December 2018 Posts

Cubic Boron Nitride – Any Use to Framebuilders?

Cubic Boron Nitride – Any Use to Framebuilders?

I have had some problems in releasing my home made seat tube heat sink from the seat tube after brazing, in as much as the heat tends to seize up the threads and cone mating surfaces making it difficult to loosen. Otherwise my simple design works very well. More sophisticated heat sinks may not suffer with the same problems.
I therefore decided to try a Cubic Boron Nitride lubricant, which is available conveniently as a spray quite widely at prices of £20-£30 a tin. Whilst expensive, a little goes along way. It is normally used as a releasing agent for stainless steel moulds for firing glass in a kiln and apparently can be used on mig welding tips to prevent spatter sticking. It is often used as lubricant for bullets in a powder form (thankfully sold only in the USA), and is the “ceramic” in ceramic lubricants.
It is supposed to be stable up to about 600 degrees centigrade or thereabouts, and still remains active for repeated use. I sprayed the components of my heat sink before use and am pleased to say it worked really well, the whole item unscrewed and removed easily and the product itself was not consumed.
IMG_4429
It is true that I was silver soldering, so the temperature would probably be well within the specification, but I doubt the internal temperature of the sink would reach brass brazing temperatures so I am optimistic it will still work. I’ve also used it to lubricate the threads on my Jig where they are exposed to heat.

Lugged Single Chainring Winter / Light Touring Bike

Lugged Single Chainring Winter / Light Touring Bike

I wanted lightweight bike with lower gears for cycling holidays and winter use. Rather than going for a mountain bike group set I thought I would try a Sram single ring road group, though I still have a healthy scepticism about it. Getting a low enough gear is not a problem with the 42 tooth inner sprocket but it does compromise the top gear because of the small front chainring. Even getting the parts was a problem as availability is sketchy and I have to thank Paul Hewitt Cycles for obtaining the components for me. However, I wanted to use caliper brakes and nobody, at present, makes a 130mm non disc rear hub to accommodate Sram’s XD cassette, which is needed to get a 10 tooth sprocket, so I have to settle for a 11 tooth.