Imported unwrapped/re-wrapped issue

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Imported unwrapped/re-wrapped issue

Postby mike.davison » Thu Sep 22, 2016 10:23 pm

I'm experimenting with creating a fairly elaborate table leg as a rotary, wrapped job, starting with a cheap commercial STL model. The model can be imported by Aspire. It is unwrapped then re-wrapped in the 'Toolpath Drawing -> wrap X Values (around Y Axis)' step. It's mostly working as expected, but there is a portion of this curved leg where the entire leg is to one side of the rotary center. This seems to confuse the wrapping gadget. A picture is worth a thousand words so see the image below. the yellow section is not part of the STL, instead it is Aspire 'filling in' material.

Is this just a known limitation of the wrapping gadget or is there some cleverness that I've not learned yet? Thanks!

[attachment=0]leg.png[/attachment
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Re: Imported unwrapped/re-wrapped issue

Postby IslaWW » Thu Sep 22, 2016 11:27 pm

Mike...
If there is a portion of the model that has no data at the centerline, you will not be able to unwrap it satisfactorily. Similar to this post: viewtopic.php?f=38&t=25415. If you can manipulate the model to have a "toothpick" center, then you may be able to do it, but that creates its own set of problems.

Best way is to set up and machine 2 or 4 sided, rather than wrapped. And as stated numerous times, better results are usually achieved when leg blanks are bolted to the table or a jig similar to Russell Crawford's than on a rotary axis.
Gary Campbell
CNC Technology & Training
Control & ATC Retrofits
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Re: Imported unwrapped/re-wrapped issue

Postby mike.davison » Fri Sep 23, 2016 12:01 am

Thanks Gary. I'll experiment with 4-sided flat machining. 2-sided doesn't adequately capture the detail on this part. Will also make use of Russell's recommendations for multi-sided hold downs.
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Re: Imported unwrapped/re-wrapped issue

Postby Rcnewcomb » Fri Sep 23, 2016 12:03 am

Two other threads about cutting legs in bulk:
Will Aspire cut legs like this
Square trestle leg profile
- Randall Newcomb
10 fingers in, 10 fingers out - another good day in the shop
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Re: Imported unwrapped/re-wrapped issue

Postby mike.davison » Fri Sep 23, 2016 5:51 am

Thanks. Interesting threads.
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Re: Imported unwrapped/re-wrapped issue

Postby rscrawford » Fri Sep 23, 2016 2:23 pm

I was never able to get an .stl of my leg designs to unwrap and wrap properly. Even when I got a pretty good wrapped image, it machine slightly out of square (the flat surfaces never came out flat.

Also took me about 3 times as long to cut one leg on the rotary as I can do them on the flat. But I use 2 sided cuts, which is a lot easier than 4 sided.

For 4 sided, you need a reference point to be able to rotate the blank 90 degrees. Easy to rotate 180 degrees, just use dowels to index. Its the 90 degree turn that kills you. I would reference off one corner (two perfect sides), and make sure that corner is run through the jointer and then planer so its a perfect 90 degree. Then butt it up against an L-shaped 'fence' so you can rotate it and butt it up again, so the two faces are perfectly referenced to each other. The other two cuts will just be indexed with dowels.
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Re: Imported unwrapped/re-wrapped issue

Postby mike.davison » Fri Sep 23, 2016 4:40 pm

My experience with wrapped jobs matches your's. It can be a useful way to cut round-ish parts, but the flat surfaces are not square and the process is slow.

I've watched your video on 2-sided milling of table legs and used that process to create back slats for a chair. I'm still refining the process, but it looks quite workable. Thanks for the thoughts on how to index 4-sided jobs. I suppose one could also create a jig that indexed from the center of a square blank. Feels like that would be a bit more complicated and unnecessary, however. Anyway.... the task looks reasonably clear now. thanks!
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