Wednesday, May 25, 2005

Falling Behind Schedule

Well, sometimes life gets in the way of work. Anyhow, I've managed to squeeze some framebuilding in since the last post but haven't had time for posting. Even this post will be without photos for the present - they'll come later.

I started Sarah's frame over from the beginning. After heating up the headtube joint it pulled apart easily saving the headtube and it's lug. Having already cut the BB off, the old downtube is now designated for use as the seattube (which is the same diameter as, but shorter than, the downtube).

After cleaning off the lug, I fit the new downtube to the headtube. Because the lug fit is now looser, I went with brass filler. All in all, I was satisfied with the way I flowed the brass, less mess and I could see it come out the far side of the lug all the way around. I'm a little concerned about over cooking the tubes, however, and will have to figure out a test for this - Freddy can probably tell me what to look for.

After mitering tubes, I fit the BB to the downtube and brazed it up again using LFBrass. I left the tube long in the BB so I could see the flow of brass come through. Then the same with the seattube. My available BB (cheap stamped type) has T-shaped windows in the sockets. Three of the windows came out perfectly clean - that is you can see the brass color where it flowed down through the window, but they have crisp edges all the way around. One window came out OK, but there's a spot where a little excess brass got into the window. I don't know if I have quite the right tool to clean this out, but we'll see.

While the flow of brass appears good throughout the BB, and the windows and edges look good, I'm again concerned about overheating. I work without shades to be able to look at the colors, but based on my color/temp chart, things aren't getting that hot. Also, the lug and tube never get hot enough to melt the rod without application of the flame, suggesting that they're below the melting temperature of the rod. But, call me paranoid, I'm just not sure. In part because there was a point where the flux wouldn't flow anymore. I was trying to draw the excess brass out of the one window with heat. It just wouldn't flow - which is what made me think the flux was cooked and that heat may have been excessive.

Anyway, I sat the head tube and seat tube each on a pair of v-blocks. Alignment was not perfect. Using the head tube as my baseline (using a flat table for my surface plate) the seattube rises 20/1000ths at the top (right side of frame down). So, here's another place where I experience don't knows. To wit, I don't know:
  • If 20/1000ths is significant.
  • If the tube warped, or if I did one of my joints crooked.
  • How to get this straight.

I'm playing with shimming the seat tube blocks to get the tube center the same height off of the table as the (larger diameter) head tube. Then I can use a square to test the BB to the plane of the headtube. I'm also working out a way to clamp the BB to the table top. The BB had been nicely faced prior to brazing, and is narrow enough that I'd like not to face it again. So, this seems like a good second test of the BB plane to the headtube.

If there is a significant alignment issue between the BB and the headtube, I'll just call this practice and cut the joints apart. Otherwise, I don't think a six-year old can feel a seat that's mis-aligned by 20/1000ths or less (the actual seat height will start about 10cm below the end of the rough seattube).

With this decision in place, I've gone ahead and fit and brazed the (mixte) toptube. The toptube is lugged at the front and filleted at the back. Both of these joints came out better than prior efforts with brass. The headtube came out clean and quick and I'm not worried about over heating. The fillet built up big - there's plenty of filing to do, but I will be able to produce nice radii for this angle.

Preliminary checking of the BB looks good, but more checking needs doing before attaching chainstays. Meanwhile, I started the process of fitting the stays in order to practice attaching dropouts, or in this case forks - single speed style because I want to use a geared hub.

The chainstays will be proportionately long - they're straight and need to accommodate a 1.5" diameter tire. This, of course, should also help the bike track straight. Small bikes turn so quickly that this shouldn't be a problem.

Freddy got my respirator and pin kit to me. Yea on both - highly recommended. Anyhow, the angle of the stays means that the fork (dropout) is at a distinct angle to the stay when viewed from above. I cut the left stay to approximate length, then cut the slots with a hacksaw and bent the tabs back so that they snapped off easily. While it was no problem to align the fork into the stay, it was loose enough to not trust gravity while brazing. So I used the first of Freddy's pins. Very cool. His supplied drills cut very well (better than my Hanson's but that set is a bit old and may be dull). Everything got a good coat of flux, especially the inside of the stay, then a tap of the hammer to set the pin and everything was lined up nicely.

At the risk of sounding like a broken record, this was my best brass braze yet. It should be noted that the stay is fairly large around when the fork enters it and I wanted a good bond between the two, lots of brass went inside. This likely will prevent me from slipping the fork the way that Paterik describes to adjust the joint. This will drive the use of some kind of fixture to make sure that the stays and forks are in perfect alignment before brazing them to the BB.

Anyhow, why did I like this braze? Well, I filled the stay with brass easily without seeming to overheat. Recently I saw a cameo from a Paterik video. I've been moving my torch around but basically keeping it in contact with the tubes. In the video, Tim moves his torch around - then pulls it away from the metal for a moment - then returns to heating. I tried this method and it has some real advantages. 1) when the flame is away, its much easier to see how the joint is coming (maybe I can start to use shades and protect my eyes), and how the brass is flowing. 2) brass can be applied with the flame, then the flame is pulled away while adjusting one's hold on the rod - meaning less heat on the joint when its not needed. 3) its easy to combine this method with using the side of the flame to keep the brass in the flames cone without pointing the cone at the tubing - again controlling the heat while melting the brass.

Netting this out, I was able to better manage the brass to stay viscous rather than having melt to water - and the brass did a much better job of staying where I wanted it. I was also able to melt some of the brass for filling the stay from above. The stay and already placed brass were hot, but I could keep the cone of the flame and the rod 3/8ths to 1/2 inch above this and have it melt into the already deposited brass - rather than placing coagulated drops of brass on a coagulated mass of brass. So when filling started, there where no holes - yea!!!! Also, having filled the stay, it was easy to draw brass, using heat, down the edge of the joint between the stay and the fork - and this went cleanly - no slopping of brass around. Finally, the slot was too long on the bottom - probably very bad form, but the hole had to be filled. It was easy to keep the brass viscous and bridge the gap & tie it back into the end of the fork. Up until now, brass seemed like a necessary evil - but this time it was fun to use. All of this may seem pretty trivial to anyone reading this site, but for me it was a major accomplishment and I'm still enjoying that.

Well, that's about it for now. The description is now current with my work. I'll try to get some photo's posted on the site this week/weekend to show the work.

PS The post office is still no help regarding my BB taps. Renaissance has indicated that they get me some info to use, but they're mid-move across the Atlantic - so I expect this to be a long slow process. Ugh.

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