I've added some extra functionality to the already wonderful Anvil fork jig. I've modified it so it can used with a tubing notcher (JD2 TN100) to create the miters for the chainstay/bb junction. This was a welcome addition to the shop since I had started TIG welding and had a new set of miters that needed to be right on.
I also configured the Anvil jig/tube notcher to make the seatstay/seattube miter but the setup time was prohibitively long and required some drilling/tapping into the Anvil jig. I'm not going to detail the process because I strongly believe it wasn't a great solution based on the fact that it took longer to set up and usually still required some hand filing after the cut was made. It could be quite accurate as the fork jig was mounted in the same way that the tubing holder of the notcher was mounted and made use of the same angle markings for setup of the cut. Since I didn't mess with accurate drop out dimensions in my CAD drawings I didn't have an exact angle to set it to. Because of all these things doing the whole job by hand was quicker. It was pretty cool though...
The only thing I use the tubing notcher for is either the chainstay/bb miter or notching tubes for practice welds. If I'm building a bike I find hand filing all the other miters using printouts from Martin Manning's Excel program to be most savory.
Basically there are two holes on the fork jig that two bolts go through to hold the steerer tube holder to the rest of the jig. I've drilled and tapped two holes in the tubing notcher that correspond to these holes. They are placed so that the fork jig attaches perpendicular to the tubing notcher.
Also, I made it so that the theoretical zero of the ruler on the fork jig would be at the center of the cut that the notcher would make ie the center of the bottom bracket. This way I could use the ruler on the jig by taking a little T-square or an equivalent and dropping it down from the center of the bolt holding the dropout and I would be able to set my chainstay length. You need to use the T-square because the built in indicator on the part of the fork jig is offset to give a correct reading while doing forks but when set up this way it will not give you the correct measurement.
The other thing is that there is a little play in regards to how perpendicular the notcher and fork jig sit to each other because of the size of the bolt holes in the fork jig. This allows you to use a T-square and make sure that the fork jig is quite perpendicular to the tube notcher while you are tightening the bolts. Tightening one bolt fairly snuggly and then checking the squareness, adjusting, then tightening the other bolt has worked well for me.
Here is a closeup of the cutting area and the forward clamping mechanism. I've made an aluminum platform and drilled/tapped holes in the bottom of the piece of the fork jig that ensures that the fork blades are both the same height above the jig and that the crown is not twisted. That aluminum platform attaches to the piece that moves up and down so the height can be adjusted. That means you can offset or center the miter. You could have the chainstays sit lower than normal on the bottom bracket or higher if you wanted. I tapped another hole to attach a small piece of aluminum on top of that platform with notches cut out for the chainstays to rest in. Another tapped hole allows a bolt to pass through a small piece of square tubing that keeps everything in place. The notches are a fixed distance apart but you can bring the chainstay ends closer or further apart from each other (ie sit closer to the middle or more towards the edges on the bottom bracket shell) by sliding the whole thing forward or backwards. I check how close to the outside of the bottom bracket shell my chainstays will be by using a set of calipers and measuring where the hole saw will cut through the stays.
Another picture from the top
For the rear assembly I've bolted a dummy axle from my frame jig to the same spot the Anvil axle sits. I used the Anvil fork axle at first but it was too specific to a fork and didn't work well. Too many spacers and thing and the bolts that attach the drop outs are very small. Using the other dummy axle gave me a sturdier grip on the drop outs and required no spacers to bring the spacing up to 120 or 130mm.
The part that the dummy axle attaches to slides up and down so, with the up/down adjustment at the front clamp section, you can adjust your chainstays to be parallel with the fork jig and be able to set your chainstay length accurately. Also, you can see in this picture the measurement indicator that faces the ruler that runs the length of the fork jig. This does not read the right length when set up this way. The correct measurement will be directly below the center of the dummy axle.
On the off chance that someone stocked their workshop with the Anvil fork jig and the TN100 tube notcher like I did hopefully this may be of some use.
