Spar bending... A question or two.

[CdnMedic]

Time to get some spars made. Buying them from Sonex and then having them shipped out to the east coast of Canada isn't really something I want to do.
I'm either going to make up a "dave's brake" and give it a go (would be good to have for bending ailerons anyways) or have a local fabrication shop with a CNC press brake give it a go. This shop was actually referred to me by a local guy building a "snoosho" racer.

The plans are stating a 3/32 bend radius... But that is really tight for the .040 2024-T3 material. I'd be more comfortable bending at a 1/8th radius or so. Are the spars really bent that tight? Am I ok to be a little bit more generous with the radius as long as my final height and flange dimensions are good? Basically I guess I'm looking for tolerances.

I have a few test pieces ready to go for them to try bending to see if we can get an acceptable result.
I wish we had an 8' brake at work instead of the 4'.

 

[John B]

The radius can be a little bigger, but look at how the 1/8" thick bars that make up the laminated spar fit on the inside of the channel. If the radius is too big, the edge of those will be sitting on top of the radius.

Also, bending 8 feet of 0.040" 2024-T3 isn't real easy. I'm not sure the Dave's brake can handle that length. thickness and material type.

When I built mine I tried the route of getting a local shop to do it, but they had no idea what setback is and tried to bend a sharp corner. They would not do it while I waited or let me watch. They tried one and the flange broke completely off and then the idiots ruined the other blank I had by continuing to try it again without changing a darn thing. Just a bit of warning. Also and nick in their equipment can put a scratch in the aluminum and ruin the job.

 

[Tom H]

WTR, I, too, wanted to make my own spars. I made a brake using some 1x2 steel tubing and door hinges spaced about 2 ft apart (not sure what a Dave's brake is, but may be similar to what I made). I tested it on some short samples, and it did a good job. When I tried to bend the 8' material, no way. I even tried to rig up some come-alongs to get enough force, but that did not work out.

So, just like John Brannen, I went to a commercial mechanical shop that we used at work. I knew the owner and he assured me that he would get it done right. I supplied a sketch with bend radii, and a warning that the material would crack if not followed. Same as John, I wanted to stick around and watch, but could not; they did not adjust their press brake properly, and the material cracked. I had just enough material for them to try again, and they got it right on the second try.

I suspect that the shop used the brake mostly for thin steel air duct where bend radius is not as critical, and did not take my warnings seriously.

Many times I wished I had access to some of this commercial equipment.

If your commercial shop has the equipment, supply some short samples to them and get results back before you let them loose on the full length stuff.

 

[CdnMedic]

The radius can be a little bigger, but look at how the 1/8" thick bars that make up the laminated spar fit on the inside of the channel. If the radius is too big, the edge of those will be sitting on top of the radius.

Also, bending 8 feet of 0.040" 2024-T3 isn't real easy. I'm not sure the Dave's brake can handle that length. thickness and material type.

When I built mine I tried the route of getting a local shop to do it, but they had no idea what setback is and tried to bend a sharp corner. They would not do it while I waited or let me watch. They tried one and the flange broke completely off and then the idiots ruined the other blank I had by continuing to try it again without changing a darn thing. Just a bit of warning. Also and nick in their equipment can put a scratch in the aluminum and ruin the job.

I was concerned about the loss of flat web due to the larger bending radius needing that extra bend allowance causing that interference.
I talked to the owner of the shop, he seemed to get what I was saying. They are a custom fabrication shop for jeeps, cars, and have done some airplane stuff before, so they are likely the type to get it as close as possible to help build something "cool".

 

[CdnMedic]

WTR, I, too, wanted to make my own spars. I made a brake using some 1x2 steel tubing and door hinges spaced about 2 ft apart (not sure what a Dave's brake is, but may be similar to what I made). I tested it on some short samples, and it did a good job. When I tried to bend the 8' material, no way. I even tried to rig up some come-alongs to get enough force, but that did not work out.

So, just like John Brannen, I went to a commercial mechanical shop that we used at work. I knew the owner and he assured me that he would get it done right. I supplied a sketch with bend radii, and a warning that the material would crack if not followed. Same as John, I wanted to stick around and watch, but could not; they did not adjust their press brake properly, and the material cracked. I had just enough material for them to try again, and they got it right on the second try.

I suspect that the shop used the brake mostly for thin steel air duct where bend radius is not as critical, and did not take my warnings seriously.

Many times I wished I had access to some of this commercial equipment.

If your commercial shop has the equipment, supply some short samples to them and get results back before you let them loose on the full length stuff.

I could possibly get access to another shop on base that might let me have access to their CNC brake as well... But, then I have to figure out a new tool.

It's a funny thing, to have someone else bend spars up for me, feels like cheating and won't be able to say "built 'er all myself"

I'll give them my little sample pieces and see if they can bend them properly.

 

[Chucker]

https://www.cannedhamtrailers.com/pdfs/davesbrakeplans.pdf

 

[CdnMedic]

https://www.cannedhamtrailers.com/pdfs/davesbrakeplans.pdf

Yep, that's the brake I intend to roughly copy.