Recasting a broken small nylon gear

[msg]

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.electronics.design/msg/93ebc61f0893eb4f?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

 

On Mon, 16 Mar 2009 13:19:57 -0600, msg <msg@_cybertheque.org_> 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.

 

[N_Cook]

msg <msg@_cybertheque.org_> wrote in message
news:_-OdnWwSE53cBSPUnZ2dnUVZ_ryWnZ2d@posted.cpinternet...

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.electronics.design/msg/93ebc61f0893eb4f?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/

 

[Tim Shoppa]

On Mar 16, 3:19 pm, msg <msg@_cybertheque.org_> 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.electronics.design/msg/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 future:

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

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

Tim.

 

[Jim Yanik]

msg <msg@_cybertheque.org_> wrote in
news:_-OdnWwSE53cBSPUnZ2dnUVZ_ryWnZ2d@posted.cpinternet:

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.electronics.design/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

 

[jakdedert]

msg wrote:

Tim Shoppa wrote:

snip

...this is the wave of the future:

http://www.jaylenosgarage.com/video/video_player.shtml?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

 

[msg]

Tim Shoppa wrote:

<snip>

...this is the wave of the future:

http://www.jaylenosgarage.com/video/video_player.shtml?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

 

[bz]

msg <msg@_cybertheque.org_> wrote in
news:_-OdnWwSE53cBSPUnZ2dnUVZ_ryWnZ2d@posted.cpinternet:

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.electronics.design/msg/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.

bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap

 

[msg]

bz wrote:

msg <msg@_cybertheque.org_> wrote in
news:_-OdnWwSE53cBSPUnZ2dnUVZ_ryWnZ2d@posted.cpinternet:


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.electronics.design/msg/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

 

[Russell Warren]

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-shop/Software/page17.html

Russ

 

[Jeff Liebermann]

On Mon, 16 Mar 2009 13:19:57 -0600, msg <msg@_cybertheque.org_> 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.

I recycled two 8505XL drives about two years ago. Too old and not
very reliable. I also dumped my pile of DDS-2 and DDS-3 drives. I'm
still using some DLT but prefer AIT for anything important.

1. Search the net for a replacement gear. There were plenty of
vendors that appeared when searching for "Exabyte gears" or "Tandberg
gears". For example:
<http://www.datanetuk.com/Exabyte%20Parts.htm#Gears>
Some of the tape driver repair shops might sell you a gear from a dead
parts drive. Unfortunately, if the gear died from nylon shrinkage,
the replacement gear may have the same problem. Be careful here.

2. Find a stock gear from some vendor that will fit or work. It
doesn't have to be nylon and might be aluminum or brass.

3. Glue the pieces back together with epoxy. This may be difficult
with a 3/8" dia gear as there's little surface area to support the
glue. I've done this for the chronically broken gears in the HP8640B
signal generators. The trick was to remove the brass hub. Enlarge
the hole in the center with a round file so the brass hub fits better.
Glue the gear pieces together without the brass hub. Use a jewelers
file to clean up the epoxy slop on the gear teeth. If your gear
doesn't have a hub, use a drill bit smeared with grease as a form. If
any of the teeth are missing, epoxy is NOT strong enough to act as a
replacement. You'll need a replacement gear.

4. Buy a dead Exabyte 8505 on eBay and cannibalize it for parts.
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270357562003>
My shop time is worth $75/hr. If your gear rebuilding exercise takes
more than about 90 mins, it's cheaper to buy the replacement drive.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[msg]

Jeff Liebermann wrote:

On Mon, 16 Mar 2009 13:19:57 -0600, msg <msg@_cybertheque.org_> 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.

<snip>

4. Buy a dead Exabyte 8505 on eBay and cannibalize it for parts.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270357562003
My shop time is worth $75/hr. If your gear rebuilding exercise takes
more than about 90 mins, it's cheaper to buy the replacement drive.

That's where I got this drive but ya takes yer chances on eBay I guess...

It's not intended for production use, just to recover tapes made on my
EXB8500 (full height) which has increasing read error issues and chokes
on the last tape of a five tape set awaiting a restore.

I'm considering getting an IBM 3590 fibre channel library (if I can
stomach the shipping costs) since I have a large box of media and the
cost of media is the limiting factor for me in newer tape technology.

Michael

 

[jakdedert]

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-shop/Software/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

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:0jivr4puv3i6ntlchat7cdif50ri10efha@4ax.com:

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

 

[msg]

Jim Yanik wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:0jivr4puv3i6ntlchat7cdif50ri10efha@4ax.com:



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

 

[msg]

tnom@mucks.net wrote:

On Mon, 16 Mar 2009 13:19:57 -0600, msg <msg@_cybertheque.org_> 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?

Michael

 

[Rich Webb]

On Tue, 17 Mar 2009 21:41:27 -0600, msg <msg@_cybertheque.org_> wrote:

tnom@mucks.net wrote:

On Mon, 16 Mar 2009 13:19:57 -0600, msg <msg@_cybertheque.org_> 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

 

[A_H]

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.

 

[Jeff Liebermann]

On 18 Mar 2009 00:02:22 GMT, Jim Yanik <jyanik@abuse.gov> 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>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Tue, 17 Mar 2009 12:17:47 -0600, msg <msg@_cybertheque.org_> wrote:

Jeff Liebermann wrote:

On Mon, 16 Mar 2009 13:19:57 -0600, msg <msg@_cybertheque.org_> 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.

snip
4. Buy a dead Exabyte 8505 on eBay and cannibalize it for parts.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270357562003
My shop time is worth $75/hr. If your gear rebuilding exercise takes
more than about 90 mins, it's cheaper to buy the replacement drive.

That's where I got this drive but ya takes yer chances on eBay I guess...

Caveat Emptor or You lose. Maybe another drive, this time from a
different vendor? (Two risky wrongs might just make one right).
Another used drive is still cheaper than the time needed to do the
repair job (which has a limited chance of success and survivability).

It's not intended for production use, just to recover tapes made on my
EXB8500 (full height) which has increasing read error issues and chokes
on the last tape of a five tape set awaiting a restore.

Worn head. It's history. I've had extremely bad luck reading tapes
that were created on a different drive, especially if there was a
difference in head wear and age. I once called a large number of
vendors trying to find a replacement with matching firmware for a
DDS-2 drive because the new and improved firmware would not read the
old firmware.

I'm considering getting an IBM 3590 fibre channel library (if I can
stomach the shipping costs) since I have a large box of media and the
cost of media is the limiting factor for me in newer tape technology.

I'm finding it cheaper to use NAS with gigabit ethernet for daily
backups. Terabyte drives and servers are about $250 from Maxtorch,
Western Dismal, Buffalo, and Seagate.
<http://www.smallnetbuilder.com/content/view/85/93/>
Or, you can built your own with FreeNAS:
<http://www.freenas.org>
I threw one together out of junk. It works nicely.

However, my customers want something they can store in the fire vault
and isn't sensitive to handling, so I'm still using tape (AIT and DLT)
and some DVD backups.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558