SPI V Weld Through Primer

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challey71e

Promoted Users
I've been reading various threads on the subject. Most say to not use weld through and just put epoxy on the flanges, then use a flat bit to clean the primer from where you weld. Is this still regarded as the best practice?
 
I have never found a "weld through" primer that was worth using no mater how much it costs or where it was made. All of them compromise the weld and burn back. Just do your welds and then flood the area with SPI epoxy.
 
challey71e said:
I've been reading various threads on the subject. Most say to not use weld through and just put epoxy on the flanges, then use a flat bit to clean the primer from where you weld. Is this still regarded as the best practice?
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I would consider that the best practice, to include flooding the area afterwards as suggested above. Here is a video on making the clean out bit. Size it to the same size you use for plug welds.

 
MP&C said:
I would consider that the best practice, to include flooding the area afterwards as suggested above. Here is a video on making the clean out bit. Size it to the same size you use for plug welds.

Click to expand...
a little unrelated, but on the bit subject. i had bought some of the short spot weld bits, the ones are just a really short twist drill.
i was not real happy with the performance, so i looked in my bit drawer and found a 5/16 twist drill that was cut down to a pilot bit and was flat on the full size part. that thing worked way better with no walking around. since the 5/16 part was a flat cutter, when i got through the outer tin it was easy to tell and stop drilling. i drilled about 50 welds before breaking the little pilot bit off. totally my fault, got to impatient.
 
End Mills will work as well and you don't have to modify them.
The pilot drill bits are the easiest to modify as you simply grind off the center point.
 
I tried this and then modifying the bit to clean the spot weld. It didn’t work well and was a pain. I had regretting priming the surface first.
 
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They are called "flat bottom drill bits" and they are common in any machine shop. The video isn't how they are properly ground to clean a flat bottom. The profile is flat across the top or very, very slightly dished to the center and the relief angle to the back ( heel clearance is slight 5-10 degrees) . Most are not sold below 1/2" and you grind your own on a pedestal grinder, a Darex, or Baldor tool grinder or Sterling for larger sizes.
 
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challey71e said:
I picked up a variety of pilot point bits, a 5/16 end mill for this.

Cool video which details how good SPI is in spot weld areas

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You won't be sorry using epoxy. It's been proven over and over how well it works for spots welds.
 
Lizer said:
I tried this and then modifying the bit to clean the spot weld. It didn’t work well and was a pain. I had regretting priming the surface first.
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Seeing as this spot weld procedure has been widely used with highly praised results, I wonder what you did wrong for your poor results?

Maybe it was just the drill bit you modified? I wouldn't give up on the procedure, especially when you can purchase a flat tip drill bit. Try again, you just might be able to master it.

Success isn't given, it's earned.
Best of luck to ya,
 
I simply use worn-out 1/8" bits for this. Grind flat, use. Cheap, and is forgiving of slightly odd angles or different size holes. Just wallow it around for a sec and you're done.
 
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crashtech said:
I simply use worn-out 1/8" bits for this. Grind flat, use. Cheap, and is forgiving of slightly odd angles or deferent size holes. Just wallow it around for a sec and you're done.
Click to expand...

Smart, very smart. I wasn't following your logic using an 1/8" drill bit until I completely read your reply.

Makes perfect sense.
 
Thanks all. I really appreciate all the assistance with this forum. Amazing to have such technical skills available to help.
 
I'm working towards replacing some panels, welding etc. Current temps around around 50-60 degrees exterior.

I've not shot the metal temp yet, and I know SPI wants 65 minimum. I may be able to get it there with a heater. But, does it seem reasonable I could use SPI in my flange/inside of panel areas so I can weld on the parts, given the current temps below spec? Or should I just wait?
 
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