Bonding Acrylic

[Nev]

Theres a Zenith Super Duty construction video that shows the manufacturer bonding acrylic to the doors, using something similar to 3M VHB tape. Apparently this is in order to reduce stress fractures from screws etc. They then add retaining brackets to properly secure the acrylic.

Has anyone tried this? I’m wondering if the same could be done on Bearhawk doors, and possibly the skylight - perhaps reduce the amount of hardware involved, and reduce the fabrication time. (They also show a very novel method of attaching the front windshield in the same video.)



https://m.youtube.com/watch?v=Bp14hfd5_4g&t=606s Skip to 10:00.

[JimParker256]

Nice video, and some interesting ideas!

[Bcone1381]

I have experimented with this some, and have positive feelings about it, but VHB alone isn't adequate. Next I will dimple the skin, use some counter sunk screws with a thicker VHB product to see how it holds. How much holding force is enough? I wonder, I believe the pressure inside during flight is negative under normal (but not all, like windows open?) conditions.

Cub Crafters experimental products use an adhesive only to secure the window to the frame, but they have a square tube window frame. Their certified products use a frame.
IMG_5792.jpg

[fairchild]

How about a nylon countersunk bolt about every inch along it. ( #8 or 10) The nylon should prevent stress in the plastic---- just figure out how strong it needs to be for the bolt spacing.
I would THINK the challenge would be manufacturing the countersinks in the acrylic --- VERY smooth and not skewed. (so you don't induce any scratches or irregularities for a crack
to start there....) Maybe nail polish (or something) the nuts in place of a locking washer. Maybe use a nylon washer on the back too (?)

Maybe that would be too much trouble ??????

I am guessing another thing might be to do your holes in such a way to ensure NONE of them-- and hence the whole thing--- is NOT in any residual
strain or deflection from the bolts.
T

[svyolo]

Almost all car windshields have been bonded on for many years. The windshield is actually a structural part of a lot of newer cars. It is a 2 part urethane that sets up extremey quickly. Why not just use the same?

[robcaldwell]

I've been using 3M Scotch Weld DP-190. Mostly on the non padded Adel clamps that I don't want slipping, or bonding a doubler and other miscellaneous stuff. It takes about a week to fully cure. I've heard of some using it to bond sheet metal to door frames.

https://www.amazon.com/gp/product/B000WXHG1Q/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

[Bcone1381]

That scotch weld would be a better product for round tubing than the VHB tape. A round tube offers only a narrow bonding area for the VHB tape, even a .062 thick foam based tape. A larger wider surface is needed.

A lot of RV builders seem to use a product called or mfg by Sika Flex.

[svyolo]

I have never used Scotchweld, but I have heard it is good stuff. Fuzor makes numerous catalyzed adhesives, and 3M jumped into the same game. You can get them at auto paint stores. Some cure very quickly. I might give it a try on the lower door glass, and maybe even the upper door glass. I don't know the brand name of what windshield installers use.

Skylight? It would probably be great, but such a large panel glued to a rigid structure - lots of stress due to thermal expansion.

[Nev]

I found a PDF file on the 3M website that itemized the characteristics of each variant in their product line. One of the properties that most of their bonding agents advertise is the ability to cater for thermal expansion/contraction. Interestingly they use it for bonding panels on trucks/vans/horse/floats/buses etc, in place of rivets and screws.

[svyolo]

A lot of exterior body panels ("skins") on cars are bonded instead of spot welding. Many have been done that way for many years. To remove a "skin" you heat it to soften the adhesive.

A big piece plexi or acrylic in a skylight would expand/contract a lot with temp. I am not sure how well that would work out if bonded, but I think I am willing to give it a shot on the smaller windows.

[BravoGolf]

I used Sikafkex to bond my RV canopy on a RV-7. The product is used to bond large windows in buildings that have a lot more thermal expansion than my canopy will experience. It’s relatively easy to work with.

[svyolo]

BG;
I don't know anything about Sikaflex, I will assume it is a great adhesive. A curved RV canopy (acrylic or polyC) can absorb a lot of expansion and contraction just in the shape, without a lot of stress. Acrylic and PC, if I remember right, have about 10X the coefficient of thermal expansion of glass, which probably includes the structural glass used in buildings. I think smaller pieces of acrylic or PC will do OK bonded, and I think I will try it. I am not sure about a 4 place skylight.

[BravoGolf]

My canopy has been finished almost three years, but the aircraft is in a hangar so I wouldn't call that any kind of test. Here is a link to my build log, scroll down to 05-23-15 to see the beginning of the process I went through. One thing about using Sikaflex, the primer almost instantly adheres to anything it touches. So you have to cover every surface you don't want it on.

[svyolo]

Sikaflex is a whole family of products. Do you remember the type of Sikaflex?

[BravoGolf]

295UV (black) is the adhesive I believe most are using, it is what I used. It also comes in white. I also used 205 activator and 209 primer. The primer is a very low viscosity liquid and it will run everywhere.