Cutting and Polishing Against the Stop
by Glenn Klein - Revised January 2001
In this paper I want to concentrate on controlling flat facets with sharp edges, sharp meets, and done at difficult low angles and/or difficult meet points. This paper is not about using proper polish laps or powders. These emphasized items are what you have to master in the World of facet competitions.
The quality of your polish is important, but it seems to me that everyone is writing articles about how they get a good polish, when they should be concentrating on managing the items I have underlined. When they talk about quality polishing methods they have devised, it will not mean a thing to me unless they do well with the underlined items. It is very difficult for a judge to tell the difference in the quality or "shine" of your polished stone as compared to the other entries. But, the judge can see in a hurry who has the flat facets, sharp edges, and sharp meets. Conquering these items will get you a higher score than just an excellent polish. Doing the fine cutting and polishing with my method of working against the Stop has been the key to my success in competition.
First of all, what is the problem? The problem is that it is so easy to exert too much pressure on the stone against the lap, when you are doing very fine cutting or polishing. And when there are facets with unusually low angles coming together from weird directions, it becomes difficult to get good meets, or flat and sharp-edged facets. Working against the Angle Stop has given me the most successful tool with which to get award-winning stones. Nothing else I have learned has done more for me. It is very time-consuming system at first, but after you get used to the procedure you will speed up, and feel confident that you can return to a facet if necessary.
All faceting machines have three characteristics that the facetor controls (See above figure): A. rotational angle, controlled by rotating the index gear to the desired position and making slight adjustments with the index vernier (cheater), B. Axial angle, controlled on the Ultra-Tec machine by moving the angular position of the spindle until the angle dial shows the desired angle and then locking it in place with the lock knob, and making fine adjustments with the fine adjust screw, C. Height, controlled by raising and lowering the riser block on the mast by using the vertical knob. In this article I am mostly concerned with the Axial angle and Height controls.
To begin with, the design we want to do calls for four square facets at the center of an apex crown, at just six degrees each. That is an extremely low angle, you will agree. Or possibly, the design calls for seven triangular shaped facets going to one meet point on the end of an oval step cut. These are just two cuts, which will give you fits, when you are trying to get flat and sharp meets. Trying as hard as I could, I used to end up with rounded facets or poor meets, until it finally dawned on me that I had to control the amount of pressure I was applying stone to moving lap. Experimenting brought me to the method of greatest success--learning to POLISH AGAINST THE STOP. This method results in resistance to my pressures, and will control angles, reduce vibrations, and result in the appropriate Constant hand pressure, as far as the gem material knows.
To illustrate this method let's say you want to polish a facet at 45 degrees. Set the angle dial at 45 degrees using the angle stop and fine adjust screw. After you have locked that angle in place, lower the riser block using the vertical knob until you first detect the stone touching the stationary lap, in the area where you want to work. After making tiny corrections up and down, you arrive at the point where you are sure the stone is just touching the stationary lap, with no hand pressure being used. At this point you can put the lap into motion, and know that the amount of pressure you apply is the biggest variable to control.
This competition facet you are working on cannot be determined by sound. If you can hear that you are touching the lap, it is already too late for you this time. You goofed. And besides, as you grow older, and your sense of hearing gets worse, you will over-cut and not have a flat facet if you try using hearing as your guide. Often, certain facets will not make a sound on a smooth stationary lap, which is lubricated with diamond or water. So, you also need to keep an eye on the angle dial, to see if it indicates that your stone is already on the lap!
My method also controls the springiness or flexing of the mast, the spindle, and the dop. There are small amounts of bending going on. The machine is not rigid. My method allows you to have more control of that pressure that you are exerting. Things are more uniform and constant this way.
If too much pressure is applied or the stone is set too high on the mast (clear of the lap), the facet will be rounded towards the point farthest away from the mast. If too little pressure is applied or the stone is too low on the mast, the result will be a rounding towards the heel of the facet closest to the mast. Varying hand pressure will result in rounding in all directions. You will unknowingly exert varied and probably excessive hand pressures when you are tired, unhappy about something, or feeling the effects of your martini. So work on your competition stone when the time is right.
I realize that not all faceting machines have the feature called an ANGLE STOP. But my Ultra- Tec machine does have one. In my opinion, other faceting machine features like a larger angle gauge attachment, electronic gadgets, or an attached microscope are useless for serious competition cutting.
The coarser laps required to get rid of most of the rough are used to speed the work, The coarser laps are all extremely uneven and not considered with this Stop Method. This whole procedure is done only with the fine cutting and polishing laps.
If you find that the stone just touches your moving lap in all areas equally, then you have a very flat lap and your machine is perfectly aligned. But there are always tolerances involved. Nothing is perfect, or stays that way. Change does happen. My typemetal lap is the flattest of my collection. My copper 1200 is very good, but noticeably uneven in comparison. In regular cutting with the copper 1200 I am riding up over hills and down into valleys. If I use the angle stop with the copper 1200, I am cutting just on the top of the hills. This results in very flat facets.
With my typemetal lap I more or less just work against the Stop with as little pressure as I can, while still holding the stone steady. I am letting the stop control the actual depth of cut. The amount of pressure that you put against the stop has to be very light, or you will still bend the mast, the dop, or the Stop itself. The power you have in your hand as you press is amazing. Just the weight of your hand can be too much. Some of the facets are extremely small in surface area you have to remember.
To set up for the first time, do this: Take your finest and flattest lap, set it in place on the platen of your machine. Set your dop at an angle such as thirty degrees by using the angle stop. Then, lower the riser block on the mast until you can detect that the stone has just touched the stationary lap. Now move the lap by hand, as you slowly and carefully sweep the stone over all areas of the lap. Determine the spot where the stone just clears the entire lap. Your lap will NOT be entirely flat. Then lower the stone again until you find the spot that first touches the lap. At the outer rim of the lap put a felt pen black line. Now remove the lap and mark the Platen directly under where the laps black line was. In the future you will always attach this lap so the two black lines are lined up together. This is the area that you will always go to when you are lowering a stone until it touches.
In determining the moment that the stone touches the stationary lap (especially polish laps) remember to watch the angle gauge as you lower the stone to the lap. Sometimes you will think you are clear of the lap, and yet the angle gauge shows that you have already touched. Sometimes you will feel the stone touch the lap. And, sometimes you will hear that you have touched the lap as you push the stone back and forth between your thumb and index finger over a small one-half inch area of the stationary lap. You are pushing back and forth, not up and down! So you are using your senses of sight, feel, and hearing. If it takes your sense of smell to tell if the stone has touched, you are pressing too hard (I am just kidding). The point is that you have to know where you really are. Take the time to be sure. You cannot check too often. I raise and lower the riser block again to be sure of that point. This adjustment is in the smallest correction amount that I can make, on the mast.
You will learn at this point that the vertical knob has slop or backlash in it. Backlash or slop in the threads is built into the vertical knob. This adds to the difficulty in determining that point of stone just touching the lap. It might take two tiny corrections up to equal one tiny correction down, etc. The mast threads have to have some clearance to be able to turn. This causes the slop. This backlash has to be understood. I guess a good machinist could explain to us why this is.
You do have to hold the stone in place on the lap as you polish; otherwise it would wander all over and result in an un-flat facet. The trick is that we barely hold it in place with the light pressure needed to hold it against the Stop, letting the lap do its work for you.
The repeatability of the faceting machines of today is remarkable. But, that repeatability works only if you have taken good and thorough notes in the first place. As you polish a facet, correct your earlier notes, which were valid when you last worked on that facet.
The notes that you made earlier were as of the last lap used with that facet. Now you put on a finer lap and begin with those old settings. You must presume some corrections will be needed, so when you first touch stone to the moving lap be very careful. Just touch and take a look. See where correction is needed. Try again to be sure you are evenly set all across that facet. You will need to cut or polish very little, but look a lot. You make slight corrections and very short tests to see where you are. Note anything that you will need to know about the facet if it becomes necessary to come back later. You will need the index setting, the angle, the amount and direction of cheater use, and you might also note the area of the lap you used as well as the direction the lap had been turning. My notes on a row of 42-degree pavilion facets might look like this:
Index Setting 12 36 60 84 Angles Last Used 42.33 42.2 42 41.95 Amount of Cheater Used L 3-1/2 0 R 2 L l-1/4
There are lots of other things you could also note, such as CW or CCW (lap rotation), 5Clock or 3Clock (portion on the lap used), 1" out (from the laps center) or 2" in (from the laps outer edge). Whatever means something to you that could be valuable if you have to go back over a facet.
Most of my cutting and polishing is done at the five clock working position of the laps. This is the area, to which I lower the stone on the mast and at the proper angle to the stationary lap. If you have to do your cutting at the three-clock position, move your stationary lap so that its black felt pen mark is at three clock, and lower the stone to that area. In each case you want the marked high spot of your lap to be in the area that you intend to do the work.
Getting back to the same previous settings in order to polish the table facet can be difficult. Just removing the dop from the spindle and then attaching it again can change your settings ever so slightly. Changing the laps will show you that new cheater or angle corrections are needed. Changing to the 45 degree Adapter (Tabling Adapter) and then back to the regular dop can result in new corrections being needed to polish the other crown facets, etc.
Determining the point of touching stone to typemetal lap is very difficult when using lOO K spray diamond. The lubricated diamond along with the very smooth lap makes it a challenge to find that correct spot. That high spot on each lap is where the stone will touch first when you cut. That is the point that you need to know. Take this another way. If your lap has wide variations between its highest and lowest spots, and you lowered your stone down into that lowest valley until the stone touched, you know that as the lap begins to revolve you will over-cut that facet.
While polishing, I am usually keeping the stone stationary or with a back and forth movement over the lap of only 1/4 " to 3/4". No large sweeps across the lap, because no lap is so level and true across that it will allow you to do a good job with such drastic movements. You are almost letting the weight of the dop and stone be the pressure against the lap.
Polishing with Ultra Laps and ceramic oxide glued-down discs are excellent with quartz. But you will get a rounded facet the moment you apply too much pressure with your hand. Using the Stop method helps to get much flatter facets because you are exerting little pressure. But it is a Constant one.
I polish only at the slow speeds. Once you get the RPM's of your lap high you magnify the vibrations, and can induce shock damage to delicate stones (like Kunzite). Besides, high speeds will result in over-cut facets, or a deep scratch across a facet which you could have avoided by polishing slowly and looking at the facet more often.
After all these nit-picking procedures that I have described, you may feel that I must be faceting on a machine that is terribly manufactured or is way out of alignment. That is definitely not the case. I have used my machine for over twenty-four years, and it looks just like new. The machine has stood up remarkably well. The accuracy it allows me to achieve is amazing. I have not been cutting for stone sales. My World has been the challenge of the competitions, with my most difficult opponent being myself. I am always trying to do better with each new stone. I have collected quite a number of trophies at the World-Class level, and I credit them all to my Ultra-Tec machine. Its repeatability is outstanding, and that is what you need to win.
My machine continues to look new because I never use messy slurries. I thoroughly clean the machine and laps after each use. I use very little polish powder. If using the diamond spray, it is only a very short burst. With the powders, I use a steady water drip at the rate of one to two drops per second onto a wet lap. The idea is to keep washing away the waste so that it does not build up and contaminate the lap.
It is my practice to do the final cutting and polishing of every facet, of every stone, using the Working Against The Stop method. Many faceters may not want to use this method because of the extra time it requires. But if you want to compete against yourself, by doing the best you possibly can, or want to make the most perfect gem you have ever done, you will benefit by using my method. If you are going to enter competitions at the level of the International Faceting Challenge you will have to have flat facets with excellent meets. The Stop method may prove to help your score. Although my method is time consuming at first, it will speed up after you get used to it. It will become habit. And you will be the winner.