Cutting miters is sort of fun but when its comes to making them perfect it can be a little frustrating. I feel like its important when trying to build a well aligned, solid frame to start off with the best miters you can possible achieve. I think most frame builders out there worth their salt have the same opinion. It just makes sense. From what I've ascertained the mitered tube should make as much contact with the parent tube as possible while still achieving the desired angle. You need nice tight miters because when your brazing the silver will have a hard time filling any big gaps in the miter and this could create a void in the braze. A good miter also acts as a support for the whole bike structure. If there is a big enough gap in the miter the tubing could possibly shift while you're riding and cause a crack. Thirdly, having good miters is the first step toward having good alignment in general.
I cut all my miters by hand by first using a hack saw for the rough cut. I get a little closer with a grinder and then I close in on the miter with a file. I do a series of checks as I get closer to the miter I want.
As I get toward the end of the miter I check to see if I have the right angle I'm going for. If that looks good I make sure that the sides of the miter are squared up.
The the third thing to do is to check the miter with the tube its going to mate up with. Some people say to have a really good miter you should be able to look at it and not see any light coming through the miter. Personally I would love to get one this close but it always seems like there is a tiny gap somewhere in mine. I'm working to close that gap though.
In the end I usually get my miters pretty damn close but never perfect. One of the things about miters that keeps causing me trouble is what to do with the sides that meet the outer most part of the parent tubes circumference. Is is better to continue up with the sides and then file the miter so it meets flush with the parent tube or do you file the sides flat and the tubing sits on the inner edge of the tube wall? Is that good enough? Is the silver able to bridge that gap? When I think about the miter I can see how you could continue filing right up the edge of the tubing and how the tubes could mate perfectly. Though when it actually comes down to doing the miter I always seem to end up with a bit of flat edge on the top. This bothers me and I think I should do a couple practice miters where I go specifically for that flush fit.
After I cut all the miters as best I can I dry fit the tubing in this sort of template/ sizing board thing I made. It's basically just a board with the drawings of the specs taped to it. Then I screwed some boards down onto the drawing to hold the frame in place.
I don't have a frame jig so this is sort of a way for me to check to see if the frame is matching up to my original drawing and specs. It also lets me see if the miters and angles are working. I wish I had a jig but I don't because they're expensive. I do subscribe to the idea that a good jig doesn't necessarily make a good a frame. However I firmly believe that a good jig could make building an accurate and aligned frame much easier and faster.
You don't even have to start telling me how my current setup could lead to inaccuracies because I already know. But it does help to get an idea of how things are coming along and when I set the frame in it everything seemed to line up really well. Nothing seemed stressed and all the miters set well against each other. The next step is to fit the frame up with the lugs.
I stuck on the lugs and things still seemed to to fit nicely. The only area that was a cause for concern was the lug connecting the DT and HT. The lugs seemed a bit stressed and kept trying to pull away from the HT.
You can see on the lower lug how the top is pulling away from the HT. When I dry fit the tubes that miter seemed fine which leads me to believe that maybe the lug itself is not completely accurate. It sucks that that miter is the one giving me trouble because the DT to HT connection is one most important miters. I think I'll try to reshape the lug a bit and see if that helps the situation. Other wise things seemed to feel pretty solid so I'll keep moving on with the build. The next step is to take care of some more prep and then take it to the "alignment table" and see what she says.
I drilled some 1/4 inch vent holes in the HT but all the 1/4 inch bits I had were really dull so it didn't go as smooth as I anticipated. I've read that you should put up to three 1/4 inch holes per lug but drilling out that much metal sort of freaks me out so I'll stick to two for now.
I went out and bought a new 1/4 inch bit and drilled some holes for the H2O bosses. Its amazing what a sharp bit can do for you. I'll braze on the little H20 bosses before I go any further with them frame.
The last thing I got to was pre-drilling hole the lugs for pins. I'm going to use 4d finishing nails and I drilled the holes out with a 5/64 bit. The last frame I built I used masonry nails ground down to small pins. I thought they would work better because they already had a sort of taper on them and I figured this would grip the holes better. It took way to long to prep them though and I am just going to give regular old finishing nails a try this time.
