Scott Will

Scott Will

Well Known Member
Without flaming me about how and why this happened...

Does anyone have any good suggestions on how fix this problem so it doesn't get much worse long term?

What you're looking at is the forward right side of my tip-up canopy. In addition to screws, I wanted to bond it on. Keep in mind, I bonded on my rear window without any problems and using the same procedure. I scuffed the surfaces with 320 and cleaned with Denatured Alcohol (the denatured alcohol is the subject of heated debate between me and my build partner). Anyway, I applied the glue and used #30 clecos to hold while it dried. Came out the next morning and found this.

img_7433.jpg


Some of the tiny, tiny cracks extend about 1/32 above the frame.

Some of the cracks are horiontal while most are vertical. Not sure if it's crazing or true cracking.

What's weird is the direction of cracks and location of cracks (some cracks are from holes that didn't have any load on them at all!!). All holes were properly drilled with a plexi bit then unibit during the hot Georiga summer. And all holes were deburred on the backside. The holes were totally fine before I put it on for the final time.

Anyway, is there a good way to fix so the cracks will hold up long term? Maybe stop drill the ones above the frame, fill with Weld-On#3 and put a higher trim strip on the inside and make slightly bigger skirts on the outside?

Thanks for your suggestions and patience and not flaming me. Believe me, I've beaten myself up over this for the past 3 days.

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I don't have any advice, but I can certainly empathize. I'm disassembling the canopy frame for deburring and then riveting. Working with the plexiglass is definitely nerve-wracking.
 
I was at the plastic distributor in my town the other day getting a Plexiclass bit and was talking to them about working with plexiglass, including repairing cracks and holes.
They have tubes of glue, maybe it was what you call Weld On #3 and he stated that you could actually fill a drilled hole with it and it becomes part of the plexiglass piece and just as strong. He had lots of advice about how to work with plexiglass, since they make and reapir pieces all the time, for industrial uses, etc.
If you have a local plastic distributor in your town, it would probably be worthwhile to make a visit and see what a pro has to say about it and the best way to fix it.
Your idea sounds like the most plausible route, in my opinion, but it is necessary to make sure the cracks don't spread.
By the way, you can usually pick up off falls of different types of plastic, in all kinds of thicknesses, for next to nothing. I have pieces of Delrin and UHMW that I got for a few dollars and have been able to make all kinds of special parts from them.
Good luck.
 
For the heavy craze this is definitely the stuff to use. I use it when I build boat windshields for custom fishing boats. You should not have to stop drill from what I can see in the Pic. The capillary cement shown will fill the damage fine as long as it is clean - so do this sooner rather than later. Even though you used the proper drill, just the fact that the plexi was drilled causes internal tension to the plastic, and makes it more succeptable to crazing. Using the alcohol usually does not cause a problem, but flooding it on or using too much would be enough to cause the crazing. The plastic supply place will sell a small syringe with a fine blunt needle tip for applying it. One small drop to an edge will fill the whole crack by capillary action. DONT drop any of this stuff on a visible surface! It will surface melt the acrylic and you will never be able to buff it out to your satisfaction.

rv8ch said:
A buddy of mine swears by IPS Weld-On 3 Cement
for all types of plastic repair:

http://www.tapplastics.com/shop/product.php?pid=131

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Thanks for all your suggestions and support, guys. And thanks for not flaming me!

I will try to get some Weld-On #3.

How do I or should I fix the crazing in the areas that are in bonded section? I can't remove the canopy at all at this point. Do I drill some holes just through the plexi and not into the frame and then use a syringe to apply the Weld-On #3? Or will the crazing in the bonded areas not spread because the loads should be evenly dispersed?

Again, I apprecaite it.
Scott
 
If it is just surface crazing, like scratches, then you can sand and buff them out. There is a kit for that, but you can also use wet dry sand paper and rubbing compound...same idea.
Start with #400 grit (Use it dry), then 1000grit, then 2000grit then 3M micro finish compound (or equivalent) and follow up with 3M Finesse-it (or equivalent). (If the scratches are minor, you can start with the finer grit, rather than 400.)
I have done this on quite a few canopy scratches and you can't tell there was ever a scratch.
 
I can't tell for sure if it's crazing or cracking because the bad area is on the side of the plexi that is bonded to the aluminum. Therefore, the plexi can't be removed to be checked. That's why I'm in between a rock and a hard place (sorry, it kinda fits the situation).

Scott
 
Scott Will said:
I can't tell for sure if it's crazing or cracking because the bad area is on the side of the plexi that is bonded to the aluminum. Therefore, the plexi can't be removed to be checked. That's why I'm in between a rock and a hard place (sorry, it kinda fits the situation).

Scott
Click to expand...
Scott,
I have scanned this thread and perhaps missed this information. Could you please let me know what adhesive you used to bond the plexi to the aluminum? (So I don't inadvertently do the same thing)
That may have been the culprit although isopropyl alcohol is known to cause crazing in acrylic plastic. I don't know if I have read that ethanol will do the same thing. It may be the denaturant that contributed.

This is not intended to be a flame in any sense, just fact finding to help the rest of us avoid pitfalls.

Thanks,
-Mike
 
Again, I used IPS Corp Weld-On #10. Here's what it says it's for:

"Two part, high-strength structural adhesive for bonding PVC, acrylic, styrene, ABS and polycarbonate. Also bonds well to steel, non-anodized aluminum, etc."

Van's uses this product for windows on the RV-10 -- that's how I got introduced to the company. They make this formulation for bonding to aluminum. Believe me, it sticks! It's not the glue - I did several test samples and glued on the rear window with no problems. The left side of the canopy has no problems.

Van's catalog for Weld-On

It was cleaned with Denatured Alcohol after scuffing with 220. The only thing I can maybe think of is when I cleaned the canopy frame - it used to have some self-etching primer on it. Maybe when I applied it, some of the Weld-On got mixed with some primer from another part of the canopy frame and this caused it. I did see a tiny, tiny amount of gray in this region (if I recall). The gray is the color of the primer.

I'd use Weld-On again.
 
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