Just put a set of Kool Stop, salmon (Campy replacement pads) on a set of NR brake calipers. These are on a Ritchey touring bike w/ VO Raid rims. I had a set of Dia Compe Grey Matter pads on there previously. They stopping power was nothing to right home about. I have a set of the Kool Stop's on another bike, same brakes & same rims. No problems.

The new set howl like crazy on the frnt. I cleaned the rim walls w/ a green scrubby and some Simple Green to make sure there was nothing on the rim. I also cleaned the pads. Still squealing. I know you can bend a brake arm to add some toe but was unsure if there was a specific amount of "adjustment" that should be used?

Secret- Bend the mount bolt a tad, enough to produce a 2° twist to the left. Squeal gone.

On the pad holder, right?

I buzz the pads on a bench grinder or file toe into them when I have calipers I'd rather not bend. Make sure there's no excess center bolt play.

You can also sand the rim.

No, the mounting bolt for the whole caliper. I learned this by having a bike where the fork brake mount hole was off. That bike never squealed from the front brake. As a test, I took another bike that did squeal and whacked the mounting bolt, (yes, you have to tear down the brake) voila, no more squealing. All were Campagnolo Record brakes, very few bikes without.

Now that, is very interesting.

^ Yes it is. So one pad winds up toed out a bit?

Yes, that is the implication. Counterintuitive to standard practice.

Yes but if the fork hole is straight all it'll do is over toe one side and under toe the other.

.......when it breaks, wherever you were a little bit before that.

After bending the brake arms with limited success, I tried and succeeded with a very thin washer cut in half and mounted under the rear of the brake shoe, against the mounting bolt (to make this easier coat the washer with some sticky grease so it will stay put). Pads are perfectly toed in with no bending, grinding or sanding.

That is usually how I figure things out......

Now, if someone made a tapered washer.....

Those would come in VERY handy! But absent that, I may try the half washer.

I agree. I'm guessing that the vibration on one side cancels out the other side, or some such.
https://sheldonbrown.com/brandt/brake-squeal.html

Yes, it does toe one side in and the other out but it works.

Seems like a pretty half-assed solution.

Believe it or not, but one French company did it right in the 80's. Mafac/Spidel, actually designed their pad holders for their sidepulls to be canted couple of degrees in relationship to their caliper arms to produce the required toe-in out of the box. They even beveled the edges of the brake blocks in their molds so you don't have to do any sort of grinding before you mount them on.
One of the reasons I love my LS2 Spidel sidepulls. It had been a plug-and-play on all of the ones I put on my bikes since the 80's.....no judders, no squeals right out of the box!

I had some of those finned aluminum Mathauser brake shoes back in the eighties and they came with tapered rectangular washer/shims to adjust toe in. I don't have them anymore but they still might exist somewhere in the world.

But without fear of cracking things. Fortunately we are discussing Campagnolo brakes, if you try to bend a Universal brand arm... you bend the mount bolt or better than 50/50 the aluminum will fracture. Your kindly editorial comments thankfully precede your frequent attitude toward things.

I'm interested in the physics of it. Should all bikes have had a slightly off-center bore through their fork crowns?

I'm no Einstein but it seems like one pad slightly toed in and one slightly out might just work. The infernal squeal might be because pads are too perfectly aligned parallel to the rim.

How's that for a half-assed theory?

Kinda strange, I've never had a NR caliper squeal, at least if the pivot fit the arms properly and teh bolt was drawn up correctly. But I've always used original Campy shoes on them.

I slipped in KS (black) pads, in the Campag holders, and I too have no squeal .

The squeal is gone, I did the following:

Very light sand to the rims with 100 grit paper, very slight bend to the right brake arm and tightened down the mounting bolt. The mounting bolt was pretty loose, like Jim had mentioned and I am guessing that may have been the main culprit. I did the other stuff first. Works well now.