Cutting and Fitting
Jump Run Enterprises, LLC

4130 Steel Tube Airframe Construction Video
Master Blocks:  "If your plans use the centerline of each tube as the reference point, you will need to make a master block for each size of tubing that will come in contact with the jig table during construction."   
"Also, its a good idea to start fitting your tubes at the front, and work your way back.  That way, when you cut a tube a little to short for a good fit, you can use it where the fuselage isn't as tall.  This will keep your waste to a minimum."
Tubing Gap:  "Its acceptable to have some gap between the two tubes.  1/16” is a good max gap to shoot for. You can make a "go" "no-go" gage with a short piece of 1/16” welding rod.  Just check as you place each tube and try to keep the gap less than 1/16”
Working from the Centerline:  "Use the centerline as the reference point for your plumb bobs.  Adjust the airframe so the plumb bobs rest directly over the centerline on the table.  This will ensure everything is squared, and centered, In-Space."
Acute angle Cuts:  "One technique for achieving acute angel cuts is to turn the clamp on the tubing notcher upside down.  You will then have to clamp it in place with a couple small C-clamps.  The other good thing about doing this is that coolant from the mist cooler won't run down the tube as easily.  This is the way I always keep mine set-up."