Rear Window Install: Source for #27 Plexi Drill Bits

Hairball192 · #1 05-12-2020, 09:27 PM

I'm building an RV-12 and it's about time to install the turtledeck and rear window. The plans call for a #27 Plexiglass drill bit to enlarge the holes on the Lexan rear window. Trouble is, I can't find a source for the #27 plexi drill bits. I've looked at Aircraft Spruce and Cleaveland Aircraft Tools and Amazon (of course).

Any suggestions on where I can source #27 drill bits for plexi/acrylic?

A 27 gage drill bit is 0.144 inches. If I have to resort to a fractional sized plexi bit, what size(s) do you recommend? 1/8" is too small, 5/32" is too bit. Spruce has them in 1/8, 5/32, and 3/16.

I've never worked on a canopy before. Any techniques or suggestions are also most welcome and appreciated.

Thanks,
Harry
RV-12, Palo Alto, CA

Kyle Boatright · #2 05-12-2020, 09:39 PM

My local hardware store has a good selection of numbered bits. Failing that, McMaster Carr has numbered bits.

Here's a link to their drill bits.

https://www.mcmaster.com/drill-bits

Note - you would have to dull these bits for use on plexi.

rcarsey · #3 05-12-2020, 11:21 PM

I usually use McMaster.. but for some reason, for the plexi bits, it looks like I used Abbeon (maybe McMaster didn't have the size I needed at the time?). Abbeon is a plastics mfg company, so they have all kinds of crazy tools for plastic.

https://www.abbeon.com/Item--i-2118

As far as advice.. nothing special. Make sure the temperature is "normal".. don't do it on a cold day.. light pressure. the bit will tend to melt away the material while it drills, so you get that weird plastic wiff once in awhile. I did crack my rear window in a place where its hard to see (so I did not replace it!) -- It happened when I was screwing in a screw near the top/center of the plexi. I think the hole was either not drilled or tapped straight.. or the holes in the plastic didn't line up exactly with the hole in the plastic.. I don't really remember.. anyway, the crack was about 1.5" and I stop drilled it and filled it with some sealant. If it breaks further, it breaks.. but I'm going to get my moneys worth out of this plexi!

Hairball192 · #4 05-13-2020, 02:09 AM

Rob and Kyle, Thanks very much for your quick replies. The order for the bits has been placed!

Thanks again,
Harry

JBPILOT · #5 05-13-2020, 07:01 AM

Use a step bit for enlarging holes. Don't ask how I know this.

rongawer · #6 05-13-2020, 08:37 AM

Ditto for McMaster-Carr
#27 Plastic drill bit

AeroDog · #7 05-13-2020, 09:04 AM

Quote:

Originally Posted by JBPILOT

Use a step bit for enlarging holes. Don't ask how I know this.

Or a reamer.

RFSchaller · #8 05-13-2020, 11:12 AM

In a pinch run a drill bit into concrete to dull it. That works like a plex bit, but practice on scrap first. It also helps to warm up the plastic with a hair dryer before you drill.

DaveWelch · #9 05-13-2020, 11:33 AM

Quote:

Originally Posted by RFSchaller

In a pinch run a drill bit into concrete to dull it. That works like a plex bit, but practice on scrap first. It also helps to warm up the plastic with a hair dryer before you drill.

That instruction was in Section 5 in the past, but I don't see it now.
In any case Review Section 5, page 19 (I think).

I used a Plexiglas bit that was just a bit larger than #27 because I was nervous about the fit. Good thing I did b/c I saw slight screw thread impressions on a couple of the Plexiglas holes.
2-cents,
Dave

flyboy1963 · #10 05-13-2020, 08:30 PM

well Harry, you asked for tips or advice. I don't have a source for bits....but...
1. can't really see a good reason to not go larger....all the bad things that happen to plexi attached with fasteners thru holes, is when things are too tight!
2. taking the stress out of the edges of the hole is as important as the hole being clean and smooth. Lots of info on the 'web', but fine, wet sand paper, and or a stone in a low speed drill or Dremel works well.
3. slow and cool cutting in warm plexi is smart. When I routed miles of Plexi letters on a router table, we blew air and coolant at the bit. Boelube would be good for manual drilling. If it's squeaking, it's not happy!
4. I can't fathom why someone would 'dull' a standard bit...ok, to keep it from grabbing I guess! Look at a real plexi bit. It's more pointed, not a bad idea, but more important, the cutting edge has been ground back to a zero angle, so it effectively 'mills' or scrapes it's way thru the material...that's why some guys like a uni-bit...the cutting edge is vertical! NO grab or snatch as you go thru.
You can make your own plexi bit with a little stone or cutoff disc in a Dremel...just grind back the cutting edge of the bit to vertical. Run it thru some scrap to get the speed and pressure balance. Stopping before going thru, and coming back from the other side is not a bad idea either.