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How to create forging draft or oscillating draft

Question asked by Don Howe on Apr 28, 2014
Latest reply on Apr 29, 2014 by Don Howe

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I used to know how to do this but it's been so long my method doesn't seem to work anymore. How do I create forging draft or what was refered to many years ago as oscillating draft. I'm a SW2004 user.

I have a very simple part which I want to create a surface loft using 3 profiles each with a pierce relationship and a guide curve. Once the loft is created I would remove the material in front of the lofted surface using a surface cut. See the images below

This is what I end up with when I create the loft

What I am looking for to happen is the following (after the surface cut)

The image above is taken from a paper I wrote years ago when I worked in the Forging Industry and at that time I was using SW97or 99. So I know it can be done...I just don't remember how to do it.

John Burrill Apr 29, 2014 12:05 AM

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Well, the interface has changed quite a bit since 2004 but, if memory servers, those are loft handles. In the absense of guide curves or centerlines, they control where the sections connect to eachother. It's especially useful if your loft sections don't all contain the same number of vertices.

If I undestand your design intent, your original was probably created as a sweep with a constant normal for the profile and a guide curve instead of a loft.

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Roland Schwarz Apr 28, 2014 4:27 PM

Draft from parting line won't do it?

Otherwise, you can make a sweep. Usweep along a straigh line and use your loft curve as a guide curve. The sweep profile is just a straight line constrained to the guide and angled to your draft.

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Don Howe @ Roland Schwarz on Apr 28, 2014 5:26 PM

Parting line draft in SW2004 wont do what I need. Imagine a milling cutter with a 7 degree taper. It starts at the parting line where the first profile curve is located, the draft is 0, it starts cutting down into the part following the guide curve as the cutter reaches the center line of the part or the bottom radius of the guide curve the draft at the parting line is now at maximum. If the radius is 1.5 inches and the cutter has 7 degree draft the draft at the parting line would be .183 inches. Now the cutter starts climbing back up the 1.5 radius till it gets to the fillet radius, it runs straight for a little bit then starts climbing back up the slope and out of the part, where the draft reaches 0 again. In this case the guide curve is the master path not the parting line. When I get a chance I will sketch out the shape of the draft at the parting line, unless of course you can visualize what I just described.

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Don Howe @ Don Howe on Apr 28, 2014 8:09 PM

Can someone explain whats going on here. If I try and pull up on the point circled in red on either side of the part the shape of the surface changes.

If I pull it back down it reverts to this shape

What do these blue dots represent?

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John Burrill @ Don Howe on Apr 29, 2014 12:05 AM

If I undestand your design intent, your original was probably created as a sweep with a constant normal for the profile and a guide curve instead of a loft.

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Don Howe @ John Burrill on Apr 29, 2014 9:58 AM

Thanks John, your suggestion worked perfectly and produced the results I was looking for; using normal constant or follow path and first guide curve seems to produce the same results at least I couldn't tell any difference.

As a side note, I was able to produce the draft using a loft method but it was not as accurate.

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5 Replies

Roland Schwarz Apr 28, 2014 4:27 PM
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Draft from parting line won't do it?

Otherwise, you can make a sweep. Usweep along a straigh line and use your loft curve as a guide curve. The sweep profile is just a straight line constrained to the guide and angled to your draft.
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- Don Howe @ Roland Schwarz on Apr 28, 2014 5:26 PM
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  Parting line draft in SW2004 wont do what I need. Imagine a milling cutter with a 7 degree taper. It starts at the parting line where the first profile curve is located, the draft is 0, it starts cutting down into the part following the guide curve as the cutter reaches the center line of the part or the bottom radius of the guide curve the draft at the parting line is now at maximum. If the radius is 1.5 inches and the cutter has 7 degree draft the draft at the parting line would be .183 inches. Now the cutter starts climbing back up the 1.5 radius till it gets to the fillet radius, it runs straight for a little bit then starts climbing back up the slope and out of the part, where the draft reaches 0 again. In this case the guide curve is the master path not the parting line. When I get a chance I will sketch out the shape of the draft at the parting line, unless of course you can visualize what I just described.
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  - Don Howe @ Don Howe on Apr 28, 2014 8:09 PM
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    Can someone explain whats going on here. If I try and pull up on the point circled in red on either side of the part the shape of the surface changes.
    
    If I pull it back down it reverts to this shape
    
    What do these blue dots represent?
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    - John Burrill @ Don Howe on Apr 29, 2014 12:05 AM
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      Well, the interface has changed quite a bit since 2004 but, if memory servers, those are loft handles. In the absense of guide curves or centerlines, they control where the sections connect to eachother. It's especially useful if your loft sections don't all contain the same number of vertices.
      If I undestand your design intent, your original was probably created as a sweep with a constant normal for the profile and a guide curve instead of a loft.
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      - Don Howe @ John Burrill on Apr 29, 2014 9:58 AM
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        Thanks John, your suggestion worked perfectly and produced the results I was looking for; using normal constant or follow path and first guide curve seems to produce the same results at least I couldn't tell any difference.
        
        As a side note, I was able to produce the draft using a loft method but it was not as accurate.
        
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How to create forging draft or oscillating draft

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