Exploding blank

[Chasper]

I have a theory about what happened, but I'd rather hear from someone else first.

I was drilling Corean, two half inch pieces glued together with CA.
I was drilling 7mm holes with a COLT brad point bit.
It was the eleventh half blank I was drilling, all of them either Corian or acrylic.
For every blank I was drilling about 1/4 inch then stopping and dipping the blank in a bucket of water. I also dipped the bit into a cup of water every time I stopped.
About 1 1/2 inches into this blank I heard a pfffft sound. I stopped, dipped the bit and blank and started up again.
When I started drilling again I felt a pressure preventing the bit from going down, so I pushed a little harder. Again I heard the pffft sound and this time there was a pop and warm, wet, gritty slurry splashed into my face.
I dipped and cooled bit and blank again and tried again, this time when I put more pressure on the drill press it popped again and the blank split in half on the glue line.
With the blank split in half I could see that there was a gummy build-up of slurry on the inside of the tube.
Why did this happen?

Gerry

 

[Rifleman1776]

You have given one of the reasons I gave up trying to work Corian. It can be done but I don't believe the effort is worth the outcome. Corian softens with heat and it doesn't take much. Slow drilling and frequent clearing of chips is probably the only approach. Some water, maybe squirting (I keep a syringe on hand for that) would help. My guess is that your drill speed it too high. Try around 600 rpm.

 

[GaryMGg]

I spray Dri-Cote on my bits while drilling; haven't had problems with that as a lube and coolant.

 

[LEAP]

I've heard that sound when I did not clear the bit often enough and keep the flutes clean. It seems to build up a slurry between the flutes and the sides of the hole sealing the hole air tight. With heat and when you press down on the bit pressure develops in the hole and that pffft is the release when it clears. I have taken to keeping a squirt bottle beside the drill press and keep some water in the hole when drilling corian. Takeing very small bites and clearing the flutes very often seems to eliminate the problem.

 

[Chasper]

Phil,
I think you are pretty much on target about what happened. I was dipping the blank in water and when I put it back under the bit the partially drilled hole was full of water. That was working until the sides of the hole filled up with pasty/chalky slurry from the Corean. The water could not escape, as I pushed down on the bit I was compressing and heating the water. The first time it blasted the slurry from the sides of the hole, the second time it popped open the Corean at the glue seam.

Gerry

 

[CSue]

I can't believe it! I actually know something that may help . . .

For about a month now I've been working with a lot of Corian. Some of the pieces I drill are 4" long. I didn't have problems until I got over 2". I don't use water at all on the Corian. The first long blank took A LOT of time, down a little at a time. But the second one I did, the 6" drill bit sealed itself in cause it got too hot going down. The drill bit ended up cemented in the blank. (Buy another) So I got maybe 4 or 5 blanks drilled okay. Then my second bit did the same thing. The Corian wasn't coming out in fine powder or shavings like the others. It was coming out in damp clumps. Same thing happend to that bit and blank. I was starting a collection.

So I went to the hardware store for another bit and told the guy there how frustrated I was with the whole thing. He told me that I had the wrong type of bit. I needed to use one made for stone, brick and such. So that's what I bought.

I now have had weeks and at least 12 corian blanks drilled with no problem at all. But there's one catch. You've got to watch the stuff that comes out. If you get down about an inch and see kind of clumpy stuff coming out instead of fine dust and paper-thin shavings be extremely careful . . . or toss it and go on to something else.

And, Gerry, I still dip the bit into a glass of water often to keep the temperature down. But I never dip the blank. Since I got this new drill bit, its even kept the temp down.

Hope it helps. This is white Corian & Black T - probably the hardest material I've worked yet.

 

[Chasper]

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Here is a Corean pen that turned out the way I wanted.


And here is another.

CSue, you are using a masonary bit? I haven't been able to find them in the right sizes. You don't need the masonary bit because the material is hard, but I guess it prevents the ground up Corian from forming into the damp clumps. I'll drill some scrap Corian with a masonary bit and give it a try. Also I noticed that when it does drill through that it is hard to get the powdery Corian off the inside walls of the hole. I didn't brush the first few hard enough with the gun barrel brush and the CA didn't stick to the accumulated powder very well.

Thanks for the help.

Gerry

 

[GBusardo]

Originally posted by CSue

So I went to the hardware store for another bit and told the guy there how frustrated I was with the whole thing. He told me that I had the wrong type of bit. I needed to use one made for stone, brick and such. So that's what I bought.

Hi, What exactly is that bit called? do you know? Is it the kind of bit made for a hammer drill?
Thanks

 

[Firefyter-emt]

Guys I have turned a lot of Corian and low speed with a lot of clearing of the bit will work just fine. Take it slow and clear often. I also do no use water with Corian.

 

[Chasper]

I don't understand the physics here. You have to drill it slow but turn it fast? Why is that so unintuitive?
Gerry

 

[Awoodfan]

Personally I use a parabolic fluted drill available at most tools supply places and drill at about 900 RPMs and turn at about 2400. Never had any blow or get stuck yet.

Ron

www.woodfan.com



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[CSue]

Well, Gerry, your right, I think. I just know it said on the package that its used for stone, cement and brick. Sounds like mason work to me. Its a dream through most of the Corian. How its made helps to carry the dust up and out much better that brad point or the like. That makes all the difference.
I clean it out as you do immediately after I take it off the drill press. I haven't had any problems with it and CA.

 

[CSue]

by the way, that's a gorgeous desk set you have there!

 

[arioux]

Hi,

Just a note from an hydrolic ingeneer here. If you are using liquid when drilling corian or any othe plastic by the way, you are building yourself a vapor piston motor!!!

The heat from the drilling litterally boil the water and build vapor inside the hole. Since this vapor can not go out, it builds pressure and this pressure goes to the side and bottom of the blank thus explosion.

If you ablolutely need to use liquid, exit the bit very often, not more than 1/4 at the time to start and 1/8 specially at the end or just drill a small pilot hole thru you blank, this will allow the pressure to exit from the other side of the blank.

Alfred

 

[Chasper]

Vapor piston motor? That makes perfect sense, I agree. The pressure was strong enough to blow apart the CA glue joint.

Over the weekend I became a convert to lathe drilling. I drilled some 7mm holes into 1/2 inch squares of Corean (square with one end turned round so that it would fit my chuck). I was making deer antler pens over the weekend, using mostly skinny little mule deer antlers. I started with 25 half pen legnth pieces of antler and only lost three of them either in either turning to get them round for the chuck, or during the drilling. The ones I lost were either too deteriorated or too curved. Until now I've been starting with only the thickest/straightest pieces of antler and still messing up about half of them. I love lathe drilling.

Gerry