I’m trying to nail the balance between stiffness and heat input on a 3/8" A36 frame with 7018, and I’m looking for a reliable calculator that ties fillet leg to effective throat and basic load so I don’t balloon the HAZ or warp the diagonals. If you’ve got an app or printable chart you trust on the floor — bonus if it includes preheat and travel speed for long 42" seams — drop it here.
I use Lincoln’s online heat input and preheat calculators on the floor: https://www.lincolnelectric.com/en/Support/Resources/Pages/weld-calculators.aspx. Size the fillet with ‘throat = 0.707×leg’ and on 3/8 A36 with 7018 I hold about 115–125 A and 10–12 ipm on long 42-in runs with a skip sequence, which keeps the diagonals from potato-chipping. Caveat: that 0.707 assumes a true 45° fillet — unequal legs or multi-pass need a quick hand calc or a weld group spreadsheet.
Piggybacking on @sandra_m89, I like Miller’s calculator for heat input/travel speed and keep a pocket note that “a = 0.707×leg” so I can quick-check 0.6·FEXX·a·L when sizing fillets for those 42" runs (https://www.millerwelds.com/resources/weld-settings-calculator). On long seams I backstep in 6–8" increments and use a metronome app to hold about 6–7 ipm — , speed drift is what balloons the HAZ and pulls those diagonals. Small caveat: on 3/8" A36 I only preheat to about 150°F if the shop’s cold; otherwise travel speed and sequence do more for distortion control.