Body panel replacement

[Mike L]

I plan to replace the outer sills on my 69 2+2 using plug welds.
Has anyone any suggestions for hole size and spacing between plugs
Mike Longmead

[christopher storey]

I suggest about 1/4 inch diameter at about 5/8inch centres

[vee12eman]

Hi,

When restoring my car and several other classics beforehand, I sometimes used a punch to make the holes, obviously this is only possible when near the edge of the panel. This gives holes of 6mm, so 1/4 inch is about right. However, I have been advised that this might be a little small, especially for plug welding, as the hole fills a little too quickly for decent penetration of the lower panel. Drilling larger holes (7 - 8mm) does actually seem to mean less grinding afterward, as the hole fills a little slower, the panel behind gets a little hotter and the weld sags to fill the area with better penetration. It is often said that a plug weld may not be as strong as the original spot, so ensuring good penetration is important. When drilling out old spot welds, an 8mm drill is normally sufficient to remove all the welded material, provided it is centred well. I use an old set of Black and decker "Piranah" drills, which have been more user friendly than dedicated spot weld removers and seem to last much longer, I bought several extra 8mm drills for this purpose. They have a fairly shallow point, with a flat outer cutting edge, meaning you can cut through with little damage to the metal below, although there is usually a shallow cone cut into it. I try to align my holes with this cone as far as possible, replicating the original spacing, filling in the missing metal and ensuring good spacing. I now tend to use the drill more than the punch, especially in structural areas. Of course practice makes perfect, the less you have to grind back, the better, both from the point of view of time and strength.

It was not uncommon for Jaguar to miss a few spots either - at least in areas where it would not be seen later, so if it appears that a few welds are missing, they probably are!

If you are worried about strength, then put them a little closer together, but the most important thing is to clamp each weld very tightly together prior to welding, don't be tempted to use just one or two clamps - use loads and try to have one within an inch or so of each side of your welds, you can buy special clamps with a copper pad on one side and a gap on the facing pad, through which you weld. The copper pad prevents blow through and so you can pile more heat in and it dissipates more evenly, clamping at the same time and giving a good weld, the disadvantage being you have to move it for each weld.

Spacing is best guided by the removed panels, some welds are closer than others, but each weld has a circle of influence, these should overlap and getting the surfaces close together is essential for this. Normally no more than an inch apart, about 3/4" to 1" is adequate, some non-structural brackets have bigger spacing.

Hope this all helps,

Regards,

[Mike L]

Gentlemen.
Thank you for your comments.
I am using a TIG welding proceedures throughout the restoration.
I have found I can get fairly good results with 1/4" holes, with good penetration.
I have also discovered another trick, where access permits.
Drill 3/16 hole through both sheets, insert short piece of 3/16 rod from one side till it is almost flush, and weld. Trim off excess rod sticking through panels and weld flush.
Panels should be firmly clamped for this operation

[Mike L]

Thank yo for your advice.
The 1/4" holes seem to work well. It does take a little practice and patience to get the hang of it, but the results are excelent
Mike Longmead