Removing Spot Welds

[Uwon]

Never done any spot weld removal before. What kind of drill bit or other devise do I use in a tight area?

[drcoastline]

Any bit will work to drill out the spot weld. Harbor Freight sells a spot weld cutter. I think they sell several sizes.

If the issue is you can not get the bit in the space to drill it out. You may need to break/cut the weld. There are tools that they sell that are sort of a chisel that will cut it. I personally use a 5-in-1 paint scraper. I slide it between the panels and then hit the back just as you would a chisel it will cut the weld right in half. I have found that using the tool down toward the point end the scraper works best. Not sure why but I am guessing friction.

[TC911e]

I've had pretty good luck with this style


The ones like these- not so much


Though they're available at Harbor Freight and Northern Tool, don't remove as much material and work ok on a flat surface, they are prone to breaking the little saw teeth on the cutter.

I seem to end up using the chisel/scraper method to get the final pieces to split, but I've never tried doing it that way without drilling most of the weld out first.

[Iciclehead]

I have tried all the methods and the way that has worked with me is to use two normal drill bits, one of them cut off square with my grinder and a cutting disc.

I try to centre punch the spot (not always possible, they are if anything harder than the rest of the sheet metal), use the normal drill bit with the conical end to start the removal until the outside edge of the bit begins to cut and then use the bit that is cut off square to finish removing the spot in the first sheet so that it can separate from the one beneath.

Benefit is that I can use several different sizes of drill bit to suit the size of the spot and I have a great deal of control as to how deep I go. I frequently end up with the sheets separating with a "pop" when I go through...partly I think because I am removing material slightly bigger than the actual spot weld.

Dennis

[Uwon]

Many thanks for all your info. You are confirming my suspicion that there is no foolproof method. Best to invest in some really good drills and a couple of those drills that TC suggested. By the way, I am updating the dash A/c vents from a '78 to a '86 so I need to extract the spot welded ad-on lower corners from the donor.
Cheers

[threewebers]

Wurth spot weld removal bits, save yourself from frustration and stay away from harbor freight...

[962porsche]

when it comes to spot weld cutters they offer many types . blair cutters are god and work well they come in deferent sizes of cutter tips and lenghts of shanks . there are also self centering type cutters that work good too the down side to them is once they become dull you have to throw them away . some times you can sharpen them but not all the time .
when your drilling thru rusted panels the rust will dull the cutters quicker than clean metal .
our spot weld cutting gun works great and because of the design it will not want to walk from the center of the spot weld but again that type also uses a self centering cutter .
when it comes to metals like boron no spot weld cutter will work you have to use a cut off wheel and grind the spot welds off .
if your going to go with the blair type cutter it's best to use a 1/8 drill and put a little dimple in the center of the spot weld 1st or use a center punch to stop the cutter from walking . you do not have to drill all the way thru the panels just a little dimple will do . you can pick up a pack of dubble sided 1/8 drill bits cheap .
i really can't say any ones spot weld cutter is any better than another . when it comes to drill out spot welds we tend to use them all even working on the same car . you may find the self centering ones will work great in one area but not so well in another and vice versa with the blair types .

[mikensam]

used the harbor frieght and had a heck of time at first.Learned that Besides center punching the spot weld,i used a small drill to further dimple the weld.When you go at it with spot weld drill you will notice high n low spots on darn near every spot weld.Kept the speed low,working the drill at different angles keeping the hole depth uniorm. Before I just center punched,and had at it and was busting teeth of the drill,and the drill would skate(!/4" hole saw at 2k rpm makes a messy hand wound.)Used my last HF drill for 70+ cuts no problems(Cept for that drill through on the top spot weld inside the headlight bucket on my 914.tight spot had to use the air drill and ooops!)Anyway the HF spot weld cutter is identical to eastwoods at 1/4 the price($4).Same with butt welding clamps(6 for $8 at HF,4 for $20 at eastwood)Would much prefer 962s set up.

[HelmetHead]

Air grinder with a cut-off wheel on the side where metal is to be replaced.

[outsider347]

I use a .125 drill bit first then a UniBit. Start on the side of the discarded panel. Drill with UniBit til weld pops. Now with the new sheet metal ready to weld in, Panel is ready to rosette weld in place
works for me

[tharbert]

Mikensam described my experience. Once I learned to keep the drill straight, the bits with teeth work the best for me. I wanted to rock the bit back and forth for it to grab. That was damaging the bit. You need slow RPM, medium pressure, and steady alignment. Let the bit do the work. And, resist the tendancy to go deeper than you have to.

[frankc]

Reviving this thread to ask a couple more spot weld cutter questions.

1. Regarding the two types of cutters - hole saw vs. square-end drill bit - it seems to me that the drill bit style would reduce the amount of work if one is keeping the bottom panel as there is no further metal to remove (disc left over from hole saw type). So when keeping the bottom panel, is it better to use the square-end drill bit style? And when keeping the top panel, is the hole saw type faster?

2. What is the recommended bit size? I have heard that the common 3/8" size is a little too large for the typical welds on the 911. Is 1/4" or 5/16" better, or will a variety of sizes be needed?

Thanks

[mreid]

Here are a couple of tips:

Use a 1/4" bit (either cheap ones in bulk you can throw away or the harder more expensive ones). In the long run the cost is about the same. McMaster Carr sells them in bulk.

Where you can access the panel from both sides, drill completely through the two panels. The resulting hole on the panel you intend to keep makes a handy guide to plug weld the new panel in place.

Buy a panel knife or a stiff paint scraper to break the panel free. Don't try to use the drill bit to get that last bit of weld. This is the key to success.

[frankc]

mreid,

Thanks for the response. When I search McMaster-Carr for spot-weld cutters, I could only find a 3/8" diameter bit:

McMaster-Carr

Were you referring to the 1/4" shank size? Or some other type of bit?

[mreid]

Frank, I was talking about a generic 1/4" twist bit.

Eastwood also sells a nice panel knife you can hit with a hammer:

Panel Separating Knife

[HelmetHead]

After several cars and thousands of spot welds, I suggest the Blair Rotobroach

Blair Spotweld Cutters

[Tom '74 911]

I've had great success w/this spot weld drill:




Here's a video showing a similar drill in action:

https://youtu.be/GVH4pTnDrl0

[frankc]

Thanks for all the suggestions for sources of cutters.

Now back to the diameter question. I measured the size of various welds on the 911 and came up with between 6 and 8mm (~1/4" to 5/16") at the surface.

Blair sells the solid cutters (Premium Carbide) in 6.5mm, 8mm 10mm sizes
Blair sells the hole saw cutters (Rotabroach) in 5/16" and 3/8"

I've seen 3/8" cutters used and the hole appears too big to me, such that when plug welded afterwards it no longer looks like a spot weld - so I would prefer to use a smaller bit, if that will do the job.

I guess I'll just purchase the 6.5mm & 8mm Carbide cutters, and 5/16" Rotabroach kits and experiment with them. If I find that the panels aren't separating easily, I'll go larger.

[jpnovak]

I have used the HF style hole spot weld cutter. They do make a big hole. The trick is to dimple the center of the spot weld with a center punch. This keeps the cutter from walking. Then I use a chisl and hammer to separate the panels.

You have to pay attention to what you are drilling. There are places where drilling through both panels makes it really difficult to weld them back up. Just make sure you pay attention to how you are going to weld them back together.

[frankc]

Hi Jamie,
Thanks (as always) for the advice. I've been looking at the various seams that I need to separate to decide from which side to drill. From what I can see, there are two scenarios:

1. Seam is accessible from only one side:

Here, the decision is obvious from which side to drill and weld. Regarding which cutter type to use - if retaining the bottom panel, use the solid cutters to completely remove the weld. If retaining the top panel, use the hole-saw type cutters.

2. Seam is accessible from both sides:

It appears that there are two options here:

2a. Drill through weld on both panels: The retained panel will be pre-drilled for the plug welds at the same locations as the factory welds.
2b. Cut weld from one panel: My plan was to cut the weld from the panel to be kept (using hole-saw style cutter) allowing me to retain the original weld locations for plug welding later. Plus, it saves from having to punch a bunch of holes in the replacement panel.

Another thought; when the seam is accessible from both sides, should one take into consideration which side of the panel is visible after assembly? That is, is it preferable to plug weld from the side that will be hidden?