Mysterious groove after finishing pass? (Pictures)

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stephensonb
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Mysterious groove after finishing pass? (Pictures)

Post by stephensonb »

Hi fellow Aspire users,

Hoping to get some feedback on why my finishing passes are cutting grooves around my models (see pictures). Prior to the finish pass, I used a 0.0" Machining Allowance roughing pass for the material boundary - followed by a finishing pass with a .05" Boundary Offset on the selected vector I made around the model using a 5.4 Degree Tapered Angle Ball Tip with a 1/16 Diameter.

My suspicion is that the .05 offset is the culprit. If correct, I'm just disappointed that I can't simply clean up what the roughing pass leaves behind by using an offset without cutting these grooves. I'm including screenshots of the Aspire toolpath preview where you can see the groove-to-be faintly before the cut. However, once cut, the groove really deepens as you can see. Side note - My re-Z-zeroing? seems to be fine when I change tools after the roughing pass.

Hopefully the pictures and description will be enough to help theorize. Any and all help will be greatly appreciated. Thank you very much.
IMG_6716.jpg
IMG_6717.jpg
IMG_6718.jpg
IMG_6719.jpg
groove3.PNG
groove2.PNG
groove.PNG

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Leo
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Re: Mysterious groove after finishing pass? (Pictures)

Post by Leo »

Most likely your finishing cutter was set a tiny bit deeper than the other cutter.
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stephensonb
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Re: Mysterious groove after finishing pass? (Pictures)

Post by stephensonb »

Thanks, Leo. I thought so too but I’ve been following the touch plate instructions and resetting the new tool’s Z height accordingly. So I feel like I should rule that possibility out…

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Adrian
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Re: Mysterious groove after finishing pass? (Pictures)

Post by Adrian »

stephensonb wrote:
Tue Oct 19, 2021 4:15 pm
Prior to the finish pass, I used a 0.0" Machining Allowance roughing pass for the material boundary
Did you do two roughing passes or one? It sounds like you might have done two? Why use a 0" machining allowance rather than leaving material as would be usual?

stephensonb
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Re: Mysterious groove after finishing pass? (Pictures)

Post by stephensonb »

Thanks, Adrian. As far as I can tell, the groove problem isn’t related to the roughing toolpath. Regardless, the benefit of the 0.0” allowance was that I could get the desired height and surface flatness surrounding the model with the 0.25” flat bottom roughing bit. If I left even a small allowance, the small diameter finishing bit would need to travel across the entire work surface and cut to the final depth. So in terms of cutting time, the 0.0” allowance was way faster for my purposes. I think a pocket toolpath could’ve worked just as well

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Re: Mysterious groove after finishing pass? (Pictures)

Post by dealguy11 »

Since the preview did not show the groove, it is happening on the machine side. Almost certainly not a g-code problem. The touchplate routine may not be working as well as you think, or the material may have moved somehow, or something may not be as tight as it might, or steps could have been lost. Whatever it is, it's most likely mechanical/physical.
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Re: Mysterious groove after finishing pass? (Pictures)

Post by martin54 »

I'm including screenshots of the Aspire toolpath preview where you can see the groove-to-be faintly before the cut. However, once cut, the groove really deepens as you can see. Side note - My re-Z-zeroing? seems to be fine when I change tools after the roughing pass.

I don't think that is a groove you can see on the toolpath preview, easiest way to tell is to mouse over it & see if the z height indicates a groove or check the gcode to see what that shows for the z height for both the rough & finish cuts. :lol: :lol:

stephensonb
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Re: Mysterious groove after finishing pass? (Pictures)

Post by stephensonb »

Thanks, Dealguy and Martin,

Pardon the quality of the photos but here are shots showing the groove more distinctly along with a difference in Z heights displayed after mousing over/off the area as suggested by Martin...
-0.3885 vs. -0.3877

The finishing toolpath seems straightforward. Material boundary. TBN bit. But here are screenshots of it in case there's a clue somewhere - hopefully there's a clue somewhere. Thanks for all the theories so far and maybe there'll be a few more.

Appreciate all the help
IMG_6788.jpg
IMG_6789.jpg
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IMG_6791.jpg
Screenshot (6).png
Screenshot (7).png

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Adrian
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Re: Mysterious groove after finishing pass? (Pictures)

Post by Adrian »

You said in the first post that the bit was 5.4 degrees but the tool description in the screenshot says 3.6. You also say it's a 1/16" diameter bit but the 46286 bit is a 1/8" diameter bit (1/16 radius).

I know it's just text and the tool parameters maybe exactly as you said but it would be worth double checking that the tool you're using and the programmed tool are the same just in case something has slipped by.

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Re: Mysterious groove after finishing pass? (Pictures)

Post by scottp55 »

Are you Z-Zeroing from the same EXACT spot as before with Same spot on ZPlate??

On something like that with so much material removed(stress released), and new wood exposed to temp/humidity,the wood can Move quite a Lot, and with more strength than you'd think.

I've had best luck in these cases with Z-Zeroing to spoilboard
(and in my case, right next to a spoilboard bolt where it's most stable).

Relatively common problem...sometimes you just have to start Z-Zero a little high,
cut a few lines, and gradually cheat ZZero down to avoid witness marks.
(and best usually to cut all in one day if possible)

It really does look like a ZZero bit difference/wood movement type of thing.
Just my thoughts.
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stephensonb
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Re: Mysterious groove after finishing pass? (Pictures)

Post by stephensonb »

Thanks Adrian and Scott,

Adrian, the tool discrepancy was because I recalculated a new toolpath last night just to see if I could trigger the groove (witness mark?) and sure enough it showed right up. I encourage anyone to quickly preview a similar job and see for themselves the virtual groove. Maybe it’s the bit choice??
And Scott, the groove is showing in the preview itself, not just in the finished piece. I’ll think about gradually cheating up on zero though and also consider using the spoilboard as zero. I’ll check out “witness marks” too since I was unaware of that term.

However, this still wont solve the problem of the previewed groove. Still taking suggestions and I appreciate all the feedback so far

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Re: Mysterious groove after finishing pass? (Pictures)

Post by martin54 »

Might be worth sending Vectric support a message, the forum is mainly user to user & Vectric staff may not see every post that is made

support@vectric.com

Have you measured that groove in the workpiece? From the pictures it looks to be a lot more than the 8 thou that the toolpath simulation is indicating so you still have a problem with your actual process, be it your machine or your z zero setting :lol: :lol:

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Re: Mysterious groove after finishing pass? (Pictures)

Post by GEdward »

From the pictures it looks to be a lot more than the 8 thou that the toolpath simulation
.0008 not .008. But your point is correct; the reality looks worse than the simulation. I'm just guessing here but could it be that the program is compensating for the tool radius? That is to say that the tool is cutting the depth based on where the radius of the tool reaches the bottom of the 3D model as opposed to the tool tip. If that is the case then the groove around the 3D model should be about .015 deep.
Do you have the backlash compensation turned on? I use backlash compensation when I am doing 3D work. I turn it off otherwise because it raises heck when interpolating curves. But it does help to eliminate some of the saw tooth marks around the model.

Ed

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dealguy11
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Re: Mysterious groove after finishing pass? (Pictures)

Post by dealguy11 »

I tried to replicate what you were seeing.

I can replicate it if I set the machining allowance to 0 as you did for the roughing toolpath and use the roughing path to clear the flat area, but don't cut the flat area with the finishing tool. I tried it both with z-level roughing and with 3d raster roughing. With z-level roughing the groove will be deeper or shallower depending on the pass depth of the tool used for the roughing path since the final cut depth of the z-level roughing pass is driven by the pass depth, not the surface of the model. With 3d raster roughing, it still left .0008" uncut in my model, which is the source of the groove (i.e., I had the model set up to leave .125" under the model, and after roughing there was .1258" in the flat area). If you follow the roughing with a finish tool that cuts over the flat area (a waste of time), the groove goes away.

Having now agreed that I see the groove, this is not an issue I would ever run into because that's not how the roughing pass is intended to be used. I wouldn't try to use it to do the final cut on a flat area in the first place. I would cut the area around the model with a pocket toolpath, not a roughing pass. When I use a pocket toolpath to cut out the area around the model, there is no groove. Not only that, but it leaves a much crisper edge around the model when I use a 1/8" endmill for the final pass in the pocketing toolpath. You have a lot more options to control the cut and use different tools with a pocketing toolpath. I would only use the roughing toolpath to rough the 3d model, as it is intended to do.

Should the 3d raster roughing path leave that .0008"? I don't know, and it isn't important enough to me to report because there's a much better way to accomplish the same thing that doesn't leave a groove.
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Re: Mysterious groove after finishing pass? (Pictures)

Post by adze_cnc »

dealguy11 wrote:
Wed Oct 20, 2021 3:58 pm
Should the 3d raster roughing path leave that .0008"?
For that matter should we worry about an artefact that is 1/5 the thickness of a sheet of paper?

Depending on how the roughing toolpath is written I can see this as all being a result of floating point numbers as represented on computers having inherent flaws and this could just be a manifestation of that kind of error.

To quote myself from a previous post:
For example in Excel if you enter the following formula in a cell: =2.6 + 1.4 + 4.62 - 8.2 the result displays as: 0.420000000000002000 rather than the exact 0.42.
Or, because the material allowance is set to 0 the roughing toolpath might be assigning some very small number to something to avoid a divide by zero error.

I'm totally in agreement with using a pocket toolpath for clearing out such a large flat area. Let 2D toolpaths do what they do best and let 3D toolpaths handle the rest.

As for the artefacts on the actual cut: wood moves in mysterious ways...

Oh, and one more thing that no one's really commented on: don't let the tapered ball-end cutter come in contact with the flat area at all. It can't clean up the vertical sides as it is tapered so why bother rolling over the edge such that it contacts the surface?

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