First screw up - lots of oversize holes

DaX · #1 08-06-2007, 08:22 AM

It was bound to happen - I'm only surprised that it didn't happen sooner. Just broke 100 hours and have been working on the rudder. I match drilled and deburred (what I thought was lightly) the stiffeners to the skin with a #40 bit. I did not knife edge any of the holes. After dimpling with the C-frame (no DRDT-2 here) I found that every one of my holes was oversized. 3/32" rivet diameter is 0.094" - all my holes fell between 0.110" - 0.115" after dimpling.

I decided to run to Spruce (only a 10 minute drive - lucky me, I know) and pick up some oversize rivets - same mfg head as a AD3, but shank diameter of an AD4. I re-clecoed everything and match drilled to #30.

My question is that is it OK for me to use the oversize (oops?) rivets for all the holes for rudder skins to stiffeners? Kind of too late to ask this question, as I've already drilled everything. I guess if it's not OK, I could re-dimple everything and use regular AD4 rivets.

The bad day didn't end there - I got my first "figure-8", dinged my first skin with the C-frame, and got a ticket on the way home.

Mel · #2 08-06-2007, 08:38 AM

Matt,
"oops" rivets are not intended to be used in a continuous row. They are only for one here and one there. If you have drilled to 1/8", then you should use AD4 rivets.

Brantel · #3 08-06-2007, 09:02 AM

Quote:

Originally Posted by DaX

It was bound to happen - I'm only surprised that it didn't happen sooner. Just broke 100 hours and have been working on the rudder. I match drilled and deburred (what I thought was lightly) the stiffeners to the skin with a #40 bit. I did not knife edge any of the holes. After dimpling with the C-frame (no DRDT-2 here) I found that every one of my holes was oversized. 3/32" rivet diameter is 0.094" - all my holes fell between 0.110" - 0.115" after dimpling.

It is normal for the dimpled hole to have some clearance over the 3/32 rivet. Some people use #41 drill bits to minimize this effect.

rivetshaver · #4 08-06-2007, 09:16 AM

Matt.
Dont worry about the sligtly oversize rivet holes. Deburr before dimpling and go easy, the skins are very thin. Dimpling streches the hole to a larger diameter. Ideally rivets neet to fit into a slightly loose hole, a rivet reaches its full shear strength after it is shot , (cold working), thus it needs a loose fit to swell. Sometimes I use a half grip length longer rivet than the callout to fill a slightly larger hole. The ding in the skin can be filled in before painting, and the figure 8 stiffener hole, I would remake the stiffener.

dan · #5 08-06-2007, 10:01 AM

Quote:

Originally Posted by Brantel

It is normal for the dimpled hole to have some clearance over the 3/32 rivet. Some people use #41 drill bits to minimize this effect.

Don't use an undersize drill bit. There are TOLERANCES associated with every tool -- including dimple dies. If you get a batch of dimple dies that are on the PLUS side of the tolerance range, and you get a batch of drill bits that are on the MINUS side of the tolerance range, what do you get?

The tolerances are intended to work with each other, and if you go undersizing one of the tools but not the other...have fun!!

DaX · #6 08-06-2007, 11:51 AM

Quote:

Originally Posted by Mel

Matt,
"oops" rivets are not intended to be used in a continuous row. They are only for one here and one there. If you have drilled to 1/8", then you should use AD4 rivets.

I have already drilled to 1/8". I guess I'll try dimpling one of them to a standard AD4 rivet and see how it turns out. I don't want to dimple again and it be enlarged again. Oh well, if it's really screwed up, I guess new skins and stiffeners will be my first re-order!

I'm used to the rivets being a little loose, but these are 0.094" going into 0.115" holes - 0.020" larger - I didn't feel comfortable doing it.

Any others think it's a bad idea to use all "oops" rivets? I guess I could call Van's about this...

I was intending to build on with the figure-8 - does anyone concur with me on that thought?

rivetshaver · #7 08-06-2007, 12:16 PM

Matt.
I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic. A MD 88 is riveted together with NAS 1097 rivets and is pleanty strong.

cytoxin · #8 08-06-2007, 12:37 PM

if you drilled to 40 then dimpled to the 3/32 dimple put rivets in it and shoot. the hole enlarges with dimpling. thats the way it is.

DaX · #9 08-06-2007, 12:47 PM

Quote:

Originally Posted by cytoxin

if you drilled to 40 then dimpled to the 3/32 dimple put rivets in it and shoot. the hole enlarges with dimpling. thats the way it is.

I've already enlarged to #30.

I have emailed Van's about it, but will probably move forward with NAS1097 rivets unless they scream NO! to me.

az_gila · #10 08-06-2007, 01:22 PM

Quote:

Originally Posted by dan

Don't use an undersize drill bit. There are TOLERANCES associated with every tool -- including dimple dies. If you get a batch of dimple dies that are on the PLUS side of the tolerance range, and you get a batch of drill bits that are on the MINUS side of the tolerance range, what do you get?

The tolerances are intended to work with each other, and if you go undersizing one of the tools but not the other...have fun!!

Dan is correct on tolerancing....

However, drill bits are remarkably close, so I would believe that most of the tolerance is in the "pin" portion of your dimple die, since these tend to be hand made (or at least low volume) items from multiple vendors.

Try the #41 drill in a test piece, and if your dimple dies work, then use the #41 drill....

The other tolerance issue you might run into is the "pin" on your clecoes... make sure you can cleco the #41 holes with your clecoes...

I've used #41 drill bits almost exclusively in dimple holes, and I get a bit less slop...

Try your tools and equipment on test samples and use what works for you....