Finally starting

[brady.blake55]

I accidentally posted in the QB group. Here is the post anyways.

Hey everyone. I’ve been researching, some might say obsessing, over all things Bearhawk for 10 years. I finally have the money, and the wife’s approval, to build. I called Bob this week and talked for a little bit. My wife said I was like a fan girl. I can neither confirm, nor deny that accusation.

Anyways, I’ve had an idea rattling around for a couple years. I’ve watched nearly every Bearhawk build video on YouTube. One that stuck out was N3UW’s hydro forming video using rubber. I wanted to ask y’all about another option for forming. Do y’all think it would work to press a cavity forming block over a normal block to sandwich the rib between? In my mind I could form ribs quickly and even put the crimps in the block. I’d cut the blocks with my CNC machine, so they would be accurate(ish). Im new to CNC stuff and CAD designing.

[U2fletch]

Pictures of your CNC machine please! I’ve used Fusion360 for many years and designing parts and jigs for 3d printing is very rewarding. Add the CNC machine to the mix and possibilities become endless. I recently had to cut to size a 10’ long 3” square steel down tube for industrial BigAssFan and it needed a certain hole pattern in the end. Started laying out the holes and marking with layout fluid on the tube to drill, and realized I don’t have a 14mm drill. 12mm was big as I had. So clamped the tube in the jaws of my mill table vice, did some edge finding to set the DRO, then wrote a quick code snippet to make a 14mm hole with 3/8” endmill. Problem solved.

[brady.blake55]

My CNC isn’t anything to write home about. It’s about $1,000 new. I’m going to get the expansion to do 4ft sheets. It should help with repetitive parts and also keep them uniformed.

https://www.amazon.com/gp/aw/d/B08L6314MW?psc=1&ref=ppx_pop_mob_b_asin_title

[TrueAirSpeed]

That aircraft in your picture looks familiar to me. Flew one out of Kandahar 2004 to 2005.

[SpruceForest]

General Comment: Love to see another builder commit to doing it all... good luck and enjoy the process!


Issues re: your proposed striking dies:

- Negative clearance angles on the die set with flutes and the flange over-bend to handle spring-back of around 12 degrees with grain of the sheet ideally situated

- You'd need closer to 50 to 100 tons to get enough pressure to form the flutes without some sort of secondary operation... one of the reasons why rubber press operations work in this use case (making the process doable without $25K worth of press)

- Multiple die sets needed with main and tip ribs... unless you have a press that can handle something as long as those components. 20 ton will press out a 10" x 10" area (12" x 12" x 3/4" steel platens and 12" x 12" urethane rubber/stall mat stack) to around 70 degree flange angle... to do the center ribs in one shot is at least a 50 ton press with a pretty beefy containment box to get the most out of that tonnage (we get a lot of efficiency/wasted force losses in an unconstrained press operation)... tip ribs would run closer to 100 ton.

- Flutes need to be micro-tuned to get a straight/true rib... there is a LOT of post-press tuning, as even factory replacement ribs for Piper/Cessna, etc. need tweaking and lots of clean-up before use


Discussion:

- The 20 ton rubber press method is doable because the tech is small-shop doable and can produce a much better component than the Piper and Cessna factories are shipping (ask Bob - he's got one of my nose ribs in his shop... not an easy guy to impress). Even long ribs may be formed with multiple/ consecutive presses working from one end to the other

- I would use your CNC to produce the forming blocks in MDF... harden with BSI Thin CA (mask up) and you have a budget version of phenolic tooling that will do a half dozen or more rib sets (mine is currently doing airplane #3 over in Michigan), and MDF is way cheaper than 1" phenolic stock

- Worth searching for my summary doc on press forming as well as the doc on doing the aileron, flap, etc. nose ribs referenced in my stuff... adds some additional info on press operations, etc.

Again - good luck!

Re: the photo: we used to call those 'realistic sling load training blocks' when I was driving the 'essential bus'.

[brady.blake55]

TrueAirSpeed I did enjoy my time on 64’s. I was an armament guy in the 211th, which I assume you were in based on some of your post history.

SpruceForest I’m not going to pretend to understand all the science behind that response. What I do understand is, my idea would not be viable. Thank you for the very detailed response! I can put that idea to rest and stop coming up with “short cuts.”

[Frank]

Great to have another scratch builder! Too bad with the new factory owner that hybrid builds are out the window. Regarding rib forming, notice in the Bearhawk LSA Book that Bob suggests the crude but effective methods. That's pretty much the route I took. Whatever method you use, make sure to debur and smooth the edges before forming. Especially before pressing the lightening hole flanges. You're gonna have a blast!