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Old 01-04-2019, 11:07 AM
TimPa TimPa is offline
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Default onion skin

seems like I am dominating the newb questions forum, sorry. I have been trying to learn the onion skin process/concept by the context from your posts, but I don't quite get it.

can someone please explain the process and intended uses for this, other than on a burger? now I'm hungry...

thanks in advance!!
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Old 01-04-2019, 12:06 PM
DVE2000 DVE2000 is offline
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Instead of cutting parts out by using material height + .003 or something like that, you use material height - .02. That means the part isn't totally cut free of the material, but the spoil board is undamaged, and if you have a vacuum holding down the material, the newly cut part shouldn't break free. It's easy enough to physically break the "onion skin" and sand down once the machine has finished cutting.
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Old 01-04-2019, 12:22 PM
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Old 01-04-2019, 01:10 PM
Ger21 Ger21 is offline
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There are lots of different ways that people "Onion Skin".


One thing people with less rigid machines do, is make the first cut a climb cut, about .01-.03 from going through, then follow with a full depth conventional cut.


On our Morbidelli, we onion skin small parts that are 350sq in or smaller to keep them from moving. We make the first pass .01 from going through, then follow with a full depth cut. These parts are cut first, then larger parts are cut in one pass.
With plywood, I usually leave a 1/8" skin, as the face veneer itself is not usually stong enough to hold the parts in place.
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Old 01-04-2019, 02:08 PM
TimPa TimPa is offline
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it seems that responses so far refer to the pass that cuts the part out (separation cut), or removes the cut part from the remainder of the sheet/board. as in maybe cabinet parts.

if carving out a sign, would the onion skin apply to the carving of the features as well, or just the bottom-most (separation) cut above the spoil board?

and my next question is when would onion skin (as in a separation cut) be beneficial over using tabs? thanks again....
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Old 01-04-2019, 02:28 PM
guitarwes guitarwes is offline
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Say you have a piece of 3/4" plywood (that measures exactly .75") on the table and you want to cut out 10 parts. You would program the first pass to cut all the parts to a depth of .72 or .73. What is left is the "onion skin". Then you would program your next pass to .755 or whatever your preference to fully cutout the parts all the way thru the material.

Tabs are a pain to cut free and sand off, especially if you have alot of parts to do. If you're just cutting a few parts, then sure, use tabs.

"if carving out a sign, would the onion skin apply to the carving of the features as well, or just the bottom-most (separation) cut above the spoil board."

Just the cuts you make to cut thru the material to break it free.
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Old 01-04-2019, 03:38 PM
guitarwes guitarwes is offline
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The climb/conventional cut strategy that Ger21 alluded to is doing the first pass with a climb cut offset .02-.03 off the line then come back with the final cut-thru pass in a conventional direction right on the line. The conventional cut will pull the bit towards the line and make it dead on (depending on machine slop and such).
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Old 01-04-2019, 03:49 PM
The real JP The real JP is offline
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Here is a screenshot of how I have my software set up for profile cuts.

This is a full sheet onion skin. It leaves 50 thousandths of material on the first cut and offsets the parts bigger by .015.

On the final cut it cuts full depth and trims that .015 off. Leaves a really clean edge. I use this a lot for melamine.
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File Type: jpg profile cut.jpg (10.7 KB, 44 views)
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  #9  
Old 01-04-2019, 07:17 PM
Doug S Doug S is offline
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Tim,
Thanks for filling in for me in the newbie category. I felt like I was bugging everyone for the first few months. I act like I have it figured out now but you never do.
You have some great advise already here so I will refrain from commenting further, except I use onion skins an all small parts to keep the parts from coming loose. You vacuum setup affects your choice of part size to start onion skinning.
I don't do anything fancy with my skins, just leave .030 for the final pass to release the part. Pay attention to cutout options in the optimizer as that is where all the onion skin settings are store and managed.
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