View Full Version : welding small holes


09-03-2006, 05:17 PM
Anyone have any tricks for welding small holes up. I am talking about 3/8" holes. I can't reach the backside of the panel and weld at the same time. I tried a piece of aluminum with a magnet behind it but it kept falling off.

Ed in SC.
09-03-2006, 06:11 PM
Turn the heat down, then put a small spot of weld on one side of the hole.
Hope pix works.
This is the 4th photo (first photo of door)

see the page at ,

see the hole on the left side of the photo. Pactice putting a spot of weld on the edge of a scarp peice of metal without blowing the edge away.
Lower heat, faster wire, and just a tap on the trigger.
After you have a couple of spots on the edge of the hole you can then build the spots to fill the hole.

09-03-2006, 06:13 PM
3/8 is fillable with patience...The way to fill holes without burning through is to give it small bursts, small tacks of welding with the mig. Do a small burst, 1/3 second, just a bzzzt on one side of the hole. This will give you a small chunk of weld on the edge of the hole. Let it cool down a little, then give it another small bzzzt...this will build the weld pool slowly. Continue this way until you have filled the hole. No need for backing plate although it's easier when you have access to the back.

What I do normally is I drill the hole to a known size just above the hole I have. Then I use my sheet metal hand punch to punch me a couple of disks that are the size of the hole. Then, I plug the hole with the disk for a snug fit. I then use a hammer and dolly to flatten the disk in the hole. Hitting the disk on dolly actually expands the disk in the hole so it holds there by itself. I then tig weld the hole shut, but you can use a mig just the same, just makes a nicer job with the tig...

If you have access to a sheet metal punch that can punch a 3/8 hole, the disk that is produced by the punch could fill your hole to a tight fit once you drill it with a 3/8 bit.

Just 2 cents worth.


Lost in NJ
09-03-2006, 09:08 PM
First off you use pure copper not aluminum or brass to back a weld.

A 3/8 hole is sort of large to fill free hand. You want to make a plug to weld in place as the previous poster was showing.

If you want to try free hand than you will need this trick.

Get some regular welding rod. Put the rod in the hole and strike the mig weld arc on the rod. Use the rod to help control the heat and keep feed the rod into the hole.

Getting a piece of copper behind will help quite a bit. Be careful as a magnet can mess with your arc in odd ways if it too close.