I can't weld 4130 outside in the wind. While I wait for the windy days to end, so I can finish welding the rudder bar, I've started sand blasting the tail surface welds. Since I have to do the sand blasting in my attic I've modified my sand blast cabinet. This is the same process I used to bead blast the spar for the Cessna 140.
From doing the spar I have a hole in the side of the cabinet but it's not big enough to fit the tail surfaces. For the tail surfaces I cut a hole in the back of the cabinet 4" high and 32" wide. I made a plug from 2" thick, closed cell foam rubber which is 6" high by 34" wide. The extra size is used as a seal by slitting it 1" deep along the center of the edges. It's like a big grommet stuck in the hole.
Instead of a big hole in the middle like a grommet I put a long slit in it for the tail surface to slide through.
In the front I used some more pieces of foam rubber as seals to allow the door to be open enough to for the tail surface to slide through. The bottom edges are slit like the back plug so they seal on the edges of the cabinet. The top just seals on the door.
I cut vertical slits for the spar and trailing edge to fit through and reasonably seal around them.
Inside the cabinet you work on a few joints at a time and then slide forward or back to the next joint. Once one side is done flip it over and do the other side.
It's a little awkward working this way. I'm only cleaning up the scale around the welded joints, so it works.
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