Drill a Hole to Stop a Crack

[thescreensavers]

So I hit a cone in auto cross a while back and cracked my bumper slightly(cant see it) but its spreading. Do I take any drill bit and just drill right at the tip of the crack?

 

[SpatiallyAware]

It doesn't work as well for plastic, that concept is geared more towards metal fractures.

If you don't care about looks, drill two small holes and use tiny zip ties to hold the crack together. Make sure you don't have any airbag modules behind where you're drilling. Stick a bandaid over the crack for laughs.


I have had good luck with using 2-part epoxy, and glueing a piece of plastic on to the back of the crack. You usually need to remove the bumper, hold the crack tight together, glob on a small amount of epoxy, clamp another piece of plastic to the back, wipe off any epoxy from the front before it dries.

 

[yhelothar]

I'd use a dremel and cut through the crack and fill it in with a strong body filler such as bondo glass. You could then sand it smooth and repaint it.

 

[Fenixgoon]

It doesn't work as well for plastic, that concept is geared more towards metal fractures.

If you don't care about looks, drill two small holes and use tiny zip ties to hold the crack together. Make sure you don't have any airbag modules behind where you're drilling. Stick a bandaid over the crack for laughs.


I have had good luck with using 2-part epoxy, and glueing a piece of plastic on to the back of the crack. You usually need to remove the bumper, hold the crack tight together, glob on a small amount of epoxy, clamp another piece of plastic to the back, wipe off any epoxy from the front before it dries.

it's still true though - you're reducing the stress concentration factor, regardless if the material is metal or plastic, especially if you're taking it from a sharp crack to a round hole

 

[Zorba]

it's still true though - you're reducing the stress concentration factor, regardless if the material is metal or plastic, especially if you're taking it from a sharp crack to a round hole

This.

Typically 1/4" or 3/8" is a good size bit to use. Remember the crack is generally longer than you can actually see, so you want to drill it so the edge of the crack is just entering the hole. If you leave some of the microscopic crack on the other side of the hole it can keep growing - this is actually why the FAA doesn't allow a stop-drill to be considered a permanent repair on commercial aircraft.

A permanent repair would be what yhelothar said.

 

[JCH13]

it's still true though - you're reducing the stress concentration factor, regardless if the material is metal or plastic, especially if you're taking it from a sharp crack to a round hole

X2

This.

Typically 1/4" or 3/8" is a good size bit to use. Remember the crack is generally longer than you can actually see, so you want to drill it so the edge of the crack is just entering the hole. If you leave some of the microscopic crack on the other side of the hole it can keep growing - this is actually why the FAA doesn't allow a stop-drill to be considered a permanent repair on commercial aircraft.

A permanent repair would be what yhelothar said.

X2

I'd use a dremel and cut through the crack and fill it in with a strong body filler such as bondo glass. You could then sand it smooth and repaint it.

X2

I would drill some distance in front of the crack, say 1/2-1in, cut through the crack to the hole with a dremel or something similar, then patch it up with fiberglass mat and epoxy (from the inside). Finish the outside to taste with bondo and sanding.

 

[slugg]

Stupid question: what about melting?

 

[JCH13]

Stupid question: what about melting?

If you are talented enough to heat weld a plastic bumper back together without warping the bumper or doing excessive paint damage, then you are a better welder than I. Or anyone else I've ever met.

 

[slugg]

If you are talented enough to heat weld a plastic bumper back together without warping the bumper or doing excessive paint damage, then you are a better welder than I. Or anyone else I've ever met.

I meant to stop the crack... Melting a hole.

 

[JCH13]

I meant to stop the crack... Melting a hole.

My arguments still stand, you'll warp the heck out of the plastic and damage local paint quite a bit.

 

[slugg]

My arguments still stand, you'll warp the heck out of the plastic and damage local paint quite a bit.

Damn you and your "sense."

 

[JCH13]

Damn you and your "sense."

Hehe. It's such a bummer sometimes...

 

[SpatiallyAware]

My arguments still stand, you'll warp the heck out of the plastic and damage local paint quite a bit.

A soldering iron would do it..

 

[JCH13]

A soldering iron would do it..

Hey, if you want to try, go for it. I'll be using a drill if I ever have to stop a plastic crack.

I've used a soldering iron to melt/weld plastic. It's a pain in the ass.

 

[ino uno soweno]

Sorry gents and ladies, but I am concerned a possible solution to stop the crack is not being noted or posted in this thread,


The ops is concerned about the crack getting bigger, and wants to drill, fill and paint,


My line of thought is “why” is the plastic stressing and continuing to crack, or be torn apart??.


And suggest the metal body mounting points in the area or on the side of the damage of cracking or stress between plastic clips or metal screws attach the plastic bar to the car are slightly bent,


A bent bracket is very easy to miss,


I check, if a plastic bumper is stressing on some or a clip, by using 2 rounded tip blunt butter knives, and just gently trying to pry a clip in and out of the bracket hole, to see if it is tight, if the bracket is miss aligned the clip will be tight, or the screw holes will be misaligned, or the plastic bar can be twisted causing holes to misalign.


Also please note, that any small impact anywhere on a plastic bumper transmits the energy through the plastic to the weakest mounting points, especially around the nose of the car, where the guard and plastic bar meet,


Bottom line is if there is any stress on any of the clips when accessing damage, or fitting, it will be likely the bar will not fit close to exactly right,

 

[deadken]

It doesn't work as well for plastic, that concept is geared more towards metal fractures...

That's odd to hear. I was taught that drilling a hole in plexiglass at the end of a crack was the way to stop the crack from spreading. I used to work at a Boat Marina (there used to be lots of plexiglass windows on boats).


I have seen a special 2-part epoxy used for bumper repairs. It keeps some of its elasticity so it can flex a bit. I'm not sure that I'd want to use 'regular' fiberglass and epoxy. Once the bumper flexs it'd likely crack where the repair was. Here is a link to the type of stuff I'm talking about:
http://www.acehardware.com/product/index.jsp?productId=20779576&KPID=15718089&pla=pla_15718089

 

[JCH13]

That's odd to hear. I was taught that drilling a hole in plexiglass at the end of a crack was the way to stop the crack from spreading. I used to work at a Boat Marina (there used to be lots of plexiglass windows on boats).


I have seen a special 2-part epoxy used for bumper repairs. It keeps some of its elasticity so it can flex a bit. I'm not sure that I'd want to use 'regular' fiberglass and epoxy. Once the bumper flexs it'd likely crack where the repair was. Here is a link to the type of stuff I'm talking about:
http://www.acehardware.com/product/index.jsp?productId=20779576&KPID=15718089&pla=pla_15718089

Plexiglass, i.e. acrylic plastic, is fairly brittle for a plastic and more susceptible to stress fracturing than your average plastic.

FWIW the reason to use fiberglass is to increase the bond area of the epoxy and 'back up' the crack. One or two sheets of fiberglass with a flexible epoxy like the one you linked will still be reasonably compliant. Note that what you linked includes reinforcement mesh, this serves the same function as a little bit of fiberglass.

 

[SpatiallyAware]

That's odd to hear. I was taught that drilling a hole in plexiglass at the end of a crack was the way to stop the crack from spreading. I used to work at a Boat Marina (there used to be lots of plexiglass windows on boats).


I have seen a special 2-part epoxy used for bumper repairs. It keeps some of its elasticity so it can flex a bit. I'm not sure that I'd want to use 'regular' fiberglass and epoxy. Once the bumper flexs it'd likely crack where the repair was. Here is a link to the type of stuff I'm talking about:
http://www.acehardware.com/product/index.jsp?productId=20779576&KPID=15718089&pla=pla_15718089

My point is that while this works really well for metal fatigue type cracks, in my personal experience it doesn't work as well for plastic. Not that it doesn't work or help at all, but the underlying problem of what caused the initial crack tends to be what really needs resolved.


From a mech engineering standpoint I'm sure it helps more than just leaving the crack, but with plastic you really need to reinforce the plastic itself or it's just going to continue cracking.

 

[thescreensavers]

Thanks for the Tips

So Went autocrossing yesterday slapped a cone with a pointer and cracked it further now you can kinda see it lol

This is a common issue with this gen Bumpers

Someone elses picture of the same deal, pretty much looks exactly the same just a little less propagated.

http://forums.nasioc.com/forums/showthread.php?t=2108977


I'm going to swing it by my body shop see what he says now. Otherwise Ill drill a hole and try some type of metal butterfly coursers and some epoxy behind and some touch up paint to prevent further cracking.