Ideal K-Factor for Cone & Cylinder

[henryjoseph9804]

Hi Everyone, 

What would the ideal K-Factor be for creating a flat pattern for a cylinder & cone.

Ideally I would want to produce a workable dxf. 

Thanks

[henryjoseph9804]

@Frederick_Law , would you mind advising me a bit further on this? 

[Frederick_Law]

K-factor depends on process, tooling and material.

How the cone will be made?

You need to run test and adjust.

[henryjoseph9804]

I believe it is going to be rolled.

When you say run test? what test am i running and what result am I looking for? How will I know when it is "Right".

[Frederick_Law]

For rolling, start with k=0.5

Cut one pc, roll it.  If it's too long, reduce k.  If it's short, increase.

k change linear with flat length.  So once you have 2 test, you can calculate correct k.

https://sheetmetal.me/formulas-and-functions/k-factor/

[henryjoseph9804]

So this test cannot be conducted without physically cutting a flat and attempting to roll it. Seeing the Diameter of what I have rolled and then adjusting from there?

[dgleis]

I agree the best way is to test bend/roll or whatever process you are using. We have a roller so sometimes we use that, but other times we bump bend the cones on our press brakes. Generally I start with a K factor of .4 and find I am in the neighborhood but sometimes that needs to be tweaked.

[Frederick_Law]

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@henryjoseph9804 wrote:
So this test cannot be conducted without physically cutting a flat and attempting to roll it.

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Correct.

Of course it also depends on how accurate you need it.

Some can use +/- 0.125"

Some need +/- 0.005"

Hardness, thickness, grain direction, bend radius of material will affect k.

[Frederick_Law · Accepted solution]

The cone will look like this after roll.

[henryjoseph9804]

I now understand what you meant by deleting the face & thickening & how it affects the flat. Thanks for your guidance.

[Frederick_Law]

On thin sheet, the different is not much.  Someone can grind it off in 5 minutes.

On 8" plate, it's alot.

[henryjoseph9804]

I understand. The biggest worry I have is for when I produce a cylindrical shell that will act as the main body for our filter. If I place a flat that is too 'short' then when they roll it to the OD I have it will be too short. The one test I did produced a difference of more than 30mm by just changing the K-Factor from 0.440 to 1.

[dgleis · Accepted solution]

I work for a sheet metal manufacturer, and I work alot with material from 24 ga to .500 thick steels, stainless and aluminum. I would imagine the cone is to be seam welded and ground? If I were to make this cone with out test bending anything and taking a guess at the k factor I would start with a k of .40.

[Frederick_Law]

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@henryjoseph9804 wrote:
difference of more than 30mm by just changing the K-Factor from 0.440 to 1.

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Diameter when k=0.440?

Diameter when k=1?

Diameter you need?

[henryjoseph9804]

Thank you for the response, yes the cone is going to be seam welded & grinded. I'll have a look at that but If im not mistaken the .40 K-Factor would produce a flat shorter than if i used k-factor of .440 or 1.

[henryjoseph9804]

@Frederick_Law , Okay so, the finished OD after rolling needs to be Ø1100. 

K-Factor 0.440 Length of flat = 2188.36

K-Factor 1 Length of flat = 2200

Here is an example of a shell for a Ø1600 Diameter. The difference is about 20mm.

[dgleis]

Like I said this was a guess at the k factor, normally i would test bend if it has to be extremely accurate. I do Leave a gap for welding normally.

[henryjoseph9804]

I understand, I unfortunately cannot do any test rolls or bends to do the process of elimination.

Thank you for the response

[Frederick_Law · Accepted solution]

If you can't test it, you can't find correct k-factor.

As I said before, k depends on material properties, forming process, tooling.

There are "rule of thumb" and they're reference to start.

My "rule of thumb" is 0.5.

dgleis is 0.4.

Do you have old design that work?  Use that to calculate k.

[henryjoseph9804]

Noted. This is unfortunate but I do understand.

Unfortunately I don't I will leave it at the default value and get some feedback from the fabricators.

Thank you for the assistance, it has been eye opening!