Main spars updrilling

[lstinthot]

Getting ready to updrill the main spar webs and have a question. What size hole are people drilling in the 0.032" (W10-02) that will be dimpled? Final rivet size (#21 drill bit) for the AD5 rivets? If you drill them smaller, do you remove W10-02 and updrill the rest of the stack to #21 then dimple? Seems like this opens up the possibility of having the holes slightly off for dimpling. Is the amount of stretch from drilling straight to #21 enough to worry about? I did a practice piece drilled up to #21, it seems to work, just not sure how much the .032 does not fill the hole.

Thanks
Mike

[Bryan Cotton]

Mike,

My spars were prebuilt, so I didn't get to do that step. I have, however, set lots of AN rivets! The drilling to a smaller size and then dimpling is a 120 degree flush pop rivet thing in my opinion. The 100 degree dimple dies for the AN rivets do not mess with your hole size as much. Also, a solid rivet has a bit more ability to fill a hole anyway. I would just drill to #21, separate, deburr, dimple/countersink and set that rivet. I have never done anything else for AN426AD3 through AD6 flush rivets and as far as I know it was the same at Sikorsky and Schweizer.

[lstinthot]

Thanks Bryan

I have not used a rivet gun in the past. I helped a guy set some rivets on an RV-8. I was his bucking bar holder. I decided to cut my test piece open to see how the parts mated together. I think you are right about the hole not stretching much with this dimple die. I think I am going to mark the holes and start to updrill.

Here is a crosscut of my test piece.

The lower piece just slide back when I tried to take a picture of it.

[n982sx]

Just to add to Bryan's note,

I am nearing completion of my RV-14A. No holes have been punched - or drilled by me - smaller than standard sizes in the whole airplane, #30, #40 etc. That's 15,000 rivets, most dimpled flush. All of the dimples and solid rivets work just fine.