April 19, 2016 at 11:27 am #2547
I am looking at cutting a stone for the single stone competition. I note that the Width for that stone [Novice] is 10 mm +/- 2 mm & the Gridle Thickness is 0.4mm +/- 0.2mm. What instruments are used to aid in achieving the correct dimensions?
In engineering I am used to the 10 by principle. If the dimension is 10mm, I would need an instrument that would read to 0.1mm.
Ian ORRELLApril 19, 2016 at 2:22 pm #2548
Measuring width is quite easy using any caliper which reads to 0.1mm. At the machine, I use a carbon fiber dial caliper, which can’t damage the stone even when I’m clumsy.
Girdle thickness is harder. It can be measured directly with an instrument like the Bausch & Lomb Lenscope with a reticule, but that’s relatively expensive and awkward to use at the machine. The best way I know is a comparison with a thin wire or other object near the desired width. I’ve found that a jeweler’s saw blade works well for most girdles. Saw blades are in various thicknesses, so you’ll have to use a micrometer to measure them. You can also use a length of wire – there’s a useful chart at AWG to mmApril 20, 2016 at 8:22 am #2555
Thankyou for the information.
Ian ORRELLApril 28, 2016 at 5:23 pm #2571
I’ve read that competition cutters some years ago used the back edge of a broken hack saw blade as a reference to determine girdle thickness.May 7, 2016 at 11:54 am #2618
For more direct measurement of girdle I use the appropriate bit from a pin vise drill set. Since you can mount it in the vise it’s easier to hold still.May 7, 2016 at 1:40 pm #2619
Good idea, Joseph. In the US, wire gauge sizes start at about 0.34mm and increase in quite small increments. Metric drills below 1mm are not common, but they are available. I just found on Amazon, listed as “Zona 37-151 High Speed Steel Twist Drill Set, Metric” a set for $16.30 which has 0.3mm-1.0mm in 0.05mm increments, and up to 1.6mm in 0.1mm increments. So they are available.May 9, 2016 at 2:35 pm #2620
I read about the use of brass feeler gauges and ordered a set from Amazon for $6.89. They are listed as “Stanley Proto J000BR 6 Blade Non-Magnetic Feeler Gauge Set”. I saw where someone cut them back into a blunted point for ease of use. I haven’t done that yet, but will soon.May 11, 2016 at 5:08 pm #2632
I use a set of wire spark plug gauges that I got from Ace Hardware or a local Auto Parts store. These are usually in thousands but you can go on line or with an app make the conversion to millimeters. The wire gauges won’t be exactly hundredths of a millimeter but you can get an good approximation. When I try to measure the girdle with my feeler gauges, my hands are not steady enough to be exact, but I can get real close.
Tom MitchellJune 7, 2016 at 10:34 am #2680
Thank you for your ideas on what use for measuring the girdle thickness.
Ian ORRELLJune 7, 2016 at 6:47 pm #2682
I second the use of ‘spark gap’ feeler gauges, readily available from your local auto parts supplier. I sprung for the better of the sets which gives me around 20 different calibrated flat pieces of metal that I could use to measure just about any girdle on any stone.
The end is rounded off, so I used a nice flat lap to grind off the rounded edge so the end corner of the flat piece of metal can be placed right on the girdle, magnified and verified very precise. The gauges can also be use to make sure your micrometer is at least pretty close (at least on the < 1 mm scale).
CarlJune 30, 2017 at 3:07 pm #3345
I use a feeler gauge set.February 11, 2018 at 6:35 am #3939
When I did my stone for the competition a few years back I just got some scrap pieces of paper, measured the width, and cut a straight piece with some scissors. Then when cutting the girdle I just would place the piece over it and eyeballed the facet till it roughly was the same width.
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