Alignment issue resurfaces

[Stickman]

An old nemesis has reared its ugly head again. I do two-sided symmetrical work (training knives and swords for martial arts). For years I used VCarve Pro and then Aspire to align, copy and flip parts to accomplish this, but some programs didn't seem to align quite right. I thought the new two-sided update to Aspire would help me spot and resolve any issues, but so far that's eluded me. The setup is a 10x4x.5 piece of material. There are mounting holes precisely located in a rectangle, and the same drill pattern aligns the material block on the table wasteboard, so when I flip the material (I flip the x-axis) there should be no deviation of centered alignment relative to the mounting screws. I engrave and bevel the top, then flip the material, run a couple of processes, and profile cut the shape from that bottom side. So why does the first (top) side seem to be about 5° off alignment every time? When looking at the bevels it's quite apparent something is off.

Symmetrical look at both sides' toolpaths

Here I've copied one side to the other and flipped the designs around the job center. They look aligned to me!

[phill05]

Have you tried XY datum position in centre instead of lower left.

Phill

[LittleGreyMan]

If I understand correctly, everything is OK in the software but the actual cut is not?

Is that right?

[martin54]

If everything seems to be alright in the software then have you checked the calibration of your machine ? First thing I would check is the calibration of your x & Y axis, check for any sort of binding or a slipping coupling on the problem axis as well

[garylmast]

Have you tried XY datum position in centre instead of lower left

I always set the XY datum position in the center, then I don't have to be concerned about the mounting holes. This is especially true if my material is slightly larger or smaller than what I put in the job size setup.

Gary

[Stickman]

My machine self-aligns with positioning sensors, and I have preset table mount locations in Mach 3 for different projects, so my positioning in the lower left corner is always going to take me to those presets to set up the material. As for the symmetry of the mounting screws (I screw into an MDF table), that's so that when I flip the material over, it eliminates (or at least minimizes) any variable in the mounted position, and as the holes in the table and material to be machined are drilled with the same program, everything should be aligned with the machine coordinates.

Now this has been a bit of an issue for years, and I'll admit some have been mistakes in setting up the material (like wearing out a set of holes and re-drilling too close, so I use the wrong set on the turn-over), but the fact that I've tightened up my procedures over the years and this persists confounds me. Now recently I had to install Mach 3 in a newer Windows 10 laptop, after the Win7 that Microsoft "upgraded" to 10 didn't like an update and refused to boot, going into an endless cycle of "Automatic Repair" and reboot. (Microsoft gave me about 5 hours of free phone time, eventually giving me a fresh "final version" replacement and license of Win7, but then Mach 3 wouldn't start so I ended up reformatting the disk ... another story). Anyway, there were bugs with my old configuration in the new (updated) Mach 3 setup which required getting tech support from Legacy (they've always been very good about that with me, and this for a 10 year old machine!) so everything seems to be functioning as always ... including this offset when I flip the material.

So yes, the programming you see in those jpg files I uploaded do appear to be correctly aligned, and the 3D model generated in the toolpath previews does not show any offset (that I can see) in the angle between sides. Now generally the error is small enough I can "fix" it in the sanding/polishing phases, but I can see the flaws, it's extra work, and they shouldn't be there. I'm just not sure where the problem lies at this point. To be fair, the problem is probably SOE (Stupid ... I mean Simple .... Operator Error), but how the heck should flipping the material with the same mount holes cause a misalignment? That does seem the most likely source of error.

[Stickman]

Here are Aspire previews of the top and bottom of this project, which appear to be accurately programmed. It's hard to see in a photo (my material is black) but those grind lines definitely do not meet at the point, which makes for some "interesting" blade geometries! BTW, anyone know how to change that background color in the preview images?

Preview of top side

Kerambit preview bottom

[adze_cnc]

If it looks good in the software preview then I'd say the problems lies elsewhere and continued focus on Aspire is a bit counterproductive.

Can you be 100% sure that screwing into MDF is keeping you material aligned? Is your machine square?

Running the attached square test without material and setting your machine to let it cut a few thousandths into your spoilboard will allow you to do corner-to-corner diagonal measurments (just like squaring up a cabinet carcase).

square test.crv

(21 KiB) Downloaded 152 times

[mtylerfl]

Here are Aspire previews of the top and bottom of this project, which appear to be accurately programmed. It's hard to see in a photo (my material is black) but those grind lines definitely do not meet at the point, which makes for some "interesting" blade geometries! BTW, anyone know how to change that background color in the preview images?

Not sure about your alignment issue, but I strongly doubt it's anything to do with the software. Maybe use dowels for accurate alignment instead of screws - the screws might be "wandering" a little, especially going into MDF.

As far as changing the background colors, it's mentioned in your software manual under Program Options, but I made a screenshot for you to illustrate (access via Edit Menu>Options>Program Options>3D View Settings). Select the line you want to change, then click on the three little dots to open the color choices box. (see screenshot)

Works for Background Color as well as Gradient Background Color. If you want a solid color, you can enter the same color values for both lines. (or turn off "Use Shaded Background" when in the 3D window - the main background color will then be used without the gradient color)

[Stickman]

I doubt it's software as well. Here are two photos of the offset in the actual machining. It's not just that the misalignment is towards Y+, but that there seems to be a slight clockwise rotational skewing in the alignment (remember this is machined from the second side, but these photos are of the top design, so direction of skew would be backwards from looking at this as a single side). How this works with symmetrically aligned mounting holes eludes me, whether set with screws or dowels! Those screws are locked down tight in the MDF, and I do have t-track fixtures to help when necessary, especially on longer pieces. Regardless, there is zero movement in the material.

[mtylerfl]

Perhaps a stupid question...so apologies in advance.

Did you recalculate all Toolpaths, just to be sure they are current with the arrangement of your aligned parts? The photos give the impression the toolpaths aren't lined up. But, if you are certain your alignment method is accurate and doesn't allow material movement, the only other thing I can think of is a toolpath re-calc to be sure the toolpaths match your final layout.

[Stickman]

Regarding machine alignment and screwing into MDF. I'll take that last one first. Again, the are holes drilled in 3/4" MDF with the exact same program used to drill the material, so those should line up. The MDF holes aren't going to move, and the material so attached has no movement whatsoever. I can hold it and shake the entire machine and it won't loosen. Now if the material is absolutely fastened down (and again, I sometimes use t-track fixtures to assist, but those holes don't move, regardless) why would there consistently be the same kind of backside offset? I have similar issues on dozens of designs, always seems the same thing. Unless the machine is cutting at a different angle from one side to the other, and again, the MDF holes are aligned by the machine, how could XY alignment cause that skew? I'm asking in all honesty, because somewhere there has to be one small variable throwing a wrench in the work.

[mtylerfl]

I don't know. You mentioned this has been an ongoing problem for years. Something is amiss, and maybe others will have some suggestions.

Personally, I have never had any issues with alignment front-to-back on two-sided projects. That's another reason I'm not much help. We learn from our mistakes and/or learn from troubleshooting mechanical issues. Sorry to say, I guess I haven't learned much, since I've not had alignment issues that needed troubleshooting, nor software issues in regard to two-sided carves (knock on wood).

[LittleGreyMan]

If your cut is clean and your issue is reproductible, I'd bet your machine is not square of 2.5°. When you flip your job, you double the error and get the 5° misalignment.

I'm not sure if you use dowels or screws to align your material. Use dowels for alignment and screws for holding. Don't rely on screws for alignment.

[martin54]

Have you actually checked the calibration of the machine in mach3 ? If you tell it to move an inch then does it actually move an inch ? Your positioning sensors as you can them are probably limit switches which are used to home the machine. If your using mach3 then this would be machine co-ordinates 0,0,0. Normally set to the bottom left corner of the machine table.
Not familiar with your machine so don't know how the axis are driven or squared but worth checking your gantry is square as adze_cnc has already mentioned. How you do that will dependant on the number of stepper motors on the axis, you may have one central stepper or 2 steppers one driven & the other as a slave.