[Coco] Re: Look what's on eBay / CGP-115 split gears

[jdaggett at gate.net]

On 11 Oct 2006 at 19:36, Stan Blazejewski wrote:

> I tried a simple fix that worked & has lasted for years on a number of these
> printers.
> The gears split because they are a press fit.  When removed from the shaft you
> will notice that the split 'disappears' so I drilled out the hole in the gear so
> that it was an 'interference' fit (slides on with no slack & won't grip the
> shaft), roughed up the shaft a bit & glued on the gear with super glue.
> Works a treat & will never give problems again.
> 
**************

Gears split due to fatigue of the material when pressed onto the shaft. This usually happens 
over time with Forced/Interference fits. These rely on the tension and compression of the 
gear material to hold it to the shaft. Nylon,  a common low tier material for gears, with age 
will fatigue and therefore cracks in the material will propogate away from the hub.

A Transitional or Loose fit will allow for glueing the gear to the hub. Now the attachment is 
dependant on tension between the hub and the glue and with the glue and the shaft. The 
glue now  will shoulder the forces when turning.  

That is why I also suggested Delrin. It has greater strength than Nylon. Though it has a 
higher associated cost. IF a gear could be fashioned so that there is sufficient room on the 
hub to place a set screw that to would work. Drilling out the interference fit to allow glueing 
is a fast and easy repair. Only issue with that is the right chioce of glue for the materials 
being used. Cyano Acrylic (superglues) glues do not work well with Polycarbonates and 
polystyrene plastics. So you do have to choose the right glue for the materials being used.

james 

> On Tue, 10 Oct 2006 18:21:32 -0400, you wrote:
> 
> >I would be carefull as to what you replace the gears with. Make sure the shafts 
> >and the motors can handle the extra weight that a metal gear would present. I 
> >might sugggest usig a gear made of Delrin instead of metal, unless it is a 
> >lightweight metal like aluminum. Small Parts Inc in Miami has a nice selection of 
> >Delrin gears that might fit. 
> >
> >Delrin offers more strength and durability over that of nylon which is commonly 
> >used plastic for cheap gears. 
> >
> >james
> >
> >On 10 Oct 2006 at 14:25, Rogelio Perea wrote:
> >
> >> Been thinking of replacing that plastic gear with something more solid but
> >> it is one of those projects...
> --
> 
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> 
> stanblaz at netspace.net.au
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> http://groups.yahoo.com/group/cobra-cat/
> 
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