Sizing stop drill holes

Good question... Watching with interest.

It's pretty loose - almost any small drill diameter will be far larger than the tip of a growing crack.

If ABS (which is quite tough) is cracking, it may be that the bulk plastic is degrading from age and/or chemical attack.

Joe Gwinn

There's not much opportunity for chemical attack, the part is a Givi motorcycle topcase. It's stored in a garage and only exposed to a bit of rain and occasional sun. Age is an issue, it was bought by a previous ownerat least twenty five years ago. The cracking is near two screwed-on metal lugs that form the static part of the quick-release mounting system, so there's obvious stress concentration.

There's no other visible degradation, so I'm going to stop drill the cracks and try to reinforce the case with fiberglass fabric and ABS pipe cement. The cement is just a sort of lacquer, but it sticks well and permeates the cloth readily.

If nobody recommends larger holes I'll use a handy small drill, say less than one-eighth inch, to minimize leaks.

Thanks for writing!

bob prohaska

ABS does seem to get hard with time and crack. I've seen it in a fair number of inexpensive ABS pond hoppers.

I don't know if modern plastic kayaks (the vogue these days for one person "inexpensive" watercraft) are ABS or something else.

Use your Givi bags as a mold to make molds to make fiberglass bags. When you are done you already have all the hardware.

I once got a bit of ridicule of ridicule in the RMHVB&G for asking if anybody had ever put Givi bags on a Harley.

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The plastic repairs I've made that lasted used a pop-riveted sheet of aluminum pre-formed to shape. A good anvil for 3D curves is a wide shallow depression in wood. It doesn't need to be the shape of the plastic, only deep enough to form the same degree of concavity so you can bend the soft metal to fit. M3 or #5 screws or Clecos can temporarily replace 1/8" pop rivets during fitting.

A stronger approach I've used under my car is to slit galvy steel to fit it to a compound curve and then spot weld it together at the overlaps.

It's been my experience that most of the Assholes are , well , assholes .

There's no reason not to caulk those holes with a compatible rubbery material.

Joe Gwinn

AC 43.31-1b - the aircraft repair "bible" calls for a 1/8" stop drill for cracks - wheather aluminum, plexi. abs. or steel. The idea is to interrupt the stress and "stop" the crack. Less than 1/8 would work too as long as it totally inturrupted the crack - and less than 1/8 is very difficult to positively locate to endure it DOES totally inturrupt the crack. After stop drilling inspection at 20 hours and every 100 hours thereafter is required and patches must be at least twice the length of the crack, of the same material and same thickness or up to half again the thickness of the base metal. Rivets must be no less than 3 rivet diameters apart and no closer than 2 rivet diameters from the edge of the patch and from the crack.

Most are rotationally molded Polyethelene or PET

I agree - I'd use a 1/8" bit and then fill the hole with a flexible caulk. Also use a bit of acetone or MEK or Methylene Chloride drizzled into the crack ti "weld" the crack???

I'd verify that acetone exposure won't cause later cracking or stress cracking.

But I don't think that acetone will stop the crack, because at least in hard materials the crack is atomically sharp.

Joe Gwinn

Acetone won't harm the ABS and it won't stop the crack. It WILL help seal the crack by "chemically welding" the 2 surfaces togeter. Don't soak the thing, just drizzle a small amount into the acuial crack with a syringe or a toothpick. Not on other plastics - just ABS