Advice for tape drive repair / maintenance

[CRC]

Around Mon, 18 Dec 2006 23:21:23 +0000 (GMT),
> 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.

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.

>> 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

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