mounted from the outside.

The needle (this one is 1.2mm thick filler material from TIG welding) is put through an angled hole in an aluminium rod and fixed by a thread screw from the front. A V-spring 3D-printed out of PLA holds the aluminium rod in place but allows it to move in the desired directions.

Also two 3D-printed cones are glued to the membranes of the speakers to transmit the vibrations to a short piece of brass rod. Two more brass rods (0.8mm) are glued to the aluminium rod 90° to each other and soldered to the other short brass pieces on the PLA cones. The speakers can later be disassembled by removing the solder, but it also are rigid enough to transmit the higher audio frequencies.

Also the stepper motor controller had to be designed in a simpler way. I always had to connect a computer to set the speed. But this can be done simpler by using a COTS stepper driver + NE555. The NE555 is wired as an astable multivibrator. C1 has a value between 10nF and 100nF. The potentiometer and the resistor are selected by testing to get the needed freuqencies for the motor speed.

The maximum speed of the cutterhead is now adjustable between 4mm/min and 12mm/min. A 8mm/min feedrate was a good speed to use.
The whole controller did fit perfectly in an empty external hard drive case.

The stepper motor was salvaged from an old scanner. Because it has a gearbox already attached to it, it was ideal for such slow movements. However, the frequency of rotation needed for 8mm/min feedrate lies quite close to the resonance frequency of the plastic gears, which results in a nasty rattling noise.
One solution would be to use a M10 oder M12 threaded rod instead of a M8, or I change the gearing ratio. From the same scanner I got the gear on the top and also the belt, which I had to shorten a bit. Now the gears rattle only on lower feedrates below 6mm/min.

Until now the carriage was moved by a wooden block with a thread pressed in it. This was meant as a temporary solution and is now exchanged by a square steel rod with half of a nut welded to it. Both wooden block on the sides are still adjustable in distance and the backlash can thus be minimized.

As mentioned in the building process of the HDD disc sander, I replaced the Dremel by a Proxxon LSB/E. The rotary tool is also now attached to an old hard disc as a bearing which makes it also more round and precise.

Now I was able to carve some more. The needle used here is a 1.5mm tungsten anode ground to a 70° tip. As always I used 45rpm with a CD. A 5 minute long track needed a feedrate of 36mm/5min = 7.2mm/min to fit on a single CD.

I am still not shure how sharp the needle needs to be. Also I havent decided on a good cutting weight. Until now I had been using 100g +- 30g.
Compared to the previous recordings I did made some progress, did I?
If you have some experiences, tips, whatever to help me; please write me an email: Questions are still welcome too ;)

The recording of the talk about my record lathe at CTDO BBQ 2018.

English subtitles are available.