Spar Radius Issues, DIY Metal Brake

[NSLaw]

Evening All -

I thought I might share this in the General Discussion area in case it might help others find motivation through building setbacks. (Please feel free to move to a more appropriate section if needed.)

I am currently scratch building a Companion, working on the wings. Needing to get my aileron and flap spars bent, and not having an 8.6' brake, I turned to a local shop to bend both sets of spars for me. Despite providing a sample piece and making sure their brake bent the spars within spec (.10"), when I get the spars back ($85 bucks later), they were under the allowable radius and even included a crack in some places. So, frustrated that I just wanted two weeks for parts that were unusable, I decided to just build my own brake so I know the job will get done right.

I followed some of the posts/write-ups that have previously been shared here. Nothing fancy. 3x3 angle, stainless steel hinge, some hardware, and about 10 or so hours of work. I used rattle can paint and some plasti dip rubber on the handles. Total cost was about $230, which I'm fine with. I'm glad to have the ability to do the bends myself.

I've included some photos of the ~$150 bucks worth of aluminum that the shop ruined, and my brake. After a couple hours of complaining to my wife I realized that scratch building or kit building is challenging, and there will be days or weeks when you accomplish a lot, and others when you don't. My love for building isn't deterred!

Thanks for the resources here, and the community.

[Nev]

Nice brake !

[nborer]

Looks great. I too have been having trouble finding anyone that will bend my spar webs, and I have three 9' sections of 3" angle iron waiting to be transformed into a brake. I was planning on modifying some plans for an 8' brake I had found on this site - by the looks of it, the same plans you used. One thing I noticed is that you seem to have used a single hinge that doesn't quite go the full length of the brake. I was wondering if I should do the same or try to get a 9' hinge assembled from multiple sections. McMaster-Carr seems to sell it in 1', 2', 4', and 8' sections, last I looked (which was a while ago). I was debating between a single 8' hinge or two 4' sections with a 1' section in the middle. Any thoughts on this vs. your hinge setup? Have you tried the flap spar web yet?

Thanks for sharing. Highly topical for where I'm at with my build.

[N3UW]

Very nice job. That was also the most challenging job for me while building my spars.

[NSLaw]

Looks great. I too have been having trouble finding anyone that will bend my spar webs, and I have three 9' sections of 3" angle iron waiting to be transformed into a brake. I was planning on modifying some plans for an 8' brake I had found on this site - by the looks of it, the same plans you used. One thing I noticed is that you seem to have used a single hinge that doesn't quite go the full length of the brake. I was wondering if I should do the same or try to get a 9' hinge assembled from multiple sections. McMaster-Carr seems to sell it in 1', 2', 4', and 8' sections, last I looked (which was a while ago). I was debating between a single 8' hinge or two 4' sections with a 1' section in the middle. Any thoughts on this vs. your hinge setup? Have you tried the flap spar web yet?

Thanks for sharing. Highly topical for where I'm at with my build.

I too tried to source a longer hinge but failed. Doesn’t seem like there are any in production really. Mine is 72”. My concern with using multiple hinges is straightness. I had to pay special attention when drilling because the middle section of the steel wanted to creep forward about 1/8 of an inch. (I drilled the ends first, then used clamps to hold the middle section into a straight line)

I say that to illustrate my concern that multiple hinges increase the complexity and risk of not creating a straight bend.

I haven’t bent up the blanks yet. During initial tests the hinges seemed plenty strong, no flex at all, resulting radius is 1/8, just over the spec we need. I even did some bends on the outside of the area with the hinge.

[NSLaw]

Very nice job. That was also the most challenging job for me while building my spars.

Thanks - and thanks for the videos you’ve posted online.

[NSLaw]

Nice brake !

Thanks Nev - hope that nice new plane you got is treating you well. I’ve appreciated watching your videos.

[rodsmith]

I've found that a big part of scratch building is finding solutions to problems you encounter. Very satisfying when you find a workable solution. Good job on the brake!

[sjt]

What is the youtube channel that has videos?

Also, you can use the failed bends as brake shoes for the second try.
You can used failed bends as material for c- channel stiffeners.



I use tape to strap shoes to brake.

shoe.jpg


This (bellow) is a previous bend that was not good enough but, I could use it as a shoe.


Also - at least on the patrol - Bob suggested adding 5/16-3/4-5/16 c channels to stiffen the skin.
I needed to make a shoe that allowed for bending 3/4 c channels. The lip of the flange of the shoe had to be
small enough that it allowed for the over bend of the c channel stiffeners.

http://bearhawksafety.com/Patrol/february2020.html

nose1.jpg


stiffeners to be used on leading edge:
In addition to stiffeners for the leading edge there is a suggestion
of using stiffeners behind the main spar for wing skin.
stiffener.jpg

[sjt]

I found a 10 foot brake necessary to crush the trialing edge as recommend by Bob.
crush.jpg

trailingedge.jpg I tried to protect the bend radius with several lengths of 3/16 drill rod while crushing.

[RobinDeMarco]

Very nice brake! Is this based off of Dave Clay's brake? This is the brake I'm planning on making this spring, but I have a few concerns. I saw a YouTube post be a fellow who was building a Zenith using this type of brake and he was having serious difficulties doing 8 foot sections of .062" 6061-T6. Did you do any modifications to strengthen it so it doesn't bend when making the longer bends? Thanks!

[NSLaw]

Very nice brake! Is this based off of Dave Clay's brake? This is the brake I'm planning on making this spring, but I have a few concerns. I saw a YouTube post be a fellow who was building a Zenith using this type of brake and he was having serious difficulties doing 8 foot sections of .062" 6061-T6. Did you do any modifications to strengthen it so it doesn't bend when making the longer bends? Thanks!

Thanks Robin! One of the resources I used was a PDF titled "Dave's Cheap Brake" so I think it's the same resource, yes. I don't currently have any plans to modify it to create more strength. I don't think us bearhawk builders ever need to bend anything that long of that thickness (.062). I could be wrong, might just have not encountered it in the plans yet.

I think modifying it to add strength could be done fairly easily. I'd just weld a long triangle to the top hold down angle, with a bolt on the middle piece to put more tension on the middle. I think that would stiffen it up enough to bend without any flex. I could be wrong though, and maybe because we're only bending .032 it won't be an issue at all. Open to suggestions.

[NSLaw]

I've found that a big part of scratch building is finding solutions to problems you encounter. Very satisfying when you find a workable solution. Good job on the brake!

Thank you Rod. I'm really enjoying the process.

[Frank]

Nice job on your brake NSLaw and thanks for revisiting this topic. I too am at that stage where I need to bend the spars and joggle the ribs to match. Because of the joggling and testing, I didn’t even try to find a local fabricator to do the job. Instead I started with John Bannon and others who followed Dave Clay's “Build-it-yourself: sheet metal bending brake” which can be found at EAA Sport Aviation archives or by googling.

For me it has been a slower more difficult process than advertised, but is progressing nicely. My problem is I tend to sabotage myself. Using 3/16 steel for the hinged pieces is considerably cheaper and easier to handle than 1/4. But beware: this hot-rolled steel isn’t necessarily straight!

The clamping angle (the “foot”) is 1/4 steel and straighter, but first I tried making a foot using MDF which I could make perfectly straight and with a precise 0.1 inch radius. This has proven problematic for a couple of reasons so I removed the MDF and currently testing the steel angle as the foot. String and eyeball indicates one edge of that angle is straight.

But the proof is in the pudding, and that will be full 96 inch bends which are straight. Haven’t tested that yet. It’s too cold in the shop to paint.

One thing I did which I think is an improvement is to clamp the pieces together and then drill and bolt the hinge in place. In my case I used two 48 inch hinges. The advantage here is clamping takes out the bow and the hinge keeps it straight. Also you don’t need to take out the hinge pin and try to put it back together. When you open it up, though, the hinge projects above the clamping surface. So I used strips of 1/8 primed fiberboard to raise the surface which has the advantage of being smooth. (The aluminum drags across the surface of the “bender” as you raise it up.)

Still need to work out the joggling blocks, precise dimensions of the spars to match, confidence in the long bends. But I still have confidence this may work. Seeking out a sheet metal shop to do the bending will be a reluctant last resort.

[NSLaw]

What is the youtube channel that has videos?

Also, you can use the failed bends as brake shoes for the second try.
You can used failed bends as material for c- channel stiffeners.



I use tape to strap shoes to brake.

shoe.jpg


This (bellow) is a previous bend that was not good enough but, I could use it as a shoe.


Also - at least on the patrol - Bob suggested adding 5/16-3/4-5/16 c channels to stiffen the skin.
I needed to make a shoe that allowed for bending 3/4 c channels. The lip of the flange of the shoe had to be
small enough that it allowed for the over bend of the c channel stiffeners.

http://bearhawksafety.com/Patrol/february2020.html

nose1.jpg


stiffeners to be used on leading edge:
In addition to stiffeners for the leading edge there is a suggestion
of using stiffeners behind the main spar for wing skin.
stiffener.jpg

Both N3UW and Nev have shared some of their builds on youtube. Those were the videos I was referencing.

Thats a heavy looking brake! Thanks for the info on stiffeners. I'm working on Flaps and Ailerons now. After I finish those I'm going to build the spars for rear and forward wings. Most wing ribs are rough finished, need tuning.