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gsjames  
#1 Posted : Tuesday, January 20, 2009 1:25:36 PM(UTC)
gsjames

Rank: Junior Member

Joined: 4/7/2007(UTC)
Posts: 27
Location: TX

In aircraft sheet metal work, the term "setback" is used to describe the changes to the flat stock part layout that must be made when the part is to be bent around a radius. Sometimes it's referred to as "bend allowance". Example, if you took a 10 inch long piece of metal and bent it around a 2" radius, right in the middle, the legs would each measure longer than 5" (from a flat surface) because the distance around the radius is less than than the distance if it were a zero radius curve.

I'm trying to learn the "bend" tool to make a spring steel landing gear leg which is 1/2" thick and uses 1.5 " radius bends. There doesn't appear to be any settings for bend allowance within the bend tool. Is this correct, or am I missing something. Perhaps there is a better tool for the job?

Any hints?
File Attachment(s):
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tmay  
#2 Posted : Wednesday, January 21, 2009 1:22:18 AM(UTC)
tmay

Rank: Senior Member

Joined: 2/21/2007(UTC)
Posts: 278

Shark doesn't (yet, anyway) have the ability to flatten or unfold a part to create a flat pattern. Unless you are actually fabbing the part yourself, I would just pass on the model in a format the fab can handle and let them deal with it.

Another route would be to forward the model to someone who has Solidworks, Pro/e or some other package that does have sheetmetal functionality, and let them create the flat pattern using your bend data.

tom
gsjames  
#3 Posted : Wednesday, January 21, 2009 8:05:42 AM(UTC)
gsjames

Rank: Junior Member

Joined: 4/7/2007(UTC)
Posts: 27
Location: TX

Thanks Tom! I'll use the "setback charts" to adjust the pattern by hand.
bobc  
#4 Posted : Friday, January 30, 2009 1:55:54 AM(UTC)
bobc

Rank: Junior Member

Joined: 6/3/2008(UTC)
Posts: 6

Hi
Yes the bend tool will bend parts but does not flatten them.

You talked about set back and bend allowance.

Bend allowance is easily determined by construction if you know where you want the neutral axis of bend to be. Forty four % of the material thickness, measure from the inside of the bend, has been use in the aircraft industry for eons. But depending on the material and the method used to bend the part other values have been used. A test part can always help determine the correct percentage.

I was able to open your model second bend in VC6 and flatten the part using simple construction methods. The first thing I created were the neutral axis lines shown as dashed lines (I used 44%). By using menu > verify > length I got the arc lengths of both bends (bend allowance). The rest was simple. It took less than 30 minutes to construct. You really don™t need a set back chart if know were you want the neutral axis.

Regards - Robert Chubb
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Steve.M  
#5 Posted : Saturday, January 31, 2009 1:23:11 PM(UTC)
Steve.M

Rank: Senior Member

Joined: 6/18/2008(UTC)
Posts: 978

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Long time since I have had a need for calculating bend allowance, but sure I used a "zeus data chart book" for ref.
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