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Depends on material you are welding. For most automotive sheet metal 3/16th's to 1/4" usually work well. I did these with 1/4" if I remember right.



Mark
 

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5/16? The metric system is your friend. ;)
6.35mm equals a 1/4". I was just making the point that "6mm" is in between 3/16th's and 1/4" as I said in my first post... :thumbup:
Mark
 

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My bad. I often use metric bits but don't have a conversion table handy. Thought I had messed up by saying something in metric speak, lol. Carry on.
 

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Brian Martin,Freelance adviser
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Yep, 5/16-3/8 for me.

Brian
 

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I don't drill unless I absolutely have to. I use a hand held RW hole punch. I made a base to hard mount mine to the fab bench. I can have a hundred holes punched in less then 10 minutes. :)



Having it hard mounted makes a simple one handed operation to punch holes.
Mark
 

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My bad. I often use metric bits but don't have a conversion table handy. Thought I had messed up by saying something in metric speak, lol. Carry on.
No problem, I use metric at GM and Inch at home so I know either one as well as the other. :)
 

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Punching holes is good. I use one of the pnuematic flanger/punchers. It is one Harbor Freight tool I bought 20 years ago that still works perfectly. It does not make a large enough hole for plug welds but you can punch fifty pilot holes in 3 minutes and then drill the rest in quick order.

Chamfering the holes is probably not necessary but I like to do it if the panel is primed.

I marked, punched, drilled and chamfered this piece today and was in the basement for less than an hour total.

John






 

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As long as we're discussing how to make the holes...

I bought a BluePoint pneumatic punch / flange tool. POS. It self destructed before a hundred holes. The 3/8 size of it is too big for 18 ga and it won't punch 16 ga anyway. So I usually end up with pilot holes quickly made with a Snap-On double-end 1/8" bit then chased to correct size with a HF nitrided stepped bit which is also quite fast. No comparison to a punch though. I normally de-burr / chamfer the backside with the same step bit for a nice hole. Once the panels are together I like to clean the base piece through that hole with a Zebra 6mm flat-faced-but-with-pilot spotweld removal bit.

But I normally don't make a great many plug welds in a given day. Usually small numbers of them since I repair more than fab.
 

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Brian Martin,Freelance adviser
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I honestly believe that these two punches are in the top five of the most valuable tools to me that I have ever acquired.







The big one cost me about $190 as I remember and the smaller one was about $20 at a garage sale and one of the best deals I have ever got. No kidding guys, if you don't have them, get them, they are GOOOOOLD.

Brian
 

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Punching holes is good. I use one of the pnuematic flanger/punchers. It is one Harbor Freight tool I bought 20 years ago that still works perfectly. It does not make a large enough hole for plug welds but you can punch fifty pilot holes in 3 minutes and then drill the rest in quick order.

Chamfering the holes is probably not necessary but I like to do it if the panel is primed.

I marked, punched, drilled and chamfered this piece today and was in the basement for less than an hour total.

John






I don't know why the air flange/punch has such a small punch but one way to work around it is double punching each hole so your making an oval instead of a round hole. another way to get around it is cranking up the heat on the welder.
ALSO, you should test your plug welds by doing one and trying to twist the two pieces apart. when I did this I very surprised when I found out I needed more heat ,the welds looked perfect but had very little penetration and came apart easily. .double punching cured the problem best.
I also like to chamfer primed steel before welding and find the unibit works like a charm.
When the hole is made but before its chamferd the bottom piece also needs cleaning if its primed and a flat bit cleans that up nicely while its all together a spot weld cutter works well but you can make your own with a dewalt pilot drill bit for a couple bucks ,you just carefully grind off the pilot and sharpen it ,it only takes off the primer where the hole is.
 

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Brian Martin,Freelance adviser
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A great trick I learned was to drill the hole with a short tip spot weld bit after it's clamped in place instead of punching a hole. This cleans the primer off right were you are welding, and leaves the metal right were you are welding perfectly clean. :D

And if holes have to be drilled and you aren't using a punch the drill going through the metal will leave a little flipped out edge at the hole so the panel doesn't fit nice and flat. If you are going to drill the hole and you don't want to use the clamped into place method at least clamp it down on top of another piece of metal so that the drill doesn't make that little edge.

But nothing beats the hole punch! :D

Brian
 

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I have to admit I was brought up on USA /SAE fraction system. I remember when I was young we were told the metric system was taking over. I am one of those type of people that resist change just to be the same as the rest of the world. Borne by SAE I will die SAE. With maybe some metric hidden in the background. :cool:
 

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I just know I made a bunch of plug welds today, whew! :sweat: More than usual! The only thing that irks me is needing both SAE and metric for the same car. The puddle is laughing at our attempts to be specific. After all, its metal and fire and its kinda gonna pick the exact size on it's own.
 
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