plexiglass cutting questions.

JimWoo50 · #1 02-06-2006, 06:28 PM

I am full of questions lately so please pardon me if some of these have been previously covered. How warm does it have to be to cut the plexi? I have heard 90 degrees farenheit is this true? I can only attain about 60 in my garage now. Also it seems that Van's has scored some markings (lines) down the sides of my canopy, are they to be used as a guide of any kind? I'm told to use special drill bits for the plexi; what makes them different? Thanks. Jim.

aadamson · #2 02-06-2006, 06:56 PM

I'm sure others will chime in with specifics as what i'm about to mention is not RV specific.

Cutting a canopy is one of those "critical" items in my book. When we did mine at the Lancair build assist, it was probably only 70ish degrees. Temp will play a part tho and I'd wait till you can get it warmed up or for a warm day.

We used one of those roto tools with a bit made for the task. It won't chip the plexi. Chips are what then lead to cracks.

I would expect that the scribe lines are just "best guesses". There must be specific alignment instructions in the manual that tell you how to position the canopy and mark it for your specific airplane? At least in my Lancair, no two are the same, so you have to transfer lines back and forth from the fuselage to canopy and vise-a-versa until you have all the right lines to cut.

Lastly, with mine, i also used a 1" belt sander, after it was cut, to take any remaining roto tool marks out of the edge.

Course on a glass airplane, there's lots more after that part, but it won't be applicable to a metal airplane.

So, probably not much help, but someone will know....

Alan

robertahegy · #3 02-06-2006, 07:07 PM

Places like Aircraft Spruce sell special bits for drilling into plexi. Regular bits can grab into the plexi and damage it. The plexi bits have a steep angle on the tip. Unibits have been used to drill plexi. I have not used them, but I did use the plexi bits with no problems.

90 degrees is not necessary to work on the canopy, but 60 might be too low. I did my canopy in about 75 degrees. When you cut your canopy, use some judgement and make your first cut removing only the obviously not used material. Don't leave any sharp or jagged edges that could propagate a crack. When splitting the canopy, brace the edges with small boards on a table large enough to hold it. Make short cuts like dotted lines, then connect the dots to finish the cut. This is a good practice to follow for any cuts. The edges can be finished using a dremmel with 1/2" sanding drums and a sanding block.

Good luck,

Roberta

JimWoo50 · #4 02-06-2006, 07:37 PM

I will wait until it warms up to at least 75 or so.

N24YW · #5 02-06-2006, 07:57 PM

I used a 4x8 sheet of particull board to set the canopy on. This allowed me to be able to put strips of wood along the side to keep it from moving around alot. The marks that you are seeing on the side may have come from the forming of the canopy. Just a guess. I also tried a aircut off tool that holds the little cut off wheels vans sends with the kit. to slow. I found that my dewalt 4.5 grinder with .045 wheels worked much better. I also used sanding disk on the same grinder to get it into shape. I drilled out the latch hole with a step bit but did have the plexi bits for the smaller holes. If in doubt you will have trimmings off the edge that you can experiment with to see how tuff it is. I would have the garage as warm as possible. I did mine in the winter and I let it warm up for several hours.

Jim

Hawkeye7A · #6 02-06-2006, 08:12 PM

Hey Jim,
I used the 3" cutting wheel that Vans includes in the finishing kit. I put in on a pneumatic die grinder(actually Harbor Freight calls it a "muffler cutter") after removing the shield. Yeah, I know, removing a safety guard is usually a no-no but it improved the vis enough I felt it was worth the risk. I used it on all the trimming and final cuts. I found that making shallow, fairly speedy cuts made it easier to follow the lines I had drawn with a Sharpie and it took 4-6 passes to completely get through the plexi. This even worked very well when I got to making the "BIG CUT". And like Roberta said, after that sanding blocks for the long, straight edges and drums or just a folded piece of abrasive paper in your hand will take out the cut marks. This is another one of the many procedures that turns out to be more stressful contemplating than actually doing. Take your time and don't over-analyze it; you'll be fine. Good luck! BTW, those 3" cutting wheels work great on fiberglass too, when you have a significant amount to trim.

--hawk
RV-7A (finishing)
N728E (reserved)

Build9A · #7 02-06-2006, 08:29 PM

The manual has a pretty good description of the cutting process and provides a few pics. A couple of tips that I remember are; 1)as you are making the big cut and at about the 1/4, 1/2, 3/4 points, tape the portion that has been cut back together. This can prevent the cut portion from sagging and stressing the area not yet cut. 2) get at least 75 degrees in the shop, add a little heater under the canopy to help raise the temp. if needed. 3) When using the plexiglass bits you still have to go slow; don't introduce too much pressure on the drill. I cracked two holes by getting in a hurry and pushing too hard on the drill. Take your time and you will do fine.

ericwolf · #8 02-06-2006, 08:45 PM

My shop was around 70 degrees when I was cutting my canopy. I used the cutoff wheel that Van's supplied attached to my air drill. The air drill is slower speed compared to a die grinder, but has more torque and doesn't get bogged down as easily.

If you can warm up your shop to 65-70 degrees, you are probably ok, but make sure that the canopy has had an hour or so to "heat soak" before cutting.

Rene Bubberman · #9 02-07-2006, 12:31 AM

We put a 2000Watt electric heater/fan underneath the bubble and directed it to the trimming area. Outside temperature was about 18degrees C, so not very warm. It is important however that you make long straight cuts and that you smooth the cut edge directly after the cutting. I have a description with pictures on http://websites.expercraft.com/PHVII...ry&log_id=4581
As for drilling: we chose to glue the canopy, it is looks better and leaves out the stress (es)
Good luck!

TrueAirSpeed · #10 02-07-2006, 09:32 AM

Just finished cutting the canopy for my RV-7 and had the hangar at about 80 plus degrees. Everything worked fine. I used the cutoff wheel Van's furnished, but instead of using a die grinder, I used a 90 degree air drill. I feel, it allowed better stability in cutting and the drill turns at a slower speed which helped in reducing temperatures on the plexiglass and wasn't so apt to "get away" from me. Good luck

TAS
Finnish kit, engine ordered