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I don't know if this belongs here or exterior. Welding the perimeter of the belly pan to the frame should be easy. When welding the floor to the interior bracing will be (at least for me) a bigger challenge. Is there a trick to getting a good weld and not going through the floor?

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RacerDan
+442 Chevy 2.8
Never be afraid to try something new. Remember, amateurs built the
Ark, professionals built the Titanic.

When you are doing circles/Cs/Vs with the torch to make the bead, try to concentrate a little more of the bead on the tubing instead of the floor.

You could also try to set the heat and wire speed for the lighter material but you may have trouble welding to the tubing.

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-Andrew
Build Log
Youtube

Is welding in the floor a good idea?

I realize it helps up the stiffness by a good bit and it's relatively simple, but are there times when it would be nice to be able to remove the floor?

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mobilito ergo sum
I drive therefore I am

I can explain it to you,
but I can't understand it for you.

When welding .125" floor plates to the floor [ say on an IT car ] I always used overlapping circles, speed up when you have the torch pointed at the thinner metal, slow down when pointed at the thicker metal. .023" wire.

It's almost like you are getting the puddle a bit too big up on the thicker metal and then letting it overlap the floor metal. The faster movement with the torch across the thinner metal gets the metal hot so the puddle has the correct penetration/bond . Practice on the bench until you have it down pat. If you look at the underside of the floorpan you can tell when you have the heat/penetration correct

Before I welded my floor pan, I laid out 1/4 inch holes on cross members and bracing, then piled on the weight to hold flat (and clamped down where I could reach) and plug welded the holes.
Then perimeter welds and stitch welded inside.
There has been no oilcanning with the floor. Can't see future problems. There are access holes for the necessary bits.
Regards, Wilf

I thought about maybe drilling 1/4" holes in the pan every few inches over each member. Then weld into the hole, kinda like a spot weld.

I've also heard about copper, or even aluminum "spoons" that you can back up the weld with and it disipates heat well enough that you won't weld through. I'm not sure how you would go about that being on both sides of the frame, to weld on the inside and hold the spoon on the bottom.

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RacerDan
+442 Chevy 2.8
Never be afraid to try something new. Remember, amateurs built the
Ark, professionals built the Titanic.

I can't think of a time when it would be critical to have the floor out. I wouldn't recommend welding in side panels, since those would need to be removed at some point. But the floor will always be there.

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Build Log (not much there yet): http://lotus.reddeth.com
442e frame, 3.4l Camaro donor

My entire locost was made of tubes and sheet steel welded together so I may have something to say. As others here have already told you use .023" wire and low amp. My own strategy was to tack weld any piece of sheet metal to tubes moving the electrode from the G16 tube to the G18 sheet steel. Then I would do another run of short welds everywhere and then another one. After checking that the tubes had not been warped I would join the welds, welding a bit on one side moving to the opposite side and so on. I ended up with a slight warping of the frame which was not difficult to correct using clamps. Hope this is useful.
Philippe

Myself I welded it using .035 and had no problems, I went from outside edge jumping from front to back and then to the opposite edge of the tunnel jumping from back and forth and then went around to the other side and repeated the steps in reverse, no warping.
I used 16ga steel for my floor.
Al

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Super Seven 3.4

Ditto, except I used .030 and I did end up with some light oil canning in a few places (Al's probably a better welder than I) that got really worse when some guy (you know who you are ) I let drive it slid it off a curb. (presumably stretching it in the higher stressed areas.) You really couldn't tell much with the seats in though. If I could do it again I'd likely use 18g and plug weld predrilled holes as mentioned earlier.

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He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

I saw some pictures on here that I swear the seat frame or rail was mounted to the floor pan rather than to the frame members. I'm very long waisted and I stick out the top more than most, so mounting the seat an inch lower would help me, but mounting to the pan doesn't seem very stable.

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RacerDan
+442 Chevy 2.8
Never be afraid to try something new. Remember, amateurs built the
Ark, professionals built the Titanic.

Welding to the pan is trouble in an accident. As the frame starts to cave inward, the seat's just going to sit there like a target rather than being gradually accelerated sideways by the frame.

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Midlana book: Build this mid-engine Locost!, http://www.midlana.com/
Kimini book: Designing mid-engine cars using FWD drivetrains, http://www.kimini.com/book_info/

Mine were mounted through the pan and a 1/8 thick band welded across it on the rear points and just through the pan toward the front, but I had other support diagonals nearby that made it sturdier than the common pan.

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He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

Is it in your build log? I'll take a look. I really would like to get my seats down as low as possible. I've got some 1/8 by 3 inch plate. I don't know what that would do for weight, but I could span between tubes with that. I don't want to feel any movement.

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RacerDan
+442 Chevy 2.8
Never be afraid to try something new. Remember, amateurs built the
Ark, professionals built the Titanic.

I was going to start a new topic but saw this so desided to bring in back to the top. I'll hopefully be welding in my floor this weekend and I had an idea that I hope will help with oil-canning and I wanted to bounce it off a few of you. Anyway, I thought about pre-heating the floor using a propane weed burner. This would cause it to expand. Welding would start in the center of the car and work outwards. This would make the expansion caused by welding heat to expand the floor sheet out towards the unsecured perimiter instead of towards an already welded seem. When the floor cooled down it contract and be streatched beween the tubes making the floor a drum instead of wrinkly oil can.

Is there any sence to this thinking?

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My Build Log: viewtopic.php?t=5850
CAD Drawings:http://locostusa.com/forums/viewtopic.php?f=26&t=6376&p=62465#p62465