Patch repair: clamping and cutting

[webhead]

Hi there,

I've recently been practicing on a scrap door I have here. I tried cutting out some rusty bits and patching in some new sheet metal.

There's no going around it: I'm terrible at it.

I tried cutting out a rectangular patch now with a disc grinder and welding in a new one. Seemed like a simple exercise. I planned on making a flange to drop the patch in but a supporting beam prevents my flange-pliers from doing so.

So no alternative but to fit it and butt weld it in.

I have the greatest problem exactly fitting my patch. My nibbler will arrive soon so I only had a scissor. But how do you cut it so precise?
I tried cardboard but even then it's fitting, cutting, fitting, oops too much.

And when it finally fits... How do you keep a patch in place half way a large panel...
I've heard about screws? Screw in what, how... like between the edge of the patch and the panel? Don't I need to make a hole then ?

I need help

 

[grim_d]

I am very much an amateur at properly patching stuff too but making templates helps tremendously, I tend to use the piece I have cut out if possible.

Cut it slightly over size and then just trim it down where required, if it requires several goes then so be it. trim down tiny bits at a time, using snips. I have found that a Gap of up to around 1mm can be filled with weld and a bit of practice, it goes without saying that the closer the better though.

Magnets may help you to hold a patch in place for tacking but I don't have any so tend to wedge it in as close as possible and stick a tack on just to hold it, then persuade it into place with a hammer, I should add this is all on floor pans etc so might not work so well on thin outer bodywork, and I am certain it is horribly bad practice.

 

[webhead]

I probably need some more practice but I seem to be burning more holes then filling gaps. I tried filling some with a copper piece behind it which works to some extent...

Does someone perhaps have a practical advice on making templates?
And on keeping the patch in place

 

[grim_d]

Have also seen the dirty finger technique a few times for making templates on paper, put paper over the hole and run dirty finger around the edge, a bit like wax crayon impressions, make sure there's no sharp edges though!

 

[octo0072000]

magnets

use a magnet to keep the patch in place till it's tacked

 

[mike 109444]

Webhead first grindback / clean up rusty area. Then rough cutout the rot. Then get a piece of patch metal cut a bit bigger than the hole in yor door. Place patch metal over hole and scribe / mark around it. Cut out then to the mark you have on door and you patch should be same size and shape. Now you can use magnet clamps to hold in place. Tack weld just a few spots around edge. Remove magnets and use the "Thin metal method" discribed else ware on forum If you are that new to thin metal welding try practice just putting tacks and short welds on some small pieces from your scrap door (150mm x 150mm pieces) till you get your welder setup wel for thin metal.
Good luck and post pics of your trys and other will guide you
Mike

 

[gavuk]

As above ,good advice....

 

[webhead]

A whiteboard magnets... good idea!

When welding in a patch, you just keep "spotting" around untill it's sealed?
Do you weld on the inside or outside of a patch?

What do you guys use to cut out pieces...
... and to trim the patch.

I bought a nibbler for patches and plan on using my disc grinder to cut out bad parts.

 

[webhead]

And oh! Mayor question :

Where do you attach the ground clamp to and where do you aim the wire at?
Do you ground the panel or the patch?
Do you aim at the grounded part or the opposite part? What gets hotter?

 

[mike 109444]

Whiteboard magnets prob not strog enough. Spot around, yep (SEE thin metal methord on this forum) Usually weld on outside, cos you will need to grind it back when done (how you going to grind inside of a door, wont get grinder in). I use a bench sheers to cut the over size plate before marking round then mix of tin snips, grinder, and what ever you have to hand. To attach ground clamp, clean up an area on the door or look for a chunk of metal bolted to the door (hindge? mabe) and clamp to that. Aim at the metal of the door 1st cos that is connected to the ground, Once you have a tack the patch will be electricly connected to the door. Just think you look at the door and there is a rust hole about the size of a golf ball. you have a poke at it with a screw driver and now it's the size of a peach (but don't look peachy). Then you set to it with an angle grinder to grind back the rust and paint. Now your peach is a grapefruit.. doh. So you have a hole aprox 100mm diameter with nice clean metal all around the edge. You could cut out a circle patch, but will be easer to cut a square ( not yet!!.) Now get a piece of plate and cut 110 x 110. place over the grapefruit hole. Draw round the 110 x 110. you now need to caerfully cut to this line. There are some very thin (1mm or less) cutting disc that will fit your grinder and are good for these fine cuts, take care fingers cut easer than metal!. Now using magnets and if possible a hand at the back fit plate in hole and tack then the "thin metal methord". If you can get a auto darkining helmet as when you are starting seeing where the weld needs to go can be the hardest part esp for thes new to welding.

 

[rikrobson]

To hold the peice in you can get rear earth magnets that are incredibly strong for their size. these are quite cheap off ebay but can damage magnetic tapes, credit cards etc. They can also be found on old computer hard drives on the liniar motors that control the head arm.


As the are powerful and small they can fit in to very small and awkward spaces.

They also conduct Electrickery so it don't matter where the are is struck and the more points on contact equals greater current. You can then clamp onto the nearest convenient piece of bare metal.

there was an article in last months Practical Classics (The one with the E-type Mini and Landy on the front) They went over all the methods that are available to cut panels.

I'd love a plasma cutter, but funds won't currently run to this. Fave tool is 3" air grinder for cutting panels as its easier to handle than the 4 1/2" leccy ones.

Trimings done with aircraft snips or grinding or filing

 

[stealthbob]

I feel your pain on this as I'm am just as new and had the same type of job.

I have to say that there are no shortcuts to practice and time spent fitting. I use my 3" air angle die grinder for cutting and a stone on the same tool for finessing the fit. It took me an hour of playing with this one but it fit with the angle and the bend.

Once in I used those cheap Ebay panel clamps you see all the time and spotted it in. The one surprise is that the gaps all shrunk after this first round of spot welds.

...I ran out of wire soon after this pic!

 

[webhead]

That's good advice here. I'm going to try some more fitting and try the magnet trick.

I do have some trouble getting the MIG set right. I've set the voltage and the wirespeed and it now sizzles nice. It also lays good welds and it has good penetration but it's just a bit too hot.
When I lower the voltage 1 setting I find that it doesn't really "melt soon enough" for the wire speed. A big blob forms on top. When I lower that too it starts sputtering because the arc isn't kept going.
I'm running 0.6mm wire here and I keep getting the idea I need to run it too quick to keep the MIG in the sweet spot.

On another topic:
I've seen some wonderful sheet metal results here. It's amazing what people can do with a hammer.

 

[Chipper]

Fine-tip permanent markers help a lot, nice precise line. The cheapo stationery store flogs these. Posh people can buy Sharpies
I like thin transparent plastic sheet (as in overhead projectors) for templates, it's great to see exactly where to draw. Got a big roll and a bag of sheets from Freecycle (they also make tear-offs for the grinding visor).

Use decent tin snips or shears; sneak up on the shape, cut outside first by 5-10mm, makes less distortion. Grinder with slitting disc on the car, keeping part-worn discs can help with some cuts, being smaller.

Earth clamp, close as poss to the patch, it doesn't have to be on the patch itself (mostly not poss anyway), just needs a good contact.

If the gap's nice & small aim the wire in the middle. If a gap does need a fill, aim more at one edge and weave, pull over, roll, move the torch slightly, however you like to do it, to get the bridge. Once thats done you can keep spotting like normal. But you want small gaps with thin sheet, best re-do a patch if it's really gappy, than chase gaps with weld.

 

[pedrobedro]

If I'm doing something like a sill I tend to make my patch big enough to reach good metal with plenty of overlap then cut a hole to fit the patch by putting it in place and scratching round it. Cut it with a thin disc and hold it with grips on the bottom flange and you can push it down tight with a gloved hand while tacking strategically.

 

[webhead]

So I gave it another shot.
I cut out a better fitting patch and welded it up. It worked reasonably well aside from massive heat warping because I refused to wait

The welder is still causing me troubles. I thought I always had to have my wire setting too high and I needed quite some voltage as well or I had massive build up.
I changed to another role of 0.8mm wire and that made a world off difference. I can turn the wire speed way down and I can even lower the voltage with good penetration!

Everybody always said MIG was slow and even youtube videos showed a slow speed but with the 0.6mm wire, stay on the same spot for like a fraction of a second and there was a hole. Closing holes was even more of a disaster. I mostly made them worse.
Now, with the 0.8mm I have time. I can weave and patching up a hole is much easier. The arc is more stable as well, it doesn't "stutter" as often.

How about that, it was (partly) the machine.

 

[nodeward]

seems obvious, but file the edges of the whole to get a good fit, if you try with a grinder you always end up take off too much. spend alot of time making sure you get the fit right and the welding will be 10 times easyer

 

[octo0072000]

car repair work is 90% prep work and 10% welding
read the Tutorials on here watch a few videos on you tube loads on there
but as said you must get the panel fit right when butt welding even on overlap must be clamped with no gaps or you burn back and blow holes
also old car radio speakers are a good source of magnets for free