Chipping - running in reverse

[RoughCreations]

I was going to include this graphic in an earlier thread, but will create a new thread instead.
It is meant to show how chipping on a facet edge can occur with long keel facets, and usually when the keel is on the trailing edge during polishing.
Quartz seems particularly vulnerable, however it also seems to happen with other gems too.

• Picture A shows the direction of lap movement least likely to cause problems,
• Picture B shows the direction of lap movement most likely to cause problems,
• Picture C shows the actual chipping event when polishing these types of facets

The cleavage or micro-fractures shown may or may not necessarily be required for chipping to occur. I have also heard other facetors say that the lap direction should be parallel to the keel facet edge, however my experience is that this is an improvement, but not the full solution. It is a halfway solution between the situations in Pictures A and B.
Let's be clear - the chipping I'm talking about here is not big chunks, often very slight chips or roughness, and not easily visible with the naked eye, a 10X loupe is usually required. Because the keel facet is often at the bottom of the pavilion, this means any chips can be magnified or optically multiplied when viewed from above.

Comments etc. if you have experienced this, or is it just me?
n.b. be sure to download Facetips – A Gem Cutter’s Notebook by facetor Duncan Miller if you visit the link.

[Bucket]

RC, I've had a few pieces of Citrine I collected from Victoria chip on me. Not only did the edge chip but the faces themselves chipped. I haven't tried to fix them at all, yet, but have heard that reversing the direction of the lap may help. It only happened to these particular pieces from the one stone from the Powelltown area of Victoria, so I haven't worried about it so far. When I recut them I'll be trying that method.

[RoughCreations]

Thanks Bucket, good to know. I guess it should be added - more for beginners out there - that cutting with the lap rotating towards your facet edge can be dangerous especially at lower angles if the edge ever catches the lap for some reason... take care!

[Alaskan]

Bucket, I'm early on experience as an old newbie but any experience is useful - what cutting material and size if Diamond is creating chipping? I am currently cutting lab Zircon on a Corian 8" lap using 3K to start then 5K - 8K Diamond on approach. Smallish crown facets on MB's supernova page 30 Vol #1 - it takes longer and speed of cutting C4 (9hours) may be crazy too. Finishing at 14K on another Corian to touch down on C1. What kind of lap and # grit diamond are you getting chips - just looking for more experience to add to my own, thanks.
PS: saxophone musical instrument oil with 3K diamond on carnauba wax on Corian lap begins the cut today on C5. 🤞

[Bucket]

The Citrine that I had chip, and I emphasise that this was the only stone that has (small pieces of a larger single stone), chipped on a finer grit, if I recall now it was around 600, or maybe 1200. I've thought about it and figure it could have been a dodgy lap or maybe the stone ran a little warmer. I've since cut many stones from the  same area without a problem, so I just put it down to that stone. I generally use plated laps and pre-polish on a very well worn 1200, I figure it would be cutting at the equivalent of around 3000. I polish quartz on a pewter lap with cerium oxide without a problem. The chips were that small I didn't pick them up until I started polishing.

[Alaskan]

This morning my Supernova will get C5 16.22* past C3 ~ 46* and it feels like stepping out of the door at 3000'... is this chute going to open or did I miss something in the preparation?
And... it's working...  wow!😳

[Ghost]

If your machine does not have a reversing function it may be possible to simulate one.
Starting with the dop on a line between the lap centre and the faceting mast, cutting on one side of that line will have the lap approaching the facet edge, and cutting on the other side of the line will have the lap cutting away from the facet edge.
From the diagrams above it appears the you need the first of these two situations to avoid chipping.
Cheers,
Ghost.