Discrepancy with preview vs reality

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GEdward
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Discrepancy with preview vs reality

Post by GEdward »

I ran the preview for a cabinet door V-Carve which depicts the veins of the grape vine leafs fading away before they reach the edge of the leaf. In general the preview has finer detail than the end product. I am not unhappy with the end result but I do wish it would have turned out more like the preview. The finished product looks almost like what I'd expect if I had zeroed the engraving bit a little below the surface. I zero my tools on the surface using silicone coated paper (the backing paper from carpet tape) which is .003 thick. The screen shots show the original vectors vs the preview vs the end result. What did I do wrong?
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Cabinet door example 1 (2).jpg

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martin54
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Re: Discrepancy with preview vs reality

Post by martin54 »

ouple of thoughts to start you off, did you measure the paper you use to zero or just assume it was the same size as normal?
Did you check the depth of the pocket before you vcarved the text & graphic?
How long was the gap between cutting the pocket & the vcarving? I know wood can move a bit quite quickly :lol: :lol: :lol:

GEdward
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Re: Discrepancy with preview vs reality

Post by GEdward »

Yes I measured the paper shim AFTER I saw the results and it conforms with the standard I assumed. I zeroed from the pocket plane. The cabinet door is a pre-made pre-finished sample dated Aug 20, 2017 and the pocket is actually a separate panel captured in a tongue and groove frame all made of solid maple. Thanks for the thought though. It is always possible to overlook even the simplest of things.

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TReischl
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Re: Discrepancy with preview vs reality

Post by TReischl »

You said you V carved it.

Does your V Bit have a sharp point? A lot of V bits actually cut a flat on the bottom of the groove. Which would totally explain why your carving looks the way it does.
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highpockets
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Re: Discrepancy with preview vs reality

Post by highpockets »

Something else to consider. The geometry of the V-Bit may not be as advertised.
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GEdward
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Re: Discrepancy with preview vs reality

Post by GEdward »

It is supposed to be an engraving bit with 45 deg. angle and .2 mm flat. I am still using it on another project at the moment but when I take it out tomorrow I will take out my handy dandy magnifying glass ( my eyes aren't what they used to be ) and confirm that it does indeed have the appropriate geometry. Good thought though as I did not even question that possibility.

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highpockets
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Re: Discrepancy with preview vs reality

Post by highpockets »

You might also check out a post by Paul Z. Paul created a method for testing the true angle of a v-bit http://forum.vectric.com/viewtopic.php?f=3&t=2164
CNCnutz (Peter Passuello) created an instructional video based on Paul's information. https://www.cncnutz.com/2017/06/test-yo ... e-151.html

Just food for thought.
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highpockets
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Re: Discrepancy with preview vs reality

Post by highpockets »

Here's another thought.

When defining a v-bit tool the "included angle" is used.
When defining an engraving tool the "side angle" (half the include angle) is used.

Defining the tool geometry in the tool database would cause a difference between the Preview and Actual results.
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martin54
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Re: Discrepancy with preview vs reality

Post by martin54 »

Have you got this entered as a V bit or an engraving bit in the tool database?

As far as the software is concerned a V bit comes to a point, if you have this entered as a V bit then as Ted has already pointed out carving would look very much like yours does once carved but the preview would differ. :lol: :lol:

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Re: Discrepancy with preview vs reality

Post by Mobius »

It appears to me that the finished product matches your vectors, and so it cut as it should have?

In the preview, the detail is too small for the 'pixels' to accurately depict, and so it looks like it is fading away. You may be able to increase the resolution of the preview (At the top, under Toolpaths: Preview Simulation Quality), and/or make sure the size of the material in the program accurately matches the size of the stock you are using.
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Adrian
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Re: Discrepancy with preview vs reality

Post by Adrian »

It definitely isn't matching the preview. Look at the curve gaps on the letters. It's either the z is set too deep or the bit doesn't match what VCarve was programmed with as suggested by others.

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Re: Discrepancy with preview vs reality

Post by sharkcutup »

Questions:

Are you using Quick Engraving Toolpath or V-Carve/Engraving Toolpath with the Engraving 45 degree angled .2mm flat bit? From the images posted it looks to me like you used an Engraving bit with the V-Carve/Engraving Toolpath.

If you did use the above noted toolpath - What are your Cutting Depth settings, Start depth (D) Flat Depth (F)?

what I am seeing from the images posted and what some of the others may have noted is the actual carving seems to be cutting a bit deeper than what the preview shows.

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GEdward
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Re: Discrepancy with preview vs reality

Post by GEdward »

Thanks much to all of you for your thoughtful responses. The link Highpockets referenced for checking V bit angles will be useful and thanks for that. I sure do miss the days of having access to a complete machine shop with good measuring equipment like a B & L optical comparitor.

Since the piece to be machined was an assembly not originating from my machine I should have dialed the surface to check for flatness. However, the piece appears to be pretty high quality and flat, I assumed that it was flat. I placed the piece back into the machine and did what I should have done in the first place and dialed the surface. And behold, it is .032 higher throughout the center than it is near the edge where I zeroed the bit. So yes, the bit was cutting more than twice as deep as the programmed max cutting depth for that tool path.

The good news is that, once again, it is not the fault of VCarve; but then I already knew that. The bad news is that I had to re-learn a lesson the hard way.

Again, thanks all.

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highpockets
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Re: Discrepancy with preview vs reality

Post by highpockets »

Glad you figured out the problem. If you have more door panels to do you might look into GCode Ripper https://www.scorchworks.com/Gcoderipper ... ipper.html. You can use it to "map" the surface so the carving will follow the irregularities of the surface.
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