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Water Jet Rock Cutting

Write-up By Jim Keffer with information and photos by Mick Hill


Cutting Knappable Rock into knappable slabs to get the most number of workable pieces has been around for at least three decades. The usual method is to invest in a saw designed for cutting rock, i.e. a slab saw.   The Challenge has always been to cut the largest slabs possible which requires larger and more expensive saws. Even with a 24 inch slab saw the length is usually limited to less than half the diameter of the saw.   PSK Member, local obsidian expert and Master Knapper Mick Hill has come up with a new an unique way of cutting large rock into large slabs - Water Jets!

A Expert at making large blades, Mick is alway on the lookout for large rock.  And given the relative scarcity of large rock, ways to get the most out of what he finds. When the idea of using a water jet popped into his head he decided to investigate further.  After contacting and visiting several shops that had the capability of Water Jet Cutting, Mick chose ****, first because the were intrigued and second because they were the least expensive.

To say the idea worked would be a huge understatement!  Obsidian up to 5 inces thick and up to 24 inches long were cut with relative ease - and a LOT faster than a slab saw would cut.   While it wasn't cheap ($15/slab), getting seven slabs up to 24 inches in length from a single rock is no easy task!

One discovery during the rock cutting experiment was that when the rock reached a certain thickness, about 4 inches, the bottom of the slabs started to chip and flake.  Not a significant problem if you're planning on knapping them!

Below are some photo of the Water Jet and the obsidian it cut.  Note the difference between the top of the slabs and the bottom. Try doing this on a 24 in slab saw!

Water Jet Machine w/Obsidian

Water Jet Machine w/Obsidian

Water Jet Slabs - side view

Water Jet Slabs - top view

Water Jet Slabs - bottom view


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