K

Kato's 8

Well Known Member
What ya think?
I cut the excess off the top and bottom and one side using a dremel with cut off wheel. I then only lightly filed edges and some light sanding. I knew I wasn't finished with edge finishing but I decided to clean the sharpie lines off the plexi. I had some isopropyl alcohol that I put a dab on a towel and wiped off the marks. What resulted were thes stress cracks. They were not there before the alcohol wipe.
Temp in hangar was 90 and lens was at room temp as was the alcohol.
Do you think the fast cooling effect of alcohol caused the unfinished edge to stress??
I can tell you, I won't be using that stuff on anymore plexi edges even if they are finished from now on.
At least it's only 15 bucks and shipping and waiting. Oh well
 
Noah said:
Which lens are you talking about?

Isopropyl alcohol tends to cause crazing in acrylic and other plastics and is a big no-no around your plastic airplane parts:
http://www.acuitybrandslighting.com/Library/LL/documents/specsheets/Acrylic-Compatibility.pdf
Click to expand...

LP Aero, who make canopies would differ....

"Some alcohols are safe, such as isopropyl alcohol, but not all."

http://www.lpaero.com/CAREINS.html

I've been told to use Rubbing Alcohol by other canopy makers too...

The sudden cooling efftect of a cold liquid on a hot plastic surface would not be good though...:(
 
The lens is the plexi lens for the wing landing light by duckworks llc.
Also the alcohol had no effect on the surface areas or the edges not cut on. only the edge where I cut off material.
Also, the rubbing alcohol was same temperature as lens. I was talking about the cooling effect alcohol has when it evaperates so quickly. It seems somewhat far fetched Idea to me but cant think of anything else. Anyway, Thanks guys!
 
Kato's 8 said:
The lens is the plexi lens for the wing landing light by duckworks llc.
Also the alcohol had no effect on the surface areas or the edges not cut on. only the edge where I cut off material.
Also, the rubbing alcohol was same temperature as lens. I was talking about the cooling effect alcohol has when it evaperates so quickly. It seems somewhat far fetched Idea to me but cant think of anything else. Anyway, Thanks guys!
Click to expand...

Perhaps it was because the edges were unfinished that this happened. The stresses were already in the edge and just needed a little change (the evaporation) to turn into cracks.

You need to retry the experiment with a finished edge...:)
 
Plenty of info (as usual) on this in the archives. Here's a link to one thread.

http://www.vansairforce.com/community/showthread.php?t=1397&highlight=acrylic+solvents+cracking

I recommend you read ALL posts in the thread and bear in mind that some comments are pure nonsense (like the suggestion to use lacquer thinner).

It's good that you struck this problem before you got to your canopy and ruined that !!!!!

I was involved in the manufacture of formed acrylic components. To clean acrylic I know that it is safe to use soapy water, or an approved specialised acrylic cleaner such as Plexus. If that fails I'll go to kerosene as a last resort. Nothing else.

Even substances that you might consider to be "mild" solvents such as methylated spirits can cause cracking of acrylic.
 
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az_gila said:
Perhaps it was because the edges were unfinished that this happened. The stresses were already in the edge and just needed a little change (the evaporation) to turn into cracks.

You need to retry the experiment with a finished edge...:)
Click to expand...

That is what I did. The finished manufactured edge did not crack. I will finish an edge that I cut and see what happens just for curiosity.

Though I dont plan on using isoprpropyl alcohol again to clean edges that have been worked, I find it interesting that had I not done that, I would possibly never known that the edge could have microscopic cracks just waiting to spread. Lesson? Yep. Finish those edges to a gloss finish and be very careful of cleaning solvents.
 
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