Flat pattern length

[soggys3]

All,

I have a simple 2 bend Yoke I made using Inventor 2015 sheet metal function. It is made from 5/16 material and my sheet metal defaults are set up accordingly (0.3125). The factory default bend radius calculation is dependent upon the material and thickness and was unaltered. I created a flat pattern and pulled dimensions for our manufacturer, then double check the flat patterns flat length by manually calculating the outside length (9.588), inside length (8.606) and the midpoint length (9.097). None of these 3 calcs equals inventors flat pattern length of (9.039). This inconsistency could cause a fit-up issue with this particular part. Any ideas??? I have attached the .ipt for reference.

Thanks in advance!

[TheCADWhisperer]

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@soggys3 wrote:

.... manually calculating 

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What formula did you use for your calculation?

Outside length, inside length, or midpoint length (of bent part) are all incorrect methods of determining flat pattern length.

[mcgyvr · Accepted solution]

And flat pattern length will also change depending on the process/machines being used.. Air bending,etc...

You should NEVER.. NEVER provide a flat pattern length to an outside vendor unless they have given you the specific K-factor for that material/bend radius/process..

If you know what the flat pattern length should be then simply adjust the Kfactor for that sheet metal style and the flat will be perfect..

You should always provide a vendor with an "as folded" drawing only.. Its their job to make the part to the final "as formed" dimensions.

If they can't work without a flat pattern then find a better vendor.. 

[soggys3]

Calculated by polyline length of outer and then inner and also 40% of thickness polyline length. Please enlighten me if you would on the correct method. 

Thanks

[Thomas_Savage · Accepted solution]

Hello,

Your manufacturer probably used different radius and k-factor. That is why it is different. Your radius is thickness. But I use Vee width x .15 for my inside radius, for example. Because it is more accurate. Most people do use .044 as K-Factor in inventor, but I change it so other people also could. Can you not get the information off your manufacturer, so you can apply it to your sheet metal defaults?

Thomas 

[TheCADWhisperer · Accepted solution]

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@soggys3 wrote:

... 40% of thickness polyline length.

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This question comes up so frequently that I set out to make a definitive video, but ran out of time for now.

Set your Default_KFactor = .4 if that is your intention. (rather than .44)

[IgorMir]

I think - that statement is a bit harsh. In my line of work I always send an DXF file of a flat pattern for laser/plasma cutting. Or for the turret punch for that matter. Which in a sense means that I provide the vendor with the unfolded part length, etc. And I yet to see a problem with that. 

Cheers,

Igor.

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@mcgyvr wrote:

And flat pattern length will also change depending on the process/machines being used.. Air bending,etc...

You should NEVER.. NEVER provide a flat pattern length to an outside vendor unless they have given you the specific K-factor for that material/bend radius/process..

If you know what the flat pattern length should be then simply adjust the Kfactor for that sheet metal style and the flat will be perfect..

You should always provide a vendor with an "as folded" drawing only.. Its their job to make the part to the final "as formed" dimensions.

If they can't work without a flat pattern then find a better vendor.. 

[mcgyvr]

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@IgorMir wrote:

I think - that statement is a bit harsh. In my line of work I always send an DXF file of a flat pattern for laser/plasma cutting. Or for the turret punch for that matter. Which in a sense means that I provide the vendor with the unfolded part length, etc. And I yet to see a problem with that. 

Cheers,

Igor.

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@mcgyvr wrote:

And flat pattern length will also change depending on the process/machines being used.. Air bending,etc...

You should NEVER.. NEVER provide a flat pattern length to an outside vendor unless they have given you the specific K-factor for that material/bend radius/process..

If you know what the flat pattern length should be then simply adjust the Kfactor for that sheet metal style and the flat will be perfect..

You should always provide a vendor with an "as folded" drawing only.. Its their job to make the part to the final "as formed" dimensions.

If they can't work without a flat pattern then find a better vendor.. 

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Thats your choice.. And if its working for you then fine.. 

I get sheet metal parts made everyday.. I NEVER send a flat and never need to.. Its their job to make the part to my final dims..

The biggest potential issue is that if your purchasing department sends that file to another vendor whos process may be slightly different then parts may be out of tolerance if they use the flat dims as their kfactor may be different for their process..

If you don't supply a flat.. You never have that problem.. 

All our sheet metal vendors will ignore a flat provided by a customer anyways.. Because they know the potential issues too.. 

Every vendor we have wants a step file too.. They use that and unfold themselves to program the laser/turret press or whatever..