Spar bending
- Thread starter Bradrock
- Start date
Yeah, I do some sheet metal. You will stretch the flange material, and the spar will wind up trying to curve toward the flat side. I've considered trying to radius the edge of my bench top and hammer over it, but would need a long block to hit with the hammer. Probably an 8 foot piece of 2x6 or 2x8. Get someone to lean on one end while I beat on the other, and trade places every couple whacks. I may destroy some aluminum trying this.
Cherokeedriver
Member
I may need to build a brake as well. Can you show us some pics of yours and possibly we can compare ideas. If anything, if your brake design didn't wok, I'd like to avoid having the same troubles. Thanks,
Joe O'Keefe LSA 083
Joe O'Keefe LSA 083
bestbearhawk1231
Well-known member
I used a piece of angle clamped to the bend bar to get mine past 90 degrees. The c clamps worked but I would have been better off bolting them together, one of the mods I haven't done to mine yet. The c clamps allowed the piece of angle to bend a slight bit in the center which made the flange vary a bit, easily workable but an extra step. I made an angle checking block and fixed the angle variation with a pair of seaming pliers. Is it perfect? No, but the plane will never know the difference in flight.
No Title
Hey Joe.
This photo probably is the most explanatory of how the brake goes together. There is another thread in here about bending brakes where a few guys have contributed plans. My plans came from someone else and seems to be working really well, despite the issue over not being able to get more than 90 degrees. I also posted the brake plans I used in that thread if you're still looking....
Hey Joe.
This photo probably is the most explanatory of how the brake goes together. There is another thread in here about bending brakes where a few guys have contributed plans. My plans came from someone else and seems to be working really well, despite the issue over not being able to get more than 90 degrees. I also posted the brake plans I used in that thread if you're still looking....
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bestbearhawk1231
Well-known member
No Title
Hey Brad, I hope these pictures help explain it better. I didn't used a MDF nose, I just bent it around the piece of 3/16" angle hold down bar. All steel surfaces were covered with painter's tape. If I were to re build the break, I would have used piano hinge rather than door hinges which would reduce the gap and I would have match drilled the bending angle to the extra angle and welded nuts on the bottom so I could simply bolt them together and not have to deal with c clamps. Live and learn...not bad for the image in my head that I came up with at work though. Hope this helps.
Hey Brad, I hope these pictures help explain it better. I didn't used a MDF nose, I just bent it around the piece of 3/16" angle hold down bar. All steel surfaces were covered with painter's tape. If I were to re build the break, I would have used piano hinge rather than door hinges which would reduce the gap and I would have match drilled the bending angle to the extra angle and welded nuts on the bottom so I could simply bolt them together and not have to deal with c clamps. Live and learn...not bad for the image in my head that I came up with at work though. Hope this helps.
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(Untitled)
Thank you. I suppose you wouldn't know if those diagonal braces were necessary or not? I have piano hinge on mine (welded the entire length!). I will bend my front spars next as they don't need to go past 90, then I'll re assemble my brake with new holes to emulate your brake without the MDF nose. Thanks for the input.
Thank you. I suppose you wouldn't know if those diagonal braces were necessary or not? I have piano hinge on mine (welded the entire length!). I will bend my front spars next as they don't need to go past 90, then I'll re assemble my brake with new holes to emulate your brake without the MDF nose. Thanks for the input.
bestbearhawk1231
Well-known member
I have no idea if they are needed or not, in fact they will be getting cut out so I can bend the trailing edges. I added them not knowing if the hold down bar would be strong enough but I am pretty sure it is after having used it.
bestbearhawk1231
Well-known member
One other thing, with a 3/16 hold down, the bend radius comes out to around twice what is called for in the prints. I haven't found it to be a problem anywhere so far.
N3UW
Patrol Scratch Builder
I have been looking at finding a 8' brake or building one. I would love to see a photo of the spars you bent. What size bend radius where you getting? how did you end up shutting your spar blanks to width? what did you end up paying for the steel?
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Pretty hard to do the spars justice with photos, but after pulling them out of my brake, they lay flat on the table with no bow to them. Very satisfied so far. I used 6mm thick, 3" angle iron. Pretty close to 3/16" in your language. The finish on the the angle iron gives a good radius without messing with it. The radius is greater than that called for in the plans. General consensus is that this is ok. Obviously a tighter radius would not be ok. Steel price may not be relevant to you since I am in New Zealand. I can guarantee you that yours will come out cheaper than mine! But my brake cost me about $200 New Zealand dollars. Building the brake gave me an opportunity to further my welding and general engineering skills, plus I can bend anything on demand, rather than finding a shop to do it. I am in pretty small place that doesn't offer much by way of assistance for these sorts of projects, so I am having to be mostly self sufficient.
Pretty hard to do the spars justice with photos, but after pulling them out of my brake, they lay flat on the table with no bow to them. Very satisfied so far. I used 6mm thick, 3" angle iron. Pretty close to 3/16" in your language. The finish on the the angle iron gives a good radius without messing with it. The radius is greater than that called for in the plans. General consensus is that this is ok. Obviously a tighter radius would not be ok. Steel price may not be relevant to you since I am in New Zealand. I can guarantee you that yours will come out cheaper than mine! But my brake cost me about $200 New Zealand dollars. Building the brake gave me an opportunity to further my welding and general engineering skills, plus I can bend anything on demand, rather than finding a shop to do it. I am in pretty small place that doesn't offer much by way of assistance for these sorts of projects, so I am having to be mostly self sufficient.
(Untitled)
Sorry - I missed your question on cutting to width. I used some scraps to work out exactly how the brake was going to work and nail down the size. Then I used a router with a flush trim bit, using the table edge as a guide. Very easy and repeatable operation.
Sorry - I missed your question on cutting to width. I used some scraps to work out exactly how the brake was going to work and nail down the size. Then I used a router with a flush trim bit, using the table edge as a guide. Very easy and repeatable operation.
bestbearhawk1231
Well-known member
I am planning on bending the initial 15 degree edge, move it out to the center bend and get as much bend as I can then complete the bend with a 2x4. Then finish the other 15 degree bend. Haven't gotten this far yet so I have no idea if it will work or not.
bestbearhawk1231
Well-known member
No Title
Hi John, my brake is 10' long since steel around here is sold in 5' increments so I didn't get charged for cutting. I used 20' of 3x3x1/4" angle, 10' 3x3x3/16" angle, 20' 1x1/8" square (handle), 1' 1 1/4" square (pockets for the handle to slide into), 5 3" door hinges ( I would use heavy piano hinge if you can find it), maybe a square foot of 1/4" plate for the handle hinges (it was scrap, overkill for this), misc bolts and nuts for bend bar and handle. I think I had $350 into it but I could be wrong I am not sure where the receipts are and it was over a year ago. The steel I used was all new, new steel is pretty pricy but I didn't want to spend all afternoon at the scrap yard. I had to buy 5' of the 1 1/4" tubing, I don't remember what thickness but it was a slip fit...14 gauge stands out in my mind. This is all of the top of my mind so I may be off of some of the dimensions. One of the primary goals of mine was to be able to knock it down and store it on end in the garage, hence the removable handle that folds up. A 10' stick of 3" angle 1/4" thick is pretty heavy and awkward to handle around 70 pounds or so...help would definitely be appreciated. I used a engine hoist to help me out. My original plan was to use 1/8" angle for the hold down bar but they didn't have any in bigger sizes. That would have given a radius pretty close to the plans without getting tighter than what is called for.
I simply measured out the spars on the aluminum and cut them out by hand with my tinsnips that I used for rough cutting the rib blanks. Nothing fancy, I think I paid around $20 for them at menards, Midwest brand I think. They are pretty good sized, made of aluminum or magnesium, have removable cutting edges... they are not aviation snips. The edges were then deburred with a scotchbrite wheel in my grinder.
Hi John, my brake is 10' long since steel around here is sold in 5' increments so I didn't get charged for cutting. I used 20' of 3x3x1/4" angle, 10' 3x3x3/16" angle, 20' 1x1/8" square (handle), 1' 1 1/4" square (pockets for the handle to slide into), 5 3" door hinges ( I would use heavy piano hinge if you can find it), maybe a square foot of 1/4" plate for the handle hinges (it was scrap, overkill for this), misc bolts and nuts for bend bar and handle. I think I had $350 into it but I could be wrong I am not sure where the receipts are and it was over a year ago. The steel I used was all new, new steel is pretty pricy but I didn't want to spend all afternoon at the scrap yard. I had to buy 5' of the 1 1/4" tubing, I don't remember what thickness but it was a slip fit...14 gauge stands out in my mind. This is all of the top of my mind so I may be off of some of the dimensions. One of the primary goals of mine was to be able to knock it down and store it on end in the garage, hence the removable handle that folds up. A 10' stick of 3" angle 1/4" thick is pretty heavy and awkward to handle around 70 pounds or so...help would definitely be appreciated. I used a engine hoist to help me out. My original plan was to use 1/8" angle for the hold down bar but they didn't have any in bigger sizes. That would have given a radius pretty close to the plans without getting tighter than what is called for.
I simply measured out the spars on the aluminum and cut them out by hand with my tinsnips that I used for rough cutting the rib blanks. Nothing fancy, I think I paid around $20 for them at menards, Midwest brand I think. They are pretty good sized, made of aluminum or magnesium, have removable cutting edges... they are not aviation snips. The edges were then deburred with a scotchbrite wheel in my grinder.
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Gavin Chester
BearHawk 631 & Patrol 237
your only problem with to large a radius is if the cap strips will not sit flat at the required spacing.
bestbearhawk1231
Well-known member
Gavin, I had thought of that. I cut some strips out of pine to the size of the capstrips to see if I was going to have a problem. I don't believe that I will. Worst case is that the capstrips will have to be moved towards center slightly. The plane will never know the difference between the capstrips being dead nuts to the prints and being inboard slightly. If they need to be moved any it would only be an 1/8" tops. If this change needs to be made, it is a matter of a couple strokes of a file on the wing attach plates, spar splice plates, and the spacers which are made to fit anyway.
Hey Nick. I ended up removing the form block, although this was unnecessary. the leaf was not getting sufficient travel to bend the spar far enough - the brake is powerful enough, so for me it was about making the bending leaf "fatter". All I did was take the form block and after bending to 90 degrees, placed the form block between the flange and the bending leaf. It's pretty low-tech, but it gave me the extra travel required to get the bend i needed. One word of advice - bolt your table down! It requires a serious amount of grunt to bend the 8 foot lengths. You'll spend half your energy holding the table down. If I had to rebend them, I would bolt it down. I don't know if I made sense, but feel free to ask question to get to a solution. My spars look good.