Inventor General Discussion

## Inventor General Discussion

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Message 1 of 7 (774 Views)

# Bend 90 degrees - L=A+B-x

774 Views, 6 Replies
01-23-2013 01:24 AM

Guys,

Can somebody please confirm I am not an Idiot?

We have bought a new copper machine and the company we bought it from has supplied bend tables for the machine which they same is extremly accurate.

so for example - If I have A=100mm B=100mm and correction value .7mm for a 90 degree bend on a 10mm thick piece of copper. I sould get 199,3mm flat length.

AM I missing something here? Because machine is saying flat length is longer than this.

Really appreciate some help on this.

Michael

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Message 2 of 7 (749 Views)

# Re: Bend 90 degrees - L=A+B-x

01-23-2013 05:43 AM in reply to: michael.shelley

Inventor's bend allowance system is a one-size-fits-all. If you need to get accurate flat patterns from Inventor then you need to configue it properly. You'll need to copy the bend table that came with your machine into an Inventor bend table and use that as your unfold rule.

By the way, I'm not sure about copper, but most materials shrink when you bend them. This means you would need to be adding the correction factor rather than subtracting it. It's not unheard of for some materials to grow, though, and I work with steel not copper.

Mike (not Matt) Rattray

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Message 3 of 7 (697 Views)

# Re: Bend 90 degrees - L=A+B-x

01-24-2013 06:31 AM in reply to: mrattray

mrattray,

I have been in sheet metal for over 25 years not sure where you get sheet metal shrinks.

There is a bend deduction and bend allowance.

Bend deduction is use when bending. Material stretches

Bend Allowance is used for forming. Material is drawn.

Does not matter the material if I bend a 90 degree bend to get the right length I add the flange lengths and deduct the stretch when bending.

If I am forming a rib it draws the material so I would take the finish size with the rib and add material to allow for the shrinkage.

James Letcher
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What happen to my Inventor :-(
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Message 4 of 7 (692 Views)

# Re: Bend 90 degrees - L=A+B-x

01-24-2013 07:13 AM in reply to: jletcher

James,

I get metal shrinking from the fact that when we take a piece of steel and brake it 90 degrees it shrinks. I think it may have to do with the sharp dies we use here. I made up a bend table based on our equipment shortly after I started working here. For example if we put a 90 degree bend in a 10GA sheet of HRS using a 1/8" radius die we measure a material loss of .030". 16GA aluminum shrinks by .030" with a .040" radius die. The only time we recorded stretching was with stainless steel plates. 1/4" stainless plates grew .038" in a 1/8" die.

Mike (not Matt) Rattray

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Message 5 of 7 (679 Views)

# Re: Bend 90 degrees - L=A+B-x

01-24-2013 08:20 AM in reply to: mrattray

mrattray,

Are you ID not OD? When you measure a flange? This could be why, all material will stretch when bending has to or you could not bend it.

Now if you dimension ID then this is way you think it don't...

I never go off of ID to many issues with ID because of the stretching of the material. Much harder to hold tolerance also..

I hold a .005 tolerance.

Few shops I have as clients went of ID but always had issues with tolerance once I converted them to OD they was amazed at the difference it made...

James Letcher
2012 Factory Design Suite ( will not load 2013)
What happen to my Inventor :-(
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Message 6 of 7 (673 Views)

# Re: Bend 90 degrees - L=A+B-x

01-24-2013 08:27 AM in reply to: jletcher

Ah, that makes sense. We are ID, but we hold to a +/- .030" tolerance. Our fab guys consider high precision to be switching from measuring tape to a scale.

Mike (not Matt) Rattray

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Message 7 of 7 (669 Views)

# Re: Bend 90 degrees - L=A+B-x

01-24-2013 09:06 AM in reply to: mrattray

Wow just seen I put way instead of why... It's Friday..

OK. I thought so I am at a shop now that does that and I am trying to convert them to O.D.