Car bodywork questions (Lots of :-)

[Rich.C]

Hi Fellas,

Would very much appreciate your advice to help me learn how to tackle some car bodywork.

I've got an elderly BMW and among the many jobs needed doing is to cut out and replace the rear outer wheel arches. I bought the repair panels and hope to use as little of them as possible.

The first question is: what is the best tool/saw for cutting both the new repair panel and the quarter panel of the car without distorting the cut edges or leaving them very rough?
(I have an air compressor)

Would you butt joint this sort of work? If so, what size gap would be needed? and are those Intergrips useful for this sort of stuff?

Do you cut the repair panel to shape and then offer it up to the car and mark around it?

The black paint that repair/replacement panels come covered with, is this suitable to leave on the inside of (e.g. an outer sill) or does it have to be removed and primers etc used?

Finally what is the best technique when welding this sort of thickness (0.8mm)? I've got a Clarke 160en which I'm practising with at the moment on some scrap 0.8 stuff (using 0.6 wire, Argon/CO2 the lowest setting is 30amps.) Am finding tacking it then coming back between the tacks with some longer runs seems ok but can be hard to avoid distortion and am not sure how long the runs should be or how much gap to leave between tacks.

Apologies for the essay but I guess If I don't ask I'll never learn.

Thanks a lot,

Rich.

 

[irondarren]

best tool for cutting body work imo an air saw with out question www.machinemart.co.uk/shop/product/...peed-air-sabre-saw/path/air-saws-screwdrivers
take a look at that.
distortion is your worst enemy, tack and leave a gap, then go back and fill it in. thumb size stiches are not a bad way of doing it. leaving a good gap between one stich and the next, and just keep going back and filling. i wouldnt worry about the black primer its not a problem, but do clean it back where you need to weld. Nothing wrong with asking questions here, its the only way to learn, and we all had to learn at some point

 

[rtbcomp]

In a lot of cases the black primer is for preventing corrosion during storage. I'd go back to bare metal and use an etching primer and paint on top of that. Finally a good layer of Waxoyl &c.

I'd butt weld, leave a gap equal to the size of wire you use.

 

[nickburt]

First, cut out the area of the wheel arch you need to repair (air saw or mini air grinder, it can be done with a 4" elec grinder, but it'll take a bit of tidying up afterwards. Then cut the repair panel slightly oversize to match. It's then a matter of choice. Some body repairers cut the repair section down to end up with a close butt weld, others leave it slightly oversize, joggle the edge of the repair panel and tuck it under the original.

Remove all the black paint on the repair panel - it's only there to protect in storage, it hasn't been keyed to the metal properly, so anything you paint over it will lift off eventually. Also, a lot of manufacturers use real carp paint that reacts with some paints/primers.

When welding, start with a few small tacks to hold it in place and make sure you're happy with it's shape and position. Then do some well separated short seam welds (or long tacks), leaving time to cool in any area, before you return to that area. This is to avoid heat build up and distortion (distortion happens more during the cooling down time). Keep doing the short seams until a full weld is achieved. (Good excuse for a couple of mugs of tea during the job !!)

 

[ozzman]

remember to take your time, tack up half your work leave for 10mins the tack the rest leave again for 10mins or so.

then do a couple of inches of weld from the middle outwards leave till totally cold then repeat process,

oh yea after you dun your tack welds grind them down so they are just proud of the surface then beat with a hammer and dolly to re-stretch the weld, only hit the weld not surrounding area, and do the same with each couple of inches of weld that you do, then planish area to smooth out and high a low spots and polish to a mirrored finish.

and theres no need to use filler if you take your time have a look on http://www.metalmeet.com loads of good info on there and if you look at some of the resto projects on there you will inspired to do a propa job!

 

[Rusty]

Hi Fellas,

Would very much appreciate your advice to help me learn how to tackle some car bodywork.

I've got an elderly BMW and among the many jobs needed doing is to cut out and replace the rear outer wheel arches. I bought the repair panels and hope to use as little of them as possible.

The first question is: what is the best tool/saw for cutting both the new repair panel and the quarter panel of the car without distorting the cut edges or leaving them very rough?
(I have an air compressor)

Would you butt joint this sort of work? If so, what size gap would be needed? and are those Intergrips useful for this sort of stuff?

Do you cut the repair panel to shape and then offer it up to the car and mark around it?

The black paint that repair/replacement panels come covered with, is this suitable to leave on the inside of (e.g. an outer sill) or does it have to be removed and primers etc used?

Finally what is the best technique when welding this sort of thickness (0.8mm)? I've got a Clarke 160en which I'm practising with at the moment on some scrap 0.8 stuff (using 0.6 wire, Argon/CO2 the lowest setting is 30amps.) Am finding tacking it then coming back between the tacks with some longer runs seems ok but can be hard to avoid distorsion and am not sure how long the runs should be or how much gap to leave between tacks.

Apologies for the essay but I guess If I don't ask I'll never learn.

Thanks a lot,

Rich.

Here's how to do it mate - http://www.mig-welding.co.uk/wheelarch.htm

 

[Rich.C]

Lads,

Thanks for all your replies, much appreciated.

Rich.

 

[piman]

Hello Rich,

I favour aircraft style tin snips for final cutting as they are far more accurate than any power tool and easy to use. (Problem is you need at least two, a right hand and a left hand cut). Certainly use a power saw, angle grinder whatever for the rough cutting.

I don't like lap joints at all and always butt my welds, as the lap is water trap. Also much harder to dress out any distortion.

Alec

 

[Rich.C]

Thanks Alec,

Do you mean these type of snips? Do they give a good edge?

Cheers,

Rich.

 

[shenion]

For straight cuts, I like HVAC snips.

 

[piman]

Hello Rich,

yes, that type, although in my set the yellow are for straight cuts, red and green for left and right (although it could be right and left).

They leave a very clean cut unless you try and do a very small radius.

Alec

 

[Rusty]

Snips are OK for cutting you new wheel arch repair panel to shape before you start your welding but are awkward to use to cut the old wheel arch out,I use a hand nibbler which although a little slow is accurate,very maneuverable,and only needs a 1/4" hole to start off.

 

[rtbcomp]

Those nibblers go by the name Monodex (tm) Cutters, you can get pneumatic nibblers as well.

 

[piman]

Hello Rusty,

each to his own but I have found hand nibblers to be slow and tedious. I can cut 16 gauge steel with tin snips of the type I recommended. The more usual 18 and 20 gauge is a doddle.

Alec

 

[loiner1965]

i work in a bodyshop as a painter so this is what we do....
use an air saw to cut panel
if new rear wing complete etc then cut old panel off but leave enough metal behind as you need to overlay new panel then clamp it down with self tapping screws / molegrips then airsaw through both panels when it is correctly in place. remove panel and the metal underneath then relace as before and butt weld joints....the primer unless they are good quality manufacturer panels are only transit primer and basically crap...if the car is a good restorable classic i would strip the panel to bare metal and then etch/prime/and colour as normal