Thread: Acrylic pen blanks - help needed

Originally Posted by petersemple

Also, don't drill too many at a time. The bit will heat up, and the later ones don't work as well as the first ones. Even if you get a nice enough hole, in my experience the hole ends up bigger on the later ones, and then you don't have a lot of thickness to play with when you turn it.

Thanks for that Peter.

For this project their will be only one blank (I hope! ), so that problem should not come up. I will hang on to your advice for future projects.

When I split my first acrylic blank, I googled "drilling plastic", and found several sites clearly showing how to modify a drill bit for drilling plastic.

Other posts have spoken about using scrapers when turning - the same applies when drilling - you don't want a cutting edge on the drill bit, but a scraping edge.

A sharp cutting edge will pull the bit into the acrylic, and cause splits or a breakout when exiting. Scraping edges will behave much more controllably.

I have drill bits dedicated for acrylics - all you need to do is swipe the sharp edges of the drill bit with a diamond file so they have a blunt edge, rather than a razor sharp.

I also squirt water into the hole, for cooling and lubricating.

Since blunting my brand new drill bits, I've never had a grab, split or break out when the drill exits.

Eg: from Drilling in Plastic Machining by Aline Components Custom Plastic Injection Molding

"Finding the Right Drill Bit

To drill a satisfactory hole in any thermoplastic material, the correct type of drill bit must be used; additionally it must be used correctly and be sharpened appropriately. Aline's basic strategy in drilling into any plastic is to use the right bit at a slow speed to minimize heat.
Not only are plastics soft enough to be drilled with dull bits, most manufacturers prefer to use dull bits to sharp bits. Sharp drill bits tend to create tiny splits in the plastic when it breaks through the bottom surface."

Cheers,
Andrew

Here's another link to info on working with plastics -

Plexiglass Fabrication Manuals, Plastic Fabrication

in particular, regarding drilling, check out

http://plexiglasssheets.info/howto/images/Drilling.pdf

it has diagrams of drill bits for plastics. I didn't bother regrinding the point - I found that blunting the edges fixed my problems.

Cheers,
Andrew

When drilling wood or plastic, I cut the blank over long, and then don't drill all the way through. I then just off the extra length at the end. No worries about break through splitting then.