CNCShark HD3 Randomly digs into wood - HELP!

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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby Rando » Wed May 10, 2017 8:50 am

It almost sounds as if it's having an issue with a flat-bottomed v-bit, where the toolpath imagines it goes to a point. Does your v-bit have a true, sharp point on the end? Or is it a wood-carving bit with carbide cutting surfaces welded onto a steel body, that has a flat tip. Those are normally chamferring bits, not true v-bits, which are expected to reach a true point. After all, you can't get a true V carved with a real point in the bottom of the V, if the bottom of the bit is in fact flat. Okay, maybe a picture will help?

Flat-tipped VBit.jpg


When there's a flat-bottom v-bit being used, and the toolpath wants a cut at a certain XY location, it calculates the Z ordinate based on its understanding of where the cutting faces are with respect to the very tip of the bit. That is, it assumes the cutting at a particular Z ordinate goes all the way to the center of the bit. But, when there's an "undeclared" flat spot on the tip of the v-bit, the touchoff tells it that the flat end of the bit is that point, and so the actual cutting edge is "lower" than what the software thinks it is.

Try this: instead of a v-bit for the failing cuts, try creating that exact same tool, but as an engraving bit. Specify the diameter of the v-bit's flat spot as the TIP diameter of the engraving bit. Remember that, like with the v-bit, the Diameter parameter is NOT the shank, but the OVERALL DIAMETER of the cutting edges. If, as I suspect, your v-bit doesn't actually reach a true point, measure that tip diameter, and enter that in the engraving bit.

As you start the run in the part that is failing, if you notice it's not doing it right, STOP THE MACHINE. If you can tell it's not running right, DO NOT let it run to completion. Why? Because the "bad" cuts are removing too much material, which means that if you re-ran a correct cut on that same part, it wouldn't touch anything, so you can't tell if it's right without redoing the entire thing. Stop wasting your wood. The moment you see it not cutting correctly, stop the bad cut. Then just re-run that one toolpath as you adjust it, letting it get a little farther with each adjustment. But again, only so much farther that you can tell whether it's working properly. That way you can use the same failed part to test a whole bunch of ways to fix it. Makes the whole debugging process faster as well. And, slow the machine down so you can watch it carefully. Pause the cut when it's doing a bad thing and check what the system says the Z is. See if that value really makes sense (yes, requires math with the V-bit). Being a very careful and close observer (eye and hearing protection required!) will get you to a solution faster than running it "for reals".

Also, the amount of current used to sense the touchoff is on the order of 2-3 milliAmp. The likelihood that it's a "conductance" issue and gives you that much incorrect depth is essentially zero. You'd only see that if the v-bit visibly pressed itself into the touchplate, which would definitely leave a mark.

Getting closer...maybe

Regards,

Thom
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Wed May 10, 2017 10:26 am

Hello Thom,

Here are a couple pics of the Amana 1/4in v-bit we have been using.
It is an Amana #45705

As you can see, there is a split in the tip of the bit.

P1020524.JPG


P1020523.JPG
Last edited by xoneeleven on Wed May 10, 2017 10:30 am, edited 1 time in total.
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby sharkcutup » Wed May 10, 2017 10:30 am

Paw.jpg
Note: Actual cut/carved condition is raised lettering in pocket

Is this the type of transition between lettering and pocket that you are looking for? Cut with 60 degree v-bit Amana 45705 in premium Pine board!!!

Sharkcutup

P.S. The above photo is really awesome because when it was in my cell phone it would show up in two different ways (lettering up with pocket and the reverse of that) when you looked at it. Tricks the brain!!! Most of the time though when I looked at it it was the reversed attitude (lettering as pocket with everything else raised). Really strange!!!
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby Rando » Wed May 10, 2017 10:54 am

xoneeleven wrote:Hello Thom,

Here are a couple pics of the Amana 1/4in v-bit we have been using.
It is an Amana #45705

As you can see, there is a split in the tip of the bit.

P1020524.JPG


P1020523.JPG


Thanks for the photos. It certainly LOOKS like the right kind. If you just barely touch your bit to the top surface with the router/spindle spinning, is it an actual point? Or a circle the thickness of the carbide weld-ons? Any chance one or both of the points is chipped? They look maybe okay from the photos, but having it in hand with a magnifier is the only way to be sure :D.

And, that is NOT a quarter-inch bit. It has a 1/4" SHANK. It's a 1/2" overall diameter bit, at least according to Tools Today's page:

https://www.toolstoday.com/p-4926.aspx? ... ords=45705

I mentioned that tool-diameter definition discrepancy a few posts back ;-).

Thom
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Sun May 14, 2017 4:53 pm

OK....
So, I re-examined the vectric design, and ran more tests.
I did find that the v-bit was out of spec (user overlook), and fixed it.
Additionally, I made feed/speed changes.

According to someone on another forum, they noted that the long cuts that were deeper than the rest, might be an invisible frame around the text, and to vectorize the text and try again.
I have made the changes, and am currently running a job to test this theory.

Additionally, I changed out the 60-deg v-bit to a 90-deg bit. Two passes going slow worked well on the large letters and edge of the circle.

In order to not waste so much wood, I just created a couple new tool paths to clean out there the sentences were raised, and just cut recessed letters. It also looked good, but we have also revised the raised lettering portion to be more stable during cuts (shallower).

Here is a pic of the revised cuts (the invisible frame still exists on this piece).

I am so greatful to you gentlemen for the advice. We live in north Idaho against the Canadian border. CNC clubs and mentors are non-existant here.

1NIK_2634rs.jpg


1NIK_2628_crrs.jpg
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Sun May 14, 2017 6:17 pm

Well....
The test on MDF is showing the same issues, where the passes around the large letters dig straight grooves (like shallow flutes) about 1/64in deep.

So, vectoring the letters did not fix the issue as suggested in another forum.
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby Rando » Sun May 14, 2017 7:59 pm

xoneeleven wrote:Well....
The test on MDF is showing the same issues, where the passes around the large letters dig straight grooves (like shallow flutes) about 1/64in deep.

So, vectoring the letters did not fix the issue as suggested in another forum.


The results are looking a lot better!

In the just-posted photo, are the very faint horizontal lines the flutes you're mentioning in this post? If yes, does this occur in a separately named/defined toolpath? If yes, my I recommend my application, GCodeShim. You can apply that to a toolpath to nudge it along any axis, and a variety of other things. In this case, you'd run the command:

gcodeshim.exe -offset Z0.01625 -- toolpathname.tap

You can learn all what it does with the -help command; it's actually pretty crazy powerful...IMHO ;)

GCodeShim is a tool of last resort that I sometimes find a lot easier than fixing some unexplained behavior.

viewtopic.php?f=4&t=5308

Other than that, it certainly LOOKS like it's a safe-height issue for that toolpath, where it things there's no material at that height, so it doesn't need to get over the top in that area.

Glad to see some solid progress :D.

Regards,

Thom
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Sun May 14, 2017 11:19 pm

Thanks Thom,
I will look into your tool, as well.

So, What I did, in order to verify if it was a machine or software issue is this:
1: Turned the entire design in VCarvePro 90 degrees. I wanted to see if the same lines appeared on the X-axis as it did on the other boards, or, if the lines appear on the Y-axis and the same location on the design.
2: Ran the exact same pocket tool path with the design turned 90 degrees
3: The same grooves appeared on the X-axis, as they did on the previous attempts.
4: The grooves were NOT at the same location on the design. All previous attempts were at the same location. However, since I turned the design 90 degrees, and the grooves do not appear at the same location on the board, then it cannot be a Vectric related issue.

So, I verified it to not be a Vectric issue, and suspect it to be a machine related issue.
I am wondering if it could be the CNC Shark control software, or, if it is hardware related, What is it??????

See the photo of the new MDF board with the design turned on its side.

grooves in MDF w design turned 90deg.jpg
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby Rando » Sun May 14, 2017 11:54 pm

Sigh....

Okay, this is getting ridiculous. There are not that many variables in this that it can't be found.

If you can, please provide answers to all the following questions:

Post your .crv and tap files that produced that picture? GET RID of anything in those files that isn't directly associated with this problem. Remove the ring of text, and those associated toolpaths.

Which specifc toolpath does this occur in?

At what lines? Can you even determine that? Are you using the pendant or the PC-based control panel software?

Are moves in that direction, of that length, an EXPECTED part of that toolpath at the time the bad cuts are made?

Does this problem occur in an otherwise normal bottom-flattening?

Or, is this some part of a toolpath that's really trying to make a rapid-move?

Are you using virtual-Z?

By now you should be able to say EXACTLY where those cuts are occurring in the course of these cuts. Yes, the GCODE might appear normal, but that's not the point. Which, SPECIFIC lines of GCODE are producing those bad cuts?

I have a working conjecture, but not knowing exactly where this is happening and when means we're just shooting wildly in the dark.

Thom
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby sharkcutup » Mon May 15, 2017 6:53 am

Great to see that you are making progress!

I have to ask this though "What is wrong with using a little elbow grease and sandpaper for those few tiny discrepant areas?" Yes, the machine does well is most areas and it should perform consistently throughout but in reality it doesn't.

These CNC Shark machines are not rigidly made (table flex, gantry flex, etc...) --- too much HDPE material used in their construction so I stopped wasting my time with all the minor discrepancies I had been getting. I do monitor this forum on a regular basis for similar discrepancies and if there is a solution to those similar discrepancies I will incorporate the solution into my designs/projects.

Again it is great that you are making tremendous progress with your project!!!

Have a GREAT DAY!!! :D

Be SAFE around those AWESOME machines!!! ;)

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