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Jim

Wrote in message:
On Thursday, 17 November 2016 20:08:32 UTC, jim wrote:
"Andrew Mawson" Wrote in
message:
OK chaps - suggestions please.

I need to cut a 12" diameter hole in a workshop wall construction of which
is a single skin of 9" x 18" x 4.5" 7 newton concrete blocks. Now I've all
sorts of drills, angle grinders, hammers and even demolition breakers, so
the problem isn't removing the material, the problem is doing it without the
wall collapsing !!!

I'd be tempted to see if I could cut the perimeter with an angle grinder. Held at the right angle the curves would roughly match. AGs are faster than drills and remove a wide slot, they can easily clean up unevenness, and the result would be far neater. If you cut as far as it'd go from both sides, then sliced the remaining centre what's left would be weak.

Faster than a drill until you clean all the resulting mess up..

(this is for a huge 3900 cuM/Hour extractor for a CNC plasma table down
draught exhaust)

Andrew

Can you position the hole so the uppermost cut block is left
enough "meat" to work as an arched lintel?

not much of an issue with a 12" hole in 18" blocks.

Mmm & where do you sign again ?

--
Jim K

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