Are there any general rules of thumb for sizing the holes used
to stop cracks? As a guess, I'd imagine the material thickness
is the lower limit and anything bigger than five to ten times
the thickness would be a reasonable upper limit if there's room.

Does anybody know of a better approach? In my particular case
the material is molded ABS plastic, but I doubt that matters
very much.

Thanks for reading,

bob prohaska

Good question...
Watching with interest.

On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

>Are there any general rules of thumb for sizing the holes used
>to stop cracks? As a guess, I'd imagine the material thickness
>is the lower limit and anything bigger than five to ten times
>the thickness would be a reasonable upper limit if there's room.
>
>Does anybody know of a better approach? In my particular case
>the material is molded ABS plastic, but I doubt that matters
>very much.

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

Joe Gwinn <joegwinn@comcast.net> wrote:
> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
> <bp@www.zefox.net> wrote:
>
>>Are there any general rules of thumb for sizing the holes used
>>to stop cracks? As a guess, I'd imagine the material thickness
>>is the lower limit and anything bigger than five to ten times
>>the thickness would be a reasonable upper limit if there's room.
>>
>>Does anybody know of a better approach? In my particular case
>>the material is molded ABS plastic, but I doubt that matters
>>very much.
>
> 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.

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

On 1/3/2024 9:50 AM, bob prohaska wrote:
> Joe Gwinn <joegwinn@comcast.net> wrote:
>> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
>> <bp@www.zefox.net> wrote:
>>
>>> Are there any general rules of thumb for sizing the holes used
>>> to stop cracks? As a guess, I'd imagine the material thickness
>>> is the lower limit and anything bigger than five to ten times
>>> the thickness would be a reasonable upper limit if there's room.
>>>
>>> Does anybody know of a better approach? In my particular case
>>> the material is molded ABS plastic, but I doubt that matters
>>> very much.
>>
>> 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.
>
> 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.

--
Bob La Londe
CNC Molds N Stuff

--
This email has been checked for viruses by AVG antivirus software.
www.avg.com

"bob prohaska" wrote in message news:un2moo$33ada$1@dont-email.me...
Does anybody know of a better approach? In my particular case
the material is molded ABS plastic, but I doubt that matters
very much.
bob prohaska
----------------------

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.

On 1/3/2024 11:08 AM, Bob La Londe wrote:
> On 1/3/2024 9:50 AM, bob prohaska wrote:
>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
>>> <bp@www.zefox.net> wrote:
>>>
>>>> Are there any general rules of thumb for sizing the holes used
>>>> to stop cracks? As a guess, I'd imagine the material thickness
>>>> is the lower limit and anything bigger than five to ten times
>>>> the thickness would be a reasonable upper limit if there's room.
>>>>
>>>> Does anybody know of a better approach? In my particular case
>>>> the material is molded ABS plastic, but I doubt that matters
>>>> very much.
>>>
>>> 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.
>>
>> 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.
>
>
>

It's been my experience that most of the Assholes are , well ,
assholes .
--
Snag
Si Vis Pacem Para Bellum

On Wed, 3 Jan 2024 16:50:39 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

>Joe Gwinn <joegwinn@comcast.net> wrote:
>> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
>> <bp@www.zefox.net> wrote:
>>
>>>Are there any general rules of thumb for sizing the holes used
>>>to stop cracks? As a guess, I'd imagine the material thickness
>>>is the lower limit and anything bigger than five to ten times
>>>the thickness would be a reasonable upper limit if there's room.
>>>
>>>Does anybody know of a better approach? In my particular case
>>>the material is molded ABS plastic, but I doubt that matters
>>>very much.
>>
>> 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.
>
>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.

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

Joe Gwinn

On Wed, 03 Jan 2024 09:31:03 +0000, Richard Smith <null@void.com>
wrote:

>Good question...
>Watching with interest.

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.

On Wed, 3 Jan 2024 10:08:37 -0700, Bob La Londe <none@none.com99>
wrote:

>On 1/3/2024 9:50 AM, bob prohaska wrote:
>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
>>> <bp@www.zefox.net> wrote:
>>>
>>>> Are there any general rules of thumb for sizing the holes used
>>>> to stop cracks? As a guess, I'd imagine the material thickness
>>>> is the lower limit and anything bigger than five to ten times
>>>> the thickness would be a reasonable upper limit if there's room.
>>>>
>>>> Does anybody know of a better approach? In my particular case
>>>> the material is molded ABS plastic, but I doubt that matters
>>>> very much.
>>>
>>> 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.
>>
>> 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.

Most are rotationally molded Polyethelene or PET
>
>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.
>
>
>
>--
>Bob La Londe
>CNC Molds N Stuff

On Wed, 03 Jan 2024 14:19:37 -0500, Joe Gwinn <joegwinn@comcast.net>
wrote:

>On Wed, 3 Jan 2024 16:50:39 -0000 (UTC), bob prohaska
><bp@www.zefox.net> wrote:
>
>>Joe Gwinn <joegwinn@comcast.net> wrote:
>>> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
>>> <bp@www.zefox.net> wrote:
>>>
>>>>Are there any general rules of thumb for sizing the holes used
>>>>to stop cracks? As a guess, I'd imagine the material thickness
>>>>is the lower limit and anything bigger than five to ten times
>>>>the thickness would be a reasonable upper limit if there's room.
>>>>
>>>>Does anybody know of a better approach? In my particular case
>>>>the material is molded ABS plastic, but I doubt that matters
>>>>very much.
>>>
>>> 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.
>>
>>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.
>
>There's no reason not to caulk those holes with a compatible rubbery
>material.
>
>Joe Gwinn
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???

On Wed, 03 Jan 2024 17:25:08 -0500, Clare Snyder <clare@snyder.on.ca>
wrote:

>On Wed, 03 Jan 2024 14:19:37 -0500, Joe Gwinn <joegwinn@comcast.net>
>wrote:
>
>>On Wed, 3 Jan 2024 16:50:39 -0000 (UTC), bob prohaska
>><bp@www.zefox.net> wrote:
>>
>>>Joe Gwinn <joegwinn@comcast.net> wrote:
>>>> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
>>>> <bp@www.zefox.net> wrote:
>>>>
>>>>>Are there any general rules of thumb for sizing the holes used
>>>>>to stop cracks? As a guess, I'd imagine the material thickness
>>>>>is the lower limit and anything bigger than five to ten times
>>>>>the thickness would be a reasonable upper limit if there's room.
>>>>>
>>>>>Does anybody know of a better approach? In my particular case
>>>>>the material is molded ABS plastic, but I doubt that matters
>>>>>very much.
>>>>
>>>> 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.
>>>
>>>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.
>>
>>There's no reason not to caulk those holes with a compatible rubbery
>>material.
>>
>>Joe Gwinn
> 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 to "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

On Thu, 04 Jan 2024 11:29:54 -0500, Joe Gwinn <joegwinn@comcast.net>
wrote:

>On Wed, 03 Jan 2024 17:25:08 -0500, Clare Snyder <clare@snyder.on.ca>
>wrote:
>
>>On Wed, 03 Jan 2024 14:19:37 -0500, Joe Gwinn <joegwinn@comcast.net>
>>wrote:
>>
>>>On Wed, 3 Jan 2024 16:50:39 -0000 (UTC), bob prohaska
>>><bp@www.zefox.net> wrote:
>>>
>>>>Joe Gwinn <joegwinn@comcast.net> wrote:
>>>>> On Wed, 3 Jan 2024 04:11:04 -0000 (UTC), bob prohaska
>>>>> <bp@www.zefox.net> wrote:
>>>>>
>>>>>>Are there any general rules of thumb for sizing the holes used
>>>>>>to stop cracks? As a guess, I'd imagine the material thickness
>>>>>>is the lower limit and anything bigger than five to ten times
>>>>>>the thickness would be a reasonable upper limit if there's room.
>>>>>>
>>>>>>Does anybody know of a better approach? In my particular case
>>>>>>the material is molded ABS plastic, but I doubt that matters
>>>>>>very much.
>>>>>
>>>>> 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.
>>>>
>>>>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.
>>>
>>>There's no reason not to caulk those holes with a compatible rubbery
>>>material.
>>>
>>>Joe Gwinn
>> 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 to "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