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Cutting Plexi

SeanB

Well Known Member
Hey everyone,

It's almost my turn to cut the plexi for my tip up canopy. I've studied many posts and builder sites in preparation. I still have a couple more questions before I start trimming:

  • Should I cut all the way thru the thickness of the material and make cuts in one pass or score the line with a light pass then cut thru?
  • I made the typical table top with 2 X 4 rails to retain the shape of the canopy while in work. Should there be light pressure squeezing the sides of the canopy inward, or just retain its natural shape?
  • In between trim cuts, what is the finest grit of sandpaper I should use?
I'll be careful to keep it warm and not move anything until I sand.

Thanks for the help!!!
 
I know this is a nerve racking part, go slow and be deliberate and you will be fine.


Should I cut all the way thru the thickness of the material and make cuts in one pass or score the line with a light pass then cut thru? I used an air grinder with a thin cutting blade, I scored ahead then came back and cut through moving the score ahead a little at a time.

I made the typical table top with 2 X 4 rails to retain the shape of the canopy while in work. Should there be light pressure squeezing the sides of the canopy inward, or just retain its natural shape? I would not put any pressure either way, just set it up so nothing can move as you cut.

In between trim cuts, what is the finest grit of sandpaper I should use? This one I cannot remember for sure, smooth out all ridges or grooves made by cutting wheel, 320 grit comes to mind.

Hope this helps some

I don't know how you plan on securing your canopy, I bonded mine, so what I did was bonded the entire canopy onto frame and fuselage, it's a slider. Then I made the big cut.

Bird
 
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It helps to have a light scoring to guide the cutting wheel. Use some heavy duty pipe tape or electrical tape to define the big cut.
I would have a bit of squeeze to the side blocks, just to keep the bubble from moving around too much. You don't want it moving around during the cut, since that torsion might make it crack, but you want it nice and stable.
For all of the many cuts you will make around the edges to fit the canopy to the frame, just use some 220 grit. After you get it close, then you can move to the finer grits. I used the Plexiglass scraper tool from Avery and it works great to smooth out the small scratches left by the sandpaper. It is best to finish off the edges with finer sandpaper like 400 or 600 grit when you are all fitted. You should have a perfectly smooth edge to protect you from potential cracking.
 
Cutting plex.

Note that my canopy opens from left to right on the Rv3..
I would cut all the way through the thickness of the plex. because it could cause it to crack in a direction other than the cut area.
Like you said, "Keep the plexiglass warm", I heated the entire garage up to 85 degrees.
I would cut then measure trim the measure and trim again until it fits. I think I used 100 grit, "it's fast", just to rough sand the edge before fitting and after it was fitted then I made it very smooth with finer sandpaper.
I always finished a cut for it whole length because if you stop you are leaving a spot that could crack.
When cutting the rivet holes in a tip up canopy you will have to make the holes rather oval for expansion and contraction. At the front of the canopy the holes can be almost round but as you work toward the rear the holes must be made longer in a oval from front to back. I live in Minnesota and I worked on my canopy in the winter, "heated garage", but I let the garage cool off at night and the next morning when I came out I would measure the canopy before I turned on the heat and there was a huge difference in the canopy size mostly from front to back. So if the holes are not cut oval they will put a lot of pressure on the rivets. I think I made my rear most holes about 1/2" oval front to back and just a little lose on the rivet vertically.
I did like you and read as much as I could before cutting my canopy and it went well..
Oh make sure to use the very weak soft rivets per directions.:)
 
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good info.....not all that easy to find.....

here's a link to a good tech sheet I just found. Hey, these guys practically invented the stuff eh!
there are good general recommendations on Van's site as well.
Did we ever find out what brand of acrylic the canopies are made of?

http://www.theplasticshop.co.uk/plastic_technical_data_sheets/working_with_perspex_manual.pdf

some good reading for the technically inclined.

note; If you build and oven for any forming, be sure it's 100% fireproof.
an unfortunate friend tried to mould a canopy in a big plywood box, heated by an oven element.
Left for 'just a minute', and lost the 80% complete wood aircraft, a freshly restored camper, garage etc.:(
 
cutting plexi

We put a new canopy on Zenith 601 last week. It is the same material but only 1/16 inch thick. We used a Dremel "Saw-max". It worked very well. We could not cut too sharp of a curve but kept carving away at it until it fit. Then sanded 240 grit, then 400 grit to get a smooth and slightly rounded edge. The " Saw-max " with included plastic cutting blade worked better anything I had used before. Ron
 
I used a pneumatic die grinder with thin abrasive cutoff wheels as I believe Van's recommends, but there are lots of other good ways to do it. Multiple passes. In the end it was a non-event.

There's a lot of extra material on the raw canopy, especially along the sides. Try some cuts on that first, to practice.
 
Cut that sucker already! Get that thing flying...I need a wingman!

Seriously though, good questions. I used the die grinder and the cutoff wheel supplied by Van's...cuts it like butter. Just secure it well, dont move it (not even a little) mid-cut, keep it warm, go slow and you'll be fine. Sand edges smooth asap...before moving canopy.

Good luck! This, believe it or not, was an exciting time in the project for me.
 
Thanks

Thanks everyone. Ron, don't I recall you enjoying working with ProSeal as well? :confused: :)
 
I just did my canopy a few weeks ago. No issues and no drama for me. My opinions in-line below:

  • Should I cut all the way thru the thickness of the material and make cuts in one pass or score the line with a light pass then cut thru?

    I used a cut-off tool (i.e. die grinder) with a standard 3" wheel. I cut progressively across an area. I always took 4 passes or so to get all the way through the area. If you go too deep in one pass, the plexi gets very hot. Always feel the work that you are doing and keep it from getting too hot. I would move around all over the line to keep from heat build up. An old welding habit:). I would always make a complete first pass and take your time. This will create a valley to hold your disk for subsequent cuts. Always use sharpies to mark your lines to follows. It comes off easily with mineral spirits which are safe for the plexi.
  • I made the typical table top with 2 X 4 rails to retain the shape of the canopy while in work. Should there be light pressure squeezing the sides of the canopy inward, or just retain its natural shape?

    I did all my cutting on a $20 folding table from Menards with a 4' X 6' piece of plywood on it. I used two wood blocks and bar clamps to hold to the table. You need to support the sides of the canopy, but you don't need anything elaborate. Just enough to keep the sides from spreading. No real toleance here. Just aim to keep the canopy in it's natural state.
  • In between trim cuts, what is the finest grit of sandpaper I should use?

I used 80 grit after each cut. No need for finer. Your just need a consistent, clean edge with all scores and irregularities removed. Obviously, you should go to 220 or 400 on your final edge.

I'll be careful to keep it warm and not move anything until I sand.

As long as it's warm, don't fret movement too much. You'll need to move and lift the canopy to sand and this is ok. I encourage you to take your first piece of scrap and try to abuse it. You'll see how strong it really is.

You didn't ask about drilling and countersinking. This is the area you should be concerned about. Practice different drilling and countersink methods on your scrape and you'll quickly understand what chips and what doesn't. Lot's of ideas here via search.

Good luck.

Larry
 
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I used a vibrating saw with a fine cutting blade from Harbor Freight. It was cheap and allowed me to control the saw I thought better than a cut off wheel.
Dave
 
I have cut quite a few canopies and this is my method.
Yes to warm temperatures
Yes, secure the canopy
I use the thin cut off disc supplied by Van's. I use a piece of electrical tape for my "line" and cut in a single pass. You need to also secure the piece being cut off. A few piece of tape on cut line behind you as you go does the trick.

Here is where I go different from most.
I use a hand held belt sander, 100 grit. And sand the line straight to the tape line.
It works great, just keep it from bouncing.

I use a scraper rather then sand paper to smooth the edges. By a scraper I mean like the one fine woodworkers use to finish furniture. google it
A blade from a wood plane will works well. Hold it with the flat edge of the blade angle towards you, 90 degrees to the plexi. Using smooth strokes pull it towards you and it will pull of nice little ribbons of plexi. This method will very quickly get a rounded ultra smooth finish. I do this every time I cut.

I have never cracked a canopy or had one crack after use.

Practice on scraps.
 
go for it and enjoy the progress

Lots of good suggestions here. As you can see, there are many different ways of cutting the canopy with good results. For me, I cut the canopy in a cold garage at about 55F using the Vans cut off wheel, going straight through in one pass. I see the heat from the cutting is actually a good thing. It locally softens the plastic and expands the material, squeezing closed any micro cracks that might form when cutting.

In my opinion, the keys to not cracking are:
> restrain both halves in a stress free state so that there is no stress at the cut notch, especially when you get to the last few inches. No stress=no cracks
> do not use a cutting method that will chip the plastic as the cutter exits the plastic. That's is what is so nice about Vans cutoff disks. Cracks can form from the chipping.
> make a smooth cut with no notches, that has to be done anyway for a good fit, but if you wander off line, continue the cut back onto the line instead of starting a new cut, leaving a notch. The diameter of the vans wheel, when cutting through in one cut, provides good guidance in the slot and helps prevent wandering off the cut line.

Use some of your scrap Plexiglas and practice with whatever method you want to use. Try and crack it to help develop a feel for what the limits are.
 
IIRC, I used the crate as a work 'table' when I made the big cut on mine. It was a reasonable compromise for work height. I rested the canopy on multiple 2x4's, with cleats screwed to the 2x4's to hold the sides of the canopy.

I used a straight air grinder with friction wheels, as others have mentioned, but if it had been available at the time, I'd have used a 'bone saw' (the oscillating saw mentioned earlier). The nice thing about the bone saws is that they don't try to 'take off' if they bind, and their oscillations are so short and fast that there's little danger of them grabbing & shattering the plexi, as long as the motion isn't perpendicular to the surface.

It's been a long time, but I think that I remember a warning somewhere about *not* allowing the friction wheel to melt its way through the plastic. Something about causing the melted area to be more brittle. But that may be a defective memory...

Charlie
 
I have cut quite a few canopies and this is my method.
Yes to warm temperatures
Yes, secure the canopy
I use the thin cut off disc supplied by Van's. I use a piece of electrical tape for my "line" and cut in a single pass. You need to also secure the piece being cut off. A few piece of tape on cut line behind you as you go does the trick.

Here is where I go different from most.
I use a hand held belt sander, 100 grit. And sand the line straight to the tape line.
It works great, just keep it from bouncing.

I use a scraper rather then sand paper to smooth the edges. By a scraper I mean like the one fine woodworkers use to finish furniture. google it
A blade from a wood plane will works well. Hold it with the flat edge of the blade angle towards you, 90 degrees to the plexi. Using smooth strokes pull it towards you and it will pull of nice little ribbons of plexi. This method will very quickly get a rounded ultra smooth finish. I do this every time I cut.

I have never cracked a canopy or had one crack after use.

Practice on scraps.

+1

The cuttings will be hot and stick to anything. It will obscure a marker line on the part very quickly, something large and easy to see is good. Like a gap between the black strips of tape.

You can use a dremel with a diamond wheel for trimming, easy to hold and thin kerf. I even added a guide for some thin cuts to make them very straight.

Get some one hole countersinks, and drill bits for plexi.

Be careful about putting clecos in the holes, I chipped some in the process.

Good luck, this part is more fear than necessary. It is a pretty easy job.
 
I found when testing that the 3-flute countersink cutters gave nice clean results whereas the high-hook chipped the hole badly.
 
Thanks

There have been some very detailed and thoughtful responses provided so far. Thanks, everyone....I really do appreciate it!

BTW....I'm totally convinced to use Sikaflex.

A couple more tweaks to the canopy frame, then some riveting, and I'll go for it.
 
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