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Plans-building CH 640 Question: How long are the longest bends?
Good day, all. I am currently in the midst of plans-building my 750. I broke my bending brake on some of the thicker bends, and I am currently rebuilding. Since it is currently only 8' long, I'm wondering if that length will suffice for a future plans-built CH 640. The longest bend in my 750 was just over 8.5', so I had to bend my tail section spars on a different brake. But, since I'm repairing/redesigning anyway, I'd like it to accommodate a 640 project in the future. Anyone know what the longest bends in a 640 are? I plan to build one after my 750 is finished. Thanks in advance, Greg.
Replies to This Discussion
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Permalink Reply by Aleks Chernov on
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Hi Greg,
As I see in my blueprints, the longest part to bend is Spar Cap Angle t=0.032" with length of 3218mm dl=55mm.
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Permalink Reply by Greg Harris on
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Thanks for the reply. Wow, that's a long bending brake for the home builder! Did you fabricate your own?
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yeah! I did. I bent 2860mm t=0.040" Spar for stabilizer.
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That's awesome. I broke the piano hinge on mine trying to bend the .063" upper firewall support, which is only 863mm long. Same design of brake as yours (as I see in your kitlog site). So now I have to redesign it to be able to handle the .063" up to 1100mm.
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Greg, my brake had the same problem as yours. I rebuilt it with standard hinges. I will update my log soon with new photo.
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Permalink Reply by Michael T. on
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I was looking at your kitlog site, great pictures. I really liked your close up shots of the parts. I'm just starting my 640 rudder.
When you have a chance please upload pictures of your new hinges on your bending brake. I'm planing on making the same brake from daves brake plans, with a hinge modification also
Michael
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These are the best shots I can give you with my camera with the brake assembled. The best details I can give you about how I modified Dave's brake design is on my YouTube Channel here: Greg's Zenith STOL CH750
If you've been following my online kit log on Blogspot, I link to most of my videos there, but I don't update is as often as I should (YouTube takes up a ton of my time). If you have the ability to watch YouTube, I average about 1 "detailed" video per month, and I also mention other builder resources and YouTube channels in my videos.
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Also, I should note that the bending leaf is a slab of steel that's 5/8" thick by 4" wide. It was a piece of scrap that I bought cheap. However, if I had a choice, I'd have used a 1/2" thick piece that was 6" or 8" wide at least, with a truss and jack screw. For additional leverage, I use the original angle iron bending leaf bolted to the new bending leaf.
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I fabricated some heavy duty hinges from 3/4" O.D. solid rod & 3/4" electroweld I.D. pipe, but my brake is only 8' long. So I need to build a longer one if I want to do the 640. Plus with some of the "hat" style channels, I cant use 3" angle as the primary bending arm. Plan to replace it with 1/2" bar stock so the various flanges will clear the arm. But can still bolt the 3" angle to the bar stock for more leverage on thicker materials.
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Im just in the beginning stages of ch 640 construction. I was thinking of building the daves brake, but the hat channel your talking about. Not working on the brake, what would be your recommendation for the brake construction.
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Not having the plans for the 640 in front of me (yet), I can really only speak about what works or doesn't work for the STOL CH750. Me and a few other builders agree, it is unlikely there is a single bending brake that will do everything in the plane. Dave's brake worked really well for me on simple bends of thinner stock, but I broke it twice before modifying the hinges and eventually adding a tensioning truss with jack screws. All of the modifications I made were not great solutions, but are what worked for me after having already built a Dave's brake.
If you're starting from scratch on your bending brake, I do not recommend a Dave's brake with a piano hinge. It does certain things okay, but cannot do many other things. My 4-part YouTube series on how I bent the landing gear channel goes into a TON of detail about the modifications I had to make to get that part bent up.
If I was starting over, I'd probably build a Mac's Machine Bending Brake, or a HomebuiltHELP Bending Brake. Dan Hill put a nice series of videos together on building a HomebuiltHELP bending brake on his YouTube Channel. Even with those nicer brakes, and even if you scale them up to make the longer bends, it would be difficult to do some of the heavier/thicker bends without using a press brake. I've hammer-formed some of the smaller fittings, but things like the landing gear channel and upper firewall stiffener were challenging. The thickest fuselage channels will have to be bent on a friend's 10' industrial brake, because mine's just not strong enough and does not have the right geometry. I may have to purchase them if I can't get them to form correctly. I also plan to do a video just about bending brake choices/options/considerations in the near future. Dan Hill covers a lot of that ground in his Bending Brake series, though.
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Permalink Reply by Dan Hill on
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Having built both the Mac's Machine brake and the homebuilt help brake that I did the u-tube videos on I will say that either brake lengthened further to accomidate longer bends will probably not give satisfactory results. The Macs Machine brake is a fairly heavy brake for what I consider a home shop brake but at full 8' capacity begins to deflect on anything over .025 6061 and extending its length will substantually increase those forces. for my 701 longerons I was not satisfied with the bends and built a makeshift press brake which has proven usefull for some bends such as z channel. While I love the Mac's brake, bear in mind that it is a substantial project in itself and it is not inexpensive to build for the pieces that actually require it's full length. The homebuilt help brake is a good brake for it's size and cost to build, and will perform the majotity of bends required. I find that it is now my most used brake. If I were doing it again I would probably built the homebuilt help brake and my longer bends would be built on a brake built from basically channel iron and althread rod which was on the internet several years ago. I have the design here somewhere and will try and dig it out. It can be extended to any length and is basically a manual press brake. while slow it would be relativly inexpensive to build and I think would do a very good job.
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