Cap strip drilling.

[Bcone1381]

I often think about our superior, beloved, practical aircraft design and desire it to have more widespread acceptance. I assume that Bearhawk aircraft has considered CNC drilling/punching the wing parts for the factory, and offering them as a kit to the community. I wonder if that might be something in the future. Making the wings easy to build sure would be cool, and think it would only create more demand for the factory as the design increased in popularity.

I started down the road you guys are on. My decision to abort the scratch building project in favor of a kit was multi faceted, but the time and part quality issues I was producing was a big part of that decision.

From this side of that decision, I can say that those jigs and CNC files you are making that streamline the drilling of spar web, cap strips, spacer bars/attach angles have very high value. It would be a huge service to the scratch builder if the jigs were offered here on this website for sale or rent. Same goes for a CNC file for wing spar plates. It would be so nice to hit a local fabricator and give him materials and a CNC computer file and come back in a couple of days to pick up the perfectly completed components.

The best deal would be to have predrilled parts offered from the factory. The second best would be to have files that I could take to my fabricator to have drilled and punched. Third? Maybe have jigs to standardize the drilling available to but or rent.

I don't see how one could have easy success without the interchange duplicate spacer bars and attach angles that a nice jig would produce. For the folks who are just beginning the scratch building process.....The best practice (I believe) mandates that you make or acquire good jigs (made of steel) that produce those interchangeable parts.

[S Lathrop]

From this side of that decision, I can say that those jigs and CNC files you are making that streamline the drilling of spar web, cap strips, spacer bars/attach angles have very high value. It would be a huge service to the scratch builder if the jigs were offered here on this website for sale or rent. Same goes for a CNC file for wing spar plates. It would be so nice to hit a local fabricator and give him materials and a CNC computer file and come back in a couple of days to pick up the perfectly completed components.

.

I did what your are suggesting. I rented all my wing tooling for another builder to use on his project.

[hausburn]

Thank you all for the responses. I should have added more detail. I plan on using a drill bushing with cup and a #40 drill. I am only drilling the rib positions and using a rivet fan between. I am making the .125 plate fittings for the front spar to aid in layout. I am only stacking the fwd and aft caps that sit on the spar.

[hausburn]

Link to the bushing - https://www.browntool.com/Listview/t...=drill+bushing

[kilohotel]

I'm working on drilling my cap strips and rather than starting a new thread...I'm posting my question here...

I've drilled all the full length strips and intend to use each one as a unique master to match drill the web and stack of the other 3 at each location; therefore they are not interchangeable and are unique to each location. I have marked each with their location (left wing spar tops, right bottoms, etc).

I've started with a #30, rather than starting with a #40 hole and up-sizing twice.

I'm concerned that the holes could get "wallered-out" (I think that's a word) if they are used too many times to match drill.

Considering this concern, would it be a good idea to use a transfer punch through the mater cap strip holes instead, then drill the marked strip rather than match drill by running the bit through the master?

[Chewie]

I'm all for match drilling whenever possible. I'm personally more prone to error trying to hit a punch, and wallering out the master, even .020 skin, never seems to be an issue. Plus you will final drill #21 through everything anyway so that should eat up any wiggle room. I think I only had to match drill through each master once. Placing the shorter strips under the master and adding 1/8" strips to fill the voids worked pretty well, then drill each stack in one fell swoop.

[S Lathrop]

I am lucky enough to have a CNC mill (very old but with a updated controller so I can do 3 axis milling). For the cap strips I made a drill fixture about 24 inches long with the hole placement accurate to 4 decimal places. I use 3/32 diameter. holes. The fixture for the cap strips was the same width as the wider of the cap strips and is was machined on both ends to line up with the narrower of the cap strips. I use the fixture to drill all the cap strips. I took the time to draw the spar in AutoCad and I worked out the exact interval the rivets had to be so every thing lined up on the spars. This save me the time of laying out the holes and then drilling them. I could take the drill fixture and align it on the cap strips drill a set of holes. I then would over lap a few hole and move the drill fixture done the cap strips. This made all the cap strips almost identically drilled. I did not finish drilling to size until I was ready to rivet everything together. I used the holes to locate all the hard ware on the wings. Bottom line, I saved way more time than it took to make the drill fixtures. All of the points where hardware mounts are on rivet holes and are exactly spaced as the spar drawing. But the exact rivet hole spacing is a bit different than what Bob specifies on the drawing and over the length of the wing this small difference adds up to a significant number out at the ailerons..

[Chewie]

...over the length of the wing this small difference adds up to a significant number out at the ailerons..

How so? The patrol rivet spacing is exactly 12.25"/12. Bob calls out 1.021". 171 inches later that's only an error of .029".

[S Lathrop]

I have the A model 4 place. The rivet spacing that Bob called out was 1.026. When I drew the wing, I came up with a rivet spacing of 1.0268. That spacing had every rivet hole line up exactly with the locations of holes that were used for mounting hardware. It was those location measurements that Bob gave that I took as critical. This degree of accuracy for something that would seem minor was necessary because of the way I drilled the holes in the spar. I was using a drilling template that had to be moved down the cap strips as I drilled the holes. This process saved me having to lay out the rivet holes and made parts that were interchangeable until the final assembly when I reamed the rivet holes to the finished size..

[Chewie]

Ahhh, ok. Interesting that it rounds to 1.027. That would be significant. I forget how many rivets the patrol caps have (probably not 171 as stated above) but still less error than what you're seeing. I used a rivet fan; 12 holes every 12.25 inches.

[kilohotel]

Thanks Mark, I will go with match drilling!

[geraldmorrissey]

On the forward spars I laid out the upper and lower rib location cap strip holes then used the rivet fan to locate the rest. I used homemade drill blocks to drill each hole individually while the whole assembly was clamped together. On the main spar, I initially drilled to #30, then using step drills I had specially ground, opened the hole to #21. It was torture, I was lucky to do 30 - 40 #30 holes a day. Then when all the undersize holes were complete I had to go back and redrill to final size. This was a process I learned at Boeing. It was supposed to produce a hole quality close to reaming. I could never convince myself that I could make up the time I would spend making more sophisticated tooling. Looking back I'm sure I could have used my drill press to speed things up. It's done now and I'm happy with the results. The hole quality is absolutely beautiful and the rivets fit really well. But I sure would'nt recommend it. Locating each individual hole without some simple tooling or a NC machine is not a good use of your time. Plus it's hard on your body.
Gerry
Patrol #30

[S Lathrop]

I have a small/light floor model drill press that I used to drill the spars. I setup work holding system so that I could support half the spar on either side of the drill press. This made drilling holes square to the work piece easy and I could slide to part along as I drilled the holes.