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Finding the Flat Length of a Bent Steel Metal

03/26/2018 5:17 PM

I am trying to find the flat pattern length of a bent steel metal. If someone could please walk me through this i would greatly appreciate it.

Attached is an image for the piece (not needed though). The plate material is A36. I am trying to find the flat length of the plate needed to achieve a 5'1-11/32 " radius and 160 total degree arc with 5/8" thickness. If someone can, i would like to steps on how this is done rather than just the answer. I want to be able to do this for future parts.

By the way this is an example saddle for a vessel.

Thank you.

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#1

Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 5:20 PM

It has been too many years for me to give specific help but if I recall correctly "K Factor in sheet metal bending" is a term to Google.

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#2
In reply to #1

Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 5:24 PM

Awesome, thanks bruce.. i have started researching it. Still would like a specific walk through on this though if someone has this floating around in their head..could save me some time haha. Thanks again for the info though!

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#3

Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 5:59 PM
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#4

Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 6:28 PM

First step is to calculate the circumference of a full circle at the required radius.

Convert the whole feet to inches - 5' is 60", add the extra inch, it's now 61", convert the fractions to decimals (divide the top by the bottom) - so 11/32" becomes 0.34375".

So you have a radius of 61.3475" - is that inside or outside radius?

If it's inside, then you have to add half the thickness of the material, if outside then deduct half the thickness - I'll assume it's inside, so 5/8 is 0.625, divided by 2 is 0.3125, now add that to the original number and you have a radius to the centre of the material of 61.66"

Circumference = ∏D, ∏ is 3.1416, D is twice the radius, so the circumference is 3.1416 x 61.66 x 2 = 387.422.

Now divide your 160° by 360 to get the percentage of the circumference that you require - 160/360 = 0.44444, so 387.422 x 0.444444 = 172.1876.

Divide 172.1876 by 12 to bring back to feet = 14.34896 feet. Now multiply the 0.34896 by 12 to find the inches, 0.34753 x 12 = 4.1875 inches.

Multiply the 0.1875 by which ever denominator you want to get fractions of inches - ie x 8 will give you eighths, by 16 will give you sixteenths etc.

If you want 16ths, then 0.1875 x 16 = 3

So the length required is 14' 4 and 3/16"

I have rounded a number of times for convenience, you will get more accuracy with longer numbers.

Hope this helps.

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#13
In reply to #4

Re: Finding the Flat Length of a Bent Steel Metal

03/27/2018 6:20 PM

That's all very nicely explained. Unfortunately if you try to use just that to calculate the dimensions to cut the flat piece to be bent into the curved piece, it will not yield the correct size flat piece.

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#19
In reply to #4

Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 12:15 PM

This is a core part of our fabrication. We have a analogic controlled 3/4" x 6' capacity pyramid plate roller. Your method is almost exactly what we do. The only additional is we add 6"-8", 3"-4" each end, for trim waste. If "Garrett12345's" fab shop has a 21stC numerically controlled roller there will be less trim waste.

FYI to all yu'al: the pyramid plate (sheet metal) roller was invented by Leonardo Da'Vinci. The only tangible differences between his and a modern machine is his has bronze or wood rollers and uses a hand crank or treadmill powered top roller drive while the best modern machines have hardened steel rollers and use electric over hydraulic bottom (both) rollers drive.

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#5

Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 8:52 PM

This size of a piece (this is plate rather than sheet) would probably be formed by rolling rather than bending, but either way, the calc in the preceding post is correct in principle. However, in close-radius bending, there may be some slight stretching of the material. Not a problem for a large saddle like this, but it might need to be accounted for in thin sheet metal. (That's where the aforementioned K-factor comes in.)

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#6
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Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 9:01 PM

K factor would have to be accounted for in a tighter bend whether the material is thin sheet or thicker bar, but as this particular item has a quite large bending radius of over five feet, my consideration is that the neutral axis will be so close to the centre line of the material to be inconsequential.

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#8
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Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 10:04 PM

Just need to remember, if he gets rolled, depending on the size of roller, both ends will not get rolled, and will remain flat.

we/I always specify that the ends get bumped.

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#11
In reply to #8

Re: Finding the Flat Length of a Bent Steel Metal

03/27/2018 5:36 PM

I have learned this piece is getting rolled. How does this change the situation? Can trimming still be used for a rolled steel plate? Phoenix can you further explain what you mean by this?

Sorry for all the questions. Just very curious on this subject now.

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#12
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Re: Finding the Flat Length of a Bent Steel Metal

03/27/2018 6:07 PM

I usually put it on my scope (graphically) as a requirement when I send it to contractor... don’t have with me now.,I’ll post it tomorrow.

but basically, when rolling you have (3) rollovers in a triangle arrangement. (2) rollers on the bottom, and the single roller on the top in the middle (pinch roller).

as the sheet is fed through, when the first part of the sheet does not begin to bend or form untill both bottom rollers are engaged with the sheet.

Same as it exits the rollers.

so basically, you will have a flat area, half the distance between the distance of the (2j bottom rollers and the beginning of the roll, and at the end of the roll.

even with you have to roll it a number of times to come to the required radius.

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#14
In reply to #11

Re: Finding the Flat Length of a Bent Steel Metal

03/27/2018 7:53 PM

I would expect the fabricator to know exactly what is required to achieve your desired outcome. Whether they require final trimming and how much trimming will depend on how they do the job and what sort of equipment they use.

The straight line areas would be greatest if they are using a standard 3 roller machine. Pre-bending (either with a separate die or the roller itself) will reduce the straight as will the use of a suitably curved base plate under your sheet, but this effectively doubles the load on the machine for that portion of the bend, ie. they would need a roller with at least a 2" capacity.

Three roll initial pinch and four roll machines also enable reduction of the straight line section as the bottom rollers can be moved closer together for the start and finish of the roll.

If trimming is required, the edge finish that you want and the availability of methods may restrict the possibilities.

I'm not aware of the width of the sheet in question, if it's quite narrow, then a cutoff saw may be adequate, if it's quite wide, then you may need to look at Oxy, Plasma, Waterjet etc.

Is finish of the cut important? - you could leave a little extra and clean the edges after cutting.

Is heat effect from Oxy or Plasma going to be a concern? - then Waterjet may be the answer, but generally expensive.

Your fabricator will know what they can do.

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#17
In reply to #14

Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 7:44 AM

I would expect the fabricator to know exactly what is required to achieve your desired outcome

Maybe if there's a relationship with the fabricator that he's familiar with you needs... so not necessarily,... That is the reason, this is included in my scope. And yes, like you mention, I do have it pre-bent. or if its totally rolled , I'll have them tack welded and rolled through out. But a lot of it would need to be specified.

And this is what I was talking about the flat area on the inlet and outlets of the sheet

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#7

Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 9:29 PM

spades, gave you 2 good answers. Heres a link that might help you better understand if you read through it.

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#9
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Re: Finding the Flat Length of a Bent Steel Metal

03/26/2018 11:24 PM

Wow thank you all so much. I have a feeling I’m going to be learning a lot from this community and hopefully I will be able to pitch in to help others (well maybe eventually at least haha).

Thanks again and hope y’all have a good week.

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#10

Re: Finding the Flat Length of a Bent Steel Metal

03/27/2018 3:08 AM

Practically, it is better to bend an oversize piece and trim it to the right length. It is difficult forming accurate bends near the ends of the material properly as these tend to remain straight. Heating it up will also help.

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#16
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Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 5:05 AM

As an illustration, and also a coincidence, a piece of flat 20-thou polystyrene sheet intended for a model refused to bend fully to a curved shape with a radius of about 2.5in last night. The ends stayed straight. The solution was to make it over-long, bend it to shape, and cut the straight ends off to size.

Sort-of felt a similar sort of job...

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#15

Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 5:01 AM

Another way - trip a hoop off the cylindrical material for the vessel that is going to be put on the saddle, straighten it a bit, and trim it to size.

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#18

Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 11:11 AM

If you haven't already got your answer, the terms you might Google are Bend Allowance and Setback. Bend Allowance is a computation of how much stretch happens on the outside of the radius and Setback is a measure of the compression on the inside. In Aviation Tech School in the 70s we had to do these calculations in order to determine sheet metal sizes used in constructing aircraft wings. I haven't seen or used the formulas since.

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#21
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Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 7:39 PM

I wished I was that lucky, not having to do those calculations after I got out Aviation School! As both a mechanic and Inspector, I had to stay on top of the calculations. We had plenty of yawhos baggage handlers, gate agent's, fueler's that always seemed smack the aircraft for no apparent reason. Oh yeah, de-icer personnel did their fair share of damage too

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#24
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Re: Finding the Flat Length of a Bent Steel Metal

03/29/2018 11:52 AM

I never worked in the industry. I joined the Navy and became a Nuke instead.

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#20

Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 5:32 PM

Try this:

if [Rinside = 5' - 1 11/32'' = 61.34375'' = Ri ] => [arc length = S = (central angle, in radians) x (radius, in inches)]

then [Sinside = ( Ri = 61.34375'') x (160 deg x PI/180 deg) = 171.30407'' = (168 + 3.30407)'' = 14' - 3 39/128'' ~ 14' - 3 5/16'']

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#22
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Re: Finding the Flat Length of a Bent Steel Metal

03/28/2018 9:35 PM

GA for that response. My first thought was to do it with Radians, but the Op wanted a step by step and - I presume - simple explanation which I felt that method didn't provide.

I still would have added half the material thickness to arrive at a more accurate material length for bending, doing that and using Radians gives a length of 14' 4&3/16"

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#23
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Re: Finding the Flat Length of a Bent Steel Metal

03/29/2018 11:48 AM

Thanks for the ''GA''.

If there was such a thing, then I would give you an ''MHE'' for a ''More Helpfull Explanation'' overall...

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