[dataway]

So I'm finishing up the metal work on my 68 GTO, typical areas, corners of rear wheel wells, lower trunk side wells, and pulling out some small dents etc.

To get the metal as straight, or correct as possible I'm using layout ink and durablocking to find the highs and lows.

What should I be shooting for? It would be very optimistic to think I can make it perfectly smooth .... if I HAVE to be high or low somewhere should I opt for LOW so it can be filled with primer surfacer or some other method? We're talking like .010-0.020" low or high.

If I have an area with these very shallow highs and lows will a shrinking disc help the situation? I see areas along the waist, to the rear of the door where I think door dings have left a series of gentle ripples, or maybe it was the factory stamping ... very shallow, maybe .010" .... should I address things like that or should it be taking up at a later stage?

I know very little about what a body man might want to work with as far as the metal goes.

[tjs72lemans]

A high build primer blocked out will take care of most of that.

[TAKerry]

Not a body guy, but even the very slightest dip will show. The darker the paint the worse it will be. May not look like much in primer but as soon as you get some good gloss on it, sitting in the sun light, .
Keep at it to get things as flat as possible.

[dhutton]

Some high build primer, guide coat and blocking will get that straight.

Don

[MUSLCAH]

Guide coat will only help you so much. It more or less helps with deep scratches and pin holes. But for the “ Perfection “ your trying to achieve...it is best to put a clean shop towel over your hand and feel the panel,every which way....and then block accordingly......until said panel “Feels “ straight with your hand....it’s a bodyman thing.

[MUSLCAH]

Also use a metal file to find ...highs and lows.

[dhutton]

Originally Posted by MUSLCAH

Guide coat will only help you so much. It more or less helps with deep scratches and pin holes. But for the “ Perfection “ your trying to achieve...it is best to put a clean shop towel over your hand and feel the panel,every which way....and then block accordingly......until said panel “Feels “ straight with your hand....it’s a bodyman thing.

I think it depends on the length of the block. I have them up to 36” long and they are very effective when used with guide coat imho….

Don

[dataway]

The area of the "waist" of a 68 A body, to the rear of the door is a compound curve in about three different axis ... so far I've found a 12" block to be of limited use ... as there is no surface 12" long in any direction without a 2 axis curve in it.

I have been working on my "bodyman hands" and it does work surprisingly well on these complex curves .... used to watch the guy I worked for as a kid do it, had a pair of thin gloves he would use.

All I can spot so far by hand are the places where I have a good "run in" for my hand to feel what the level should be, then notice the deviations from that. In areas where there are numerous ups and downs my hand can't make any sense of them and I have to try a block.

[mrennie]

I am just a hobbiest but I found that it is much better to have a slight low spot that needs filling than a slight high spot that you keep breaking through to bare metal when blocking.

As you block with guide coat the slightly low spot is easy see and to fill with a skim of glazing putty (use the good 2 part stuff), or an extra coat of high build.

Compare to a high spot, where if you keep cutting though to bare metal before getting the rest of the panel straight, you either have to tap it down and risk messing up the work you've already done, or you need to spray a lot more high build over the entire panel to bring it all up to get past that high spot. That ends up wasting a lot of primer and the total thickness of your bodywork is more than it needs to be.

Note I am referring to very shallow high or low spots that remain after doing your metal work to the best of your ability, and not to just filling "dents".

As far as "feeling" high and low spots, that never worked for me. 3M dry guide coat and many many many many many many hours of block sanding in an X pattern gave me great results for never having done this before. My eyes are much more sensitive than my hands LOL.

[MUSLCAH]

Back in the day.....I did some VW Bugs. Those cars are curvy......and you could block those cars ...or Just DA them...and see no Difference. Sometime those curved panels feel lumpy.....but once painted,and you look at it with your eyes...it looks fine ...very forgiving. What you can feel and what your eyes see....are 2 different things on a curved panel. .

[dataway]

So if I used a shrinking disc .... what's it's going to do is take down the high spots by heating them up and then the metal contracting to very slightly less than it's original dimensions as it cools?

[mrennie]

Originally Posted by dataway

So if I used a shrinking disc .... what's it's going to do is take down the high spots by heating them up and then the metal contracting to very slightly less than it's original dimensions as it cools?

Yes. Run the disc until the metal is quite warm and then spray the area with water mist from a spray bottle.

I don't mean so hot that it turns blue, but hot enough to not leave your hand on it. You can also do it multiple times.

[TAKerry]

I also use a 'touch' method. I have been doing drywall/plaster for 40 years and fingers on the wall can give a lot of information. Surprisingly there are a lot of similarities in the two jobs. Only one you need to keep things perfectly flat and the other you have a 3 dimensional surface to deal with. I have told my guys its a job thats not hard to do but VERY easy to mess up.

[dataway]

Do any of you use a contour gauge for curves .... I did some patch work along the length of a lower quarter, below the break in the panel ... down where the lower trim goes. I used a contour gauge to compare it to the other side that was still original ... the patched side shows about 1/4" too much "dish" in it. Seems like an effective gauge to find large errors.

[MUSLCAH]

Originally Posted by dataway

Do any of you use a contour gauge for curves .... I did some patch work along the length of a lower quarter, below the break in the panel ... down where the lower trim goes. I used a contour gauge to compare it to the other side that was still original ... the patched side shows about 1/4" too much "dish" in it. Seems like an effective gauge to find large errors.

I just take measurements and my eye. And don’t forget....you only see one side at a time. Just don’t let the OCD set in...and it will be fine.

[Greg Reid]

Originally Posted by MUSLCAH

. What you can feel and what your eyes see....are 2 different things on a curved panel. .

Man, you said a mouthful there. Even a different shade of primer can make a spot seem low to your eyes when in reality it's perfectly level. Light shades 'come out' and darker hues 'recede'. After all, that's how the illusion of depth is created on a painting which is perfectly flat.
A soft piece of cloth or thin cotton gloves work well for me.


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[dhutton]

Originally Posted by dataway

Do any of you use a contour gauge for curves .... I did some patch work along the length of a lower quarter, below the break in the panel ... down where the lower trim goes. I used a contour gauge to compare it to the other side that was still original ... the patched side shows about 1/4" too much "dish" in it. Seems like an effective gauge to find large errors.

I use one for the same purpose, especially with repop panels.

Don

[einstein]

I recall the old-timers shrinking metal with a torch, even a simple bernz-o-matic, to warm an area, then quench with a damp rag. Not too hot, want to avoid causing brittleness. Probably some YouTube vids out there.

[MUSLCAH]

Originally Posted by einstein

I recall the old-timers shrinking metal with a torch, even a simple bernz-o-matic, to warm an area, then quench with a damp rag. Not too hot, want to avoid causing brittleness. Probably some YouTube vids out there.

I use a torch.....and my Old Solar 165 mig welder had a carbon rod shrink tip...that was awesome !

[dataway]

Might experiment with a propane torch, would not trust myself with the Oxy/Ac. As a welder for years ... shrinking hot metal was always the enemy. Spent a lot of time trying to prevent it, or compensate for it ... rarely USE it ... except flame bending long pieces edgewise. Heat with a welding torch in a series of triangle shapes with the base of the triangle on the side you want the inside radius to be ... but that was always metal at least 1/4" thick.