Corian Calamity !

I am starting to think that a 15mm hole cannot be drill into a 20mm x 20mm Corian blank !! I am now on my third try and every one has split. I have drilled a pilot hole in each one...using the accompanying 11/32 bit that is used on the Empress kit ( which drills with no problems) before tackling it with the big guy, and have drilled ultra slow ..even ultra ultra slow with the last one, drilling no more than a couple of millimetres at a time ,then leaving it to rest for a few minutes ....but still they split .The slowest speed that I can drill on my lathe is 500rpm is this the reason or do I need thicker blanks, or should I just fling these crap Empress kits

I have darkened the photo so that you can see the problem . The blank on the left is the size of the pilot hole I'm using.

Try using a few different sizes of pilot drills Ed ie start at say 6mm then 8mm then 10mm then 12mm before trying 15mm and keep withdrawing to clear the swarf also make sure the drill bit stays cool. !!!!!

Also Ed, it may be worth taping up the blank with masking tape before drilling? I have drilled many corian blanks and never had this happen which i drill on the lathe .. Also Terry may have a point in going up in steps ... Let us know how you get on ..

I always used 25mm dont forget any corian over 12mm is laminated I would say 20mm is ok for say a 10mm tube drilling out 15mm only leaves a 2.5mm joint each side of the hole and it is that joint which is splitting from what I can see in your photo

Took the the words out of my fat gob Terry I was gonna suggest a squirt of water while drilling
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I drill slower than that Ed less than 200 rpm with Corian, it's a very soft plastic and distorts so easily If you can't drill at that speed then cover your ways and squirt a coolant at it.
I use soapy water in a garden sprayer. I also go straight in with a forstner bit at 15mm just nice and easy.

For what it's worth have you tried going in very gently from scratch with the 15mm drill ie.no pilot hole
Ian

Thanks chaps for all your remedies etc...Woody has hit it on the head though, as looking at them again they are not cracking but splitting along the joint. Maybe I should switch to acrylic blanks for this project.

If the Corian has been professionally laminated there should be no join it literally fuses together.