On Friday, 11 September 2020 06:26:02 UTC+1, Paul wrote:

To drill a hole in plastic, start with one of the
smaller bits you've got. Say a 1/16th inch regular HSS.
Drills tend to skate on plastic, and a smaller drill bit
might stay put. That's your pilot hole, for anti-skate.

Then, using your first countersink bit, "ream" out the hole.
Stop before you get to the desired diameter. If you try
to advance the bit too fast, it heats up and fills the
cutting part with molten plastic.

I made LED lights for the bicycle, and the light was a
light array. To mount the array, I used perspex sheet and
drilled 48 holes in it (a bag of LEDs...). The holes are
perfect and didn't crack the plastic. But it did take
a while to drill the 12 x 4 matrix.

Regular drill bits, they catch in the work and crack it.
That's how I ruined the first one.

And no matter what kind of drill bit you use, they tend
to clog with molten plastic and then need cleaning. You're
constantly cleaning the blasted things.

I don't have a whole set of countersink bits, just two
bought individually, so I lack a nice selection for easy work.
I can't go all the way up through the drill index sizes that
way, because my set isn't complete.

Once you're close to the correct size, you'll still need
a regular drill bit to make the hole the same diameter
all the way through. Which may or may not be important,
depending on what you're doing. At the larger bit sizes,
the regular bit can still catch in the work and crack it.
Even with a very nice pilot hole to guide it, there's
still a risk.

Why do people make life so hard for themselves. Use a very small abrasive stone in a dremel to melt your way through & there's no risk of cracking, unless you do something stupid.


NT