ฝัง
- เผยแพร่เมื่อ 5 มี.ค. 2018
- WARNING - I made a dyslexic error when copying the formula. I left out a 7. The formula SHOULD read BA(deg)=(0.0078MT+0.01743BR)xdeg. This error affects all 5 of the non-90 videos I made. I will have to re-shoot. In the meantime, I will flag the error to make sure no one is harmed! - WARNING
This video is an explanation of the math on the FAA Airframe test. You can learn to bend metal without doing this math - but this video is about doing the math. It is a follow up to my previous video which explains how setback, bend allowance, bend radius, and sight lines work when bending a radiused corner on the brake. This video explains how we must modify the formulas when doing bends that are not 90 degrees. This is delivered classroom style. - ตลก
Supremely helpful. As a (relatively) math savvy person, I've always hated having formulas dropped on me without any explanation of what they're accomplishing. Actually having it explained makes things way easier to grasp for me than referring to arbitrary numbers on charts.
thank you for these videos. For us that need visual demos, maybe next time create one with a thickness. For example 1/4" thick aluminum with a 90 degree bend.
thank you for your explanation. I hope you will post more FAA Airframe test explanation
Awesome video! I have been doing a lot of sheet metal bending and riveting lately, both at work and to prepare for my Oral & Practical airframe test, and you did an excellent job of explaining bend radii.
hi can you help with one drawing
Thank you. I always measured my setback from 0° to 90° on a percentage scale, ( 45° is 50% of bend area of a 90°, ect.. ) but it's never worked right once I go acute of 90°.Its always nice to have hard math to figure out what those engineers were thinking 😁 I'm subscribing right now!
Great job
This is very helpful
Hello,
I want to make round ring of solid bar then plz can you tell me what should be the calculation for pulleys and stroke length which will avoid straight ends that remain after full rolling of round ring. Could you put video on that?
Arc length S equals radius R times angle theta.
S = T theta.
So for a full circle, S is the circumference and theta is 2 pi.
So C = 2pi R
For 90 degrees, theta is pi/2
So S = pi R/2.
The length of material from tangent to tangent in mold is 2 R.
The length of material in real world is pi R/2, which as you say, is less than 2R.
Just another way of looking at it.
Paul
hello sir, i saw all your videos related to this topic and every time i found a huge difference in calculation between my essay and yours.
you have to check your calculator because it's at he second time it makes you perform an inaccurate calculation.
2pi / 360 = 0.0174
(2pi)/(360x2) = 0.0087
so the right equation of the Bend allowance should be BA = (0.0087 MT + 0.0174 BR ) x DEG
The neutral axis is not exactly at 50 percent. The decimal formula is adjusted for the neutral axis on 2024 hardened aluminum.
Where to set the back gauge is the tricky part
nowadays we upgrade tube bender machine and we stop to calculate cut to length of pipe (arcs lengths + straight length ) but we try to calculate arc length times from inner ,outer and mean diameter after all calculations we didn't reach to accurate length .
please we need to provide us the formula that calculate cut to length pipe.
best regards.
Around 10:37, I believe that the 0.0078 value is wrong. ((2*pi)/360)*(1/2) equals 0.0087. Maybe I understood it the wrong way? Anyway, it is just to avoid confusion, I don't think 0.0009 would make much of a difference
Not wrong, that's what I get too
I need a k-factor table for 6mm wire
Thank you for your explanation. And I have a question, what can be the maximum bend angle of a steel plate for bending without cracks with supposed MT=2, BR =2, elongation limit = 20%?
Sounds like a homework problem gone wrong. You can't ask about the maximum thickness and then specify an MT (material thickness) of 2.
I'm so sorry. the maximum bend angle is what I want to mention.
OK. This is not a problem I am familiar with, but if I understand it right, you need to calculate how many degrees of bend would make the outside edge expand 20% compared to the neutral axis. The bend radius is the inside of the bend, so the neutral axis has a presumed radius of 3 inches (assuming the neutral axis is at 50%. The outside of the bent steel will be at 4 inches radius - the MT plus the BR. Your steel will have a slightly different neutral axis, so my answer is only an approximate. For each degree of bend, the neutral axis would cover 2piR/360 = 6pi/360 = pi/60 inches, while the outside edge would cover 2piR/360 = 8pi/360 = pi/45 inches. The steel fails when we reach 20% elongation, so the angle of failure is reached when the larger number is 20% greater than the smaller. Let D be the number of degrees, and set for 20% elongation.
(pi/60)D = 1.2(pi/45)D. Solve for D. Your pi/45 term will be the one that is different based on whatever exact nuetral axis figure your textbook or material handbook calls for substituted for 1/2.
Thank you for support!
i tried but the ratio comes same , can u through some light on this don with an example, it would be very much help full in solving real world problems. thanks in advance
How can you say k as 1/2 sir..
I used this formula in the late 80's when bending 3 and 4 inch NB pipework.
I get the BA=(kT+R)×A
BA= bend allowance
K= k factor = 0.43 for steel 0.25 for copper
R=inside radius of the bend
A= angle in radians.
if in degrees convert to radians by multiply by
180/pi
Can someone tell what's 0.0078 and 0.143 . Are they any constant or they change with respect to material or something
Hello! I hope this helps:
I am uncertain as to where / what .0143 is in this context. I suspect that it does indeed change with material.
EDIT: Upon reading the video description, I now understand that when he said .0143, in truth he meant 0.01743
.01743 is equal to pi / 180
.0078 is .446 * Pi / 180
.446 is the K-factor listed in the Machinery's Handbook for mild, cold-rolled steel, with a tensile strength of 60,000 PSI. This value does change with respect to material, but .446 is a great starting point.
You can look up "A grand unifying theory of bending" from TheFabricator. It is an excellent resource and there are many more articles available that dive further into getting precise sheet metal results.
What if there are more than 1 bends in product
Work the steps more than one time - once for each bend. See the example problems I also posted.
🖐hi sir I'm from India (Ahmedabad city)
Some parts are confusing and when you get there it is done for as you just keep going! You don't seem to spend enough time explaining where you get the numbers from and how you got them, instead you use them as a matter of fact. This was the issue I had with my algebra teacher 50 years ago! If I totally understood the methods used I would not have watched the video in the first place. After reading many of the comments, you can tell that most of them are from people that are using this daily and did not really need the video. Thanks anyway. I have watched it twice, and I will have to stop it and watch and try to work the numbers until I can figure out where you are getting them. Stay well.
Here the tool to unfold the sheet metal model inside AutoCAD automatically: th-cam.com/video/RbTIKeSkMyo/w-d-xo.html
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