Pneumatic Squeezer gap length
 

I'm having some trouble with this. Just started riveting my rear spar together with a pneumatic squeezer. I'm adding together the thickness of the material + half the diameter of the rivet head (470AD4's so 1/16 of an inch is what I'm adding) to determine the correct gap to set in the squeezer.

All of my rivets are coming out under-riveted, i.e. the shop head is not pancaked enough. I stuck a ruler to it and they are longer than 1 inch and narrower than the rivet gauge I have. The acceptable height listed in Section 5D is 0.50" to 0.70" for 1/8 rivets.

How do you determine gap length? If this is correct it could be that my way of measuring the gap is not precise enough. I'm putting a ruler next to it but because of the way the squeezer is designed I can't fit the ruler against the gap.

I set it the way you did i.e. close, then adjusted for proper set. I sometimes just put the rivet to be set in the jaws and close until it touches then adjust. The yoke will spring out, so precise preset is difficult, or at least not practical.

I built an entire airplane using a pneumatic squeezer anytime I could and I never measured the gap prior to squeezing. (other than eyeballing)

If you don't have an adjustable set holder, the suggestion is to get one now as dealing with the washers with a fixed length set holder is a real pain in the rear end.

It is simple. If the squeezer is too tight, it either won't squeeze at all (stalls out) or it will make the shop head too fat and short (and can cause the yoke to spread excessively). If it is too wide, you will get a tall narrow shop head.

At first you have to learn where to eyeball it to get started. Lean toward too wide and then sneak up on the right setting. Turn the adjustable set about 1/2 turn at a time till you get it close. Then fine tune from there.

It is OK to squeeze a rivet a bit more as you zone in on the setting.

The pneumatic squeezer is one of my favorite tools. I would never consider building a metal airplane without one.

As for the yoke springing open. If you have high quality yokes, this should not be excessive (when properly adjusted). If your yoke is springing open so much that it is negatively effecting the results, then you either need to purchase better quality yokes or you have the squeezer gap set too tight. Also, always use the narrowest yoke that can do the job for best results.

Exactly right. A simple and indispensable tool; no need to overthink it.

Huh, looks like I'm going to need to order one then. I have a fixed set holder right now, and it's a pain to set correctly with shim washers.

I built my 9A only using using washers, thin and standard. I found that once you learn the correct combination of washers for a given rivet length no adjustment needed. Very repeatable and quick.

Don?t know until you try it
 

Big +1 on the adjustable ram. Shins are fine for production work. Adjustable rams are cheap and usually retro-fitable. Once you use one, you?ll wonder why you waited.

gap table
 

+1 on the adjustable set, in addition in my case I set a number of different rivets and measured the number of turns from closed and built a table that I hung on the shop wall. Just set the gap and checked the first rivet and moved right along.
Figs

Follow-up comment
 

Forgive me if you're already verified this. It's not clear (to me) from your description. The mechanism in the squeezer is such that it doesn't develop full force until the very end of it's travel. Mentioning just in case your set/ram gap is too small.

That's a great idea right there!