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Hi Lucy.
You may have issues with a diamond core drill if your samples are very friable. I had to prepare 5 mm diameter cores in Triassic sandstones containing shear bands for synchrotron x-ray tomographic imaging and it was a real pain. The material contrast between the relatively well cemented faults and host rock meant that they just broke along the edge of the fault when I tried to core them. In the end I used a little 25 mm diamond coated disc on a Dremmel - cutting off slightly oversized prism shaped blocks and then shaping them into cylinders by eye. This was fairly laborious with a high failure rate (maybe 1 in 7-8 were good) but did the trick in the end. If I had material to spare I would try the core drill first (you may be ok as we successfully prepped 15 mm cores in the same material with the core drill at a failure rate of around 1:5) . We never went as exotic as a water jet by the way.
Kind regards
Thomas
 


On Wednesday, 22 February 2017, 12:45, Vasileios Antoniou <[log in to unmask]> wrote:


Just cutting with a core drill probably is the worst choice. When drilling low quality rock (fractured) we usually go with a double split core barrel type not a single one. You can go with your first option or use a dremel like tool (with diamond cutter) to cut your specimen, after all it is a very small piece that you want.
Another choice is 'cementing' your specimen before cutting with a mixture of cement gypsum and water. Let it dry for a couple of days and cut it. You need to make something with low viscocity in order to fill gaps.

Best regards

Dr. Vasileios Antoniou


On 22/02/17 11:11, Lucy McKay wrote:
Dear all,
 
I am looking to prepare rock samples for analysis on a machine more commonly used for metals and ceramics that needs v small samples – cylinders 12.5mm in a diameter and 2-3mm in thickness. Some of my samples are very friable. I can either cut out a cylinder of rock with a water jet then slice to the correct thickness or use a multi-cut core drill with an inner diameter of 12mm. The latter option is cheaper per sample, but I am concerned the samples may fall to pieces.
 
Does anyone have any advice on which technique would be best - or alternatives?
 
Any advice welcome.
 
Thank you,
 
Lucy McKay
PhD  Student
Department of Civil and Environmental Engineering
University of Strathclyde
Level 5 - James Weir Building
75 Montrose Street Glasgow G1 1XJ
E-Mail: [log in to unmask]