On Sun, 4 Nov 2012 09:00:35 -0000, "N_Cook" wrote:

Jamie t wrote in message
...
Splork wrote:

On Mon, 29 Oct 2012 10:37:59 -0500, Jamie
t wrote:


N_Cook wrote:


isw wrote in message
]...


In article ,
Splork wrote:



My low tech pencil sharpener has a drive that uses a 2.2" gear to
drive

the


mechanism from the motor. The gear broke into 3 pieces.

I can probably repair it but am unsure of the composition and what to

use for

cement/ strengthening.


Cut a groove around the perimeter, deep enough to get past the gear
teeth. Wrap a steel wire around the gear in the groove, and twist the
ends to make it tight. If cyanoacrylate will stick to the plastic, use
that to get the pieces assembled before you add the wire.

Isaac


Are you saying cut a slot through the middle of the teeth into the bulk
under the teeth?
I suspect a .4mm saw in a Dremmel would end up as a melted mess and not
a
slot, perhaps a heated scalpel blade in a jig

Or perhaps use some nicrome wire with some silone sleeve at the
overlap,
apply a weight and some adjustable current. Hope the wire melts into
the
bulk of the plastic and perhaps ypu can ignore twisting off of the
wire.
May need to recess 3 pins into the disc part , then swathe in hotmelt
or
something, if the 3 sections have failed with smooth edges, before
doing the
wire job



what is a waxy plastic gear? I can't picture any gears being made of wax
or material soft like wax?

Jamie



Thanks to all the replies!!

The unit is at least 20 years old.

The gear is brown Bakelite in color. I say waxy because it has a soapy
feel and
I can scrape the material with my thumbnail and get some to come off.
Like very
hard wax. Odd for a drive gear material so I suppose it changed in
nature over
time. The exterior seems most changed so perhaps there is some material
strength remaining.

They call it micarta
http://en.wikipedia.org/wiki/Micarta

Jamie


I suspect its this material , upper left cog but I don't know what its
called
http://www.rennbay.com/pics/928insta.../Fig.%2050.jpg
from
http://www.rennbay.com/odotutorial.html
structurally poor but decouples vibration from a gear train

Color looks about right. Will get a scan of it tomorrow and post it. I saw a
number of posts on web sites referring to odometer repair while looking for info
on this gear. Also found a site where there are dozens of people with this same
problem asking for some reason: My post "Boston Model 18 Lg Gear Needed"

http://www.merchantcircle.com/busine.../shoutout/list

There is no binder or substrate to it. Heft in the teeth and hub, body half as
thick.

I see that the center hole of the hub which is keyed to the drive shaft may have
worn a bit allowing the shaft some slack and instead of all force delivered to
driving the gear, some was directed against small points on the hub surface.
The drive has a 15 degree or so pitch and this slack would allow the gear motion
off axis which would also work to crack it.

A little slop may be what killed it.

If I go with a JB Weld repair I will grease the shaft and use JB weld on the hub
also.

Thanks to all for the conversation.