Just after brazing:
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After a quick cleanup:
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Another attempt after brazing:
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And after cleanup:
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And another joint after quick cleanup. I got this up to just the right temperature and flowed the right amount of silver around the junction. By moving the flame around I was able to smooth out the silver so it was evenly distributed. This is how the bridges will be done, and by adding more silver I have been able to produce small fillets that will look good where the seat stays join the seat lug:
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A joint that didn't go so well:
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I sliced through the tube to check penetration on some joints I did at the end of the tube earlier this week. They weren't tidy at the edges, but I just wanted to see if the silver had flowed properly. It's just possible to see a thin line of silver between the layers of steel:
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So, it looks like I tend to scorch the flux just as I add silver at one corner of the joint for the first time (see the bottom right corner of each 'patch' i've brazed). As I move the torch around to draw the silver across the joint I'm beginning to be able to hold it at the right temperature, and even add extra silver without overheating if there isn't enough to draw through. Why I can't get this temperature right initially, I don't know. I think part of the problem is also that I return to the first corner with the torch to flow any excess silver and draw it across, so this area gets more heat. The blackened circle on the patch is when a bolt was clamped down to hold the patch flush. This acted as a heat sink and scorched the flux around it.
I'd ideally like the whole patch to end up with a glassy covering of flux with no scorching. I'm going to be ordering frame parts from Ceeway soon and will buy some cheap lugs to practice with. I've used some nasty pressed ones but want a couple of cast ones that are closer to what I'll be using on the frame.
Bear in mind that this is with a mapp torch with the flame held a good few inches from the metal. It does produce a lot of heat, which goes against what I've read pretty much anywhere else on the web.
Any suggestions for improving technique are welcome!
Ewan