The Joint-Jigger

    
     
Tight miters are important to frame integrity.    

The way to go about making miters for fitting the tubes is unique to every shop. There are tools that cost about $140 to what ever you want to spend on laser technology. I use the Joint-Jigger. It is accurate to about 1/2°. My file takes it from there to produce miters that allow no more of a gap than about my thumbnail to permit the silver solder to flow to the back side of the tubing

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The clamp's angle is adjusted by loosening and tightening of the anchor bolts.

 
Angle is very accurate for this type of miter.