19 Dec
2006
19 Dec
'06
12:29 a.m.
Around Mon, 18 Dec 2006 23:21:23 +0000 (GMT),
I've had extremely good luck using Plasti Dip <http://
www.plastidip.com/industrial/plastidip.html> to repair capstans. The
product lays up in layers of 2-8 mils (depending on dilution) and
produces an extremely uniform coating. I have repaired several HP
tape decks out of 30 year old test equipment which required a layer
of 70 mils. The worst runout was less than 1/2 mil. The material
appear to be sufficiently durable for the task. The only drawback is
the requirement for patience - each layer requires 30 min. minimum
drying time. After a bit of experimentation I found that floating a
bit of solvent on the surface maintained the coating consistency from
dip to dip.
Cooling to LN2 temperatures has its drawbacks: the rubber either
separates from the mandrel or it shatters - or both... The rubber
becomes glass-like and you cannot use cutting tools to machine. A
number of years back back in grad school I attempted to repair a
roller for a Van de Graaff generator using LN2 and failed miserably.
An old machinist got his chuckles watching my many tries. He took a
CO2 fire extinquisher to cool the roller and used a grinder mounted
on the lathe to surface the beast. You have to warm the object up
every so often to find out what the dimensions really are.
I've since surfaced a laser printer's pickup roller using a Dremel
grinder mounted on my mini-lathe at room temperature with good
results (didn't help one bit in the printer - those rollers are not
just rough, but have a directional nap).
CRC
ard at p850ug1.demon.co.uk (Tony Duell) wrote:
The drive
itself: the rubber roller driving the aforementioned
plastic
roller had melted. Clearly visible is the area where the rubber meets
[...]
Baiscailly you have to replace the roller. Replacements that have been
successfully used (depending on the machine, etc) include silcone
rubber
O-rings (possibly with a grobe machined in the original hub, or a
new hub
made), heatshrink sleeving, silicoe rubber tubing (fuel line for
glow-plug engines, for example), etc.
I've wondered if the 2-pack elastomer materials sold by e.g. Devcon
would
work. Make up a mould and cast a new roller. A lot of work, but if it
does the job well it'd be worth it in some cases. For those of
us with machine tools, I wonder if a roller can be "fine
tuned" to the proper diameter by fitting an oversize piece of
neoprene tubing to the roller, cooling the whole affair in dry ice,
then machining it (on a lathe) to the proper size. I can't recall
I believe it can, although cooling to liquid nitrogen temperatures is
recomend (if only beacuase it takes longer to warm up again, so you
have
longer to take a cut).
I've also heard you _can_ machine 'rubbers' at room temperature,
but that
the tools are totally different from those used for metal turning.
May be
worth investigarting.
I've not tried either though.
-tony