Magnets can be used for holding small plugs into place while tack welding (as shown here), but this might not be the best way. This column explains the problems, and offers a good alternative.
Q. I’m building a 1972 Chevrolet C10 pickup, and there are lots of holes in the body sheetmetal I want to fill. I’ve tried a number of ways to cut small plugs and to hold them into place as I tack weld them, but they have a tendency to fall out just as I get my MIG gun in position. I’ve tried using Duct Tape behind the panel, which holds the plug OK, but the heat of the tack welds melts the adhesive on the tape and makes a real mess, often fouling the weld. How do you suggest doing this job?
Also, what sort of sheetmetal should I be using for this? I’ve been buying 18-gauge steel from a local steel yard, but it seems to have some sort of dark gray surface coating, which flakes off when you cut it with hand shears or bend it. I have seen sheets of steel that are clean and shiny, but my local supplier seems to stock some other type. Where can I get the “good” stuff, and how do I specify what I want?
Rob Marsh
Via the Internet
A. There are many ways to hold small plugs into place as they are tack welded. My favorite technique is to open up the hole with a step drill, so I know the edges of the hole are crisp, clean, precisely sized, and perfectly round. Then, I place a plug into the hole, back it up with a dolly, and hammer on-dolly a few times, swelling the plug, and fitting it tightly into the hole. This can be a little tricky until you get the hang of it, but the advantage is that the plug won’t fall out of the hole, and there will be nothing in the way once you start tack welding.
This works well for holes up to about 1 inch in diameter. You can get step drills larger than this, but I like using a cordless electric drill to open up the holes, and it takes a pretty powerful drill motor to turn a bit larger than this. You can make the plugs in several ways. If you have a hand-operated punch, you can easily make your own plugs, and this will ensure perfect roundness. Otherwise, you can use hand shears to cut plugs any size and shape you want, but it’s sometimes a bit challenging to cut them just the right size and to get them accurately round. Bob Drake sells a “Weld-In Hole Repair Kit” that has numerous plugs from 5/16- to 1-1/4-inch diameters, and these are very convenient if you have a lot of holes to fill.
You can use a magnet to hold plugs into place, but you’ll find that the magnet will attract an electric arc, so it’s actually pretty challenging to use this technique for small plugs.
The type of steel I recommend is called Cold Rolled Sheet, often abbreviated as CRS. If your material has a flaky gray scale on it, it is Hot Rolled Steel, and the scale on that material makes it unsuitable for bodywork. Most steel supply houses have both types, so you need to shop around some more. If you simply can’t find a local supplier, there may be an industrial sheetmetal fabricator near you that may sell you some drops. Alternately, you can find online suppliers who can ship smaller pieces of CRS to you.
You can email your questions to Professor Hammer, covell@cruzio.com, or mail a letter to Covell Creative Metalworking, 106 Airport Blvd., Suite 105, Freedom CA 95019. You will receive a personal reply! Ron Covell has made many videos on metalworking, and they can now be STREAMED or DOWNLOADED from his website! Check these out at covell.biz, along with his ongoing series of workshops held across the nation, or call for a current schedule of workshops and a free catalog of DVDs. Phone (800) 747-4631, or (831) 768-0705. Also, check out Ron’s YouTube channel: www.youtube.com/user/covellron.
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