Spar web forming

[nborer]

It's been a while since I've posted, but I've lurked plenty, and appreciate all the great advice here. I've made good progress on my rib forming (COVID-19 has kept me from traveling for work, which means more shop time!), and I'm about to need to think about what to do next! My plan is to start on the spars next, starting with the aileron. I'm undecided about building my own bending brake - I've found some plans on this site - but I do know that finding a 9-ft brake in my local area will be tough (the longest spar web on the model B is the flap spar).

But, before I get started, I just thought I'd confirm... there is no practical way to bend the spar webs such that the bends are 90 degrees to the grain, yes? I've been getting my aluminum in rolls from Spruce, and have thus far been getting 4x4 ft rolls (easier to handle that size when making rough cuts with my bandsaw for the ribs). It looks like I now need to order a 4x12 roll or two of 0.032" for my spar webs, and I'm assuming that the grain will be aligned with the long dimension (12'). Is best practice here to just give a generous bend radius?

While we're on the topic, any other good tips for spar web forming? (I already know one... order webs from Bearhawk Aircraft... I thought about it but would like to try bending my own at first.)

[S Lathrop]

I found a shop in Indy that had a press brake long enough to bent my spar webs. I made a drawing of what I needed and they produced all the webs. It was not all that expensive and the spars were very accurate.

At one time I had an 8 foot bending brake and while it was a good quality, it was no match for a proper press brake. One big advantage for a press brake is the accuracy of the radius of the bend.

The spar is the foundation of the wing so get the best job possible on that part..

[geraldmorrissey]

Yes, the bend axis is paralell to the grain of the material. I measured a factory main spar web and the inside radius measured 1/8". A false spar web, 1/8". A flap spar measured 3/32". I used a radius guage to measure the bends. A press brake is very repeatable and accurate. I highly recommend it.
Gerry
Patrol #30

[nborer]

So how do you find people with brakes? There is a local A&P school here, but they don't have a press brake, they just have a leaf brake, from what I recall.They were my only lead thus far... they host the local EAA SportAir workshops when they come to town. The local machine shops seem to cater to the engine rebuilding crowd, not the build-your-own-airplane crowd. I was either going to try to cold call the A&P school (I took the EAA electrical, welding, and sheet metal classes there) or build my own brake. I'll admit the former seems cheaper and more reliable than the latter.

My plan right now is to rough-cut the blanks with a circular saw and straightedge (or perhaps my bandsaw), and then finish cut with my router and a deburr of the edge. A shear would be nice, but again, that seems like I need a friend with a kick-@$$ machine shop. I had some good access to a great shop in Atlanta when I volunteered with the local CAF chapter back in grad school, but they're now about 600+ miles away. That said, it may be worth the road trip, I still have some street cred with them... and a trip there is probably more precise and less costly than building my own...

[geraldmorrissey]

If you can get access to a shear and a press brake, load up and go. ROADTRIP. Go alone, you can sleep in the truck and save money. Think of the time you will spend screwing around just cutting the blanks plus the cost of any scrap you produce and compare that with a couple of days of sitting on your ass driving. Plus your parts will look professional and fit your ribs. Its just part if the adventure of scratchbuilding. There's plenty of plane left for you to build.
Gerry
Patrol #30

[jaredyates]

Have you already ruled out getting the spar webs pre-bent from the factory? They are sounding cheaper and cheaper as the thread progresses.

[Russellmn]

That's what I did, bought the Rib and Spar package. I think I saved about 6 months to a year of work doing it that way...

[nborer]

Heh. Yeah, I brought up the idea today with my wife. She has friends in Atlanta, so maybe we just call it a family road trip! Plus, the CAF unit that I volunteered with is in Peachtree City, which happens to be the location of Aircraft Spruce East, so I could even save on shipping! (So much for that being a cheap trip... I can see loading up on lots of goodies!)

I've thought of the factory spar webs, and not just because of the ease and reasonable price, but also because the spars are such a critical part of the wing. However, I'm a bit wary, since I'm forming my own ribs, and I don't know how well the factory webs will fit to my ribs. Anyone have experience with matching the factory spar webs and homebuilt ribs? I think my ribs are fairly consistent, but I can imagine an overzealous pass with the sander on my original formblock may be enough to cause some fitment issues with the factory spar webs and my homebrew ribs. It's probably able to be solved with a joggle, but I'd be disappointed if I found that my hundred-odd ribs I've spent the last year forming don't fit my spar webs. That, and... I like building stuff. There is an intangible benefit to me associated with doing it myself, even if it ends up costing more or taking more time. I'm really enjoying this journey (okay, I've had a few moments of doubt!), and I'm looking forward to learning the next skill.

[nborer]

Just a quick bump... anyone have experience with buying the factory spar webs and fitting them to scratchbuilt ribs? I'd like to think I'm not an idiot, but occasionally experience proves me otherwise. I'm a bit leery to spend $1445 plus shipping to find out that my scratchbuilt ribs are all something like 1/8" too short or too tall for the factory webs, in case the idiocy does reign.

[Chewie]

You could possibly order the factory spar webs and send them a representative front and back end of your center rib for them to match (i.e. an ICD if you work in manufacturing).

[Russellmn]

Call around to your local welding shops, metal supply houses, etc... around me, about half of them have some fairly big equipment. My local shop has a press brake that's gotta be 16' long. If I'd wanted to spend some time polishing one of their die sets they'd have let me so I could get a good clean bend, we did some test bends but the dies are too beat up from decades of use. I ended up buying the rib and spar package from Mark instead, but it was an option...

[way_up_north]

Just a quick bump... anyone have experience with buying the factory spar webs and fitting them to scratchbuilt ribs? I'd like to think I'm not an idiot, but occasionally experience proves me otherwise. I'm a bit leery to spend $1445 plus shipping to find out that my scratchbuilt ribs are all something like 1/8" too short or too tall for the factory webs, in case the idiocy does reign.

I would call or email Mark....I sure you can work out something...

[geraldmorrissey]

It depends on the accuracy of your tooling and the quality of your work. Check your formblock to the mylar, check the fit of your ribs to the formblock. Finally check your ribs to the mylar. Ideally the edge of your formblock should split the mylar curve provided you didn't add springback allowance. If it doesn't, measure the deviation. I would be concerned if I was off by more then +/- .030. I have found the factory parts are very close to the mylar.
Gerry
Patrol #30

[nborer]

Thanks all. Gerry piqued my curiosity and I rechecked against the Mylar (which I had cut from the roll ages ago but had saved) for both the master formblock and a sample set of .025 ribs. They’re not factory perfect but I think they’ll fly. If the factory webs match the Mylar, and I have no reason to believe they wouldn’t, then I’d think these would work. Looks like I have some decisions to make about the spar webs.

But first, today’s job is to flange the lightening holes on 16 more nose ribs... and then all the .025 ribs are done!

[nborer]

Question on the Bearhawk Aircraft spar webs (probably for Mark G, or for someone that has ordered them): do the spar webs come with the lightening holes cut? Or are these cut afterward? I've been searching for a 3-pulley drill press that turns slow enough for a fly cutter but also doesn't cost a zillion dollars, but if I don't need one (I used the router method for my ribs), then that goes into the price differential... not that I still won't lust after a 3-pulley drill press!

[nborer]

Thanks, that's the way it looked in the photo on the website; I thought I'd confirm.

I'll admit that I haven't spent too much time looking over drill presses... my lack of a 3-pulley press was one reason I abandoned my original plans to use the fly cutter for the rib lightening holes. My cutter is limited to 500 RPM, and my press turns no slower than 630. I briefly searched for other pulleys but did not find much. I'll admit that I could be using the wrong search terms.

Of course, the spar holes are all largely the same size... so I could probably buy a couple of hole saws that are the appropriate size.

[Russellmn]

I believe BTAZ bought his hole saws on Ebay, pretty cheap it sounded like. You'll still want to slow it down more than just 630rpm. Bigger the hole, slower the drill. I think I bought my pulleys for my old drill press at McMaster Carr... just need to know your shaft diameter and key size, then pick the two pulleys that will give you the rpm you want.

[nborer]

We’ll see what happens, but I just came to terms on a 3-spool 1950s “helmet head“ Craftsmen drill press on OfferUp. I’ve been looking for months (casually) and this just popped up. My shop is small but now will hopefully now have a floor-length drill press that can get below 300 RPM.