Alignment issue resurfaces

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TReischl
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Model of CNC Machine: 8020 48X36X7 RP 2022 UCCNC Screenset
Location: Leland NC

Re: Alignment issue resurfaces

Post by TReischl »

What you did not mention is how you are setting the height of the bit.

When I am doing "fussy" work, I always touch the bit off on the first and second side. I do not rely on my trusty calipers. The best way to touch off tools is to use a touch plate. Not paper, not shim stock, not a piece of bubble gum, etc.

To get good results on a multi tool job I have a second touch plate that is used for all the tools after the first tool. It sounds all sorts of complicated but is actually very simple in reality. That second touch plate is fixed to the machine bed. If you need more information you might drop Ger21 a PM. He has an excellent screen set for Mach that does wonders for the machine and my sanity.
"If you see a good fight, get in it." Dr. Vernon Johns

Stickman
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Joined: Fri May 22, 2009 5:20 pm
Model of CNC Machine: Legacy Arty 58
Location: El Sobrante, California

Re: Alignment issue resurfaces

Post by Stickman »

Periodically I use a 1" flat surface bit to level and smooth the table. I did this a week ago, and the bit appeared to sit flat both before and after resurfacing.

Stickman
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Joined: Fri May 22, 2009 5:20 pm
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Re: Alignment issue resurfaces

Post by Stickman »

I keep coming back to wondering if this is a mechanical issue regarding direction of bit spin relative to direction of carriage travel.

I just ran a different project, this with a 12"x3" blank (x=12). I made sure the exact center of the mounting screws were in alignment with the x and y directions of carriage movement; the centers were dead-on. I double checked the pathways, that the settings were exactly the same on each and the combined fluting and profile pathways were centered in the material on both sides. I used the ruler in Aspire to determine that the starting point of each of the fluting pathways (2 on each side of the material block) measured exactly 5.6017" from the center of the closest mounting/alignment hole, and that those corner holes were also exactly centered in the material. I then ran 8 pieces and measured the machined deviation, one side to the other, from what the program showed as exactly aligned. The results were thus:
Every piece was aligned and cut straight along the x-axis. There was no skew or misalignment on the y-axis. However, each and every piece consistently showed the starting cut of the bevels to be .12" offset along the x-axis from one side relative to the other, the second (flipped) direction being -.12"x.

My cuts are done with a Sears 1-7/16" chamfer bit, wide with a relatively shallow 18° v-pattern. If it's the case that the direction of carriage travel affects how the bit bites into the material, I need to be able to calculate that amount of offset in Aspire, either by adjusting the end (or starting) point of the fluting paths on one side or the other, or perhaps the Z-axis feed rate needs to be slower to allow more time for the bit to dig in on that second side. This might be something that wouldn't be apparent with a smaller diameter bit, and wouldn't be relevant for single sided projects, but credit this to backlash, the coriolis effect or whatever, could the combination of the wide bit and travel be my missing factor?

Stickman
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Re: Alignment issue resurfaces

Post by Stickman »

Thanks for all the feedback. Right now I'm stymied, because my issue really seems confined to this one design! I've checked the alignment of the table, all my mounting points are in line with XY. It's not using pins instead of the flat top wood screws. I've done some 30 or so pieces in the last week, some much longer than the problem design, and those have mounting holes top and bottom dead center. I can attach and tighten the screws in any combination of corners and still see that screw hole in my waste board remaining dead center in those middle holes, and the same when I flip my material over. Whatever minor discrepancies I had in mechanical alignment were easily resolved, and I found a few programs that needed a bit of tweaking in the two-sided rendering that were not easily spotted in the 2D view, even when measuring point to point for comparison. Then there's my little program from hell. It looked very close when I looked at it today in the 3D, but when I zoomed in, I could see room for adjustment, specifically moving a couple of fluting pathways about .02". Now everything looks absolutely spot-on in Aspire! I even checked the alignment of the mounting screws before running the program, but when I ran the program, it's not even close. So here's the thing ... I can take the side that cuts the fluting and profile perfectly, check center alignment for both X and Y, copy it to the other side, flip it around the job center, and those pathways line up 100%.
Once again I have to wonder (and don't believe I got a response) if any of this could be the direction of spin vs. movement of the spindle. I know that cutting a pathway with this 1-7/16" chamfer bit, one side of the cut is always smoother than the other, and when directions are reversed on the opposite side, results are different from the first. Could it be that I'm running the bit too quickly on a small curve like this? I'm simply running out of ideas ....

Stickman
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Re: Alignment issue resurfaces

Post by Stickman »

Meh, turns out to be SOE (stupid operator error) after all. Even though the alignment holes appeared accurate, there was something amiss there. I set up new mounting points, now I'm in business for this design again, finally.

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