Air punch tool for plug welding body panels

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Demonx2

Demonx2

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I'm working on replacing quarter panels/trunk drops and outer rockers on one of my cars (69 Charger). There sure were LOTS of spot welds to drill out or use the mini belt sander to remove!

As I go to put the new panels on, my intention is to punch holes in one of the panels (either the new panel or the one its being welded to depending on accessibility) and plug weld them with my mig welder. Given the diameter of the spot welds removed, it seems like a 3/8" (or even 7/16"?) hole would be about ideal. What specific tool do some of you bodymen use or what size hole do you recommend? So far, all I've seen are smaller hole punches that don't seem like they would make big enough holes to duplicate the strength of the original spot welds.

Thx in advance for advice/input!
 
My opinion. If you make the holes too small the arc can jump to the edge of the hole and you can't get a good plug weld. 3/8" seems big but it is about right to allow you to consistently strike the arc in the metal below and then flow the blob out to the 3/8" hole edges. I just use a step drill to 3/8"

Step Bit

Jim
 
3/8" seems excessive for a spot weld to me. I have a pneumatic hole punch and I like to use a 5/16" punch for panel work.

Trying to weld a 3/8" hole is going to create a lot of heat that you do not want.

Tom
 
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Dave I have a pneumatic hole punch if you need to borrow / buy or steal ! Punches on the edge only
 
PROSTOCKTOM said:
3/8" seems excessive for a spot weld to me. I have a pneumatic hole punch and I like to use a 5/16" punch for panel work.

Trying to weld a 3/8" hole is going to create a lot of heat that you don not want.

Tom
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I know a guy who has the 5/16 he punched the ones that go on other sheet metal. But if it is on edge and welds to frame gets reemed with drill to 3/8 size when he drills the ones it can't reach. Anything that welds to frame gets 3/8.
 
I had the little pneumatic one from harbor garbage. It had a flanger on one side and the punch on the other. My gripe was the hole was way too small. At work we use a long handled manual plier style punch with close to a 5/16. I’ve been drilling the holes larger or all by hand at home. I tend to run a drill lightly in the hole once the panel is aligned and tek screwed in place. I do this because I try to epoxy everything I can. By running the drill lightly, through the hole in the panel, I knock the epoxy off where the spot weld is going. I’ve been told just to run it, turn it up, etc. But I haven’t had any issues this way and it cuts way down on the snap crackle pop
 
Jim Kueneman said:
My opinion. If you make the holes too small the arc can jump to the edge of the hole and you can't get a good plug weld. 3/8" seems big but it is about right to allow you to consistently strike the arc in the metal below and then flow the blob out to the 3/8" hole edges. I just use a step drill to 3/8"

Step Bit

Jim
Click to expand...
That's the concern I have with some of these small pneumatic punches I've seen. They certainly would not duplicate the strength of a spot weld with such a tiny hole.

Maybe use the punch and then a step drill to open them up. Thx for the input!
 

You have to shop around for a larger punch size. I see 5mm, 5/5mm, 8mm (5/16"), and 3/16" so far. The 8mm one was a Sunnex brand through Summit.
 
Demonx2 said:
That's the concern I have with some of these small pneumatic punches I've seen. They certainly would not duplicate the strength of a spot weld with such a tiny hole.

Maybe use the punch and then a step drill to open them up. Thx for the input!
Click to expand...
I can tell you you the small hole from a HF punch is also closer to the edge so you don't have a lot of room to open that hole up more. They work great when you're welding up yard art though.
 
340six said:
I know a guy who has the 5/16 he punched the ones that go on other sheet metal. But if it is on edge and welds to frame gets reemed with drill to 3/8 size when he drills the ones it can't reach. Anything that welds to frame gets 3/8.
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I'm not aware (yet!) of any welds of sheetmetal to the frame rails. But I can sure see opening up a punched hole to maybe 3/8" for areas like the trunk drop to trunk floor since it will be challenging to get the mig gun at the proper angle. My concern is what Jim mentioned above about striking the arc only on the panel with the hole.

Thx for the input.
 
I do a lot of this work . I use the Harbor freight Punch/flanger. The hole seams small. Bit once you get use to it . Strike through the hole move to the side and circle.

There are times when there needs to have a bigger hole in thicker metal . Then I just quickly use a step drill and open the punched hole up. Sometimes a larger hole extends past the lip of what you are welding to then it just blows the metal away. Punch the holes small fit the part and open them as needed, Once they are to big you cant go back. Floors to frame drill. edges punch. Usually if you spot weld drill a part off you will be using the hole from the spot weld drill.

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Oldmanmopar said:
Sometimes a larger hole extends past the lip of what you are welding to then it just blows the metal away.
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This is a very good point too! Probably why so many of these tools have the smaller hole size.

Thx for chiming in.

(And love that Demon!!)
 
Demonx2 said:
I'm not aware (yet!) of any welds of sheetmetal to the frame rails. But I can sure see opening up a punched hole to maybe 3/8" for areas like the trunk drop to trunk floor since it will be challenging to get the mig gun at the proper angle. My concern is what Jim mentioned above about striking the arc only on the panel with the hole.
Click to expand...

Demonx2 said:
Thx for the input. things
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Oh, sorry, talking about all makes. Friend has body shop.
But I know when doing E Body trunk floors they have places where the tank support welds to floors. Ascwell as the rear rails. You can only do the edge ones. And must reem them to 3/8.
Biggest thing is reach. The cheap punches do go deep enough. And still have to drill all the others. Only saves a little time. But time is still time.
 
A punch is fast. If you don't want to spend the money on a punch and flange tool or you need holes that are out of reach, just drill them out. The Rotabroach tools work the best.
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340six said:
Oh, sorry, talking about all makes. Friend has body shop.
But I know when doing E Body trunk floors they have places where the tank support welds to floors. Ascwell as the rear rails. You can only do the edge ones. And must reem them to 3/8.
Biggest thing is reach. The cheap punches do go deep enough. And still have to drill all the others. Only saves a little time. But time is still time.
Click to expand...
You are correct though - there are places where you weld the floor pan or trunk pan to the frame rails, etc. This car just doesn't happen to need that type of work. I was asking about all the places spot weld are. Pinch seams along top and bottom of outer rockers, trunk pan to trunk drops, rear valence to corners, etc, etc. LOTS and LOTS of spot welds!!
 
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