VR T-560 Back Angle Contradictions

[ObiKutnobi]

Hi everyone,

It seems the perfect back angle for T-560 cuts is not unanimous.

Most machines appear to come with stylus holder at approx 20 degrees in relation to cutting head body. Including mine. This means if set up with cutting head body parallel to platter (as everyone seems to recommend) then we have 20 degree back angle.

Issue:

1) Souri own website says 0 degree for best cuts

2) Myshank states no more than 10 degree back angle or could damage stylus.

3) Head Body must be parallel to platter.


How do you reconcile these disparities? I know I can chew through a load more blanks and make my own mind up, and possibly end the life of another stylus. But do any of you guys have experience with this issue?

Would you........

1) Make cutting head body parallel as that’s more important and live with the 20 degree back angle?

2) Make the back angle 0 degrees like Souri says for best cuts - but fly in the face of many good people’s insistence that head body must be level?

3) Split the difference and have a slightly angled cutting head body to reduce the back angle of the stylus?


Thank you in advance for any replies that may be forthcoming, and may the force be with you!

Obi

[tragwag]

I set the head parallel and make that one of my benchmarks.
if something else is going wrong, it must be another factor.
In my experience that factor is usually the blanks, and second the stylus.
from there I do my weight and angle adjustments every so often but don't see them causing any specific issue

[kodymonroe]

I would also like to know, I have the same exact problem

[Vice Fiori]

here´s the thing:
When souri´s head reach the blank with the head in paralell, are you sure it reach a exatc 20 degrees fom the stylus?
It´s just a curiosity of mine, dont think I dont belive you or something like this!

[boryo]

since each machine is tested by souri and its owner before order i think it is ok what he suggest (parallel). i dont think setting a specific angel is possible without having some specialised equipment. i've tried to measure a few times with some simple stuff i have at home but i didnt believe in my results. one thing i have learned - more backangel won't cut the material out of the groove
best,
bob

[Dub Studio]

Hey Obi, happy Star Wars day!

So first off, technically what we are talking about here is the "rake angle" not the "back angle". I must confess I am a bit of a stickler for nomenclature at the best of times, but in this particular instance, knowing the correct name will come in very handy for working out the problem. I just did a quick google search for "cutting back angle" and got a load of guff about pruning, which is probably not going to be quite as handy. Google "rake angle" and there is a wealth of info out there.

Cutting with the stylus face at 90 degrees to the surface of the disc is called "zero rake" or "neutral rake" (because it neither leans forward nor backwards while cutting). In machining, cutting with a neutral rake seldom has any advantages at all, aside from the fact that generally speaking its easier to make a cutting tool with a zero rake angle (since the rake angle usually has to be ground into the tool itself). But given that the rake angle is already built into the T-560 head, the clearance angles on the back of the stylus are already there for us, and we are not grinding our own tips anyway, this is a moot point (no pun intended).

Cutting with the stylus face at an angle of more than 90 degrees to the surface of the disc is called a "positive rake" angle (confusingly if the angle is say 105 degrees, that is called a 15 degree positive rake, since its at an angle 15 degrees more than 90). There are many good reasons to use a positive rake angle in just about every context imaginable, and I see no reason why disc cutting should be any different. It's so ubiquitous in the machining world as to almost be a no-brainer, but I will attempt my best explanation anyway.

For one thing, it reduces the cutting forces needed (so you need to apply less weight to get the same depth of cut). Think about it, it's like trying to chisel a piece of wood by holding the tool upright and hitting it on the side. You would have to hold it down really hard, and belt it with quite a lot of force to make a deep impression. And it would probably be a complete mess. By angling it, you essentially make the tool sharper and direct the energy more efficiently. This in turn reduces the power requirements of the turntable, which is handy if you are very close to the limit of its capability (as I am).

There is also the argument that positive rake angle helps to keep the chip (or swarf to give it the correct name) flowing away from the stylus and up the suction tube, avoiding the dreaded "built-up edge" (BUE), where a clump of plastic sticks to the stylus and starts to build up. I still occasionally get BUE using a positive rake, but generally you get crappy chip with a neutral rake which is why its very seldom used.

I might be over-egging the pudding here, but in general machining operations, neutral rake also tends to cause more "chatter", so instead of giving a nice smooth cut, the cutter sort of judders across the surface. The result is a crappy surface finish, but more pertinently, you get a horrible whining noise while you cut (fingers nails on a blackboard anyone?). Assuming we are going for a quiet cut, anything we can do to reduce chatter must be a good thing.

Regarding which angle to use, different materials usually require a different positive rake angle. I note from the google page on the subject that the recommended angle for PVC is 20-25 degrees, which seems to tie in with the default angle of the T-560. Incidentally, the lathe usually comes with a stylus mounting block, that has a v-slot at an angle, which I believe is the same as the angle of the stylus in the head. This should in theory provide an easy way to check the angle of the stylus mounting.

Lastly, let's not forget that the RIAA standard angle for playback is 15 degrees from vertical, and any deviation from this angle while cutting will necessarily affect the top end of your cuts. In that regard, 20 degrees may indeed be too much, but it's certainly better than zero.

Just to be clear, I am not saying that a 20 degree positive rake is definitely the best way to cut, but just that all of the evidence that I can think of points away from using a neutral rake. I am happy to have my opinion challenged if it leads to better cuts, but I had to step in here because I just don't think it's good enough to recommend a technique without giving a thorough explanation as to why. Plus I will sleep better at night if we all use the correct terminology

[Vice Fiori]

Funny fact: if you use too much angle on a stylus, it will jump your head so high, that when it came back to your blank (because VR dashpot it´s like the same of nothing) and see the stylus broken and carving inside the blank, you going to know the real mean of the word "jumpscare"

[Dub Studio]

Maybe, maybe not. If you reduce the heat and the weight, the angle might actually be OK.

The dashpot works perfectly well if you stay within the correct heat/weight/angle range.

[farmersplow]

Hey Obi, happy Star Wars day!

So first off, technically what we are talking about here is the "rake angle" not the "back angle". I must confess I am a bit of a stickler for nomenclature at the best of times, but in this particular instance, knowing the correct name will come in very handy for working out the problem. I just did a quick google search for "cutting back angle" and got a load of guff about pruning, which is probably not going to be quite as handy. Google "rake angle" and there is a wealth of info out there.

...

Just to be clear, I am not saying that a 20 degree positive rake is definitely the best way to cut, but just that all of the evidence that I can think of points away from using a neutral rake. I am happy to have my opinion challenged if it leads to better cuts, but I had to step in here because I just don't think it's good enough to recommend a technique without giving a thorough explanation as to why. Plus I will sleep better at night if we all use the correct terminology

Thank you for this detailed explanation! It makes real sense! I myself do not have a VR T-560, but I cut in PETG and if the "rake angle" is less than 5° for me, then the squeaking starts. Currently I'm still experimenting with 8° -10° and it works fine. I haven't tested 20° yet for fear that my diamond will take off towards the moon and only return as a debris field (although I have a dashpot). ...and thanks for the nomenclature! Since record cutting is a rare (almost extinct) craft, many terms are forgotten and replaced by "similar" terms by the enthusiasts who still exist. - Also from me! Therefore it is time to learn the right terms. (I would have done it long ago, but there is no dictionary for Lathe Trolls).
Greetings from Austria
Thomas

[dmills]

Don't forget that the material you are cutting is plastic and so deforms under the cutting forces and then springs back to some extent.

This argues that for a 15 degree RIAA standard rake on the disk you probably want more then that on the cutter and this is usually a mix of the angle of the torque tube relative to the cutter body and the wedge in the mounting arrangements.
The T560 does of course have its own mechanical limits as well as (usually) a torque limit that may impose restrictions as to what is possible.
I highly recommend the two volumes of the AES Disk recording anthologies if the geometry of this whole thing interests you, there are some fascinating papers there.

One nice trap for those pushing the limits is that this angle impacts the velocity limit when it comes to cutting the top end, the more angle you have the lower the effective limit on stylus velocity before you start destroying the groove wall and the more aggressive you need to get with the HF limiting.

I would note that from what I have read, The American and German machines tended to differ on the detail here and nearly no one actually followed the RIAA standard.

[boogievan]

Indeed, the Ortofon cutting head is held at the target vertical cutting angle - plus an additional 5 degrees for lacquer-springback compensation and another 5 degrees for stylus-holder-flexion compensation - so, for lacquer cutting, a 25-degree VCA would create groove modulation that can be nicely picked up with a 15-degree VTA. The stylus rake of the Ortofon cutter is just 1.8 degrees more than 90, however, as the bridge, which holds the stylus, is tilted to compensate for the body of the cutting head being so very angled. {Fwiw, the first Neumann stereo cutting head used a rocking bridge.)

[kodymonroe]

ive been wondering the exact same thing. seems impossible to get a level cutting head and a good angle.
trying to find the perfect balance of angle and weight is tough.
The straighter the angle the better swarf ( doesnt get stuck under the diamond ) but background noise is worse.
the more angle i have the swarf gets tricky ( more like spiderweb, breaks and sticks to disc more or has more of a cotton
consistency and can build and under the diamond ) but i can get almost no noise at all.

[Dub Studio]

Perhaps this is an XY problem.. it's worth bearing in mind that some styluses are more prone to getting BUE than others, making the process of finding the perfect angle harder to pin down. Other factors can be used to remedy this, and in so doing the angle becomes less of an issue. It's also worth bearing in mind that the stylus length will vary from stylus to stylus, so even if you do find that illusive perfect angle, it might need resetting with each stylus change. I would set the head parallel to the plate as a starting point and then look at the follwing:

- stylus weight
- the suction tube position, I usually try to get it as close as I can to both the plate and the stylus
- the stylus temperature
- the heating coil winding
- lubrication
- atmostpheric conditions
- the condition of the stylus tip itself

[ObiKutnobi]

Hey Obi, happy Star Wars day!

So first off, technically what we are talking about here is the "rake angle" not the "back angle". I must confess I am a bit of a stickler for nomenclature at the best of times, but in this particular instance, knowing the correct name will come in very handy for working out the problem. I just did a quick google search for "cutting back angle" and got a load of guff about pruning, which is probably not going to be quite as handy. Google "rake angle" and there is a wealth of info out there.

Cutting with the stylus face at 90 degrees to the surface of the disc is called "zero rake" or "neutral rake" (because it neither leans forward nor backwards while cutting). In machining, cutting with a neutral rake seldom has any advantages at all, aside from the fact that generally speaking its easier to make a cutting tool with a zero rake angle (since the rake angle usually has to be ground into the tool itself). But given that the rake angle is already built into the T-560 head, the clearance angles on the back of the stylus are already there for us, and we are not grinding our own tips anyway, this is a moot point (no pun intended).

Cutting with the stylus face at an angle of more than 90 degrees to the surface of the disc is called a "positive rake" angle (confusingly if the angle is say 105 degrees, that is called a 15 degree positive rake, since its at an angle 15 degrees more than 90). There are many good reasons to use a positive rake angle in just about every context imaginable, and I see no reason why disc cutting should be any different. It's so ubiquitous in the machining world as to almost be a no-brainer, but I will attempt my best explanation anyway.

For one thing, it reduces the cutting forces needed (so you need to apply less weight to get the same depth of cut). Think about it, it's like trying to chisel a piece of wood by holding the tool upright and hitting it on the side. You would have to hold it down really hard, and belt it with quite a lot of force to make a deep impression. And it would probably be a complete mess. By angling it, you essentially make the tool sharper and direct the energy more efficiently. This in turn reduces the power requirements of the turntable, which is handy if you are very close to the limit of its capability (as I am).

There is also the argument that positive rake angle helps to keep the chip (or swarf to give it the correct name) flowing away from the stylus and up the suction tube, avoiding the dreaded "built-up edge" (BUE), where a clump of plastic sticks to the stylus and starts to build up. I still occasionally get BUE using a positive rake, but generally you get crappy chip with a neutral rake which is why its very seldom used.

I might be over-egging the pudding here, but in general machining operations, neutral rake also tends to cause more "chatter", so instead of giving a nice smooth cut, the cutter sort of judders across the surface. The result is a crappy surface finish, but more pertinently, you get a horrible whining noise while you cut (fingers nails on a blackboard anyone?). Assuming we are going for a quiet cut, anything we can do to reduce chatter must be a good thing.

Regarding which angle to use, different materials usually require a different positive rake angle. I note from the google page on the subject that the recommended angle for PVC is 20-25 degrees, which seems to tie in with the default angle of the T-560. Incidentally, the lathe usually comes with a stylus mounting block, that has a v-slot at an angle, which I believe is the same as the angle of the stylus in the head. This should in theory provide an easy way to check the angle of the stylus mounting.

Lastly, let's not forget that the RIAA standard angle for playback is 15 degrees from vertical, and any deviation from this angle while cutting will necessarily affect the top end of your cuts. In that regard, 20 degrees may indeed be too much, but it's certainly better than zero.

Just to be clear, I am not saying that a 20 degree positive rake is definitely the best way to cut, but just that all of the evidence that I can think of points away from using a neutral rake. I am happy to have my opinion challenged if it leads to better cuts, but I had to step in here because I just don't think it's good enough to recommend a technique without giving a thorough explanation as to why. Plus I will sleep better at night if we all use the correct terminology

Thank you so much for such a considered reply Top man!

[farmersplow]

Dub Studio described it perfectly and I'd like to chime in here and support the terminology with a few images. And because I agree with everything except comparing the Rake Angle 20 degrees to the RIAA standard 15 degrees from vertical. I also have a few pictures to explain this.

VTA 01.png

VTA 02.png

VTA 03.png

VTA 04.png

VTA 05.png

VTA 06.png

VTA 07.png

VTA 08.png

Finally, my opinion on the RIAA standard 15 degrees from vertical.
As far as I know (and please correct me if I'm wrong), the RIAA standard for the vertical angle (VTA) used to be 15 degrees. Since about the mid 70's that has been changed to 20 degrees +/-5 degrees (so 15 to 25 degrees). But the VTA has nothing to do with the rake angle. You can have a rake angle of -20, 0 or +20 degrees and still keep a VTA of 15 degrees. - If you only change the angle of the stylus.If you leave the entire geometry of the cutting head the same and want to get a different rake angle, you have to rotate the entire cutting head. But if you do that, you also have to keep in mind that ALL ALL ALL angles shown in the pictures above will change as well!

VTA 09.png

(The farmer plows his field more easily with a positive rake angle. The horse does not have to make such an effort...)

Greetings from Austria
Thomas