Thanks, Mac; very thoughtful of you to flag this one!
Yes, hobbyist framebuilding is a fun and wonderful pursuit, and will surely tell you if want to do it professionally (a hearty "No!" from this hobbyist; for one thing, the liability insurance here in the 'States would surely kill any profit. For another, it is a *lot* of very hard work to produce even one frame from scratch. Add in the demands of a custom build for fussy/unpredictable others and...no thanks).
I have tried a more primitive version of this coping calculator in the past (it wasn't as nicely smooth-edged), but now use a tubing notcher...a little fixture that holds the tube in place at a set angle while I run an electric-drill-powered bimetal hole saw through it, while using lots of cutting fluid. Using a file for cleanup, all my joints are light-tight and tube edges are plane with the mating tube.
One of the toughest things about mitering is getting both copes (at each end of the tube) to be in the same plane (so the head tube is in vertical alignment with the seat tube, for example). If you're fussy like me -- I am not happy unless everything is "true" to within 0.1mm/.003in -- it can be a real challenge. So far, I've found the best method is to set the uncut tube on a surfaced table and then draw a machinist's scribe the length of it, then rub some machinist-blue dye into the scribed line to use as a hard reference for aligning the copes at either end. I also spent a lot of time getting my notcher dialed-in so the cope is centered on the tube laterally as well. I've seen frames with the tube in plane, but the top tube offset a millimeter or two to the side.
Boy! A hobbyist builder sure does learn about and soon comes to appreciate the challenges faced by custom and production builders!
Tubes aren't always rolled or drawn "round", the walls vary in thickness, butting isn't always accurate or internally unflawed, and odd-shaped tubing can be twisted. I used a rare Phil Wood elliptical tandem keel tube for the main frame spar on my Folder, and the ends were over a degree out-of-plane. It wouldn't have mattered much in tandem use, as the tube would have been set the "wide way", but I employed it with the long section vertically, and had to deliberately mill it off-center to get both ends to align. The fillet hid the needed fudging -- it aligns and I know what was needed to do so, but a buyer would have no idea as the cake is already baked by the time it is ridden.
Lugs often require a lot of cleanup, and the published angles aren't always as-claimed. Fillet brazing gets around the lug issue, but there can variations in the same brand of flux, and even gas-fluxers pop and fuss from time to time. I take great care to braze in a draft-free environment, but I've seen other builders braze in the breeze of an open window; not great for controlled cooling of the joint.
It makes me sympathetic and empathetic to manufacturers who occasionally have an unexplained failure of unknown origin. Some flaws just don't show, even in the building! Annnnnd...some flaws do show but go out anyway as the fault of the builder. For example, a friend recently paid USD$8,000 for her complete custom-built frame/bike. She was thrilled with it until she tried to shift the cassette into high gear and found the builder had forgotten to notch the lower end of the right seatstay for clearance at the dropout. Oops. Her other similarly-priced custom from another builder had a misaligned fork, a sad reminder that sometimes production bikes are made to higher basic standards than full-on customs.
Returning to that topic of liability here in the 'States...a person really can't build a frame and then even gift it to a relative or friend to ride; it just isn't worth it. Insurance companies are now going back through two or three parties to recover their payout costs, so I don't sell or pass-on any of my creations, making them only for myself.
Thanks again for the thoughtful link, Mac; very much appreciated!
All the best,
Dan.
