Concave Facets

[beryl]

. Attached is a concept for a faceting machine which produces theoretically concave facets – to compensate for the convexity often found with flat laps when polishing too fast. Sergey Sivovolenko has mentioned the need for this twice now.
. Calculations (checked by enlarged layout) show that a 125mm (5 inch) radius lap surface will produce concavity 1 micron deep in a 1mm wide facet.
. The concept shown here shows components similar to my Raytech-Shaw faceter (similar to those used by most professional diamond cutters). The BIG difference, other than the spherical lap and platen surface, is that there is no means of ‘vertical’ adjustment for depth of stock removal; the ‘platen’ (tripod bearing surface) must be spherical and concentric with the lap sphere (not necessarily the same size, as shown here). This adjustment is another problem for another day.
. Note the that the change in dop tilt is not the same as the change in facet slope; this would require a non-standard protractor, graduated according to slope.
. A while back I told him about cylindrical laps used to fast-facet synthetic at least 35 years ago – so they could facet them faster with flatter-resulting facets. Too few of us are aware of what's going on in both fields - diamond and colored-stone cutting; we could learn more and progress faster if we were.

 

[beryl]

. Here is pic of Raytech faceter used as a model for above conceot illustration. A beauty of the tripod-type faceter is that you can lift the handpiece off the machine and turn it over to check progress on a facet. This is similar to machines I have seen in Europe.
. My son saw similar in Burma, for cutting sapphires and rubies, except there the two back feet of the tripod rested on a shelf behind the cutter; it was so long that the arc radius was too great to have significant effect on the angle of the dop to the lap. The tripod was a tree branch, the dop was a nail, indexing was by eye - turning the nail in a slot which was tightened with a wing nut. Four cutters used the same wheel at the same time. It doesn't have to be fancy to be adequate.

 

[Serg]

Bruce, I never saw spherical lap for diamonds.

we use cylindrical lap for bruiting Fancy cuts and can polishing( block) flat facet on girdle.( we have plans to develop similar for other facets.
But current cylindrical laps are good enough only for blocking diamond cut. this technology is not good enough for final polishing yet

If we are speaking about last microns for diamond facets everything become very difficult even for cool polishing process by cylindrical lap
I doubt what is possible compensate 1 micron convexity by such way , because it could be 1 micron for one facet but 2 microns or zero for other facets

 

[beryl]

Sergey: To clarify:
. This is concept. I have not seen it either. I will not pursue it unless there is interest.
. The 125mm radius lap is 1 micron crown for 1mm width, 2 micron for 2mm, etc.
. If you are worried about beam exapnsion, you will prefer spherical to cylindrical concavity, yes?

 

[beryl]

. Attached are ways to produce PERFECT spherical surface without precision equipment. I have done it both ways and also with cast-iron lap (as for lenses). I show this only because many shop people are not familar with these methods.

 

[Garry H (Cut Nut)]

. If you are worried about beam exapnsion, you will prefer spherical to cylindrical concavity, yes?

Beryl do you suggest that polishing each facet as concave would reduce the dispersion of the fire exiting a facet?
(I assume the effect on entry would not have as much effect as the exit effect?)

 

[beryl]

Garry:
. That would be true.
. Sergey's desire is to eliminate conVEX facets, which are the result of fast lapping (too much polish flowing under leading edge of facet), because they make a beam more divergent (see his comment in 'Fire' thread). Laps which theoretically produce conCAVE facets shoul reduce this tendency; it is not suggested that they produce concave facets (thread title is incorrect).
. Note, above, that he(?) is already using cylindrical laps but spherical would be more correct. I am just suggesting a way to do it, and had expected a positive response. I have several things in mind for the 'vertical' adjustment problem described in the opening post, but will not waste time pursuing them if there is no interest.
. Paul (Infinity): do you think ADRI* might be interested?
* ADRI = Belgian manufacturer of diamond-cutting equipment I visited with Paul.

 

[Garry H (Cut Nut)]

Beryl the would wear on the cylindrical or spherical lap influence facet accuracy?

What diameter / radius would you envisage the spherical lap as being?

 

[theclaw]

are these patented?

 

[Garry H (Cut Nut)]

are these patented?

The tools or the faceting styles?