Cracks on Hatch cover

Cracks on Hatch cover

Post by Dick Burto » Thu, 14 May 1998 04:00:00


I have two cracks in the plexiglass main hatch cover (sliding) that start on
the aft corners and go for about two inches.  They are bad enough that water
is starting to seep in when it rains.  I am concerned that they will get
larger.  Is there any product that can fix this without replacing the hatch.
I am thinking some type of liquid epoxy that I flow into the cracks.  Any
suggestions are appreciated.

Dick (Whisper)

 
 
 

Cracks on Hatch cover

Post by Anders Svensso » Thu, 14 May 1998 04:00:00

Plexiglass (if it really is, there are many other see-thru compositions)
can be glued with a special solvent. To stop the stress crack from going
further, you can drill a small hole at the end of the crack. Any
cyano-acrylate glue will work fine for glueing, and if you glue in a piece
of suitable plexi rod in the hole, it might turn out quite nice.

--
Anders Svensson
----------------------------------------



Quote:
> I have two cracks in the plexiglass main hatch cover (sliding) that start
on
> the aft corners and go for about two inches.  They are bad enough that
water
> is starting to seep in when it rains.  I am concerned that they will get
> larger.  Is there any product that can fix this without replacing the
hatch.
> I am thinking some type of liquid epoxy that I flow into the cracks.  Any
> suggestions are appreciated.

>*** (Whisper)


 
 
 

Cracks on Hatch cover

Post by Dick Burto » Thu, 14 May 1998 04:00:00

Sorry about the double post.  I did not think the first one posted.

Quote:

>Dick (Whisper)


 
 
 

Cracks on Hatch cover

Post by Greg Jackso » Thu, 14 May 1998 04:00:00

Quote:

> I have two cracks in the plexiglass main hatch cover (sliding) that start on
> the aft corners and go for about two inches.  They are bad enough that water
> is starting to seep in when it rains.  I am concerned that they will get
> larger.  Is there any product that can fix this without replacing the hatch.
> I am thinking some type of liquid epoxy that I flow into the cracks.  Any
> suggestions are appreciated.

>*** (Whisper)

There are two different issues here, stopping the crack and repairing
the crack.
RE: Repairing the crack. Here I would refer you to the other people who
have posted replies with various acrylic solvents or epoxy formulations.

RE: Stopping the crack.  A crack in acrylic is similar to a crack in
many other materials.  The external forces create a distributed stress.
If that distributed stress is large enough, it will propegate into a
failure at a point, the beginning of a crack.  As soon as that crack is
created, it forms a stress concentration and will rapidly develop into a
longer and longer crack.  The distributed stress suddenly becomes a
concentrated stress and will easily move through the material.  If you
don't believe this, just try pulling along the edge on opposite ends of
a piece of paper, then repeat the pull after having put a 1/8" cut into
the edge of the paper.  Not only will a tear always occur at the 1/8"
cut, but the force required to begin  a tear is a tiny fraction of what
it takes if the tear is not present.  The solution is pretty simple.  If
you drill a hole slightly in front of the current end of the crack, as
the crack opens further, it will open into the hole.  The hole will turn
the stress concentration of the crack  into a distributed force, shared
over the diameter of the hole.  Note: this will not work if the hole you
drill is rough or chipped.  A rough hole will have microscopic cracks
along its edge that are likely to restart the crack.  The best solution
is to drill a smooth hole, and then rub the hole with some acrylic
solvent.  The solvent will smooth the surface of the hole to a
microscopic level and greatly reduce the potential for the crack getting
started again.

G. Jackson

 
 
 

Cracks on Hatch cover

Post by RW Salnic » Thu, 14 May 1998 04:00:00

Mr. Jackson makes an excellent point, one which I failed to address.

The only thing I would add is this:  BE VERY CAREFUL in drilling the
hole.  Drill slowly, and do not let chips of plastic build up on the
drill bit and make heat - if you are careless, you will cause the crack
to propogate as you drill.  And then you have to drill another hole...
and another...

bob

Quote:

> There are two different issues here, stopping the crack and repairing
> the crack.
> RE: Repairing the crack. Here I would refer you to the other people who
> have posted replies with various acrylic solvents or epoxy formulations.

> RE: Stopping the crack.  A crack in acrylic is similar to a crack in
> many other materials.  The external forces create a distributed stress.
> If that distributed stress is large enough, it will propegate into a
> failure at a point, the beginning of a crack.  As soon as that crack is
> created, it forms a stress concentration and will rapidly develop into a
> longer and longer crack.  The distributed stress suddenly becomes a
> concentrated stress and will easily move through the material.  If you
> don't believe this, just try pulling along the edge on opposite ends of
> a piece of paper, then repeat the pull after having put a 1/8" cut into
> the edge of the paper.  Not only will a tear always occur at the 1/8"
> cut, but the force required to begin  a tear is a tiny fraction of what
> it takes if the tear is not present.  The solution is pretty simple.  If
> you drill a hole slightly in front of the current end of the crack, as
> the crack opens further, it will open into the hole.  The hole will turn
> the stress concentration of the crack  into a distributed force, shared
> over the diameter of the hole.  Note: this will not work if the hole you
> drill is rough or chipped.  A rough hole will have microscopic cracks
> along its edge that are likely to restart the crack.  The best solution
> is to drill a smooth hole, and then rub the hole with some acrylic
> solvent.  The solvent will smooth the surface of the hole to a
> microscopic level and greatly reduce the potential for the crack getting
> started again.

> G. Jackson

--
----------------------------------------------

        S/V Eolian, Seattle

Those who do not study Unix
             are doomed to recreate it...  poorly.

 
 
 

Cracks on Hatch cover

Post by Dick Burto » Fri, 15 May 1998 04:00:00

Thanks for all the advice and input.  One more questeion.  How do I tell if
the hatch is plexiglass or lexan?

Quote:
>>Dick (Whisper)