As reward (HA!) to you all for the advice, guidance and warnings, I thought I'd post an update in pictures from where I started back in October or so to progress on #1.5. I'm calling my first complete frame (pictures at bottom of this post) #1.5 because I only completed the front triangle of my first attempt before making a fatal mistake. I let the ST/BB assembly twist out of phase with the TT/HT assembly as I was brazing the TT/ST joint. The BB was pointed one way while the front triangle was pointing another by a few degrees.

I have a couple boxes of junked practice joints but here's an early sample of seatlug work. Mmmm, toasty!

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With lots of practice I got a tiny bit better.

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The following few are of frame #0.5:
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You can see how I wrapped the DT around the bottom of the BB. I already had a full fillet around the base of the ST and I wasn't sure how to miter around that so, I offset the DT to the lower side: I kind of liked the detail after I cleaned it up and may try it again on other frames.
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At this point, I realize the BB was out of phase but, I had made what I felt was decent progress and learned a ton. With some offline advice from board member Alistair who lives up the street, I abandoned the effort at this point and cut it up to see if I was getting good internal fillets. I was pleased to see that I was. I'll use the shortened tubes on a kids bike or something.

The next series are from frame #1.5. Same design. Single speed utility bike with 700c wheels and 28mm tires. In these photos you can see brazing is coming along somewhat - still blobby at times. My next hurdle is positioning while brazing. Knowing where to rotate to to get best aim at the joint and best flow from the filler. I am using just standard LFB from the welding store and either Cycle Design Nickel Silver flux OR Gasflux C-04 paste. I clean the joints with isopropyl alcohol before applying flux.

All of my work is done with hand files, a vice, Paragon tubing blocks, my new marble slab and some machinist squares/rulers. The only power I use is a drill to run a flex hone to clean out the insides of the tube.

My approach was different for my 2nd attempt. On #0.5, I mitered and brazed each joint in sequence and to completion. Because sometimes there are days between my work, my brazing would deteriorate and all joints were of equal mediocrity. On #1.5, I mitered everything except the seatstays and then tacked and aligned the front triangle before putting it in the Park stand to do the fillets on all joints. With each joint getting slightly better as I worked my way around the triangle, I'm sure on average, it's better than before. I was amazed to put it on my slab and see that it was VERY close to flat with well less than a 1mm difference across the front triangle (at least by my measurements).

I made a simple fixture to hold the dropouts/CS assemblies while I tacked them. It seemed to work pretty well but the chainstays pulled in a bit during brazing so I had to cold set the right out a couple mm to restore the 130 rear spacing.

I haven't added bottle cages or other braze-ons as I didn't want to waste them just to chop the frame up again. Now that I'm confident that it'll be rideable, I'll add the fittings for bottles, racks and other stuff. As you can see in one picture, the right drop out/CS junction is not offset properly to allow the cassette to pass when the wheel is at the most forward position. I will put that in the notes for #2.5.

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I found a nice flat slab of marble from a local countertop dealer. That helped remove some of the uncertainty about whether I was aligning correctly. I changed from a Victor 100 to a Victor J28 with TM hoses which helped immensely and finally I purchased a pair of ACE/Didymium glasses with 150 magnification which also helped immensely.

This is definitely challenging, addictive and expensive...a very bad combination .

I hope I got all of the pictures attached/uploaded properly.

Thanks again for all of the guidance. I'll post more as I get closer to completion.
Duane