7-06>07: Rudder Trailing Edge drilling

Page 7-06 completed in preparation for rudder match drilling:

Rudder skeleton cleco'd together ready for the skins. 

7-07 is a big page with a lot of steps! It started with attaching the trailing edge wedge to the skins, marking it, and cutting to length. I left it a tad long so i could file to the skins after final drilling.

Drilling the Trailing Edge

After many hours of research on this (see the Good Ideas Page), i decided i wanted to drill off an angle (i went with a 30 x 30 x 3mm angle from the big green box shop), and use it to help keep the rudder assembly straight when gluing etc. However, the danger here is that you ruin the skins, wedge or both in the match drilling process. So - crazy idea time!

I read in Kitplanes about Centre drilling large holes using brass tube, so figured i could use this idea to match drill the angle using the rudder wedge as the guide. The tools i needed were some 3/32" brass tubing (which turned out to fit a 1/16" drill exactly inside), and a 3/32" drill bit (the same size as the pre-drilled holes in the AEX wedge.

A tool was made, by chucking up the brass tube in the drill and using some sandpaper to bring it to a size which just fit in the AEX wedge holes. Since the holes were drilled perpendicular to the chord of the wedge, it was just a case of trimming the tube to match the angle on the bottom face of the wedge, and i now had a drill guide to guide the 1/16" bit and centre drill the AEX wedge holes, without enlarging them.

One issue i had was that the AEX wedge when on its own, was slightly bent - by about 1/64th of an inch in the middle. I pondered if this was the best thing to use to match drill the angle, and considered using the skins instead. However, the disadvantage of the skins is that the holes in the angle would not end up perpendicular to the hole very accurately (as the tool above had nothing to support it, other than the chamfered end). Plus, if a screwed up a skin it was $$$$ to get a new one to Australia (an AEX wedge would be a lot cheaper). The skins are like pure gold!

The slightly bent AEX wedge.

How would i make sure the holes drilled in the angle matched the skins and were straight? Thanks to advice from VAF, i simply clamped the skin to the angle and marked the holes with a marker. Then aligned the AEX wedge and clamped it in place, making sure every hole in the wedge was aligned with a marker dot from a hole in the skin. It was then a case of using the brass tube tool to pilot drill each hole to 1/16", then swapping drills i pushed the 3/32" drill into the AEX wedge hole (to minimize any cutting of this hole), and updrilled the hole to 3/32" - it would then accept a cleco and i eventually had the whole wedge match drilled to the angle, and cleco'd to the bench top.

Clamped over the holes, prior to drilling. Ply shims prevent the clamp putting any side force and moving the wedge, or twisting it. 

Aligned with the holes drawn on from the holes in one of the skins

Once the match drilling was done, i removed the angle and deburred all the holes. I could then attach it to the rudder assembly, and continue with 7-07 Step 3 - final drilling the trailing edge to #40. I was happy with the trailing edge, and think it came out pretty straight.

I also match drilled the R-903 tip Rib and R-912 counterbalance rib at this time, as well as match drilled the hole on the left hand skin overlap.

All parts were removed and all holes that had been drilled were deburred.

I was getting tired, so in Step 7 of page 7-07 decided to skip the dimpling of the skins (too much chance of making a mistake), but did dimple all the flanges which coincided with where a skin dimple would be. Since i was tired, i made sure to tape over any holes which shouldn't be dimpled.

For the substructure, I am using the cleveland substructure dies, but found these **barely** touched the corners of the rib flanges on some of the smaller parts (like stiffners), so i gently ground a larger radius on one side of the die, as i didn't want to use the reduced diameter die here.

This was a satisfying end to a fun day in the shop.

Ready for cleaning, etching and priming. 

Next up will be putting a break on the rear edges of the skin (hope i don't stuff that up!), deburring and dimpling the skins. My paint should be here tomorrow, so we may even be able to spray some parts this weekend! Flying by the end of next week i think.