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hello all, I am currently about to start boxing the frame rails on my 35 ford chassis, I've removed the X brace and cut the boxing plates (11 gauge)to tuck neatly inside the factory C channel frame. question is,.. if you mig weld the plates in, and then grind them for a "smooth" look, doesnt that extremely weaken the joint? I'd much rather have a weld bead on my joint than have cracks when the car hits pot holes etc. driving down the road. any of you experienced hot rodders have good advice for me? thank you in advance.
 

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Frame boxing

Unless you are going for a Riddler award I would just weld them and leave 'em. The biggest problem you will face is warpage while welding. I would recommend getting two 2" X 4" rectangular 3/16" thick sticks at the very least to tack the frame to before welding. Build a strong K member too. Can't build a house on shifting sands! You may want to think about insetting the boxing plates about 1/2" then you will not have issues with the welds and brake, fuel and wires will be set in just a bit.
 

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also, the boxing plates are already tacked in flush with the outside, some guys i see inset theirs a tad to allow better weld penetration. is this necessary? I hate to go backwards.
 

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Frame boxing

With a little practice you can get a good weld on an outside edge. I think the best way is to not set the two pieces flush but leave a little offset gap. Hard to explain but like you hacksawed a piece of metal in two except for one spot, then bent it to a 90. The result is a 90 degree joint with just one edge touching. Here is a picture of that type of weld that I made while making a new crossmember for my '39. Note the starts and stops. I have a short attention span, shake and must reposition my hands rather than glide along.
 

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More for Less Racer
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Set in flush and ground smooth is fine....but you should always properly prepare the joint first. Without prep you have to leave the weld bead intact for strength, but even then it is still less strong than a properly prepared weld joint

To set a plate flush into a C or U Channel you would bevel the edges of the channel and bevel the edges of the flat plate being welded in, so that your weld bead is being laid into a "V" valley formed by the edges of the pieces being welded together......then you can grind it flush and still maintain full material melding of weld and parent material.

It can also be done with just the bevel on the flat plate, the bevel in this case needs to be shallower than 45°, more like 30°, to give you enough room to flow the weld bead into.

39 Master is correct about an outside step being left to place the bead into, it achieves the same result as beveling but without the added time spent with a grinder in hand. Either way works well if you plan for it.

75% of good welded construction is prep before the actual weld.....similar to bodywork :D Too many guys just think "just crank up the heat and burn it in" but that leads to crystallization and cracking.
 

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Just weld hot enough to get good penetration, then you can grind away if you like, there will be few really concentrated loads upon that seam. What I really want to mention is the story of the first frame I ever boxed...I was, what...nineteen? I welded all the way up one side, then down the other, and repeat. When I was done, what we got was something that looked like a giant potato chip. Virtually ruined the frame by doing that, what a dumb a##. Fortunately the car owner (also nineteen) wasn't seeing it and didn't mind. Anyway, that's what you get when you just start welding away without a plan for heat/warpage management.
 

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greetings consider 'stitch' welding (1.5'weld X 3' space for instance). to minimise warping. Stagger the welds and wrap the ends . as mentioned by a previous hotrodder i think the best joint is to inset the plate 1/2' to form a T joint. weld on ! gc
 

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Brace it so it can not twist, stitch it as described above, Prep is the most important aspect of this. You also need to consider the use of the frame.

I am a huge fan of Dimpling steel. This can add massive amounts of strength to what would otherwise be a flimsy flat piece.
The downside it that dirt and other stuff loves to get into the new holes you made. If it is a track/show car then talk to a shop and see about cost. If you cut the piece, fit it, then drop it off to the shop you can save a good amount of weight and cost of one time use tools.
 
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