Metal thickness

[tim78]

I need to do a few repairs and was wondering what thickness/gauge of metal should be used in different area.
- Inner wing
- Outer wing
- Floor pan
Also what mig wire should I be using 0.8?
Thanks in advance

[haasad]

Call it over engineering but I would go with 16 gauge and yes 0.8 wire...you'll grind 75% of it all off anyway

[MT]

You really want to try and match the thickness of the new section with the old if possible - so cut back to good metal. clean up and measure. A bit thicker is ok, but not too much, because if you're doing a butt weld - preferred - you'll find it easier to get good penetration and no blow-throughs if the metal is the same on both sides of the weld. Wire thickness is of secondary importance to correct amps, although they are interdependent obviously. Some prefer 0.8mm (like me) some 0.6mm - depends on how you weld (pulse or continuous) and your machine.

So in summary - same thickness as good original and 0.8mm for me.

Mick

[911hillclimber]

I would agree with same gauge and 0.8 but you need a good well controlled MIG and an experienced hand (steady too!) for good results.

Have you seen how much Barry cuts the corroded area back and in a clean wide curve too?
He certainly makes sure there is no metal with any chance of rust.

Good luck!

[Bruce M]

"If in doubt, cut it out"

[stuby]

Ditto - don't be afraid to cut well past the corroded area - the main objective is to weld to clean metal....

Stu

[tim78]

Thank you for all the replies. I'd forgot that I'd asked.
I'm stuck into the repairs now with varying degrees of success.
Thanks for the help.

[Barry]

Managed to miss this first time round:

Floorpan / chassis etc basically anything 'inside', 18 'gauge' (SWG), which in theory is 48 'thou', although in reality will be nearer 45th. Nearest metric is sold as 1.2mm.

Outer panels: wings, doorskins etc 20 'gauge' (SWG) which in theory is 36 'thou', although often nearer 33-34. Nearest standard metric is sold as .9mm.

Sometime the hardness varies a little, if it's very soft, it's steel produced for pressing, which can be very useful to have in stock if you need to be moving metal around (like forming in floor details for instance). It'll be luck of the draw from most suppliers though, and most will be a standard half-hard sort of thing.

One tip, if it's sold as a SWG steel, the closer to the theoretical thickness, the higher the quality: therefore a 18swg measuring 46 thou is probably much nicer than one at 44. Seems to hold true in my experience.

Another tip, if you're not too sure about your abilities welding outer panels where they want to heat-distort, use 18 gauge. It'll help stabilise the area, and gives you a little margin for linishing off in the end. I rarely use the method now (as I've been practicing ), but on, say, roof repairs where rear access is hard, it can be useful.

One more tip: when cutting to a line (assuming you're using blades of some some: snips, aviation snips, bench shears etc), cut say, 1/2-1/4 in out from the line first, and then on the line. Two advantages: 1) It makes fine tuning the 'steering' of the snips much easier, and b) When you make a cut using blades the metal on each side is compressed slightly, distorting it. The two-cut trick really helps to minimise this. In short, go wide first, then go accurate.

Are you enjoying the work Tim? I know Mark (Sladey) has really got into it (And Mr 'MT' Mick is an old hand of course ).

[MT]

(And Mr 'MT' Mick is an old hand of course ).

Anyone else and I'd be complaining about the 'old' bit, but from you, Barry, I take it as a compliment

Mick

[Barry]

[Fitz]

Barry, Why is there the such a variation from the nominal size in sheet steel? We have the same swg (18swg - 0.048" and 20swg - 0.036" etc.) in my industry but the tolerance is less than 0.001" so I am just curious.

[Barry]

It seems to be a quality control / 'what we can get away with' type issue: it always seems to have varied to one degree or another, but it seems to be getting worse.

Recently I had a delivery clearly marked '18 Gauge', and it came out at 29 thou, so was actually nearer a 22g. Clearly there had been some sort of sorting / labelling issue, but it was so different I was amazed no-one had picked up on it. Needless to say, when I outlined the possible consequences of selling something the fraction of the strength it should be, things were promptly refunded, removed, replaced, and the whole batch returned to the main supplier.

Strange how these things are never over-sized though .

Anyway, name of the game is always to measure the sheet before you get cutting, and if you have some 20 and 18 gauge together, mark them clearly. It's easy to tell them apart when they are full sheets (weight difference), but as the bits get smaller, it's quite easy to mistake 20 for 18.

[tim78]

Thank you for your response and the tips.
I am really enjoying it. I’ve read countless threads, books and articles but the best way to learn seems to be to get stuck in. I have Classic Le Mans as a deadline which is a little worrying.
I have read Mark’s thread with interest as I’ve just cut a large lump out of a wing. There was about 20mm of filler.
It’s a very steep learning curve and the only experience I have is from your sheet metal day but I seem to be improving all be it slowly.
I’m currently working on reconstructing the sill below the B post which was only a little blister to begin with. It’s only a temporary fix as I’d like to replace the whole sill when I have more time.
I think you can rest easy knowing your metal work guru crown is more than safe.
I’ll update my restoration thread if it’s still there.
Many thanks
Tim

[Barry]