Plexiglass problems

[Bob552p]

First I'm back building after TEN years.
Anyway I was installing the the rear window in my 9A tip up. I have two problems.
One is I taped through the nut plates in the roll bar and two is I am getting spalling in the glass at the screw holes.
At first I thought I tightened the screws too tight because of the nut plates. Which I my have. Then I read through the instructions and found out I did not enlarge the holes in the plexiglass.
The spalling did not happen right away. I was two days later when I went back to the hanger.
Why I drilled out the canopy correctly ten years ago and not the rear window I have no Idea.
So Gentlemen, what can I do to fix both of these issues.
THX
Bob Moore
CNO
9g

 

[rvbuilder2002]

Post some clear close-up photos.

 

[Scott Hersha]

Pictures will help. Not sure I understand your problem. If you remove the screws, can’t you just enlarge and re-countersink the holes in the plexiglass?

 

[Bavafa]

You didn't use Loctite by any chance, did you? Loctite will destroy it.

 

[MacCool]

It's going to all come down to what OP means by "spalling" in reference to plexiglass. From his post, I envision small radiating spider web cracks that would develop from a hole drilled a little too small or a screw that is tightened just a little too tight. If that's correct then my experience is that those tiny cracks will ultimately enlarge to big cracks.

 

[Ralph Inkster]

It's going to all come down to what OP means by "spalling" in reference to plexiglass.

Could also refer to plexi damage that shows up after cleaning surface with laquer thinner or other strong solvent.

 

[Bob552p]

Thank you all for a fast response.
I will get some pictures tomorrow so you all can see what it looks like.
I have removed the screws and re-drilled. I didn't get a chance to tighten them back up.
But it pretty much looks like what Mr MacCool posted.
THX all.

 

[Bob552p]

Today I checked all the holes in the canopy to make sure there correct and they were all good.
So heres som pictures of the spalling/cracks

 

[Bob552p]

Ok I figured it out. Sorry about that.
Here are the photos of the spalling/cracks I posted about yesterday.
It's not all the holes.
See #2146
Thanks
Bob

 

[RV7A Flyer]

Looks like you used a regular drill bit, perhaps, instead of the plexi drill bit?

 

[MacCool]

Ok I figured it out. Sorry about that.
Here are the photos of the spalling/cracks I posted about yesterday.
It's not all the holes.
See #2146
Thanks
Bob

Yup, that's what I was envisioning. My experience with exactly that wasn't a happy one. I'm no plexiglass expert and don't have an expert solution, but if I had to try to solve the problem again it would involve a slightly bigger drill bit, some silicone in the hole (mitigate vibration) and stiff fiber washers to spread out the load.

 

[Carl Froehlich]

Plexiglass is temperamental. What I have found to work well:
- Open the plexiglass holes up with a unibit (not a drill bit). Drill your #30 hole with a plexiglass bit, then enlarge the holt to ~1/4” using the unibit.
- Counter sink the hole for a #6 tinnerman.
- Use the per plans fastener (e.g. a tapped #6 hole for stuff like the RV-8 windshield and pop rivet for the canopy frame).
- For stuff like the RV-8 canopy skirt, the fiberglass skirt does the function of the tinnerman.

The objectives are:
- You spread out the glass holding pressure over a much wider area.
- You eliminate “hot spots” like you experienced that tend to do the most damage.

Carl

 

[Estevanb]

Ok I figured it out. Sorry about that.
Here are the photos of the spalling/cracks I posted about yesterday.
It's not all the holes.
See #2146
Thanks
Bob

I did everything by the book and I have the same issue...

I suspected it could be because the canopy lip that rests against the roll bar has some pressure in it or even that I over tighten the screw...

 

[Bob552p]

Thank you all for response's.
I think Ill put a thin layer of silicone for now and see what happens over time.
I still have a ways to go in the building process.
Thank you again for all your help!
Bob