I have been experimenting with embossing/impressing and cutting with different styli on different materials. On this thread I will be posting some of my results, using the same source material to demonstrate the differences.
The source material is an analog recording which I transferred onto cassette tape to be able to repeatedly play it without wearing out the master tape.
The signal chain is exactly the same for all examples: Modified Tascam 122 cassette deck, Thermionic Culture Custom Green Fat Bustard, Manley Massive Passive Equaliser, Manley Variable Mu Compressor/Limiter, modified Lipshitz RIAA encoding stage,120W no name PA Power Amplifier, RCA MI 4896 Mono Cutterhead, Fairchild Lathe.
First example is impressing on polycarbonate with a tungsten cone stylus. Groove width is 4 mil.
Decent sound, but increased likelihood of "landsurfing" and less recording time available per side.
The second example is again impressing on polycarbonate using a tungsten cone stylus, but this time making a 1 mil groove.
Pretty awful sound, but less likelihood of "landsurfing" and the ability to record close to 30 minutes per side. I would personally never choose this option.
The next example is what "landsurfing" sounds like.
This is a phenomenon often encountered on impressed/embossed records, where the stylus is riding on the land between the grooves instead of riding in the grooves. Here is some theory about all this:
I will be posting further examples with different materials and techniques and maybe some more theory to go with it, when I have some time. I hope, some of you will find this helpful. Any corrections, additions or comments are welcome.
Thanks for the post! Very interesting, I would love to hear the difference between embossing a polycarbonate disk (preferably with a backwards sapphire / ruby) and then cutting a polycarbonate disk using a diamond stylus, both on the same machine with the same program material like you have done. Don't know if this is something you have the setup to do, but it would sure be great to hear the difference, I haven't taken the plunge and bought a diamond myself yet, so I am very interested to see a comparison between the two methods. One other thing, (you probably already know) the soundclips of the playback examples are all slightly higher in pitch than your reference, meaning that either the turntable you are playing your disks back to record the soundclips with is running fast or your lathe is running slow when you are cutting / embossing.
The pitch difference is caused by the reproduction turntable. It had a worn out belt which left so much gunk around the platter that it actually made a clearly audible effect on the ratio of the motor pulley to the platter pulley. Enough to translate to slightly higher than normal pitch. I have since cleaned it thoroughly and replaced the belt with a new one.
The lathe itself seems to run bang on, as it is was checked with a strobo and it is driven with a quartz locked drive system. Another difference which probably shouldn't matter is that the lathe runs on 60 Hz mains while the turntable runs on 50 Hz mains. However, this should only produce a difference at 45 rpm, considering that both units run with synchronous ac motors, which lock their rotational speed to the mains frequency.
I will be making some cutting experiments soon, but I have not yet tried cutting polycarbonate. As far as I know only Opcode66 makes diamonds that are meant for cutting polycarbonate. I haven't bought one of these yet. Todd, if you are reading this, do you also make long shank versions of your diamonds?
All the examples have been and will be recorded at 33 rpm for a fair comparison.
Sorry, forgot to mention the interesting stuff. I am using a Fairchild model 199, with a RCA MI-4896 monophonic cutterhead. The stylus for the first examples is tungsten cone embossing stylus from John Farmer. I think he calls them GoodTurn embossing styli. They are pretty good and I am getting around 7 hours from each one before the tip wears out. On these examples, I was using blanks that I made myself from sheets of 2mm thick polycarbonate plastic with UV protection. This is the only thing I can easily find locally so I got it to experiment.
On the photographs of my setup, I am impressing with the GoodTurn stylus on black PVC. This is one of the blanks made by Myshank. They are normally meant to be cut with a diamond, but I was experimenting with embossing on them to see what it will sound like. The sound is very good, but there is a lot of stuff coming out which is getting lodged between the stylus and the groove walls causing sudden bursts of surface noise. The obvious solution is a vacuum suction system which is the next thing I will be implementing on this setup.
For all the impressing experiments so far, I have been using good old motor oil. It works well on polycarbonate but I'm not sure if its the best thing to use on PVC. I will be posting some sound samples of my latest experiments soon.
I'd be interested in some exploration related to the angle of the embossing stylus with relation to leaning back the cutting head. Is there a correlation between the angle on the embossing stylus to the angle the head being leaned back? Is it possible to grind the appropriate angle on the embossing stylus to match use of the stylus in a 85 to 90 degree angle like a cutting stylus is used? I think that would be very useful for folks who impress and cut records/plastic in that they could use the same head angle for both applications for the most part.
The tip angle of the stylus is only producing an equal angle between the two side walls of the groove, when the stylus is at 90 degrees to the record surface. Changing the angle of cut will immediately result in a different groove geometry, which can cause a multitude of problems. Monophonic recording is less complicated in this respect. For monophonic cuts, the main consideration for introducing an angle of cut other than 90 degrees to the record surface is to minimise surface noise and aid the cutting or impressing of the material. My observations on this phenomenon are very interesting.
A lagging angle, commonly used for embossing/impressing only seems to work well on polycarbonate blanks. It does not seem to work on PVC or lacquer, where a lagging angle introduces more surface noise and in some cases a vertical oscillation of the cutterhead. Interestingly enough, I was able to impress silent grooves on PVC using a cone stylus of my own design, set for a slight digging angle. I will try adding modulation to this soon. It appears that with a suitable stylus, it would actually be possible to impress on PVC at the same angle as you would set for cutting PVC. However, due to the nature of impressing, you will need a lot more weight for impressing compared to cutting.
Another issue complicating things further is that changing the angle of cut will usually result in the needle moving ahead or behind the center line of the record, which will result in distortion. So, adjustments will need to be made for the hight and protrusion of the cutter head, which most older lathes did not allow for. On my Fairchild, I have to make different cutter head mounting adaptors, when I need to change the angle of cut by more than a few degrees.
Each stylus is only able to produce an accurate groove geometry at a very narrow range of cutting angles. The disk will still be playable with an incorrect groove geometry, but that is where tracking problems begin and we start moving into serious Lo-Fi territory. So, each stylus manufacturer usually offers some information on the angle of cut intended for their styli. If you want to experiment with radical angles, you would need a stylus specifically made for this purpose. Radical angles also cause other problems, relating to wavelength and frequency response. The more you lean the angle back or forth the longer its foot print would be on the record. The difference can be visualised as trying to steer a small boat in water compared to trying to steer the Titanic. I am not referring to the weight but rather the length. The tip lies ahead of the sides!
In stereophonic territory, things get more complicated. Since apart from lateral modulation we also have vertical modulation, the vertical recording angle becomes very important as it relates to correct, undistorted reproduction with a reproduction stylus with the same vertical tracking angle.
There are also other factors that need to be considered such as the plasticity of the material and the thermal expansion when using a heat lamp, which differ between polycarbonate, PVC and lacquer.
Great explanation, thanks! I was thinking on the effective angle applied to the polycarb with relation to the head angle combined with the angle on the stylus without full consideration of the foot print on the blank and final groove geometry.
I had read elsewhere on the board that learning to use your lathe you should start by cutting, not impressing. This seemed contrary to what most were discussing and the set up requirements (for cutting you need a good needle, vacuum system, heat, etc) so I've focused on impressing. Having cut some Laserdiscs recently using an old sapphire and working on an effective vacuum system, I can say with certainty that starting with cutting is absolutely the way to go to get good audio results. Not to say I haven't had success with impressing at times, but nothing consistent yet.
Back on topic, I've come to the conclusion that the offset of the head due to impressing angle is more of an issue that I had originally appreciated. I'm not sure if I can overcome this issue significantly given I'm using a Presto with overhead carriage but there must be a sweet spot that I just haven't found yet with my particular equipment. I do know that I haven't found the correct range related to down force weight and useable tracking. Too much weight introduces a lot of noise from the platter/overhead and not enough results in poor tracking.
Thoughts on conical stylus vs wedge stylus for impressing? I would think that a wedge (reversed cutting stylus) would lessen resistance yielding need for less down force on the blank making for easier impressing and improved window for an accurate groove but that's just a guess.
How does a backwards stylus with no apparent 'leaning back' come into play here for you guys? What's your experience if you have tried this technique. In my experiments I have found that I have got the best results when using a backwards sapphire to emboss (on polycarbonate) VS a steel or tungsten styli. Whilst the result from the steel / tungsten is good considering the price, the backwards sapphire sounds a bit more 'Hi Fi' with more extended top end response and more 'detail'. Have you found the same, or if you 'lean back' the cutting head you are able to increase the fidelity / frequency response when using steel / tungsten? Interestingly for some styles of music the steel / tungsten actually work better, by imparting more of a 'vintage / old school' vibe!!
Inconsistency in embossing/impressing has a lot to do with the blanks, more than with the setup. Even if you keep the impressing setup the same, you will most likely get slightly or hugely different results between two blanks, depending on the quality of the blanks. Consider lacquer as an example. It took ages to develop and the process of making it is insanely precise. You can't expect to get the same consistency from sheets of plastic that you can buy at a hardware store, originally intended for green houses and so on. This does not only apply to polycarbonate, but to any kind of blank that is not very precisely made. On the sheets of polycarbonate I got, there were even thickness variation along the surface, before heating it up. Not to mention tiny scratches and so on. Myshanks blanks on the other hand are very well made and have a proper mirror surface. I haven't seen that sort of thing in a hardware store yet. Still, I doubt that even these are made to specifications as tightly controlled as lacquer. Of course, there is a price difference to be paid.
Using a cutting stylus backwards for impressing is an interesting approach which I have not tried yet. The first thing that comes to mind though is that these styli are usually intended to be used between 0 and 8 degrees, or between 90 and 98 degrees from the surface of the record. If you use them outside this range, you will not get a proper groove geometry.
Leaning it back is mainly done to reduce surface noise, so it is a compromise between surface noise and frequency response. The more you lean it back, the more your HF will disappear. The less you lean it back, the more your HF will be buried under the surface noise. You need to find the best angle for the material you are using and then worry about getting the stylus back on the center line of the record while keeping the angle. This usually translates to a custom mounting adaptor.
The depth of cut (cutterhead weight) mainly has to do with how loud you intend to make it. Deeper grooves can be much louder. However, when impressing, deeper grooves usually mean more noise and also more landsurfing incidents. Keep in mind that the recommended limits for groove width lie between 1 mil and 4 mil for unmodulated grooves. Outside this range you may have problems in tracking. It is not easy to get a 4 mil groove by impressing. It takes a lot of weight, a lot of heat, and a lot of lubricant. It also wears out the stylus faster.
As for whether you should start with cutting or embossing/impressing. My view on such questions has always been that you should consider whether you can afford to have a choice. You can get started a lot cheaper with impressing and you can even make your own needles and blanks, so it may take you one week to make one record but at least you will make one record. If you really are determined to make records, there is no point in wishing you could cut while not being able to do it. Just grind some nails and get some pieces of plastic. If you make mistakes they are usually not as expensive as mistakes done when cutting. If you can afford cutting, then you have a choice, so you start with anything you feel like. To be honest, I'd rather drop a few steel needles the wrong way on some cheap blanks until I get the hang of it rather than having destroyed diamonds, sapphire and lacquer just as a learning process. Even the vintage literature used to recommend using steel cutting styli when starting out and upgrading to sapphire when you get the hang of it, both for cutting lacquer.
I guess this recommendation has more to do with the fact that impressing is highly experimental as a technique and you will have better result with it if you already have a solid background in a very well documented technique such as cutting, where it is easy to figure out whether you doing it right or wrong. With experimental techniques you can never be quite sure.
This example was created while impressing on PVC using one of my own quick and dirty needles. The angle of cut was adjusted for a slight leading (digging) angle similar to what is normally used for cutting. I designed my stylus to have the same length like a cutting stylus and a tip angle that allows correct groove geometry when only a few degrees away from vertical to the record surface. There is a lot of distortion which I will attribute to the fact, that I ground the needle in something like 5 minutes. So it is far from a carefully made thing. The results achieved in this way are far superior to anything I could get when impressing PVC at a lugging angle, with the head leaning back. The groove width is around 1.5 mil. Using such small angles for impressing means that if you try increasing the depth of cut you actually start having chip coming out. The chips get in the way, greatly increasing surface noise. I will try again with vacuum soon.