DIY Video Housing a success...

[MichiganDiver]

. . .When we were done, they came off no problem but left just small traces of the hot melt glue on the lense. My brother told me that alcohol cleans it off. SO anyway, I was trying to clean the glue off with the alcohol. Right before my eyes, the plexiglass began to crack at the the places where the screws had been installed to hold the hardware. At first I thought it must have been like that from the beginning when I screwed the screws into the plexiglass. As I continued to clean, it continued to crack worse and ALL places where the screws were installed cracked. Eventually it got so bad that pieces started to fall off in my hands. Needless to say I was shocked. Obviously we learned a big lesson not to clean it with alcohol, but DAMN!

Has anybody experienced this, and more importantly, does anybody know why? We are pretty sure it is a chemical reaction. At first I thought is was due to the cooling effect of the evaporating alcohol, so to test the "cold" theory I put it in the freezer with fresh drilled and installed screws. No problems and no cracks.

This phenomenon is called "environmental stress cracking." It is caused by a combination of stress and environmental factors. I'm not sure exactly how it works, but I would guess that the alcohol absorbs into the plastic, doing several things: it introduces stress by swelling the plastic, it softens the plastic, and it may reduce the work required to cause a (microscopic) crack to propagate. The place where you drilled the holes is undoubtedly full of tiny cracks which serve as stress concentrators.

The phenomenon is well known, but it's still a shock to witness.

 

[FunkyDiver]

JSMITH89--We routed the plastic, then I drilled the holes and mounted the hardware. If you are going to do this, make sure you don;t clean it with alcohol. It is very weird. It only seems to happen if the screw is in the plexiglas. I drilled a hole and left it empty. then when alcohol was introduced it did not seem to crack. this only happens when the screw is in. I even scratched the face of the plexiglas to see if it would do it, and it did not seem to. It does seem to be a combination of physical and chemical.

MichiganDiver-- you are right. it was shock to see especially at first. I was dumbfounded that I could have missed those cracks when I installed the hardware, but then I realized it was happening as I was cleaning the plastic. Once I got over my disappointment, it was actually pretty cool to watch and to see how thoroughly the plastic was destroyed.

 

[MichiganDiver]

. . . It only seems to happen if the screw is in the plexiglas. I drilled a hole and left it empty. then when alcohol was introduced it did not seem to crack. this only happens when the screw is in. I even scratched the face of the plexiglas to see if it would do it, and it did not seem to. It does seem to be a combination of physical and chemical.

You are obviously a natural scientist. Apparently the drilling did not introduce stress, just the tensioned screws. Very interesting. Thanks for sharing your experience.

 

[mddolson]

Chemical attach on stressed plastics is a well doumented phenomenon.
There are also various test procedures available to access polymers reistance to chemical attack. The bent dog bone test is a common one. You can find it on GE's web sight. Basically plastic strips are bent/stresses in a bowed shape. Then the chemical is applied and allowed to sit for 24 hours. It is trully amazing to see the unbent samples are perfect, but the stressed/bent ones are all cracked, where the chemical is applied.

For the record I design plastic moulded parts for a living.

Mike D

 

[KingNeptune]

Interesting item on UK eBay - Item Ref: 170086093008

 

[Warthaug]

I've got a question that I'm a little embarrassed to ask. How do I determine if PVC is pressure rated (i.e. what schedule it is). Reason I ask is the only local plumbing store that I've found with 4" pipe has "PVC drain pipe", which as far as I can tell is regular PVC pipe with a flange on one end. However, neither the store, nor the label on the pipe, knew if the pipe was schedule 40. Nor was there any info if the pipe was solid or foam core, etc.

But there was a lot of writing on the side, anyone know how to decode that into something which would provide we with the info I need?

Bryan

 

[engdiver]

I suggest measuring the pipe to see what the wall thickness is. 4" SCH 40 pipe should measure 4.50" O.D. and 4.026" I.D. (wall thickness=0.237"). This should tell you if it is SCH 40 or something less.

 

[cjfox]

I have never found schedule 40 in a regular store like home depot, I've always had to go to a large plumbing supply house, and they unfortunately will not sell small quantities. It will say "schedule 40 " on it, and only takes special schedule 40 fittings.

I have had luck building 6" light housings out of regular PVS drain pipe reinforced by glueing couplings on it, thickening the walls. I've had the housings down to 140fsw.

 

[engdiver]

I got my tubing at Lowes. Although I used 6" PVC pipe they have 4" also. Menards also carries this pipe. The downside is as cjfox said in that they only sell it in certain lengths. I had to buy a 10 foot long piece to make my housing. They had 4" in 5 foot long pieces though.

 

[MichiganDiver]

I got my tubing at Lowes. Although I used 6" PVC pipe they have 4" also. Menards also carries this pipe. The downside is as cjfox said in that they only sell it in certain lengths. I had to buy a 10 foot long piece to make my housing. They had 4" in 5 foot long pieces though.

My local hardware store (Ace Hardware) will sell PVC pipe by the foot. Lowes and Home Depot don't carry 6" pipe, but Ace has it.

Try your local store. Besides, we have to keep the little guys in business!

Edit: I didn't think that Lowes & HD carried 6" pipe, but the previous poster says they do. OK! (Still have to buy 10 foot lengths, though.)