Improvised slide hammer 'welded' to dent in car's floor

[Mike McLeod]

Being unable to obtain one without pre-ordering locally, I've cobbled up this slide hammer to pull out a ding in the underside of this car I bought. Some clod had missed the jacking point and ended up pushing up the floor close to the cross-member the J.P. is mounted to. The sliding weight should have more than enough grunt to get it out, but I'm wondering if my scheme will work because I plan to 'weld' the end of the shaft to the indented part by passing up to 220 amps through it and thrusting it up against the floorpan, hoping it will stick sufficiently for me to be able to tap the ding out. I'll turn the current off as soon as it tacks to the floor, obviously; should only take a fraction of a second? I'll be attaching the live cable of an arc welder to the ring-end of the shaft. The pointy end is shaved down to a flat point of 5mm diameter. This'll be the part that I hope will fasten itself to the bottom of the floorpan.

Any tips/suggestions as to how to make this idea work most effectively?

[Chris Green]

I think it's much more likely that you will simply burn a hole in the floorpan, it's very difficult to arc weld thin steel.

I think you'd be better off screwing a plate to the floorpan with several self tapping screws and attaching the slide hammer to that in some way.

[newshound]

+1

Also, does it matter? Can't you attack it from the other side?

[Brian Gaff (Sofa]

Where should we send the flowers after the explosion? Brian

[Mike McLeod]

No, it's a blind void. And I'm *not* trying to arc weld it to the floorpan like the other fellah said. I'm planning to jab the shaft up against the car chassis while it's hooked up to the welding transformer in the hope that they fuse together under the heavy current. There is a variation of this technique in common practice in pro body shops. Here's how it works in principle:

[Mike McLeod]

Very droll I'm sure. I'll be using a proper industrial Oxford oil-cooled arc welder circa 1973 for this job, not some crappy Chinese "turbo" fan-cooled, low-duty-cycle job, so there won't be any explosions.

[newshound]

Well it might work although stud welders and spot welders usually rely on an adjustable timer (or fixed timer and adjustable current). And you saw how clean the body shop guy got the surface. But I still wonder why you feel the need to fix it if it is only protruding into a blind void.

[Mike McLeod]

Fair point. If you could see it, you would notice it's torn away the jacking point from the surrounding metal so there's a fissure you can trace your fingernail though. This is an old classic so the metal is not as pliable as a new car would be. By the same token, some rusty holes have opened up on the other side which had it been undamaged, would not have been apparent. Need to fix these issues, not just for the sake of completeness, but my conscience! I can get the area clean no problem, but am inclined to leave it be as a little resistance would be no bad thing, since it generates a hot-spot when high current is passed through it, which is in this instance at least, desirable!

[GB]

I know nothing about these things, but the weld has to be strong enough to take the hammering, so how do you remove it later?

[alan_m]

Dent pulling for thin body panels uses hot melt glue and attachments to the slide hammer with different surface areas. Sprayed IPA will release the glue from the panel. I've got very limited experience of this technique and it is not just pulling out a dent but also knocking back high points (ridge lines etc.). In the OP case cosmetic perfection may not be required on the underside of a car.

[newshound]

I disagree. You will get the peak current density at the contact from the constriction resistance effect. You do *not* want to include oxide in the weld, because this will reduce its strength.

[Andy Burns]

I've seen glued ones & spot welded ones

[Cursitor Doom]

Or multi-tool with metal-cutting blade fitted.

[F Murtz]

Can't you just cut the whole shebang out and weld a new bit in like they have done for generations before this dent pulling carry on

[Cursitor Doom]

Which decade of late 19thC are you referring to? Light dents, fair enough. Trouble is, some dents are bad enough to draw in the surrounding metal and depending on where this happens, the only remedy is to fully restore the correct geometry around the affected area, which can only be achieved by pulling whilst tapping down the resulting 'caldera' with a metal shrinking hammer.

[Jimk]

Angle grinder

[Jimk]

Angle grinder

[Jimk]

...& large stack of "metal cutting blades"...