I feel like I’ve tried every trick in the book at this point and still have tons to learn.
Here are some random tips:
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A gas fluxer isn’t necessary to make smooth flowy fillets or even TIG style dimes, that’s all in your technique. It’s really best for tacking the frame and doing some small braze-ons without flux. Don’t think you need a gas fluxer to improve your fillets. You just need more guidance and practice.
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For a while I used to tin my front triangle together in the frame jig. Now I just apply tacks. I found that adding all that heat for tinning increased distortion, especially at the head tube. Crank your flame and apply tacks really fast. Dave Bohm taught me to count to 8. If the joint wasn’t hot enough to lay a tack my torch was too cool.
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I don’t spend a lot of time pre-heating a joint. Again, the more heat sunk into the joint the more chance for distortion. When starting a joint, get your flame in real tight and point it more on the thicker tube. Dab your filler in when it’s come to temp then move the flame away from the joint. Wait for the filler to solidify (you can usually count to two) then move the torch back in slightly overlapping the solid filler. Get it to temp, dab the filler, then get out. It’s kind of like the TIG pulse setting: Apply heat, dab, turn off heat.
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The TIG stack of dimes raw fillet look seems to be popular right now. I get it. It saves a ton of work cleaning up the fillets to make them smooth. BUT if your fillet has a thick edge beware that you’re creating potential stress risers. Several years ago a friend requested that I leave the fillets raw on his hardtail. After a year or so of riding, he took the bike off a small drop and either the top tube or the down tube (not sure which) cracked right at the fillet edge causing the whole head tube to pop off! Luckily he walked away with only some bruises. The fillet joints were perfectly intact. It was a tube failure. I can’t say for certain whether it was an imperfection in the tube or a stress riser from the fillet edge that caused the tube to crack. But I always file my fillets with a smooth transition to the tube to be safe.