Did you use a plexiglas drill bit on Duckworks plexi lens?

[AX-O]

I am in the process of installing the Duckworks landing/taxi lights. The instructions say to use a dull drill bit or a plexiglas bit and a unibit. Do I need to order a plexiglas drill bit or can I use a dull one and not crack the lens? Did you warm up the plexi prior to drilling and cutting to final shape? If so, how did you do it (in the oven)? My garage is about 50 deg.

[RV7Factory]

Axel,

I used regular bits and ended up cracking one of the lenses. I borrowed a plexi bit for the next lense and it made drilling much easier with no cracking. Where I went wrong was that I enlarged a hole using a regular bit. The bit dove through the hole like a screw and cracked the lens. As usual, YMMV. Good luck.

PS - I didn't warm up the shop or the lense, but the temp was around 70.

[rlo1]

The dull drill bit did not crack the plexi on my lenses.... The squeezing of the nutplate rivet did.....

-Ron

[GAHco]

I drilled the Plexiglass with a fairly well used #30 or 40, at a medium to low speed and very little pressure, then I used the Unibit, and once again the amount you push will almost be imperceptible. Your really should gauge how fast to feed it by looking for just a little bit of very thin plastic curl coming off the bit.

A variable speed drill is a must.
(If your building an RV I would hope you already have one.)

The weight of even a small hand drill could be too much pressure, so keep it light.

You will always be able to add more pressure if necessary, but once you crack it. you can't add less.

The analogy is like cutting a rope,

"I cut the rope three times and its still too short"

The instructions I thought I read (years ago) did not include drilling rivet holes in the plexiglass, just the metal nutplate strips. If not thats the way I did it.
The metal strips can be fastened to the plexiglass with a small amount of clear silicone, and held in place with the screws and Large area washers until cured.

Hope this helps, have fun, and

[Rick6a]

Originally Posted by AX-O

I am in the process of installing the Duckworks landing/taxi lights. The instructions say to use a dull drill bit or a plexiglas bit and a unibit. Do I need to order a plexiglas drill bit or can I use a dull one and not crack the lens? Did you warm up the plexi prior to drilling and cutting to final shape? If so, how did you do it (in the oven)? My garage is about 50 deg.

As expensive as Plexiglas is, I never could understand why one would risk cracking it with a resharpened, modified or dulled drill bit. Better to use a dedicated Plexiglas drill or Unibit for larger holes. Plexiglas bits are sometimes available locally at better hardware stores, but I'd go with Avery and get all the common sizes used in aircraft construction. That said, it is usually okay to drill the FIRST hole with a regular #40 twist drill....I did on dozens of holes through the canopy, but would NEVER dare go through the same hole again with anything other than a Plexiglas drill or Unibit. As for temperature....warmer is better and reduces the chance of generating a crack yet I drilled through the windshield in 60 degree temps with no problem. Remember...with Plexiglas you want the final hole slightly oversize so the fastener can "float" around a bit because Plexiglas can and will expand and contract as the weather changes. Several builders have seen a crack develop in the canopy glass.....sometimes years later....after enduring an extremely cold temperature event.

A minor heads up on the Duckworks lens: When you assemble the retainer strip with its three nutplates you may find that because of its location relative to the curvature of the lens on the upper surface of the lens, the retainer may not sit against the 'glass perfectly flat. If you run the screws down with that condition, it tends to generate a preload on the corner of the retainer and the glass and may eventually start to crack out...at least mine did after 100 hours or so. When I replaced the lens, I made sure to slightly bend and chamfer that edge of the aluminum retainer so it sat perfectly flat against the 'glass. I noticed the same condition existed when I fitted the same lens in the (under construction) RV-8. In short, you ALWAYS want to avoid any degree of localized stress from occuring when cutting, shaping, drilling and assembling Plexiglas.

[David Johnson]

Originally Posted by AX-O

I am in the process of installing the Duckworks landing/taxi lights. The instructions say to use a dull drill bit or a plexiglas bit and a unibit. Do I need to order a plexiglas drill bit or can I use a dull one and not crack the lens? Did you warm up the plexi prior to drilling and cutting to final shape? If so, how did you do it (in the oven)? My garage is about 50 deg.

I had good luck with a fresh, sharp drill bit. I mitigated the cracking risk by heating the plexiglass up by holding it in front of my reddy heater for a spell before I drilled each hole. I used a cordless drill so I could control the speed very precisely, and hopefully keep it from grabbing and screwing itself into the plastic. The bit did grab a few times, but the warm plexi never cracked.

Dave

[Steve]

AX-O,
I decided to wait a couple of months before trimming and drilling my lens. I can reach maybe 60 degrees in my hangar workspace this time of year in northern Utah. I bought the 4 pak of plexi drills from Avery last Oshkosh.

Plenty else to do in the meantime,
Steve

[briand]

New/sharp #40 then Uni-bit to enlarge. Warmed the part slightly above room temp. (72 F). You can put it in the oven set it on the lowest temp. and remove the lens once the oven reaches preheat.

[RScott]

I did mine before mounting the LE on the wing, so I had the LE facing up and set a drop light under the lens to warm it up. 5 minutes got it nicely warm to the touch in a garage that was in the 40's.

I used a bit designed for plastic that I got from Tap Plastics, which has a local store, or if you are out in the boonies, see: http://www.tapplastics.com/shop/product.php?pid=161&

Dick Scott
RV-9A Wings

[sportpilot]

I carefully studied what Tony Bengelis said about grinding off the cutting edge on a regular bit and so I did that. Grind off the sharp cutter edge and make the face flat with the flute. It worked without any problem. What cracks the plexi is when the sharp cutting edge on a regular bit grabs the thin soft plastic and "screws" itself frocefully into the hole without removing any material. An instant crack.