Cage Pad Question

Just want to clarify something I know I saw here somewhere. When welding the pads for the cage attachment points, I remember folks recommending not welding the entire perimeter, just "stitch" welding, inch long welds with an inch or two between them to prevent punch through from weakening of the sheet metal due to heat from welding. Is this true? If so, does that apply to element welded to the sills as well, or just to the pads on the floor?

Finally, for the folks who do annual tech for cars, is there any issue with this? Any guidance to insure trouble free tech?

Thanks for the feedback. I'm happy to say I am FINALLY at the point of my cage build to make this matter. I actually welded today. YEAH!!

Rory

Spotting to the floor pan is much stronger but may not pass tech. The floor pan is just there to keep water out.
Try to hit the sills and floor corners where multi pieces come together. Running a tube, sitting on the sill connecting the front and rear cage down tubes is the best way. Just on the driver side is fine.
When you fit the seat, allow the seat mount tube to lay on the floor and connect to the cage legs and or door bars or prior mentioned sill tube..
Ideally you want the driver box to push out of the floor taking the floor and cage assembly with it.
Modern cars have some strong points built in. Three layer areas, extra thic tin here and there. Play tappy tap with a small hammer to find them. weld to them.

As far as tubes joint and such, small angles are much stronger than 90* angles. triangiulate where you can and run straight tubes as opposed to bent tubes.
IE pass door bar can be straight and much stiffer than bent door bars. sameon the driver side, one straight angled tube is way stiffer than bent door bars, if you have room.
https://www.youtube.com/watch?v=1uJ9XCFZBvA This dash bar is angled across the car to help with stiffness.

I wanted to see if someone who does annual/initial tech could confirm that cage pads need to be welded around the entire perimeter and can not be "skip" welded.

Thanks.

The GCR is mute on that point. It thus becomes a subjective opinion, primarily based on the inspector's experience and expectations.

If I see stitch welding, I would not automatically reject it, but I would give it more-detailed inspection. I recognize that those pads are there not for tension or shear but for compression, so my decision will be subjective based on if I think the pad would retain its attachment in an incident, compared to how strong I "think" the point is that it attaches to.

I would be far more hard-ass on stitch welding if that pad was in a lot of shear versus primarily in compression (e.g., most of its attachment was on a vertical rocker surface).

But in the end, there is no regulatory requirement...

GA

Thanks Greg. On the vertical attachments I have continuous welds. I really have just one spot where the floor is contoured in such a way that there is a large gap. I personally don't see a need to fill in the gap with a weld (and some additional material), but it would be easier to do it now than to have to "correct" it later.

It would be a lot easier to fill any gaps now ,than after the door bars are in .For sure!
One method I've used is that after the base plates are welded where its' tight ,use a floor jack with an old socket or something and push the floor up to meet your base plate. Floor pans seem to be the lightest gauge steel in the car. It's worked for me and I prefer to have them welded continuously, just like the bars. Hope this helps.
Chris

I will usually rosette a floor plate in addition to perimeter welding it.

Showing my ignorance. Explain rosette.

http://lmgtfy.com/?q=rosette+weld

:P

While we are at it, what's really kicking my ass is the plates for the tubes coming forward toward the firewall. Between difficult access, multiple seams on the car, weird joint orientation, and thin sheet metal, I'm having a hard time finding the balance between adequate penetration and blowing a hole in everything.

If anyone has any secrets to share I'd love to hear them!

Oh. Like a plug weld. Got it.

Copper plate back-up is your friend.

Heck..don't fret; everyone blows holes through sheet metal.

Unfortunately a copper backing plate is not an option. Thanks for the reassurance that everyone blows holes in sheet. I think part of my problem is I am worrying too much about blowing holes instead of just doing what I know will work (most of the time).

"Hopscotch weld" basically you spot weld and move around the plate until you get enough tacks to be continuous or near so.
Spark/initiate on the heavier plate and melt onto the tin in short burst. Move an inch or so and repeat . around the plate.
That lets the weld cool between hits and will burn through less often. looks like poopsie tho but is strongerr than continuous burn weld due to less brittleness .

Thanks Mike. Once again it's good to be reassured it looks like poopsie. I must be doing it right:).

I basically do it the way Mike mentioned as well.
Another way when you have more access is to keep the arc on the plate and let the weld puddle kinda 'drip' down onto the sheet metal. gotta move quick enough that you don't blow through the sheet, but I had good luck with that welding the plates to the floor.

Quote:

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Originally Posted by Matt93SE

I basically do it the way Mike mentioned as well.
Another way when you have more access is to keep the arc on the plate and let the weld puddle kinda 'drip' down onto the sheet metal. gotta move quick enough that you don't blow through the sheet, but I had good luck with that welding the plates to the floor.

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I have used the same method as above and it works but does take a bit of practice to get the right balance.

I've had good luck with that method on the floor pans and other accessible areas too. The u!
Ultimate challenge is the upside down seam with a little bit larger than perfect gap. Talk about ugly! Fortunately it is a hard to see as it is to weld.

While we are all sharing secrets, what settings does everybody use for the above techniques? Settings for the thicker plate, the sheet metal, or something in between?

I've tried all with varying success using slightly different techniques for each. Just curious what people's preferences are.

Slightly Higher than for sheet metal

Quote:

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Originally Posted by backformore

While we are all sharing secrets, what settings does everybody use for the above techniques? Settings for the thicker plate, the sheet metal, or something in between?

I've tried all with varying success using slightly different techniques for each. Just curious what people's preferences are.

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All depends on the welder..
or are you talking about what setting do I use to perform the plate-to-sheet weld? In that case, it's 'hot enough to melt the plate, not hot enough to burn the sheet.' usually it's a middle of the road thing on my welder.. I'll run the sheet metal current and a lower feed speed so I can get enough penetration on the plate, then just move across the sheet a bit faster to keep from overheating it. Seems to work OK for me. YMMV.

I haven't actually done a test to confirm this, but my suspicion is that a stitch welded plate on top of thinner sheet metal is stronger and more resistant to punch-through than a continuously welded seam. When you weld you change the metallurgy and likely also affect the thickness of the sheet metal immediately adjacent to the weld for the thin sheet and I suspect that the stitch welds result in a lower residual stress concentration around the welded areas. Anyway, needs a well documented test to prove.

When welding a thicker plate to thinner sheet metal you need to build up heat (by lingering with the torch, using a slower feed speed in a Mig) in the thicker material to ensure penetration in that piece, and then "draw" the arc & the heat onto the thinner sheet to actually make the weld. With practice avoiding blowouts is not too hard once you have fine-tuned the voltage & feed speed. It is not too hard when you are welding the edge of the thick material on top of the thinner sheet. The opposite situation is harder but fundamentally the technique is the same.