What’s your process of making the slots in the stays for plate dropouts - by hand? I find it very difficult to do it with any kind of real accuracy, since:
there’s some moving the stay between the blueprint and the vice to make any adjustment,
the dropouts on the dummy axle hover more or less awkwardly above the blueprint (more awkwardly if the d-hanger is not removable),
as nothing is connected yet, there is little fixed reference points,
I tried a block so that at least the stay rotation between the adjustments in the vice stays the same, but that’s just another awkward thing to make the positioning of the stay on the blueprint more difficult.
I have used a universal paper template/blueprint for chainstays at The Bicycle Academy, made my own slightly different version and that’s what I’ve been using. I’m on my fifth frame and don’t have any ideas how to improve this.
I’d try doing it the other way round. You can work out pretty easily what the angle of the slot is likely to be so cut the slot wherever you like on the stay. Some do it on centre, some actually cut away one side of the stay, it doesn’t really matter, find what works for you. Once you’ve brazed your dropout into the stay, use that as a subassembly and tweak your spacing and BB mitre to work with you have.
I wanted to ask specifically that. This was one thing I struggled to do accurately during my class with Dave Bohm. Here’s how we would do it:
Draw a centerline on the top of the chainstay. With a digital caliper, measure the width of the dropout plate. Mark that thickness on the stay, evenly on both sides of the centerline (we’d used Dykem to see the lines easily). Then we’d use a half-round wood tube block that accommodates tapered and ovalized tubes to clamp the stay in the vise. With a digital level, we would zero’d it at 90deg (perpendicular to the ground) and then use it as a reference to tilt the stay to around 5deg. Then with an hacksaw, starting from the top of width lines, we’d cut going straight down at 90deg from the ground, i.e not following the lines along the tube since they’re now tilted to 5deg. Next we’d check the fitting on the jig. If the angle wasn’t enough, we’d bend a little the drop out tab to match the needed angle.
I can visualize becoming precise with this after doing it for a while, but I must say I struggle with that procedure. Plus, it caused problem with my rocking dropouts because of the bent tab.
I would think you can figure the needed angle with trigonometry, but I’ve never done it and don’t know how to operate once you know the angle either.
I do a full scale drawing of the rear end, including the thickness and depth of the dropout tabs, and lay the stays out on top of it. Eyeballing and drawing in the angle of the cut with a fine point sharpie gets me close enough. If I have to tweak the dropout a bit after brazing it’s not too much.