flyingfinn
Kona Fan
Repairing a badly worn Kona Dog Collar
I posted before about undue wear on the dog collar that came with the Lava Dome I was refurbishing, basically the brake cable had sawn a groove (outward and downward) in the body of the collar - see picture. Although many do not seem to have suffered like this with the increasing rarity of replacements I decided to analyse the cause and come up with a repair that would result in long term use of a previously unusable part. I know others on retrobike have adapted the dog collar to take a piece of brake cable outer as a runner for fitting v brakes but as mentioned in one of my previous post I am determined (for the moment) to retain the original Curve OM Cantilever brakes, on which details like the straddle wire end fittings and pad adjustment were well designed and very effective.
The repair was effected by turning up some bar stock to the 28.6mm frame tube size and clamping the dog collar to this. The bar was then mounted so that the cable run hole in the dog collar was aligned under the centre line of a mill head. The standard hole was then enlarged with a 5/32" flat faced mill cutter to a depth of about 7mm. Although I have trained as a machinist (nearly 30 years ago) due to lack of time I left it with a friend to do in his spare time in the machine shop at the garage (massive understatement, more like car repair and modification centre of excellence) which he owns.
The resultant hole was then ready for an interference fit of a a piece of 3/16" cunifer (copper nickel) car brake pipe (after slight surface reduction with fine emery cloth). The pipe was trial fitted and then positioned with a surface coating of loctite thread-bond.
At this stage the 'tail' was left at a protruding length of about 4.5cm so that it could be manipulated into the correct double curved orientation on the bike so as to perfectly align with the centre of the cantilever straddle cable. Basically it had to curve out to run longitudinally and then down to run directly towards the straddle wire centre. Cunifer pipe can be manipulated with relative ease with the advantage of a degree of work hardening occurring but not becoming too stiff and brittle after bending. To control the point of curvature I used a small drill bit inserted into the tube and slowly withdrew it for each added stage of curvature. Finally after a trial fit the 'tail' was cut to a 3cm length to allow a good range of movement and adjustment for the straddle wire pick-up.
Second picture shows the result which has been test ridden and proved a massive improvement; although the cable runs extremely well (much better than the high level of friction sitting in an ever growing groove) I may add the internal liner from a V brake tube guide.
So my Lava Dome (or, due to improved spec, Cinder Dome / Lava Cone) refurbishment is now complete and I can get back on the trail in old school hardtail heaven!
Next project is a complete rebuild of my brothers 96 Saracen Hardtrax, possible as a hub gear commuter or slightly modernised and with a suspension fork added.
flyingfinn
I posted before about undue wear on the dog collar that came with the Lava Dome I was refurbishing, basically the brake cable had sawn a groove (outward and downward) in the body of the collar - see picture. Although many do not seem to have suffered like this with the increasing rarity of replacements I decided to analyse the cause and come up with a repair that would result in long term use of a previously unusable part. I know others on retrobike have adapted the dog collar to take a piece of brake cable outer as a runner for fitting v brakes but as mentioned in one of my previous post I am determined (for the moment) to retain the original Curve OM Cantilever brakes, on which details like the straddle wire end fittings and pad adjustment were well designed and very effective.
The repair was effected by turning up some bar stock to the 28.6mm frame tube size and clamping the dog collar to this. The bar was then mounted so that the cable run hole in the dog collar was aligned under the centre line of a mill head. The standard hole was then enlarged with a 5/32" flat faced mill cutter to a depth of about 7mm. Although I have trained as a machinist (nearly 30 years ago) due to lack of time I left it with a friend to do in his spare time in the machine shop at the garage (massive understatement, more like car repair and modification centre of excellence) which he owns.
The resultant hole was then ready for an interference fit of a a piece of 3/16" cunifer (copper nickel) car brake pipe (after slight surface reduction with fine emery cloth). The pipe was trial fitted and then positioned with a surface coating of loctite thread-bond.
At this stage the 'tail' was left at a protruding length of about 4.5cm so that it could be manipulated into the correct double curved orientation on the bike so as to perfectly align with the centre of the cantilever straddle cable. Basically it had to curve out to run longitudinally and then down to run directly towards the straddle wire centre. Cunifer pipe can be manipulated with relative ease with the advantage of a degree of work hardening occurring but not becoming too stiff and brittle after bending. To control the point of curvature I used a small drill bit inserted into the tube and slowly withdrew it for each added stage of curvature. Finally after a trial fit the 'tail' was cut to a 3cm length to allow a good range of movement and adjustment for the straddle wire pick-up.
Second picture shows the result which has been test ridden and proved a massive improvement; although the cable runs extremely well (much better than the high level of friction sitting in an ever growing groove) I may add the internal liner from a V brake tube guide.
So my Lava Dome (or, due to improved spec, Cinder Dome / Lava Cone) refurbishment is now complete and I can get back on the trail in old school hardtail heaven!
Next project is a complete rebuild of my brothers 96 Saracen Hardtrax, possible as a hub gear commuter or slightly modernised and with a suspension fork added.
flyingfinn
