Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Recasting a broken small nylon gear

On Mon, 16 Mar 2009 13:19:57 -0600, msg wrote:

I needed to repair an Exabyte 8505 8mm tape drive which had a broken 14 tooth
approx 3/8 inch diameter nylon gear in the cartridge handling mechanism, and
lacking suitable spares, I decided to attempt to reform the gear; this post
describes the method and results.


Gear sizes are standardized. It would be easier to find the raw
spur gear stock and re-machine the bore and length to suit your
purpose. Check the "Machinery's Handbook" for sizes.

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Default Recasting a broken small nylon gear

I needed to repair an Exabyte 8505 8mm tape drive which had a broken 14 tooth
approx 3/8 inch diameter nylon gear in the cartridge handling mechanism, and
lacking suitable spares, I decided to attempt to reform the gear; this post
describes the method and results.

A suggestion was made in a previous Usenet post to assemble the fragments
of a broken nylon gear and immerse them in a pot of epoxy heated to a thin
consistency, allow it to set, and then heat the works until the nylon
reformed. No mention was made of actual results or how the gear would be
removed from the epoxy mold:

http://groups.google.com/group/sci.e...f?dmode=source

I wired together the two pieces of the broken gear with a bit of small gauge nickel wire
around the arbor portion of the gear, mixed up "steel" JB-Weld into a small metal bottle
cap just a bit larger than the gear diameter, heated the epoxy with a heat gun until
thinned and immersed the gear to the level of the top of the arbor section. The assembly
was allowed to cure overnight. The following day I heated the assembly from beneath
using a heat gun set to a low setting while observing the bit of nylon visible from
the top of the pot. After a few minutes, the nylon began to expand and extrude from the
assembly. I stopped heating and using a flat tool, pushed the nylon back down flush
with the rest of the epoxy mold. I repeated this heating and pressing procedure another
time and then allowed the assembly to cool.

Using a small drill bit in a Dremel tool, I milled a groove around the perimeter of the
epoxy mold and popped-out the slug containing the gear. Sanding the underside smooth
revealed the pattern of gear with the teeth clearly visible, but also revealed that the
epoxy had disappeared from the center hole of the gear. Grinding the epoxy mold
material away from a gear tooth using an emery wheel in the Dremel tool also revealed
that the epoxy had fused with the nylon and was inseparable. I wound up "carving"
the gear out of the mold with the emery wheel.

The center hole was restored by milling it out with a number 60 drill bit in the Dremel
tool, working from both sides to preserve centering (under magnification parallax can
become distorted) and to cut a D shaped hole to accommodate the drive shaft.

The key points to be made are that using this process will produce a solid gear but it
will be fused with the epoxy mold material and cannot be simply separated from it.

The results are pictured in this photograph which shows the gear installed in the
tape drive mechanism:

http://www.cybertheque.org:81/ext/gear/gear1.jpg

It works as intended but long-term reliability is as yet unknown.

I did not apply any grease to (or even degrease) the original gear parts before immersing
them in the epoxy; I don't expect that using grease or mold release would have altered
the results or permitted removal from the mold. Perhaps a multistage casting process
starting with a latex mold, followed by a casting of a slug of the gear which then
could be used to cast a mold from a pot metal which then could be used for casting
fresh gears is another solution, especially if quantities of the part were useful
to have (since this failure mode is common in this tape drive, it may make sense),
but for me, reforming the original gear was adequate.

Michael
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Default Recasting a broken small nylon gear

msg wrote in message
.. .
I needed to repair an Exabyte 8505 8mm tape drive which had a broken 14

tooth
approx 3/8 inch diameter nylon gear in the cartridge handling mechanism,

and
lacking suitable spares, I decided to attempt to reform the gear; this

post
describes the method and results.

A suggestion was made in a previous Usenet post to assemble the fragments
of a broken nylon gear and immerse them in a pot of epoxy heated to a thin
consistency, allow it to set, and then heat the works until the nylon
reformed. No mention was made of actual results or how the gear would be
removed from the epoxy mold:


http://groups.google.com/group/sci.e...c61f0893eb4f?d
mode=source

I wired together the two pieces of the broken gear with a bit of small

gauge nickel wire
around the arbor portion of the gear, mixed up "steel" JB-Weld into a

small metal bottle
cap just a bit larger than the gear diameter, heated the epoxy with a heat

gun until
thinned and immersed the gear to the level of the top of the arbor

section. The assembly
was allowed to cure overnight. The following day I heated the assembly

from beneath
using a heat gun set to a low setting while observing the bit of nylon

visible from
the top of the pot. After a few minutes, the nylon began to expand and

extrude from the
assembly. I stopped heating and using a flat tool, pushed the nylon back

down flush
with the rest of the epoxy mold. I repeated this heating and pressing

procedure another
time and then allowed the assembly to cool.

Using a small drill bit in a Dremel tool, I milled a groove around the

perimeter of the
epoxy mold and popped-out the slug containing the gear. Sanding the

underside smooth
revealed the pattern of gear with the teeth clearly visible, but also

revealed that the
epoxy had disappeared from the center hole of the gear. Grinding the

epoxy mold
material away from a gear tooth using an emery wheel in the Dremel tool

also revealed
that the epoxy had fused with the nylon and was inseparable. I wound up

"carving"
the gear out of the mold with the emery wheel.

The center hole was restored by milling it out with a number 60 drill bit

in the Dremel
tool, working from both sides to preserve centering (under magnification

parallax can
become distorted) and to cut a D shaped hole to accommodate the drive

shaft.

The key points to be made are that using this process will produce a solid

gear but it
will be fused with the epoxy mold material and cannot be simply separated

from it.

The results are pictured in this photograph which shows the gear installed

in the
tape drive mechanism:

http://www.cybertheque.org:81/ext/gear/gear1.jpg

It works as intended but long-term reliability is as yet unknown.

I did not apply any grease to (or even degrease) the original gear parts

before immersing
them in the epoxy; I don't expect that using grease or mold release would

have altered
the results or permitted removal from the mold. Perhaps a multistage

casting process
starting with a latex mold, followed by a casting of a slug of the gear

which then
could be used to cast a mold from a pot metal which then could be used for

casting
fresh gears is another solution, especially if quantities of the part were

useful
to have (since this failure mode is common in this tape drive, it may make

sense),
but for me, reforming the original gear was adequate.

Michael


This is the method I've used

Hint for repairing broken plastic cogs / worn cogs
For the situation where a section of teeth only on a
plastic cogwheel are worn or missing.
Wrap a piece of thin polythene sheet around a section
of the undamaged cog teeth.Wrap copper wire diametrically
around the cog pulling the wire into the root of each
tooth over an "arc" 2 teeth wider each side than the broken section.
Coat with epoxy to form a mould and allow to cure.
Undercut the edges around the broken section,demount the
mould and reposition over the broken section.
Bind on and make good the cog with epoxy in 2 or 3
stages.Finally fettle with a file.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


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Default Recasting a broken small nylon gear

On Mar 16, 3:19*pm, msg wrote:
I needed to repair an Exabyte 8505 8mm tape drive which had a broken 14 tooth
approx 3/8 inch diameter nylon gear in the cartridge handling mechanism, and
lacking suitable spares, I decided to attempt to reform the gear; this post
describes the method and results.

A suggestion was made in a previous Usenet post to assemble the fragments
of a broken nylon gear and immerse them in a pot of epoxy heated to a thin
consistency, allow it to set, and then heat the works until the nylon
reformed. No mention was made of actual results or how the gear would be
removed from the epoxy mold:

* *http://groups.google.com/group/sci.e...sg/93ebc61f089...

I wired together the two pieces of the broken gear with a bit of small gauge nickel wire
around the arbor portion of the gear, mixed up "steel" JB-Weld into a small metal bottle
cap just a bit larger than the gear diameter, heated the epoxy with a heat gun until
thinned and immersed the gear to the level of the top of the arbor section. The assembly
was allowed to cure overnight. *The following day I heated the assembly from beneath
using a heat gun set to a low setting while observing the bit of nylon visible from
the top of the pot. *After a few minutes, the nylon began to expand and extrude from the
assembly. *I stopped heating and using a flat tool, pushed the nylon back down flush
with the rest of the epoxy mold. *I repeated this heating and pressing procedure another
time and then allowed the assembly to cool.

Using a small drill bit in a Dremel tool, I milled a groove around the perimeter of the
epoxy mold and popped-out the slug containing the gear. *Sanding the underside smooth
revealed the pattern of gear with the teeth clearly visible, but also revealed that the
epoxy had disappeared from the center hole of the gear. *Grinding the epoxy mold
material away from a gear tooth using an emery wheel in the Dremel tool also revealed
that the epoxy had fused with the nylon and was inseparable. *I wound up "carving"
the gear out of the mold with the emery wheel.

The center hole was restored by milling it out with a number 60 drill bit in the Dremel
tool, working from both sides to preserve centering (under magnification parallax can
become distorted) and to cut a D shaped hole to accommodate the drive shaft.

The key points to be made are that using this process will produce a solid gear but it
will be fused with the epoxy mold material and cannot be simply separated from it.

The results are pictured in this photograph which shows the gear installed in the
tape drive mechanism:

* *http://www.cybertheque.org:81/ext/gear/gear1.jpg

It works as intended but long-term reliability is as yet unknown.

I did not apply any grease to (or even degrease) the original gear parts before immersing
them in the epoxy; I don't expect that using grease or mold release would have altered
the results or permitted removal from the mold. *Perhaps a multistage casting process
starting with a latex mold, followed by a casting of a slug of the gear which then
could be used to cast a mold from a pot metal which then could be used for casting
fresh gears is another solution, especially if quantities of the part were useful
to have (since this failure mode is common in this tape drive, it may make sense),
but for me, reforming the original gear was adequate.


Cool. When plastic parts of my toys broke when I was a kid, my dad (a
patternmaker) would make molds from the originals with a little hands-
on and bring back a polyurethane replacement.

Non-functioning Exabyte 8505's must be a dime a dozen on the surplus
market, or well they were in the past decade, don't know if they're
still cluttering up storage rooms or landfills today. But once they
become truly rare, this is the wave of the futu

http://www.jaylenosgarage.com/video/...tml?vid=944641

It's incredible, complete working mechansims can be made this way!

Tim.
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Default Recasting a broken small nylon gear

msg wrote in
:

I needed to repair an Exabyte 8505 8mm tape drive which had a broken
14 tooth approx 3/8 inch diameter nylon gear in the cartridge handling
mechanism, and lacking suitable spares, I decided to attempt to reform
the gear; this post describes the method and results.

A suggestion was made in a previous Usenet post to assemble the
fragments of a broken nylon gear and immerse them in a pot of epoxy
heated to a thin consistency, allow it to set, and then heat the works
until the nylon reformed. No mention was made of actual results or how
the gear would be removed from the epoxy mold:

http://groups.google.com/group/sci.e.../msg/93ebc61f0
893eb4f?dmode=source

I wired together the two pieces of the broken gear with a bit of small
gauge nickel wire around the arbor portion of the gear, mixed up
"steel" JB-Weld into a small metal bottle cap just a bit larger than
the gear diameter, heated the epoxy with a heat gun until thinned and
immersed the gear to the level of the top of the arbor section. The
assembly was allowed to cure overnight. The following day I heated
the assembly from beneath using a heat gun set to a low setting while
observing the bit of nylon visible from the top of the pot. After a
few minutes, the nylon began to expand and extrude from the assembly.
I stopped heating and using a flat tool, pushed the nylon back down
flush with the rest of the epoxy mold. I repeated this heating and
pressing procedure another time and then allowed the assembly to cool.

Using a small drill bit in a Dremel tool, I milled a groove around the
perimeter of the epoxy mold and popped-out the slug containing the
gear. Sanding the underside smooth revealed the pattern of gear with
the teeth clearly visible, but also revealed that the epoxy had
disappeared from the center hole of the gear. Grinding the epoxy mold
material away from a gear tooth using an emery wheel in the Dremel
tool also revealed that the epoxy had fused with the nylon and was
inseparable. I wound up "carving" the gear out of the mold with the
emery wheel.

The center hole was restored by milling it out with a number 60 drill
bit in the Dremel tool, working from both sides to preserve centering
(under magnification parallax can become distorted) and to cut a D
shaped hole to accommodate the drive shaft.

The key points to be made are that using this process will produce a
solid gear but it will be fused with the epoxy mold material and
cannot be simply separated from it.

The results are pictured in this photograph which shows the gear
installed in the tape drive mechanism:

http://www.cybertheque.org:81/ext/gear/gear1.jpg

It works as intended but long-term reliability is as yet unknown.

I did not apply any grease to (or even degrease) the original gear
parts before immersing them in the epoxy; I don't expect that using
grease or mold release would have altered the results or permitted
removal from the mold. Perhaps a multistage casting process starting
with a latex mold, followed by a casting of a slug of the gear which
then could be used to cast a mold from a pot metal which then could be
used for casting fresh gears is another solution, especially if
quantities of the part were useful to have (since this failure mode is
common in this tape drive, it may make sense), but for me, reforming
the original gear was adequate.

Michael


go to a hobby/crafts store,and you can buy rubber casting material.

BTW,PAM no-stick spray works for a release agent.

--
Jim Yanik
jyanik
at
kua.net


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Default Recasting a broken small nylon gear

msg wrote in
:

I needed to repair an Exabyte 8505 8mm tape drive which had a broken 14
tooth approx 3/8 inch diameter nylon gear in the cartridge handling
mechanism, and lacking suitable spares, I decided to attempt to reform
the gear; this post describes the method and results.

A suggestion was made in a previous Usenet post to assemble the
fragments of a broken nylon gear and immerse them in a pot of epoxy
heated to a thin consistency, allow it to set, and then heat the works
until the nylon reformed. No mention was made of actual results or how
the gear would be removed from the epoxy mold:

http://groups.google.com/group/sci.e...sg/93ebc61f089
3eb4f?dmode=source

I wired together the two pieces of the broken gear with a bit of small
gauge nickel wire around the arbor portion of the gear, mixed up "steel"
JB-Weld into a small metal bottle cap just a bit larger than the gear
diameter, heated the epoxy with a heat gun until thinned and immersed
the gear to the level of the top of the arbor section. The assembly was
allowed to cure overnight. The following day I heated the assembly from
beneath using a heat gun set to a low setting while observing the bit of
nylon visible from the top of the pot. After a few minutes, the nylon
began to expand and extrude from the assembly. I stopped heating and
using a flat tool, pushed the nylon back down flush with the rest of the
epoxy mold. I repeated this heating and pressing procedure another time
and then allowed the assembly to cool.

Using a small drill bit in a Dremel tool, I milled a groove around the
perimeter of the epoxy mold and popped-out the slug containing the gear.
Sanding the underside smooth revealed the pattern of gear with the
teeth clearly visible, but also revealed that the epoxy had disappeared
from the center hole of the gear. Grinding the epoxy mold material away
from a gear tooth using an emery wheel in the Dremel tool also revealed
that the epoxy had fused with the nylon and was inseparable. I wound up
"carving" the gear out of the mold with the emery wheel.

The center hole was restored by milling it out with a number 60 drill
bit in the Dremel tool, working from both sides to preserve centering
(under magnification parallax can become distorted) and to cut a D
shaped hole to accommodate the drive shaft.

The key points to be made are that using this process will produce a
solid gear but it will be fused with the epoxy mold material and cannot
be simply separated from it.

The results are pictured in this photograph which shows the gear
installed in the tape drive mechanism:

http://www.cybertheque.org:81/ext/gear/gear1.jpg

It works as intended but long-term reliability is as yet unknown.

I did not apply any grease to (or even degrease) the original gear parts
before immersing them in the epoxy; I don't expect that using grease or
mold release would have altered the results or permitted removal from
the mold. Perhaps a multistage casting process starting with a latex
mold, followed by a casting of a slug of the gear which then could be
used to cast a mold from a pot metal which then could be used for
casting fresh gears is another solution, especially if quantities of the
part were useful to have (since this failure mode is common in this tape
drive, it may make sense), but for me, reforming the original gear was
adequate.

Michael



There is a plastic 'shape lock' or 'friendly plastic' that comes as white
pellets.
It 'melts' at ~ 60 C, turning clear.
It can be melted in hot water.
When it is melted and cooled slightly, you can mold it with your finger,
like clay.
It can be pressed into a mold. It takes details well.

After it cools, it turns white. It is tough, like nylon. It can be
machined.
As long as your machine doesn't get close to 60 c inside, it seems to make
a very good substitute for nylon.

Oh, when it is hot, it will 'stick' to most other plastics.

I bought a container of it and have used it to fix several things,
including my wife's sewing machine(a plastic part on the threader broke), a
broken gear in a printer(I used shape lock to fuse the pieces together and
re-enforce the gear), a broken paper tray in a printer(I replaced a couple
of broken plastic pieces), and a broken paper shredder(replaced a broken
piece of plastic).






--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap
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Default Recasting a broken small nylon gear

msg wrote:
Tim Shoppa wrote:

snip

...this is the wave of the futu

http://www.jaylenosgarage.com/video/...tml?vid=944641

It's incredible, complete working mechansims can be made this way!


Our local SAGE building, which once housed the mighty AN/FSQ-7 tandem
CPU, 100 CRT stations and several floors of peripherals and realtime
film projection systems, now hosts the Natural Resources Research
Institute (sort of swords to plowshares); the NRRI has a rapid
prototyping system that could have made my gear from a CAD drawing
in a few minutes, but alas I don't have access...

Michael


....or a CAD drawing. With that, there are a multitude of options.
There are companies which can take your CAD file and deliver a finished
gear in less than a week.

jak
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Default Recasting a broken small nylon gear

Tim Shoppa wrote:

snip

...this is the wave of the futu

http://www.jaylenosgarage.com/video/...tml?vid=944641

It's incredible, complete working mechansims can be made this way!


Our local SAGE building, which once housed the mighty AN/FSQ-7 tandem
CPU, 100 CRT stations and several floors of peripherals and realtime
film projection systems, now hosts the Natural Resources Research
Institute (sort of swords to plowshares); the NRRI has a rapid
prototyping system that could have made my gear from a CAD drawing
in a few minutes, but alas I don't have access...

Michael
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Default Recasting a broken small nylon gear

bz wrote:

msg wrote in
:


I needed to repair an Exabyte 8505 8mm tape drive which had a broken 14
tooth approx 3/8 inch diameter nylon gear in the cartridge handling
mechanism, and lacking suitable spares, I decided to attempt to reform
the gear; this post describes the method and results.

A suggestion was made in a previous Usenet post to assemble the
fragments of a broken nylon gear and immerse them in a pot of epoxy
heated to a thin consistency, allow it to set, and then heat the works
until the nylon reformed. No mention was made of actual results or how
the gear would be removed from the epoxy mold:

http://groups.google.com/group/sci.e...sg/93ebc61f089
3eb4f?dmode=source

I wired together the two pieces of the broken gear with a bit of small
gauge nickel wire around the arbor portion of the gear, mixed up "steel"
JB-Weld into a small metal bottle cap just a bit larger than the gear
diameter, heated the epoxy with a heat gun until thinned and immersed
the gear to the level of the top of the arbor section. The assembly was
allowed to cure overnight. The following day I heated the assembly from
beneath using a heat gun set to a low setting while observing the bit of
nylon visible from the top of the pot. After a few minutes, the nylon
began to expand and extrude from the assembly. I stopped heating and
using a flat tool, pushed the nylon back down flush with the rest of the
epoxy mold. I repeated this heating and pressing procedure another time
and then allowed the assembly to cool.

Using a small drill bit in a Dremel tool, I milled a groove around the
perimeter of the epoxy mold and popped-out the slug containing the gear.
Sanding the underside smooth revealed the pattern of gear with the
teeth clearly visible, but also revealed that the epoxy had disappeared
from the center hole of the gear. Grinding the epoxy mold material away
from a gear tooth using an emery wheel in the Dremel tool also revealed
that the epoxy had fused with the nylon and was inseparable. I wound up
"carving" the gear out of the mold with the emery wheel.

The center hole was restored by milling it out with a number 60 drill
bit in the Dremel tool, working from both sides to preserve centering
(under magnification parallax can become distorted) and to cut a D
shaped hole to accommodate the drive shaft.

The key points to be made are that using this process will produce a
solid gear but it will be fused with the epoxy mold material and cannot
be simply separated from it.

The results are pictured in this photograph which shows the gear
installed in the tape drive mechanism:

http://www.cybertheque.org:81/ext/gear/gear1.jpg

It works as intended but long-term reliability is as yet unknown.

I did not apply any grease to (or even degrease) the original gear parts
before immersing them in the epoxy; I don't expect that using grease or
mold release would have altered the results or permitted removal from
the mold. Perhaps a multistage casting process starting with a latex
mold, followed by a casting of a slug of the gear which then could be
used to cast a mold from a pot metal which then could be used for
casting fresh gears is another solution, especially if quantities of the
part were useful to have (since this failure mode is common in this tape
drive, it may make sense), but for me, reforming the original gear was
adequate.

Michael




There is a plastic 'shape lock' or 'friendly plastic' that comes as white
pellets.
It 'melts' at ~ 60 C, turning clear.
It can be melted in hot water.
When it is melted and cooled slightly, you can mold it with your finger,
like clay.
It can be pressed into a mold. It takes details well.

After it cools, it turns white. It is tough, like nylon. It can be
machined.
As long as your machine doesn't get close to 60 c inside, it seems to make
a very good substitute for nylon.

Oh, when it is hot, it will 'stick' to most other plastics.

I bought a container of it and have used it to fix several things,
including my wife's sewing machine(a plastic part on the threader broke), a
broken gear in a printer(I used shape lock to fuse the pieces together and
re-enforce the gear), a broken paper tray in a printer(I replaced a couple
of broken plastic pieces), and a broken paper shredder(replaced a broken
piece of plastic).


I used to buy "PlastiPair" (powder and solvent kit) at Radio Shack until it
was discontinued (apparently due to hazardous materials issues); it worked in
the same fashion and was particularly useful to copy knobs and of course was
not a thermoplastic so it could be used to make insulators and to reinforce
and repair standoffs and whatnot installed near power amp. tubes, etc.

I imagine that modelers still have a variety of malleable compounds for
custom shape making. I used to save the waste plastic from the PlastiPair
kits, grind it to a fine powder and reuse it with solvent. The issue
is determining the exact composition of the solvent, the last bottle of
which in my stash, sadly, has long since evaporated. It probably was
a mixture of xylene, toluene, TCE and who knows what else.

Michael


Michael

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Default Recasting a broken small nylon gear

These guys make getting custom parts pretty easy by providing you with
simple/free CAD software and taking you all the way through to getting
a part. No need to be a fully set up mech eng.

http://www.emachineshop.com

The simple example posted on their site is actually a gear...
http://www.emachineshop.com/machine-...re/page17.html

Russ



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Default Recasting a broken small nylon gear

Russell Warren wrote:
These guys make getting custom parts pretty easy by providing you with
simple/free CAD software and taking you all the way through to getting
a part. No need to be a fully set up mech eng.

http://www.emachineshop.com

The simple example posted on their site is actually a gear...
http://www.emachineshop.com/machine-...re/page17.html

Russ

One of the places I was thinking of when I mentioned many resources
available...if you have the drawing. IMO, it would be a little
difficult to draw a gear with their software (at least the version I
looked at a couple of years ago); but not impossible.

Otherwise, their site, software and their business is pretty amazing.
They'll build you *anything*--out of almost any material--as long as you
can spec' it accurately enough.

Well worth downloading their application just to play with....

jak
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Default Recasting a broken small nylon gear

Jeff Liebermann wrote in
:


3. Glue the pieces back together with epoxy.


does epoxy bond to nylon??? I'd not bet on it.

I think I'd glue it back together as best as possible,then use the casting
materials one can find at hobby/craft stores to make a mold and cast a new
gear.

--
Jim Yanik
jyanik
at
kua.net
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Default Recasting a broken small nylon gear

Jim Yanik wrote:

Jeff Liebermann wrote in
:



3. Glue the pieces back together with epoxy.



does epoxy bond to nylon??? I'd not bet on it.


I certainly discovered that under the right conditions, the epoxy-nylon
bond is very good, however I suspect that the bond I observed is
just the molten nylon conforming to the irregularities of the epoxy
mold in a very complete fashion. However I don't expect to be able to
simply 'epoxy' broken nylon parts together, but perhaps there may be a
way to liquefy the (set and cured) epoxy-nylon joint with a hot air
pencil to create a permanent bond (I will need to try this next time).
Thinking a bit more, perhaps hot air welding of a cyanoacrylate-bonded
nylon repair would work also.

I don't know how I would do this on the tiny gear that is the subject
of this thread however without distorting it beyond usefulness, without
using a mold, at which point I am back to my original approach of recasting
it.

Michael



Michael
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Default Recasting a broken small nylon gear

On Tue, 17 Mar 2009 21:41:27 -0600, msg wrote:

wrote:

On Mon, 16 Mar 2009 13:19:57 -0600, msg wrote:


I needed to repair an Exabyte 8505 8mm tape drive which had a broken 14 tooth
approx 3/8 inch diameter nylon gear in the cartridge handling mechanism, and
lacking suitable spares, I decided to attempt to reform the gear; this post
describes the method and results.



Gear sizes are standardized. It would be easier to find the raw
spur gear stock and re-machine the bore and length to suit your
purpose. Check the "Machinery's Handbook" for sizes.


It would indeed by nice to have a variety of standard nylon gear stock
on hand; has anyone found a cheap source for such kits?


http://www.allelectronics.com/ has some but there's such a wide possible
variety that hitting http://www.mcmaster.com for a specific gear (or
two) might be useful.

--
Rich Webb Norfolk, VA


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Default Recasting a broken small nylon gear

8mm drives are selling for $30-80 on eBay, some new in box.

Better yet, move up to much faster, cheaper, and more reliable storage
media, like thumb drives or usb disks.


Sometimes is better to ust start over than to try to patch something
so ancient.



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Default Recasting a broken small nylon gear

On 18 Mar 2009 00:02:22 GMT, Jim Yanik wrote:

does epoxy bond to nylon??? I'd not bet on it.

I think I'd glue it back together as best as possible,then use the casting
materials one can find at hobby/craft stores to make a mold and cast a new
gear.


Yes:
http://802.11junk.com/jeffl/pics/HP8640B/
I didn't use any manner of special epoxy. Just the cheapo hardware
store 2 hr epoxy. I've also done it successfully with JB Weld.
Surface prep was degreasing with some alcohol and deglazeing with
sandpaper. However, the 8640B gear in the photo is much larger than
the 3/8" gear in the Exabyte. Unless there's sufficient surface area,
it's not going to hold.

Incidentally, some construction "structural" adhesive is an epoxy and
nylon mix. I'm wondering if I should have used some of that instead.
http://books.google.com/books?id=4MTUnaKjuDAC&pg=PA372&lpg=PA372

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150 Felker St #D
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Skype: JeffLiebermann AE6KS 831-336-2558
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Default Recasting a broken small nylon gear

Try these guys, they're like the mechanical equivalent of Digikey -
thousands and thousands of widgets:

http://www.misumiusa.com/

assuming you're in the USA. They have sister companies elsewhere.
--
Nemo
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