I've bought some after market plastic arch trim as on these polo's theres a lot of rust on the rear arch.

If I remove the rust and get it to steel from the outside, do I have to remove the rust from the inside?

Would this mean there is no option but to cut out the rust and re-weld another arch in?

Where would I get these arches from, although i'd rather find a easier option. Thanks

 

You'll really need to take that back to bare metal to see how bad it is. If the inner arch is still solid and you're going to use those trims you've bought, you could botch the outer with rust converter a bit of filler and then paint it to seal the 'repair. If hidden behind the trim it'll last for a couple of years if you do it well.

However...  We all know that to fix it properly you're looking at welding in new metal.

can anyone help me weld in new material , s.yorks area.

 

 

It’s really not the black art that people seem to think these days!

Look for a cheap Mig welder on Gumtree or your preferred local small ads place. Don’t go for an arc (stick) welder - it’s too hefty for bodywork. 
Check out YouTube for inspiration. Find some scrap metal - old white goods for example, anything steel and a similar thickness to car bodywork - to practice on. Then go for it! 
You can get all the supplies you need from Halfrauds but better quality & cheaper if you can find a local commercial supplier. 
Alternatively, buy a cheap 4.5” grinder and take back the rusty areas to shiny metal and hire a local mobile welder to come do the slightly tricky stuff. Should be cheap if they don’t have to do so much prep and you can tidy it up afterwards with your new grinder. Bit of filler, bit of sanding, bit of paint - and you’re done!

 

I have a new stick welder which i bought for learning how to weld box section.

ill leave the body work welding for a professional.

i have purchased the rear arch repair panels from germany. got both sides for approx £75 which isn't to bad. 🙂

Really looking forward to having it restored 🙂 the MOT lads said it looks pretty good from under the car.

Also purchased;

 

I use a KelArc pistol and 1.6mm rods with an arc welder set at 55 to 60 amps

for bodywork using 1.2mm Zincotec steel.

https://www.ebay.co.uk/itm/Car-Body-Stich-Welder-for-Arc-welders-made-in-the-uk-/124479595411

 

Push it to 65 / 70 amps and it'll patch exhaust pipes gas tight without the pistol.

 

But it's all about the prep and clamping in my experience.

 

 

Right so , use the new arch as template , draw line. Use an angle grinder and cut on underside of line . Put new plate in place and make sure it all lines up then weld it all the way along the seem. Leave 0.2mm gap??? Smoothen off weld . Simple as that ??

 

Edited 25 December, 20205 yr by damunk

I'm by no means an expert on this and a  welding forum might be best place to ask.

 

Are you planning on doing a butt weld, edge to edge?

Then holding it in place while tacking the joint together with a few stitch welds

is important. 

 

I've seen, but not used, these clamps

https://www.frost.co.uk/intergrip-welding-clamps-5pk/

or here

https://www.ebay.co.uk/itm/8-Panel-Clamps-Butt-Welding-Clip-Sheet-Alignment-Positioner-Car-Truck-Skin-/303794791555

 

Other possibility is an edge joggler, for an overlapped joint; basically presses a step in each sheet for strong flat joint, so the transition is smooth-ish. You can fix in place with self tapping screws and get the alignment right and spot weld or seam weld (or both) and then grind.

You don’t have to use the full repair panel if it’s not needed - you can cut it down to whatever size is convenient, or covers the rust damage you have.

The main thing is to make sure you get all the rust cut out of the original and leave a good, solid, clean edge to weld to. I’ve never used one of the Kel-arc guns, but seem to remember them getting a decent write-up back in the day!
Heat is your enemy here. It’s important to tack the repair panel on rather than jumping in and laying down a long line of weld. As it cools the panel will warp in that case.

By jumping about laying tacks you can keep the heat down and get the repair held securely in place. You then go back and fill in between the tack welds - a bit on one end then a bit the other end etc. 
A joddled edge join can also help here. Well described above as putting a step in the panel - it’s to allow an overlap between the two. This means you could screw or rivet the old and new panels, holding them securely together, but would also help dissipate the heat at the join.

Good on you deciding to give it a go. It’s very satisfying once you get the hang of it. A bit of practice on scrap sheet will help - the thinness of bodywork compared to box section makes a bit of a difference to technique!

Edited 29 December, 20205 yr by TheDocmeister
Clarity

This is the tool you'll need to put the "joggle" into the repair panel https://www.ebay.co.uk/itm/Carbon-Steel-Joggler-Panel-Flanging-Plier-5mm-Hole-Punch-Tool-Sheet-Metal-Crimp/363091244836?epid=21034145899&hash=item5489ecb724:g:i6IAAOSwWSJeXOOE  

I'm going to get this joggler

11 hours ago, damunk said:

I'm going to get this joggler

With that tool put the "joggle" in the repair panel and use the hole punch on the existing panel on the car then "puddleweld" through the 5mm holes to hold the repair panel in place, then gradually tack weld along the joint between the repair panel and the original metal