Achieving proper cutting depth

[Adinol]

A week ago I didn't even have a clue how records were made and now I want to make a lathe. Well, that's because I've always been a DIY-er and when I get fascinated by something I want to build it.

So, as I'm learning about this whole process I've noticed that there are basically two systems that can be used to achieve proper cutting depth. One method would be to figure out the proper weight of the cutting head pressing against the surface of the material, and the other method would be by adjusting the distance of the cutter, much like on a regular metal lathe.

When I learned that some folks cut on acrylic sheets one thing right away came to mind.

I actually have a lot of experience working with acrylic sheets. One thing I've learned, in my experience, is that acrylic sheets can vary in thickness, throughout the same sheet. First, the sheets that are called 1/4" aren't exactly that. They are usually less than the nominal value and the exact thickness varies from manufacturer to manufacturer, as well as from batch to batch. But the bigger problem is that the thickness is usually not uniform throughout the entire sheet. I've generated a lot of scraps in my productions just because the thickness would vary by as much as 0.1mm as little as 4 inches apart. That's a huge variation when doing precise work.

So, if the depth of the cut is adjusted like on a regular lathe, i.e. by setting the distance, this will result in non uniform depth of cut throughout the record, simply because, unlike turning metal, one does not make a pass to make the surface nice and even. So, in my opinion, those who are planning to cut on acrylic sheets would be better off with a lathe that controls the depth of cut by setting the proper weight of the cutting head. Or does that type of apparatus have another set of problems?

[Sillitoe]

Hi Adinol!

Simple explanation...

Setting depth doesn't necessarily mean the stylus is fixed at that level.
The cutter is attached to a pivoting bar that is suspended by a spring, with a dashpot that dampens any vertical movement (from uneven disk surface etc).
An electromagnet can be used with the above combination to "set" depth and/or control variable depth.

Keep reading and welcome!
Lots of info here, don't expect people to give you part numbers or specific measurements.
Although people here are reverse engineering designs of others who are still currently selling the given items

Be original, add to the art form.

Cheers
James

[Adinol]

...The cutter is attached to a pivoting bar that is suspended by a spring...

Ah, OK, this makes sense. I'm glad I asked, though.

...don't expect people to give you part numbers or specific measurements...

Are those considered trade secrets? Is it considered uncool to ask? Sorry, newbie questions.

Be original, add to the art form.

Absolutely. But I want to be original in ways other than reinventing the wheel and I just want to save time by avoiding mistakes that others have already gone through. Then, once I have a few builds under my belt I can help future newbies.

For example, I am wondering if 3W speakers are powerful enough for a clean signal cut. Or am I better off with 5W.

[Sillitoe]

Hi Adinol,
This is of course only my point of view.

I don't think it's uncool to ask and some people will be absolutely fine giving you specifics...
Lots of answers already here, along with answers to other questions you hadn't yet thought to ask.

Cheers
James

[thelegr]

Hello!
As i'm a DIYer as well, and i'm on making a larhe, i realised that nothing's fixed (correct me if i'm mistaking something).

I mean, there ARE the well known RIAA standards (i can post a link later if you need it), but some things are not static... For example LPI and depth of stylus.
If you try to rec on 290 LPI (Loops per inch) you should (as i measured) use quite smaller depth ( which also affects width of groove) than cutting on 190 LPI.
Something you have to consider (thanks to opcode66 and his e-mails for helping me on that) is that the width sould be over 1mill (suggested 3mil depending on your LPI).
Stylus cutting edge is about 90deg. so depth is half of width. Do the math!

[carlos820]

For example, I am wondering if 3W speakers are powerful enough for a clean signal cut. Or am I better off with 5W.

Adinol, I am new on the forum as well, and also building up a parts bin to jump into the DIY Lathe making arena.

Your question is a good one, and I also have some small full range speakers that are 6 ohm and are labeled at 3w...not sure If I can use them either.. I see on the forum that the pro-grade machines are driving the head transducers with upwards of 200w power amps... I was hoping to use a small Furman 20w amp...lol does that put me in the junior team? If any of you more experienced DIYers or Seasoned Experts can chime in that would be great!? Thanks!

[markrob]

Hi,

Maybe this will help.

Even the pro cutter heads can't handle much more that 10 watts on a continuous basis. However, at high frequencies, you need large amounts of current drive to the head to accelerate the mass of of the entire moving system such that you can get any sort of level recorded. In addition, the inductance and back EMF of the voice coil in the head (which is really just a DC permanent magnet motor at the end of the day) resists the ability to force current into the coil. So while you may only need to drive the head with a few watts on average, the high frequency peaks require large amounts of reserve to get decent high frequency response. This is made even worse for the typical home brew head as its really hard to keep the mass of the moving elements low (less than 2 grams, for example). This really works against you. If you do the math, it will become apparent. It may seem that going for a driver with higher power capability would always be the way to go. This might not be so if that driver comes with higher moving mass. Keep in mind that the pro heads are typically helium cooled and have a great deal of protection systems present to prevent smoke.

Hope that clears things up.

Mark

[carlos820]

Mark

Thank you for such a great explanation, that clears it up quite a bit!

I'm doing some more reading and study, soon I will have some newbie questions on feedback heads, at the moment I'm intrigued whether they are even at all remotely diy do-able.

-Carlos

[markrob]

Hi,

There are several projects here with feedback in mind. Check out Bryan's Grrovescribe for some detailed and promising experimental results.

Mark

[Adinol]

Hi,

Maybe this will help.

Even the pro cutter heads can't handle much more that 10 watts on a continuous basis...

Hope that clears things up.

Hi Mark,

Thank you for taking the time to explain this. It does help.

I can see that it really depends on what one ultimately wants to build. Building a recording lathe to satisfy audiophiles is not the same project as a dad building a lathe for his kid. I want to build a lathe for my kid, but I still don't want to end up with something that doesn't really work.

I've only made a few posts so far but I get the feeling that a lot of the information I'm looking for are closely guarded secrets. I totally respect that. But if that's the case I also wonder if anyone might get upset if I start sharing information that others want to keep under the hat.

Again, I'm not in this business, so I don't know. But if I get the general idea I can stick to the rules, whatever those rules might be.