Sun Mar 18 2007

Tank skin gap problems

Kody was over and agreed to help out. I put him to work dimpling all the leading edge ribs. He did a great job.

While he was doing that, I drilled all the nutplates for the joint plate. Kody and I had stopped at a Sears hardware store on the way up to the house and I picked up a handle and tap set that had 6-32, 8-32, and 10-24 taps. It was around $14 which seemed kinda pricey to me, but the handle does have a nice screw cap in the end where you can store the taps. I tapped a nutplate out and used the flange holes as pilot holes for drilling the rivet holes.

After dropping Kody off, I came home and got to work checking the straightness of everything. Charlie England on the RV List put me onto the idea that my jig might not be straight. I put the level on the spar and sure enough...

...the darn thing wasn't level.

...and down at the outboard end...'s not level either. Something I didn't get a photo of was that I discovered the bubble in this stupid carpenter's level would shift by at least 1/32" just by flipping the level around the other way. How in the heck are you supposed to do any precise work if the tools are outta whack?!?! Maybe I can borrow a precision level from someone at work tomorrow.

I discovered by peeking under the lower tank skin (which wasn't clecoed to the tank ribs) that although the outboard Z brackets were touching the spar web, the ones in between had a gap.

Here's another photo of one of the Z brackets not sitting on the web.

Charlie England had also asked raised the question whether I had over-prepped the edges of the tank skins during the deburring process. I didn't think I was taking off too much material, but since I was about to deburr one of the (outboard) leading edge skins, I figured out I'd check. I shoved a drill bit shank in one of the holes and measured from the edge of the skin to the far side of the drill shank. I managed to do a reasonable job of keeping the drill perpendicular to the skin. The distance was 0.3005 inches.

After deburring the skin edges, I performed the same check (on the same hole). It looks like I took off 0.0035 inch of the skin during the deburring process. That's actually a little less than I expected. It doesn't seem like over-prepping could be the culprit.

Well, anyway I went on to deburr all the rivet holes before calling it a night.