Sheet Metal Bending Basics
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- เผยแพร่เมื่อ 4 พ.ค. 2022
- How sheet metal bends, k factor, bend allowance explained and more. This video includes drawings, animations, formulas and press brake bends.
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Thank you. Always a pleasure to learn from someone who knows their subject and has thought about what the rest of us need to know in order to understand it. 💯👍
U R Welcome. I started to get back to some sheet metal bending projects Dec 2021. Did the deep dive on details. I'm lucky to have a press brake so I can test real parts from the drafting table. I think now with CNC controllers, most of this is push button. That said, a few out there might be on the manual system and/or want to know what's in the box. Glad you found the video interesting and informative. Thanks for the support and work safely.
What a brilliant job you did creating this video. Your explanations were clear, well-organized, concise and devoid of unnecessary information. Also, the drawings and illustrations that you displayed were extermely helpful in describing both the practical and theoretical aspects of metal bending. Thank you so much for your effort and attention to detail.
Hi Randy - Thanks for the kind words. I'm glad you found the video informative and helpful. Before this video, I scouted around and got pretty confused with details. That started me on a path of my own discovery. In my shop, I can do actual bends to verify 3D models, graphic solutions and theory. When all that came together I figured perhaps a few others might find the information helpful so I did a video on it. Much of this is contained in CNC controllers now and removes a lot of the details required to bend metal. For those of us on a basic press brake, we need to do the figuring. Work safely.
Informative. Thank you. You've given me some ideas to work with to solve my small laser bracket fabrication.
Thanks. Glad the information is helpful. Getting to a solution is always satisfying. Work safely.
Thanks a ton, sir!
U R very welcome. Hope the information is helpful.
I did sheet metal work a long time ago and recently had to find out about bend allowances which I had not learnt about .
May I say that yours is the clearest explanation that I've seen , you cover all the relevant terms and show the formula in a clear and understandable way .
Thank you for this video .
PS My Machinery Handbook is a 19th Edition . Where on earth did all that time go to ?😁
Hi Rex - Thanks for the kind words. I too did a lot of sheet metal bending work years ago. Back then it was poke, hope, tweak, try again and get close enough. My shop is slower now so time is available to dive into details & theory. I started to make some fitted bent parts and decided to move beyond trial & error. I also started to work with the sheet metal WB in FreeCAD where K-factor is required. Using my press brake, FreeCAD, LibreCAD and theory the goal was to get them all to agree. The bend allowance tables in the Machinery's Handbook were found by accident. I also have the 12th addition (1943) from my late father which doesn't have the nice bend allowance tables from Westinghouse. Time just seems to fly by now. Work safely.
way over my head but i will watch it 10 more times. Thank you for schooling.
I bent sheet metal for years with no knowledge of theory. Would cut, estimate, bend, check and adjust to finally get it right. I've had a bit more time now to look deeper into the theory. The contents in the video & blog post took quite a bit of time to digest. I easily went over the material 10X or more. The goal was to help others that might be interested in this level of detail. Thanks for your feedback.
@@muniac_llc My punch has a 1/8" radius which is approx the same thickness as a sharpie line, so I allow for metal thickness and bend accordingly .. I have no contracts with NASA and it is close enough for me..
@@SegoMan There are lots of ways to bend metal and tooling to accomplish it. Use what works best for your project(s).
@@SegoMan I used to work in sheet metal roofing and so the bend allowances weren't that important as the jobs were near enough is good enough . Recently I had to go for an interview and it was for a precision sheet metal component manufacturer .
All of a sudden it was necessary to have to know all about bend allowances .
You never know when information will come in very handy .
@@rexnemo Life's little pop quizzes..Get a job as a carpenter they still run under the "Hit to fit - Paint to match" construction plan LoL
Great video!
Thanks for the compliment. I'm glad you enjoyed the video.
i like it very much
Thanks for the feedback. Glad you enjoyed the video. Work safely.
Nice video
Thanks. Hope the information clarifies some details and helps others make better parts.
With a drawing with two - or more - flange length measurements, layout can be greatly simplified by using bend deduction. BD = (2 * Setback) - Bend Allowance
Thanks for the tip. Do you have an example that details this simplification? A drawing would help link the theory with practice and show how it applies.
@@muniac_llc Using your drawing as an example, you would measure out to 2 inches, deduct ((.126*2)-.138) .114, and then measure 2 inches for the 2nd flange. Total flat pattern equals 3.886.
The method with setback and bend allowance works great for regular brakes, but for bending on a press brake utilizing a back gauge, bend deduction is the way to go
Thanks for the efficiency tip. Feedback on improvements is good and helps us all make better parts in less time. The drawing shows a symmetric L shaped part 2" OD on both sides. So two ODs = 4" - your BD (0.114) = 3.886" It works and saves a little math. I could have included your BD in my spreadsheet and skipped the 1.875" flange but didn't know about this. Learn something new every day. Lots of ways to skin the cat.
Thank you so much for the video. I am wondering if you can give me some advice and the tool I should purchase for my bending project.
I am a small business owner and working out of my garage - which means I’m on a significant budget and can’t afford expensive equipment.
I need to make repeatable bends (well over 1,000+) for a product I am manufacturing.
The material length is 32 inches and material width is 4” - I need to make two bends, 80 degrees, on only 7/8” lengthwise, on both sides of the material. So that there is roughly 2” of flat material in the middle.
I have been thinking about purchasing a Tennsmith Hand Brake or equivalent - or a Harbor Freight Grisly 50 ton press and a 40” press brake.
The problem - using a Tennsmith Hand Brake would be extremely physically exhausting and time consuming, and I can’t imagine using that machine over 1,000+ times. At the same time, I don’t know how exact a 50 ton press would be either, while it might be quicker, can the machine be set up to make exact, repeatable bends at 80 degrees.
My question is - do you have any recommendations? Do you have other tooling recommendations that I did not mention? What would you do in this situation?
Thank you for your time and thoughtful consideration.
Kind Regards,
Adam
Hi Adam - Thanks for the kind words. I worked with a 16ga 52" Tennsmith box and pan brake for many years. Also did 1000s of bends by hand on it. What is the material and its thickness? What type of absolute/repeatable accuracy is called out for the parts? As for bend accuracy that relates to how rigid the machine is. You'll need some way to register the bend lines with accuracy. Best - Scott
@@muniac_llc Hi Scott - Thank you for replying to my comment. My apologies for not getting back to you sooner. I’ve been interviewing metal fabricators in my area as well. The consensus was that I will need a 50 ton press for my project though I’ll need to keep a close eye on the material. One of the problems with the lite version of the Tennsmith is that it cannot bend 1/4” material, I’ve tried with two guys and if we’d try to force it, one of us would brake. :-) Thank you for your time and for a great video, and for your thoughtful feedback on my project. Hope you and your family have a wonderful Christmas and New Years.
Kind Regards,
Adam
@@adamb.745 - U R welcome. 1/4" is thick material. 50 tons seems about right. Sometimes it's best to contract these jobs out to a shop that has the machinery. Your part seems straight forward and a shop with a heavy CNC press brake could knock that out easily. When I had my other shop in NJ, I'd get jobs in that I needed to contract out. It's part of doing business and getting your parts made. The challenge now is finding the skills and work quality. Good luck.
Wishing your camp a Merry Christmas and Happy New Year. I'll be in the salt mine working on projects per usual. Keeps the brain from shifting into neutral .
Thanks & Take Care - Scott
@@muniac_llc yes i would agree
I just quit a job after 3 days being a design engineer for a very small company that made sheet metal parts. My choice of software to use is sold works. For some reason, the parameters entered into Solidorks for bending allowance did not match the press brake machine. If the flat panel produced by solid works gave a bend line that was 1.112 from the edge of the flange for a required 1.25 flange, the machine would make a part out of spec. For some reason, this press brake required an extra 0.03 takeoff, which seemed odd My question is the bend line given in the Solid works flat pattern the bend centerline, and do press brakes require an additional takeoff on the stop to produce this?
Solid works is a good product but expensive for some. If your target OD is 1.250" and you're 0.030" off, that's a lot. For standard dies, there's no correction. Metal should bend within +/- 0.010" from the bend line dimension. Your K factor needs to match the metal, material thickness & bend radius. The tables in the Machinery's Handbook have been good. You can use my formulas to convert "bend allowance" to K factor. This to check what SolidWorks is using. For example, 063" 5052 aluminum bent to 1/16" radius is 0.138" BA or a K factor of ~0.4 which I've used here with good results. Misalignment of upper/lower dies can cause metal to skid off the bend line. I did a video on how to check this. Clean your dies with WD40. Masking on the metal will affect the bend too. A sloppy back gauge could be another problem. Bending metal is somewhat empirical. I hit all the above problems and ran them down 1 at a time. I did a test 2" angle to check my setup. I was able to get within +/- 0.005" on my old DiAcro. Solid model, drawing and actual bending agreed. Keep in mind you want to form the metal not coin it. Hope this helps & good luck.
@@muniac_llc Assuming the k factor or bend deductions are correct for the metal, is the bend line given in the flat pattern the location where the center of where the die should be targeted at?
You should set your back gauge so the bend line is exactly under the die's center. I have a simple 90 deg 1/16" radius die set. I had inaccuracy problems. I noticed the radius forming part of the upper die wasn't in the center of the die's cross section?? Here's a video on that ( th-cam.com/video/TxpJtLQSHgg/w-d-xo.html ). Once you know accurately how far the center is off the back of the die, you can reference the back gauge to that. Touch that, zero your DRO run that distance under the die and zero again (or use as an offset). This way your back gauge will read directly from the die center. My die was off by 0.015". Mark the front of your die and write this distance on it. I used ~0.560". It's tricky to measure but you need that number for accuracy with bends.
@@muniac_llcThanks. I was hired by some gut who does Mickey Mouse job sheet metal objects as an engineer to bring engineer standards to his very small operation so he can grow. The problem is that from the first day he thought my basic engineer speak was uppity as well as Solidworks. Things went further south after the flat pattern didn't produce a part in spec. It was revealed by the guy who operated the machine that their was an extra take off but didn't explain why. He texted us while he was at his new job. By the time everything was figured out and dialed in, the owner was determined to challenge the accuracy of Solidworks. I quit after 3 days because he was a moron.
U R welcome. SolidWorks is a recognized standard for solid modeling and design. It's capable of handling very complex designs and simple prototypes. As for sheet metal, the SolidWorks algorithms are theoretically accurate and practically so if the parameters are correct. The program has a steep learning curve which is intimidating. To allow intimidation to sabotage the technology is ignorance. One of the themes of my videos is going from the drawing board to finished parts and the challenges involved. The software tools designers have now are incredible! I'd say the same for the advancement in computer graphics. All of us need to focus on identifying problems, fixing them and arriving at the best solutions. This involves communication, understanding, facts, teamwork and compromises. It saddens me to see a breakdown in these fundamentals. I wish all of us good luck moving forward.
sir, the formulas work with metric?
If your units are consistent yes. For example, bend radius (BR) and material thickness (MT) would need to be in metric. K factor is a dimensionless constant. My old copy of the Machinery's Handbook has its bend allowance tables in inches. If you use that data, multiply by 25.4 to get millimeters. The constant 1.57 is simply 2*pi/4 which is dimensionless. Hope this answers your question. Work safely.
Very helpful, thanks a lot!
Just one remark: for me background music is just annoying when I am trying to concentrate on your valuable content. Please consider dropping it in the future.
Thanks for the feedback and encouraging words. I enjoy music but need to realize not everyone shares that joy. I've done a bunch of other videos since this one and toned down the music per feedback I've received. I'm still somewhat new to the TH-cam video publishing activities with the usual bumps on the way to better content.
@4:20 you introduce BA (bend allowance) out-of-the-blue for no obvious reason, and talk at length about it, without telling us anything about what it is, or what it's used for... it looks like it's the length of the dotted line, right? Probably should have said that...
@0:09 Bend Allowance is clearly defined. It's the arc length of the neutral axis quarter circle for 90 degree bends. Might want to have another look at the video beginning. Hope that helps. Work safely.
@@muniac_llc Ah yes - buy you've defined "BA" on the drawing, which does not have any dimension which is labelled with "BA". Remember: we're all n00bs out here; "bend allowance" might seem obvious to you, but it's a really rare chance to understand what it used to be like before you knew what that meant - when folks like us (who've never heard of it before) let you know when and where you forgot to spell it out! True, a bunch of text 4 minutes ago did that, but that wasn't the right time or place to have done it... Thanks for the awesome video by the way! - I watched it before bed-time and had the most wonderful dream of a makerspace museum full of bending machines and things folks had made!
Hi @chrisdrake4692 - Cased closed then so thanks for the input and feedback. Work safely and continued sweet dreams.