The plan has always been to build a pack/travel bike for myself. This means using couplers. Why I did not use the couplers for the first frame was that I was very unsure about brazing. The couplers, being the first parts brazed into the frame, proved daunting to a newbie. So I waited and learned from the first effort. So that said here we go!
First order of buisiness was to map out the location of the couplers in the butted sections of the tubes. The tubes I used for this application were thus..
Double butted Verus 28.6mm TT ( 102-51-309-51-152 ) x .8/.5/.8 wall
31.8mm DT ( 102-51-324-51-152 ) x .8/.5/.8 wall
I am 6' even so the frame dimentions lended themselves well enough to land the couplers in the thicker butt ends although the coupler points do over lap into the taper transition. If there is any concern about not landing the couplers over the butt sections of a chosen tube, move up to .9/.6/.9 walled tubes. Little heavier frame but the couplers are not exactly light either. Better safe than sorry right? S&S machine suggest installing in the thicker butt lengths although sometimes doing this is difficult based on frame geometry cut lengths.
Cutting the tubes. This is all done old school with two types of tools. Hacksaw and files.. although I did order a pair of tube cutters from Andy Newlands of http://www.strawberrybicycle.com/. Nice tools that will help with dead on copes. Having filed tubes of my first practice front triangle and then the second full build, I would like to try these. They were a bit of a pinch to afford but will last a good long while. I would however suggest that everybody who would build a frame hand miter the tubes for the first few frames. Doing this will teach much. Anouther reason for getting tube cutters is that I want to do fillet brazing later on. However for both lugged and fillet frames, the copes must be spot on for optimal fit and strength. I do however all of the other fitted joins by hand. I just want to see what cutters can do so I have a given that I can tweek otherwise. I will use a mill to cut the tubes at the proper angles.Strait cuts.. I use blue tape as a cylinrical line and a 1/32" kerf 32TPI blade. I like to work around the tube creating a score all the way around, rocking the blade along the line around the tube. Try to stay close to the tape but not cut it. I mean right against but not on. Takes practice and a steady hand but marking the line this way is MUCH easier to see and follow than a scribed line is. Also the tape, because it is thin and wide, it will naturally want to lay a strait edge. If the winding angle is off a bit, the two ends of the tape at the 360 degree overlap will not line up. Unwind, correct the start angle and re-wind. This process creates a squarely aligned groove for the blade to follow. Working around the circumfrence the wall is cut thinner and thinner until it cuts through the I.D. . At this point, even a 32 TPI blade will grab the super thin remnants of the cut line. However because a path of least resistance for the blade was created all the way around the tube, the blade will follow that path through. square cut.
Couplers laid in loose and aligned with a strait edge. be sure to mark the long taper end so there is no confusion as to where the long taper end is.
Un mitered tubes test fit into the couplers. The next step is to braze the couplers onto the tubes. Because mitering occurs after the coupler fitting, orientation of the tubes does not matter. Just braze 'em in square otherwise a nasty twist will be built into the frame from the start. Not good. This is why I waited until a later frame to attempt couplers. After the lay out and installation is done, treat the tubes like normal with coping and buildin. Extra care to align the points of the couplers and lugs should be taken.
I like building flat. Although the setup takes a bit longer, this system offers much flexibility from sub assembly to final fit. Not the only way to do things but an approached based on what I had available. The saddle blocks were made to be of consistant height and center. The saddle cuts are truly hemishperical so that the center line of the tube lies at the top plane of the block. I can then use these to support a strait edge to create two lines 180 degree opposed. These lines are for indicating the tube center for mitering so that when the lugs go on, the points will line up.
