CNCShark HD3 Randomly digs into wood - HELP!

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CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Mon May 08, 2017 1:48 pm

Hello All,
We are trying to successfully carve a 2'x2' sign.
However, there are a few passes that are digging too far into the wood.
Please advise...

The specs are:
Router = Dewalt
Cut depth = 0.25
Bit = 1/4" end mill
Speed = 150
Passes = 1 (single)
Cut type = raster
Wood = Cherry

P1020495.JPG


P1020497.JPG


P1020493.JPG
Mark
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby SteveM » Mon May 08, 2017 1:59 pm

Just a suggestion! I am not an expert.
If this is the first tome this has done this, check to make sure your bit is tight in the router. If that isn't the problem, I would take a close look at your file and see if there is a stray vector or two that aren't supposed to be there. Usually when I have those problems, it's mostly something I missed in creating the file with Vectric.
Try zooming in real close to see if you have stray vectors.
You could also post your file, either here or in the Vectric forum, so others can have a look and help you out.
Try checking the Vectric forum if that is the software you're using.
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Mon May 08, 2017 2:37 pm

Thanks, Steve

I am pretty sure it is not vector/software related. (I checked as you recommended)

It may be a limitation of the CNC Shark HD3.

Someone recommended splitting the clearance tool path into two or more passes.

I will try this first, and go from there.

As far as the bit, it appears to be pretty tight.
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby Bob » Mon May 08, 2017 6:26 pm

Mark,
I have to ask...Were you, by any chance leaning on the gantry during the cut, to check on progress. This can produce gouges similar to what you are experiencing.
Guess how I know...
Bob
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Mon May 08, 2017 8:29 pm

Hello Bob,
My CNC is in the corner of the shop, and I am unable to really get close enough to lean on it.
All I do is lift the clear plastic shroud that is enclosing the CNC in order to take a peek.

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

Postby Rando » Mon May 08, 2017 9:38 pm

Mark:

Conjecture here, but as the material is being cut down (before it makes the ugly marks), what is the thickness of the wood? What was the starting and ending thicknesses in the "field"? The reason I ask is because of the varying heights of those wayward cuts. If it was a data or processing error, I'd expect them to be the same depth. But, if it's a form of non-uniform material deformation....

I'm wondering if, as the material got cut thinner and thinner, maybe the natural warp of the wood become stronger, resulting in the wood effectively coming up from the surface of the spoil board, but only in the area where the material was being removed the most. If you pull the piece off the bed, and put a straightedge along the backside, is there bowing in the area?

I know that in aluminum, I have to be careful of cutting thin walls too quickly, as the heat can warp the material. And, I know that wood can have internal stresses that act differently when it's a thin board versus a thick one, and that the wood can definitely heat up from the cutting. I'd suppose it doesn't take a lot of heat to warm the residual sap/moisture and swell/warp the wood.

The other thing I'm noticing is that the wayward cuts don't have burrs...I wonder if that's because it was moving at the rapids rate (say, between areas), versus the pocketing cut, which you'd expect to not be a long straight line. Might want to check the safe-heights and make sure one isn't set to like 0.020" instead of maybe 0.200"? If that were true, and you had the warp bowing the wood upward off the bed, I could see that leading to what you're seeing. Another clue might be that those inter-section runs are always AFTER some section of the pocket is finished, as it moves to the next ramp/plunge-point. So, if it was progressive warping as the cut gets deeper, that's the kind of thing you'd see: wayward cuts as the end of some wood removal is complete, as the cutter moves to another section.

If that turns out to be true, it might be appropriate to only cut, say, 25-30% of the large-area thickness. Then if you need the whole board thinner, plane off the backside? Either way, going from 100% to < 20% thickness, across a significant portion of the part, I'd think, is very likely to result in warping when cutting that biological stuff ;-).

Might this be part of it? Please, I'm just conjecturing...even I only give that idea maybe 30% certainty :D.

Puzzling oddity!

Regards,

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

Postby Rando » Mon May 08, 2017 10:09 pm

Mark:

Okay, so here's an even stranger thought: are these wayward cuts present when the cut is all finished? I have sometimes noticed that their inter-section moves do cut into the material in a most heinous fashion. But, in every case I've witnessed it, the next depth pass made it go away, and the pocket bottoms were fine in the end. For me, it was the sound the spindle made, doing a full slot cut at the speed of the pocketing cut (bad!).

So, did the cut finish completely and as expected?

( Sorry, just throwing ideas out there :D )

Regards,

Thom
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A proud member of the Pacific Northwest CNC Club (now on Facebook)
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby sharkcutup » Tue May 09, 2017 9:04 am

It is very likely that these marks can be caused by movement of stresses being relieved within the wood itself especially if the wood is still green (not completely dry). I have seen this movement occur while a carving was taking place in a wide (22.5") long (48") board. With pockets of large areas not very much you can do to avoid this from occurring but in my situation I applied some double back tape to the board to hold it down to the spoil board along with some screws in areas which were not being carved. It helped alleviate some of this board/material movement from occurring.

Just a thought I wanted to share!!!

Good Luck in Solving your problem situation!

Have a GREAT DAY!!! :D

Be SAFE around those AWESOME machines!!! ;)

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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby xoneeleven » Tue May 09, 2017 10:09 am

Hello Thom & Sharkcutup,
The thickness of the wood is roughly .75in.
The boards are very smooth, and pretty straight.
I generally hold them down tight while cutting, to ensure no stress relief bending occurs.

So, we just tried to make two more signs using the same design, but with slightly different tool settings on each design. (this was done because of the slight differences in width of each round board)

Anyway...
All three signs have the same issues in the exact same locations.
We have had this machine for almost a year, and this is our first attempt yo cut a 2'x2' sign. So, this is the first time we have noticed the issue, as a major problem.

I took some 4k video of the examples and plan on posting an HD encoded video to YouTube.
Next, I will open a ticket with Rockler (or Next Wave Automation) [Which one provides better support?]
During this video recording, I noticed that the Y axis bearing was wobbling on the left half of the screw.

I have looked closely at the design, and have found no issues at a software level, but I am no expert on design troubleshooting.

NOTE: These boards cost me $50.00 each to have made locally. These issues are not coming cheap!
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Re: CNCShark HD3 Randomly digs into wood - HELP!

Postby SteveM » Tue May 09, 2017 11:23 am

I would try making 2 passes at 1/8" each and possibly slow down the speed to 100 ipm or less.
150 ipm and only 1 pass at full depth in Cherry, seems quite aggressive to me.
The HD4 I had would not cut that fast and that deep in a single pass, without the router bouncing all over the place

At $50 a blank, see if you can flip the piece over and try slowing it down, just to see what happens. The piece is already shot, unless you can sand the ridges out, so you have nothing to loose except for some time.

Just my opinion, but it seems everyone has already suggested the other possibilities of why you're having problems.
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