Here's how the pros handle it at the Maule plant in Moultrie GA....jig the bucking bar so it positions itself perfectly, every time.

Hi Marc. What temperature and for how long do you anneal the rivets? I have definitely noticed a variation in hardness of my rivets, so taking them back to a particular set point may be an idea.
Tom.

The preliminary answer is found in Alcoa's Technical Reference on Riveting.

The definitive answer is found in the ISM-4, the ultimate authority.

But neither mentions a critical point, that being, you only anneal rivets with a clear anodize coating, no colored, no alodine.

There are two "annealing" approaches, one, accurately called "W" temper, is in the vicinity of 775 ( I won't say exactly because I wish you to look it up, there's more info that can be related here). The other is the classic "O" temper.

With the "O" temper, temperature control is critical. You only have a 10 degree window at about 935 deg F. (Caveat: Note there is a variance between Alcoa and the ISM-4)

In the olden days, this was critical because exceeding the upper temp scrapped the rivets. The problem was the analog temp controllers had a hard time maintaining +/- 5 deg F at that level.

Nowdays, the digital controllers can easily maintain +/_ 1-2 deg F. so it's not so much of a problem. I have a recording thermometer on my HT oven as a QA back-up.

The difference is remarkable and you can achieve flush rivet installations that won't catch a finger nail dragged across.

Onward and upward.

mjb

That's what we did. I called it cheating. I never missed a chance to let the bar "ride the work". It is often as simple as taping a piece of balsa to the bar to guarantee the correct angle and placement.

As I've told many people.......when it came to bucking the rivets.......we were not above cheating ;)

The pro's that don't use jigs and fixtures to hold bucking bars learn to hold the bars so that they always have finger tips extending beyond the end of the bar face that is forming the shop head of the rivet.

This allows you to feel when the face of the bar is square to the structure (which will also make it square to the rivet) and verify that there is equal clearance around the perimeter which will prevent the bar contacting the structure and causing dents.

It is rarely possible to get a finger on all four sides, but if three sides feel the same, the forth usually will be also. Sometimes you can only get fingers on two opposite edges, but if one of those edges has two fingers you can still gauge the gap in both axis.

BTW, every time someone starts a discussion about annealing rivets it makes me very nervous.
It can be done, but the temp control to do it right is extremely critical. With a very narrow temp range that has to be hit. Get it wrong and you could be building sub standard assemblies with no way to know it.

Yes,

The critical importance of excellent temperature control cannot be over emphasized. Not so critical for "W" temper, but "W" temper is usually INTENDED FOR relief from work hardening - something you can't do when the rivet is already in the structure and hasn't been fully driven.

There is no margin to achieving "O" condition when you exceed the upper temp limit, "it was only for 5 seconds" doesn't get the chemistry - one reason why I was purposefully vague on the temp range. Get the reference book or a copy and READ IT.

mjb