How does PVC know where Z is in multiple tool operations?

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How does PVC know where Z is in multiple tool operations?

Postby huntleybill » Sun Aug 05, 2018 4:29 am

I just purchased PVC and am interested in doing some lithoplanes. I watched the tutorial below and am confused about the Z axis 0 point. The video explains the tool path for a rough cut operation. It shows the Z0 to be the top of the stock. Then there is a finish operation to clean up and produce a finer cut toolpath but Z0 is still at the top of the stock. These are two different operations so how does the second operation know that there was a first operation and the cutting depth in now lower than the first operation? If the top of the stock is 0 then the finish operation will be cutting air.

Or am I missing something?

https://www.vectric.com/media/media/coo ... arted.html

Bill
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Re: How does PVC know where Z is in multiple tool operations

Postby NormanAlbert » Sun Aug 05, 2018 2:17 pm

Hi: For lithophanes, being as the cut is usually shallow, I forgo the rough cut. I use bits as small as .020 without problems because of the diagonal cut. However, if you use a rough cut, your z zero has to be done on an untouched part of the litho. Just move x or y to such an area and bring z down to just touch with a piece of paper lightly pinched between the cutter and the work piece. Zero that setting and then raise the z so as to not drag across when restarting.
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Re: How does PVC know where Z is in multiple tool operations

Postby huntleybill » Sun Aug 05, 2018 3:52 pm

Thank you Norman. You may have misunderstood my question. If you milled the rough pass at 1/8" deep then zero the Z axis as you stated (which is exactly how I do it) for the finishing pass, the depth of cut is still set at 1/8". So the finish pass is going to cut air.

Does that make sense?
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Re: How does PVC know where Z is in multiple tool operations

Postby ger21 » Sun Aug 05, 2018 5:41 pm

The rough and finish passes should not be cutting at the same depth.
The roughing pass should be leaving a small amount of material for the finish pass. And the depth of the finish pass varies.
The actual depth is referenced from Z zero.
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Re: How does PVC know where Z is in multiple tool operations

Postby huntleybill » Sun Aug 05, 2018 8:49 pm

Thank you Gerry.

Forgive my ignorance but I did not see in the tutorial where it was to leave "x" amount of stock left over for the finish cut. The depth was set to .125 (cutting parameter: Path Depth) The same .125 is set for the finishing path with the only change being the tool itself. No depth changes. So, in my mind, the finish toolpath should cut nothing.

I'm probably beating a dead horse but I am trying to understand how this works.

Thank you for your patience.
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Re: How does PVC know where Z is in multiple tool operations

Postby Adrian » Sun Aug 05, 2018 9:10 pm

Roughing and finishing in a PVC lithopane works in a different way to similarly named operations in VCarve/Aspire which is where some confusion might be arising.

In PVC the roughing toolpath is done with a larger tool and bigger line spacing so it leaves big, noticeable furrows. The bottom of those furrows will be to the finished depth. The finishing pass is then done with a smaller tool and smaller line spacing so it's "knocking" the edges of the furrows and smoothing everything out even though the actual cut depths are the same.
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Re: How does PVC know where Z is in multiple tool operations

Postby huntleybill » Sun Aug 05, 2018 10:28 pm

Ohhhhhhhhhhhhh...ok. Thant makes sense. I ordered some corian and am going to try this out as soon as it gets here.
Thank you for clarifying this.
I will sleep soundly tonight :-) :D :D :D
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