TheSamba.com :: View topic - New welder - basic question (but probably quite important)

Sun Dec 28, 2014 5:55 pm

I'm welding in new sections of a floor pan and parts of the rear quart panel. Cutting them out was fun. Welding is a blast! The floor pan was no problem. Have a relatively inexpensive flux core MIG welder and it was just fine. Messy, but fine.

However, when doing the quarter panel I find that I'm ok where my pieces "fit" perfectly (the edges meet), but it is a complicated section of angles and sometimes there is a 1/8, maybe 1/4 inch gap. Tried to bridge it and its possible if one makes a mountain out of the weld - obviously wrong.

Then decided to add "backing strips" from spare metal and welds them as patches inside the cabin around the wheel well. It was great welding these - like it is supposed to be. And no one will ever see the "patches".

The whole thing is super strong!

But most places I won't be able to do this.

So, just wondering, how do folks get their panels cut just so? so you can do nice welds?

I have a grinder and sheers. No plasma cutter. And I have another rear section around the death foam to remove and clean. Then a whole front quarter panel (which I will place and spot weld, then take to a professional, because that's structural).

Is it just a matter of "taking more time" and "doing better"? Do people use lap welds?

Sun Dec 28, 2014 8:43 pm

Just take your time and measure and remeasure. Just takes practice.

Mon Dec 29, 2014 1:18 am

I use:

Offset aviation snips ,rights and lefts. Harbor Freight ones are okay for the money. Wiss are a lousy design ,Sears/MIdwest are the better ones.

Milwaukee Right angle aviation snips ,right and lefts.Home Depot sells them.

3' cutoff tool of some sort; Harbor Freight has an electric version that is well worth the $26.

Might have to use a Jig Saw sometimes.

Use patterns. Place a piece of thin cardboard behind the cutout and trace it. Cut on the outside of your marking. Choose your cutout pattern so it is easy to make a patch for. If your first pattern is a little off , repair your pattern with masking tape so you don't have to redo the whole pattern. Make the patch piece first ,trace on the panel and then cut section out.

Butt MIG welding with gap is where it's at. A wire welder with no shielding gas is not a MIG. Trying to get a perfect fit up with sheet metal is ludicrous , so pulse (multiple spot welds) with MIG is the answer.

Mon Dec 29, 2014 7:03 am

Thanks - very helpful.

I have good folks helping, but they have only welded >1/2 inch steel before and keep looking for a bead and pooling and such. I learned by practice that by the time I see a bead I've burned a hole through the sheet metal. My welds aren't "right" by the standards of real metal. They aren't pretty. But they penetrate and are strong, they just require some grinding.

Thanks for the tips about tools. Checking them out!

Off to trim and weld up another small panel!

Tom

Mon Dec 29, 2014 5:37 pm

Jerry Hundley wrote: Just take your time and measure and remeasure. Just takes practice.

+1 on this! Also buying a plasma cutter helps out ALOT!

Mon Dec 29, 2014 6:09 pm

Cut to leave enough to grind to a good fit.
Can you overlay the new onto the old? Great, trace it.
But cut long to grind short.
Grind to fit - Grind to fit - Grind to fit - Grind to fit - Grind to fit
Because 'cut to fit' can make you say bad words :evil:

As has been said, take your time!

Mon Dec 29, 2014 6:12 pm

There are a number of different ways to attack panel seam welding. But welding the panels is the most correct if looking at the repair as a restoration, but also takes the most skill, and you have to be pretty exact with cutting the panels to fit. I have a plasma cutter, but never use it for fitting panels, I use super thin cutoff wheels in my grinder. There are some nice cheap clamps to keep the panels aligned if you go this route. You can also back up the weld with a piece of copper. It does two things, it acts as a heat sink, to keep the excess heat at the edge of the sheet you are welding from melting the sheet and falling out, and it helps the weld bridge the gap. The weld won't stick to the copper, try it. And, instead of butt welding, you may have better luck punching a flange in one panel, then the other can lay over it and the two surfaces will be flush. Here is the type of tool

I use it where I either can't get access to the other side, and use screws to hold the pieces together while I weld, or where I have a very long, visible seam. The overlapped, flanged seam is much easier to keep flat and straight than a butt welded seam.
And when welding a new panel to a somewhat crusty old part: start the weld on the new part, and bring it over onto the old part. New steel is much easier to weld controllably, I always fare better to start my tack on the new part, and let it melt over into the old. Starting on the old, by the time you start to move, 99% of the time something has melted through.
Good luck, there are a thousand tricks and tips, you just have to keep going to learn to take advantage of them. SD

Mon Dec 29, 2014 7:05 pm

"wbrown45 "

Quote: I have had good luck with my wire feed on sheet metal by reversing the polarity on the machine, and using a good quality flux-core wire fed at a fairly high speed. Not as good as a MIG, but a cheaper, preferred method than filling those holes with rivets, screws, or silicone.

Mon Dec 29, 2014 7:41 pm

Sometimes I'll cut a patch that doesn't exactly butt together all around as well as I'd like it. So I'll tack it where its good in place and the go back with my Dremel metal cutting disc and cut it in place. Works nice as the cutting disc leaves a perfect gap to be welded up. So I guess there's lots of ways to cut your metal.

Mon Dec 29, 2014 8:56 pm

This is great advice. Thanks.

I did some more today. It went well. I was trying to make panels fit using an angle grinder to cut. Today I trimmed to size using finer tools and boy were those welds easier! I'm not too bad with the smaller patches.

I don't have these smaller tools - cut off saw, dremmel, etc. I might look to borrow them to try. Really need to keep costs down where I can. Medi. Lasting and paint will be expensive.

I need to remove front left quarter panel eventually for a full replacement. It's the biggest job I see ahead. Not sure I can do it with the grinder alone since it doesn't fit all the spaces. I'll need to really think that through. May need some help from a pro to get the fit right.

Tom

Mon Dec 29, 2014 9:07 pm

where in Pa?

Mon Dec 29, 2014 9:23 pm

Just west of Harrisburg. Near Carlisle.

Fri Jan 02, 2015 10:21 am

Disclaimer: I'm an amateur welder but I found during my resto...

Gas will help you get a lot nicer looking welds, and I'd highly recommend buying a dremel. They're not pricey, and great for getting into tighter spaces where a grinder/disc could accidentally scar other metal.

One thing I didn't realize until I was nearly done my bus (sadly) was how much metal shrinks when you heat it, both from welding and when you cut the panel with a grinder. After using the grinder to cut out the old metal, try going along the line with a hammer/dolly and hit the metal right along the cut line to stretch it back out.

I also had a lot more lucking using much higher heat settings than my unit recommended and just doing short (tack) welds and giving the area more time to cool. Gave me much better penetration and flatter welds which needed less grinding.

If you ever get stuck trying to weld a 1/4" gap, try and weld beside the last tack rather than on top, and use some extra heat so it flows into the last weld better. Copper plates are great, but you don't always have access to the backside.

So to summarize, gas, heat, patience. Keep a beer handy for while you wait for things to cool 8)

Sun Apr 24, 2016 11:24 pm

When fabricating sheet metal replacement... Has anyone had success with Cleco pliers and temp fasteners? My buddy is building an RV-10 and he uses them for panel fitting. Although he is riveting his and not welding. They looked useful.

Been practicing my welding by doing a few projects for friends. Found an appreciation for flap wheel discs and my Miller LPR-100 mask.

Going to weld all the chassis bits(beam and Boxing IRS) with Flux Core and then move to Gas and bare wire when I get to the sheet metal. I too have to deal with the dread foam fill in the panels :shock:

Mon Apr 25, 2016 7:14 pm

far rider wrote: Sometimes I'll cut a patch that doesn't exactly butt together all around as well as I'd like it. So I'll tack it where its good in place and the go back with my Dremel metal cutting disc and cut it in place. Works nice as the cutting disc leaves a perfect gap to be welded up. So I guess there's lots of ways to cut your metal.

Yep, I do the same. Err on the big side, get it to fit, fix the overlaps with thin cutoff wheel.
I run a dremel model 100 at 140 volts.
This seems to be the best setup for RPMS!

For initial fitting, try making a template out of posterboard.

I avoid lap joints, because they tend to rust out, but a backing should be ok otherwise. You can also use copper for backing, and it doesn't stick. I use a copper chunk on a stick for backing when filling holes.