Faceting

There is no provision on these machines to individually preform a round girdle. the picture shows a home made preformer using 4 ball bearings. It works very well, fast and easy to use.

Any cut that has a straight girdle can be done on the machine as the offset rotating mast assembly can be positioned to do the girdles. Most available jamb peg machines will have a slotted base, so cutting flat girdles won't be a problem.

Set the height of the arm above the first lap you are going to use, a 12-15mm spacer will work fine. Use the spacer for each lap you use, this will eliminate the need to find that first facet when you change laps. Once the height for each lap is set, that's where it stays. Avoid using the cheater adjustment on the first half of the stone.

The upper part of the table attachment is permanently fixed to the machine. Once the table is cut it makes it a lot easier to judge the size of the main facets. Adjusting the table attachment will be trial and error at first.

The lower part of the attachment just clips on to the side arm. Remember to set the cheater to the correct position before starting a stone. If the cheater is off then the table will be off.

The table is always cut with the lap running in reverse- anticlockwise
The lap direction must be switched back to the normal cutting direction- clockwise when tables are finished, a lot of damage can occur to the lap, machine and yourself if the dopstick happens to dig into the lap at high speed.

Jamb Peg Conversion

If I'm trying a new cut and not sure of the indexing, I can use this conversion chart to convert the indexing from a faceting diagram to get the indexing I need for the Jamb Peg. In the chart the octagonal lines represent the 8 mains, the curved section shows part of the standard 64 index gear. Eight mains are cut using the 8 flats on the dopstick. then 8 stars at number 4, then 8 break facets at -2 and then 8 break facets at number 2. (-2 equates to 62 on a standard index gear and 2 equates to 2 on a standard index gear).Any diagram can easily be converted to the jamb peg method of indexing, if the ratio is close between your stone and the diagram, then it should work.

Jamb Peg Diagram

A jamb peg diagram, if used, are numbered as follows - 0 for main facets, 4 is used for star facets
and break facets 2- for left side and 2+ right side. so on a SRB only 4 index changes are used to cut the stone

This is not a protractor in the photo, just numbered holes on the jamb peg quadrant to hold the point of the dopstick. There is no protractor or hard stop, you have to choose your own angles. I will check the pavilion main or culet angles with a digital inclinometer to make sure I'm cutting above the critical angle of the stone. From then on it's all by eye.

The meter in the photo shows 37.70 deg, I would have no problem using this for sapphire, the rest of the stone would be cut by eye. Depending on the stone size you get to know the range of numbers on the quadrant you can use, for example, 10.5 would be as low as I can go for zircon, 9.5 for sapphire and 8.5 for quartz.A larger stone may need to be checked with the inclinometer.

After the stone is preformed the table is cut as this will make it easier to cut the mains all the same size, this is the hardest part, if you achieve this then all the other facets will fit. After pre-polishing, the table may be a bit small, just go back and redo it.
Once the table and mains are done then I cut the stars then the break facets, it pays to under cut a bit as it's easy to go back and redo any facets that need a bit more. Polish in the same order. Repeatability is very good,

Begin your creative journey today

At the factory where I first tried the Jamb Peg I started cutting as I would with a mast machine, I was told it doesn't work that way and to stop for a minute and listen to the music...which was the sound of the other cutters in the same room, More cutting and less looking. Some stones like zircons where you encounter hard and soft facets, will need more care, so more looking than with sapphire, quartz etc. Cut the complete row then have a look. Because of the feel and sound of the stone on the lap you can cut tiny facets easily and accurately.

First SRB

Cut the table first then start the main facets on number 10 on the quadrant, if you want a particular angle you can check it with a gauge, keep the table about 50%. Now for the prepolish lap. Prepolish the table and mains, set the index to 4, star setting, just touch the lap on number 15 on the quadrant first and this will give you an indication whether the angle of the cut is too high or too low, may have to drop it to 14.5, you will see when it looks right, Now for the break facets, try number 8.5 on the quadrant to start with, index set on minus 2 for left break facet, just touch the lap to get an idea of where the facet will be, you may have to move up to number 9 or down to number 8. When the facet looks right go ahead and cut the 8 left side facets, don't over cut. Now do the same for the 8 right side break facets with index set on plus 2. Avoid using the mast height adjustment, if you can't make perfect facet meets on the numbers you chose, fix theses meets at the polishing stage.
Repeat the sequence for polishing. You will make mistakes on the first few stones but it won't take long for it to all come together and then mistakes are rare.

Dopping Small Stones

The stone is most likely not 100% centred on the dopstick but a transfer block can still be used for small stones as it keeps the stone level, The stone may be offset after transferring but as long as it is level it won't be a problem. Use wax for the first half and epoxy for the second half. Larger stones are not that hard to transfer by eye, use wax so that the stone can be moved if needed.