I have a new UltraTec V5 classic and I'm having issues with the pavilion girdle facets being offset prior to transfer.

To explain - I cut my P1 facets to a temporary center point (culet) using a hard stop, and then bring my girdle facets one by one, chaining them. By the time I make it back to the first girdle facet, I'm off by about 0.5mm. I've also tried not chaining them, and I can split the error visibly over every girdle fgacet, but I see no reason that I shouldn't be able to just chain them if I'm being careful with every meet.

I've tried this with 2 different stones and 2 different dops - issue persists.

I've checked my index wheel / cheater alignment using the UltraTec alignment bar (bar goes in dop and then site square on a lap, and you can set your zero this way).

Is there anything else that could be causing this weird offset? Maybe there is something obvious in my work process that I'm missing (I'm a new faceter).

Thanks a lot!!

Sounds like by your explanation that the platen is not in alignment to the quill and mast assembly, assuming the lap is not the issue. Have you contacted Ultra-Tec to see if they can assist you with getting it corrected or explain what your experiencing?

what shape you trying to cut?
you sure you have a perfect center point?
when you cut pavilion first from a diagram, with a specific L\w ratio and exact angles, without a perfect center point you cannot meet to a perfectly even girdle. at least as far as I know...
you can spread the error around the stone, makes it less obvious, or you can try to cut the girdle first and see if this method works for you.
depends on the design you're trying to cut, and the L\w ratio, it can be more complicated to to achieve a perfect center point.

If you are trying to see if your machine is straight, try to cut a perfectly straight girdle on a square stone.

Don't use the meet point of the culet as your control point. To much room for operator variance.

In fact, don't use the meet point at the culet method to cut any stone. Too much wasted stone, and lack of control of color and clarity issues. Pre-form, cut the girdle outline, then lay the facets down in the desired pattern.

I should have read this more clearly!
Start here, like stated is it truly a center point, or should be because it is a hard stop.

There are two potential sources of this problem - the machine, and your technique.

If you suspect the machine is out of alignment, before doing anything else like contacting UltraTec, please work through Paul Head's test procedure thoroughly. (It is worth learning to do this anyway.) If there is something wrong with the machine this procedure will reveal the problem. Then you can communicate about it meaningfully. Until you have done this, blaming the machine is just speculation. https://usfacetersguild.org/faceting-machine-alignment/

You are a new faceter. There are plenty of potential sources of error in establishing an initial center point. A coarse lap will not allow you to obtain an accurate center. On a fine lap, unless you are cutting glass, differential hardness may make some facets slower to cut. The temptation is to increase your finger pressure. You need to stop cutting each facet with the same finger pressure and on the same place on the lap. I use a 1200 grit lap to establish a center point. On my digital UT I stop when the flickering of the second decimal place just stops. On my analog UT I tap the stone gently on the lap to hear if it is tapping on the lap or the stop lever. I always finish at the same place on the lap. It is tricky. You have to work at learning how to achieve an accurate center point. If you cut the girdle facets first, as some recommend, it is easy to press the UT quill beyond the stop. This is why I don't cut the girdle first on most stones, and recommend the meetpoint faceting technique, at least for beginners (unless working on a platform machine with a short quill, like an Imahashi or a Raytech-Shaw).

As you can see there are completely different approaches to gem cutting.

My preference is to preform the cut the girdle, not the meet point of the culet. In fact, many of my designs don't even have a meet point at the culet. My preference is for a keel because it gives higher yields.

I also do not use the machine to set the angles or the depth of cut as one does when he cuts with the hard stop method. I use the machine with a soft stop. The index wheel, protractor, and dial gauge are used to measure the angle rather than set it.

This method enables me to cut either the crown or pavilion first depending on the challenges presented by a piece of rough.

Different strokes for different folks. Neither method is more correct than the other.

I always found this article to be a tad controversial, but speaks to the point of a opinion and that we all have a reason for our individual technics and methods.
https://usfacetersguild.org/be-a-performer-not-a-preformer/

I think this line sums up the position of the author of that article perfectly.

" Let’s face it. Your finished stone will only be 20% to 25% of the weight of the rough you started with."

His position is that preforming results in smaller stones. His expectations of recovery disproves that statement. You could really stop reading the article at that point.

I have found that those who use meet point faceting are in fact getting 20% to 25% recoveries.

If you really are only getting those kinds yields you are wasting material, money, and profit, for no functional gain in stone performance.

He then goes on to describe what he views as his efficient cutting and polishing lap sequence. He must be kidding 6 laps!

This is just plain ridiculous. The vast majority of time I use only two laps to cut and polish a stone. The second lap is a two banded pre-polish/final polish lap so you could count it as 2 if you like.

Without exception, the best cutters I know in the World all preform. They work on an optimized progression of laps designed to minimize the number of laps used, and the number of times each facet is touched in the process.

Personally, when my recovery falls below 40% I am very disappointed. I often achieve 50% and up.

I don't achieve these results by sacrificing performance. I do not accept windows in the stones, and my end result must achieve the "Excellent" grade when graded with the G.I.A. cutting grade criteria. These are precision cut stones, and not commercial cuts.

Greg (gdHayes) and I had a mutual friend who was a World class performer. He taught Greg, and I was taught by the same Germans who taught him. So we share a common respect for this skill. Greg understands the value of good preforming, and employs it in his cutting. The truth is that to a great extent the art of gemstone cutting is the art of the preform. The majority of profit made in gemstone cutting is made at three levels. When and how you buy the rough, when and how you preform the stone, and when at at what level you sell the stone. The laying on and polishing of the facets is one of the least determinant parts.

In cutting shops that work with high end material the most senior and highest paid person is the pre-former. The facetors are the junior people. It is the pre-former that the owner depends on to help select, sort, and value rough to be purchased.

Another benefit is that a properly trained gemstone cutter using the pre-forming method can take a piece of rough of any L/W/D ration, look at a facet pattern and cut it without the aid of any diagrams. Thus maximizing recovery. I spend a great deal of time training my students to cut without diagrams. Cookbook following of diagrams is the enemy of proper gem cutting.

Understanding pre-forming is the difference between a gemstone cutter and a hobby facetor. Two very different approaches.

I think you meant Pre-Former not performer.

You are both a good pre-former and an excellent performer.

Thanks for catching that but is seems I am unable to edit to fix it.

First off - wow! Thank you everyone for your responses.



I am trying to cut this newbie design:
https://static.wixstatic.com/media/2cb8e7_d276e54e5fcd4791907fd4879f5df445~mv2_d_4701_5206_s_4_2.jpg/v1/fill/w_403,h_446,al_c,q_80,usm_0.66_1.00_0.01/2cb8e7_d276e54e5fcd4791907fd4879f5df445~mv2_d_4701_5206_s_4_2.webp

When you asked if my centerpoint was accurate, I immediately responded 'yes' in my head because, by the looks of it, my center point was very accurate. However, I now realize how minorly over or undercut a pavilion facet could be in order to present an issue at the girdle and I do in fact believe that I was not cutting it as accurately as is required based on some of the other posts I read.

Thank you for your response! I went back to my stone and went back and forth between girdle and P1 facets, cutting as I went. I managed to get the centerpoint as accurate as I could under a 10x loupe and improved my girdle by probably 75%. I think that this was the issue all along... boy I could really use a mentor when it comes to these types of things.. especially with pre-polishing lol



I was able to cut a square stone just fine and I think that mostly ruled out the machine being an issue.

Thanks for this idea.



I'm sure many of you would be inclined to want to give me the benefit of the doubt and assume the machine may have had even a chance at being the cause of the issues, but I do in fact believe it is my technique causing the issue. I did not follow Paul Head's test procedure but I did verify the following things and the machine seemed to be fine. The platen was flat to much less than 0.001" and the quill was also centered within much less than 0.001" as well. I don't see any issues there, but there may be other critical items I'm missing. I really doubt it's the machine though. I will read that procedure just for my own knowledge purposes. Thank you.



Thanks for sharing. Looking forward to asking more questions and getting such detailed responses from you guys.

WOW your right, this paragraph seems like your saying "POM" its not my machine. And I'm very happy its not, its a real PIA to deal with one that it is, especially when there are great distances requiring shipping back and forth with a manufacturer, so contacting a manufacturer for support should not be a last resort if its not that old.

No there was no assuming or inclination's for me on your original post if that's your inference.

What it appears you discovered from your on words, are what all faceters and gem cutters have at some time in their journey is "PERFECT" is in the eye of the beholder.

And I will ask if you would be so reciprocal in providing your methods of verifying "flat to much less than 0.001", I have a $17k machine in my shop that I would love to calibrate to your methods.

I am as proud of my machines as you appear to be of your UTV5 Classic and rightly so. PERFECT! not likely.

I measured the runout relative to the base using a calibrated mechanical dial indicator with 0.0005" resolution increments. My dial indicator has a steel block that sits flat on the base of the UltraTec and has a rigid arm that extends upwards and onwards which holds the dial indicator tip in the air. I placed the dial indicator tip on the top of the platen at 3 different locations across the platen radius and rotated the platen by hand. The maximum vertical deviation I saw during rotation was less than 0.001" which would coincide with the measurements reported on my initial calibration certificate from UltraTec.

As for the quill. I inserted a dop into the quill, set the mast angle to 90 degrees and placed the dial indicator on the OD of the dop body. I rotated the quill and monitored the readings on the dial indicator as it rode around on the OD of the dop. Once you baseline your quill, I'm sure this is also a good way of measuring if your dops are possibly bent. I did this for a number of the dops and got very similar readings.

By measuring the dop runout and then inferring that the quill had no runout, I was assuming that the dop was machined in a way that would land it in the center of the quill which I believe is true but I can't be sure without directly measuring the dop dimensions. I have no reason to suspect that there is an issue with the dop, so I left that issue alone.

I'm not sure this is the best method, but it seems to make sense to me and I think it provides some valuable info.

I read Paul Head's post and what I did is certainly no substitute for that thorough procedure when it comes to assessing the dimensional relationships between the parts of a faceting machine.

Very much appreciate the detailed methods, it will help others as well in the future who may stumble across this thread.
With all that, and any cutting technics your machine should provide you P1 TCP to work from, and not a work around by going back and forth to achieve a 0.25mm. Even with that result, the ending CP of P1 is still off after P3, ultimately transferring to the Crown, which ends in the table.