back on the grind…

#RecordLathe

man, the grinding is not qwoperating today… ;-;

the edges keep chipping, the motor on my record lathe keeps overheating, the mount really needs a height adjustment, it's too fucking hot…

I need to get myself some better motor drivers and a beefier motor for the platter. maybe I should just go with a servo motor instead…

@slyka E-Bike motor?

@lasse probably a little overkill. ideally it'd be something like a gimbal motor with FOC control with lots of low end torque, but I've kinda designed myself into a NEMA 17 sized hole that I'm stuck with. So I'm thinking of maybe just using a NEMA 17 BLDC servo

fucking finally…

@jmorris a sapphire stylus for a record cutting lathe. maybe. I haven't tried it out yet.

@slyka awesome 💪!

@lasse we'll see…

aaaaaand it cuts like shit. I'mma throw this whole thing and myself into the nearest dumpster…

@slyka 🤞
It certainly looks the part!

@lasse turns out the looks might be deceiving…

honestly kinda impressed by just how bad that is…

@slyka The third groove in the video suggests that there may be instabilities in the depth actually cut (and then probably in the pressure actually applied, too). Is there any active regulation or would oscillations in the arm holding the stylus transfer fully?

@slyka 🤔 you move the cutter in the opposite direction from what I would assume correct for that setup,
also hardly any chips, massively (edit)negative cutting angle (rather pushing, not cutting)
Do you rely on doing it this way so the cutter gets pushed out of the surface and doesn't dip/stall? (If so, this can't ever work)

@chris that's cause it's not a cutter, and it's not supposed to cut or create any chips! it's an embossing stylus that displaces material to form a groove.

@drahflow well, I'm moving everything by hand here, so that's not surprising. And well, I mean, oscillations of the arm holding the stylus transferring into the stylus is kind of the whole point of cutting a record. There is the possibility of using closed loop control but that's not easy to do and is mostly done to flatten frequency response.

@slyka I thought one attempts to have a stable _arm_ and then do some piezoelectrics very near the stylus. (But I've never attempted to cut grooves and might very well be 100% wrong on how this is "usually" done.)

@slyka Does it do better the other direction? (Flat leading, edge trailing)

@AMS oh no, much much much worse

@slyka ok, it caused a little confusion with me when the words cutting and embossing are used interchangeably.
I googled around what this is all about, saw videos of similar machines, and they leave me with more questions than answers. What bothers me most is relying on a force equilibrium (by using weight) to define the embossing force/groove depth. Looks rather crude. I don't know if you apply this principle in your lathe, but when it comes to comparing it what others claim is possible: many doubts 🤔

@chris hah, sorry, I know I'm kinda inconsistent about it as well unfortunately, but the fact that it's generally referred to as "record cutting", even when using an embossing stylus and no actual cutting happens really doesn't help the situation.
And believe it or not, just varying the down force of the cutter is… kinda how it's done? Even in the "proper" record cutting lathes from the 60s and 70s like the neumann machines. It's usually just an arm held up by a spring or counterweight, sometimes with the addition of an electromagnet pulling the arm up/down to vary the cutting depth. I've only seen one instance (westrex lathes) that use an "advance ball", a small sapphire sphere that rides on the blank ahead of the stylus to hold the cutting head at a constant distance from the blank and control the cutting depth.

@drahflow ohh, yeah, in regular operation the depth of the groove is controlled solely by the down force applied by the head and relies on the head and suspension being quite heavy to achieve a smooth groove. Though none of that really applies for the video because in that the cutting head is just laying on it's back under my microscope. The stylus itself is attached to a smaller "torque bar" inside the head which is actuated by two voice coil drivers, as illustrated in this little animation of the head

@slyka For the lathes that actually do cut chips, with a very sharp tool and what looks like an cutting angle near neutral (=perpendicular to the surface, this all looks much more likely to me without first hand experience.
For no better comparisons of tools that work with weight, ride on a surface while working it, the chip cutting lathes use a road grader while the embossing lathe uses a steam roller, trying to achieve the same result in one go at constant angular speed. This all might look
off at first glance but having the potential to cut a rough surface into a flat one versus cutting a very precise groove into an already flat surface, not so much of a different story to me.

@chris I'm sorry, I have to admit having a bit of trouble parsing your post and I'm not really sure what you're getting at… >.<
If you doubt that this works I'm not really sure what to tell you aside from, like… that it does? I've cut plenty of good sounding records on this thing, what I'm doing right now is mostly about achieving reliability and repeatability in my DIY embossing styluses. For an example of what it sounds like check out this video, for example https://www.youtube.com/watch?v=yOyvipzLYiI

@slyka the info is for your process to be precise, you probably need more control over the tool position than riding the surface with a force defined by a weight

@chris I don't know what else to tell you besides that that is how literally every major manufacturer of these machines has done it.
no matter if we're talking cutting or embossing. The depth/size control of my grooves is good. I can hit a consistent 50µm groove width using this system and tracking is excellent. like, this has been a solved issue for me for the last three years or so. even when dealing with surface finish issues (which is what I'm trying to optimize right now) the cut depth is consistent and not a problem at all.
Here's a photo of some modulated grooves (Left channel, right channel, in phase, out of phase, filled with blue paint to make them more visible) and the cut depth is nice and consistent all throughout.

@slyka "surface finish" or roughness is essentially secondary, tertiary, ... effects on your measure of cut depth, tracking, modulation.
Therefore calling some aspect a solved problem while having directly related issues, it does not really work that way 🫤

@chris k