I figured it out (I think)

[jedgerton]

So, I've been breaking about 10% of the acrylic blanks that I drill with my fancy drilling vise (sold by one of our more talented members). As I'm sure you would guess, the problem has nothing to do with the vise.

Per the instructions, I use a piece of scrap wood below the blank to provide support and minimize chip out. What I've figured out is that when the scrap has some holes already in it, breakage occurs. What's happening is the bit hits a hole in the scrap wood but isn't centered. This results in deflection of the bit and breakage of material as brittle as most acrylics.

From now on, I will be using a fresh piece of scrap for support or at least one that's fastened down so the hole remains centered.

Has anyone else had this happen?

John

 

[DurocShark]

Yup.

 

[its_virgil]

Cut the blank a little long and drill short of the end. Then, cut off the end to the proper length exposing the drilled hole. This is the best way to prevent chip outs in all types of materials. But, I still use a block under the blank in the vise for support when not drilling on the lathe.
Do a good turn daily!
Don

 

[jedgerton]

Don,

Yes, I've heard the advice you give many times but I guess I never put two and two together. It never ceases to amaze me that at whatever skill level we think we aspire to, there are improvement opportunities in even the most basic of operations.

John

 

[wolftat]

I agree with what Don said about leaving the end and cutting that off after drilling, but sometimes that just isn't an option so the scrap wood underneath should be there and it should not have a hole in it at all. You want to drill through the blank and continue drilling , if you already have a hole there you are drilling into air and that will cause your blank to crack also.

 

[dow]

I drill everything on the lathe now. Haven't had a chip out in I don't know when.