bubble doors

[Flybyjim]

I am going to start mounting the bubble glass to the door frames tomorrow, any advice out there of what to watch for and things not to do.

[Esser]

This one is pretty obvious but really make sure you get rid of your acrylic shavings before pulling the 3M tape out. I didn’t do this and I have white stuff all stuck to the black tape which doesn’t look great.

I can’t stress this enough, do not over tighten the screws. The tape holds the door on. The screws are just a mechanical fastener. You basically want to go finger tight and then a 1/4 turn. Anymore and you are likely to crack the acrylic.

[Flybyjim]

Good point, I am concerned with making the cuts, these doors are oversized a lot and I am going to have to cut the top off to even get into any alignment for the other dimensions. I am planning to cut it with a fine tooth blade band saw to start and finish with hand sanding. It seems to me if I cut away too much at the top of the door or do not cut it at the correct angle I am going to be ordering a new door. I do not want to go there.

[Esser]

I went through his too. Go slow and it makes sense. I started by getting the first cut out of the way off the top of the door. In hindsight, I did cut off too much because the bottom of my hinges hit where the bubble started. I rounded the bottom of my hinges to make it work so all the pressure wasn’t in one spot. I hope this makes sense. You can avoid what I did by basically putting your hinges on so they lay flat and make your first top cut in reference to that.


Secondly, I put the door frame in with the hinges. I held the bubble door up with a hand from my wife and marked where the holes for the hinges would go. I drilled those holes in the acrylic door, and then took strap cut off acrylic and drilled another hole. I then attached my door to the hInges with clecos using the scraps as a sacrificial piece that would take the stress. So it would be hinge, bubble door, scrap clecoed together in that order. No door frame at this point

With the one half of the hinge permanently mounted to the fuselage, I used 3/32 drill bits as temporary hinge pins. I would hold the door up, put the pins in the hinges, and then I took a straight edge and drew the edge of the door frames onto the bubble door, I’d unpin the door, lay it on the table and trim with an angle grinder. I would then put the door back on to check for fit and do it again.

Maybe not the best way but it’s what I did and it worked out well.

[Flybyjim]

Thank's Josh,

The top of the door glass, did you try to make that even with the hinge line of the door hinges? Or did you keep the glass even with the door frame? It seems if you go higher there would be binding of the glass.

[Esser]

I went to the top of the flat part of the hinge. I basically tried to have enough acrylic so that it covered the gap between the door frame and the fuselage to help elementary drafts.

[ken nougaret]

Do not use loctite! It will cause crazing.

[efwd]

Apply the adhesive tape to the door frame. Leave the backing on the tape that will adhere to the bubble. Have all the holes drilled. use a few screws to have the glass aligned and while the glass is on, peel the backing off the tape. It can be tight but you can peel the backing off while the glass is laying on the frame.
Eddie

[aviator79]

I'm far away from that step, but in another thread someone recommended using a bandfile for final shaping. I had never heard of this tool before, but bought one at Harbor Frieght when prepping for my kit, and it's becoming a favorite tool. Very nice for shaping anything (false ribs under the tank, fuel sight gauge plates, and I assume door acrylic.) Fills the gap between Dremel and belt sander nicely.

[efwd]

LOL, if your trimming acrylic on the door then your much closer to that step than you think. Sometimes steps seem distant but before you know it a couple hours later your finished with the part. Those are the times that you realize the build process is gratifying from start to finish. Kitplane magazine had an article once that reminds you to not go into the shop saying "Im building an airplane". When you continuously come out without an airplane youll become discouraged. I live the process of building parts/assy's etc. I am frequently pleased with a days work.
Eddie

[jrevens]

LOL, if your trimming acrylic on the door then your much closer to that step than you think. Sometimes steps seem distant but before you know it a couple hours later your finished with the part. Those are the times that you realize the build process is gratifying from start to finish. Kitplane magazine had an article once that reminds you to not go into the shop saying "Im building an airplane". When you continuously come out without an airplane youll become discouraged. I live the process of building parts/assy's etc. I am frequently pleased with a days work.
Eddie

Man, how true that is... wise words, Eddie.

Jim, for what it’s worth I wouldn’t use a bandsaw to cut those acrylic doors. I know some have had good results, but IMHO it’s just too easy to crack it. My suggestion would be to use a small abrasive cut-off wheel and make several passes - don’t try to cut too deep in one shot. Then grind/sand to the line. Polycarbonate (Lexan) is a whole different animal... you can cut the heck out of it with a bandsaw if you want to.

[Esser]

Yes I would avoid anything with teeth as it pulls. Like I said previously. On the windshield and the bubble doors I used a 6” angle grinder with excellent results.

[Guy Buchanan]

I like using diamond Dremel disks to saw the plastic. It's very safe. Make sure you use zero rake angle drill bits specifically designed for cutting plastic.

Take your time. Work the doors into shape. When done cutting, sand and polish all the edges, as this is supposed to deter cracks. A Dremel makes very short work of it.

I'd avoid any sharp corners, or any other design that might lead to a stress concentration.

Make sure the doors have room to thermally expand and contract, especially if attached to a steel frame. Likewise make all bolt holes oversize.

And as said, don't get even close with Loktite. My own expensive lesson. (The guys at LP Aero took pity on me and sold me the replacement at cost. Very nice.)

[Flybyjim]

I would like to thank all of you for your information on cutting the acrylic doors. After taking in all this great info I decided to call LP Plastics and talk to them. Here is what they told me. This info is from their main guy on the floor who works with the acrylic every day. LP cuts their door two ways, one is with a router but their main cutting tools are bandsaws. After a discussion with this fellow, I cut my doors with a bandsaw but not a wood blade bandsaw. I have two bandsaws in my shop, one for cutting wood and the other for just cutting metal with fine blades. I used the metal bandsaw with a new blade with 24 teeth per inch, 1/2 inch wide and .025 thick. On the advice of this fellow, I followed his instructions to go slow with the cuts, keep the acrylic as tight to the table top as possible and keep air blowing at the blade directly on the cut to keep the area clean from all cuttings. I had a helper to keep the angle as flat as possible, a bit difficult with the bubble in the door but in the end, it all worked well. I made the 6 angle cuts starting with the top to set the top edge centered with the hinge line. Once this was accomplished we clamped the door in place, used blue masking tape to mark the door angles and made the cuts. I had to go back a couple times on each door and make a few more cuts as I was afraid of taking too much off at one time. This worked out for me. I will post a few photos tomorrow.

[jrevens]

I'm really glad it worked out well for you, Jim. My advice was based on my unfortunate experience of ruining a very expensive canopy about 30 years ago with a bandsaw... and yes, it was a nice metal cutting saw with a fine-toothed blade. The LP guys know what they're doing and I would've probably followed their recommendations also.

[Flybyjim]

Thank you, John

I have cut several Lexan pieces over the years and in 2015 I cut an acrylic windshield for my L-16A project that also came from LP Plastics. I really worried about cutting it due to the size and handling it. I only made a couple small cuts on it and finished to fit with a Dremel sanding wheel. As with anything aviation, we make the best decisions with the info we have and from those who have gone before us. This site in my humble opinion is one of the better sites for builders.
Saying this the cut could have gone south and my outcome not so good, luck is with all of us from time to time.

[jiott]

I used a Dremel tool w/cutoff wheel, and then used a belt sander to take it down to the final line. Then of course fine hand sanding. The belt sander removed material fast and kept the line straight.

Other than using proper drill bits, cutting tools (above all avoid reciprocating saws), etc. I believe the next most important thing to avoid cracking is super careful handling when installing and trial fitting on and off (I am speaking here mostly about the windscreen). Putting stress on that bent area between windshield and skylight is a sure way to cause a crack. Also, excessive pushing to get it to fit is a no-no. A method I used to visibly insure no stresses when handling was to put a long piece of masking tape diagonally from the extreme rear corner of the skylight to the extreme lower corner of the windshield- do this on both sides when the plexiglass is in a totally relaxed position under no stress. Then when you handle it just make sure the tape stays taught but doesn't break or pull off. Use two people, watching the tape on both sides, to lift it on and off the airframe.

[Esser]

I think it really really helps if you don’t trim for the front spar until it’s in position as well. I got mine in place with no issues. Months later I cracked it being dumb. I repaired it but I still feel stoopid :rolleyes: