Thank you big time for this great work you are doing.
I missed such detailed data.
Blunt question, why are we cutting there the most accurate? (at least April 2017)
Because there are many factors that contribute to an accurate cut and we have the chain positional accuracy pretty well dialed in. Other factors that are better at the center include less drift due to the load being mostly on one chain. The math also was more accurate at the center, but this could be getting better now.
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This comment is also entirely wrong. I have deleted the chart to avoid propagating inaccurate statements, but left the rest of my wrong comment here.
old comment totally wrong, donât believe a word of it
I was thinking about this more and realized my conclusion about accuracy is probably wrong or at least a bit misplaced. This is the same chart selecting for the minimum value. This shows the chain movement necessary to cause a 50mm movement at that point.
As you can see, out at the edges it gets as low as 8mm (edit wow even ~3mm infact) of chain movement to cause a 50mm error. While the middle still hovers around ~35mm.
So my conclusion was completely wrong. The prior chart is a good means for determining where the machine can move the fastest, but this chart does a better job showing where positional errors have the greatest effect.
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I dunno, something still seems off about these numbers. The general chart seems right, but something strikes me as wrong about 3mm causing 50mm in error.
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Wouldnât that 3mm be cumulative to that point?
No, what I tried to do was take each of the points on the grid and do four calculations to determine the amount of chain movement:
- difference in the amount of chainA at start point and then Y-50mm
- difference in the amount of chainA at start point and then X-50mm
- difference in the amount of chainB at start point and then Y-50mm
- difference in the amount of chainB at start point and then X-50mm
Then depending on the graph, I took the min or max value. I was initially trying to determine where the sled can move the fastest based on our limited motor RPM.
Again, the appearance seems right to me, but something is off about those numbers at least in the second minimum case.
That doesnât sound right. The point where a small chain movement results in the
largest error is in the top center where the angles are shallow and the tension
the highest, at that point a small error in chain length can result in a large
vertical movement
rather than looking for what causes a 50mm error, plot how much error a 1mm
error in chain length will result in.
There is no way that a 3mm error in chain length will result in a 50mm error in
position anywhere on the sheet.
It does seem like at the side edges most of the error would come from the closest motor, and so be close to equal to the movement from there�
Has any one designed a layout cutting a 3 inch X in the 4 corners and the middle of a 4x8 sheet to test this?
Thank you
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@krkeegan Those charts are an excellent visualization! If I gather correctly, youâre saying 1400mm/min might be possible near the center of the machine with stock hardware? Itâs funny, because Iâm nervous about pushing that with the stock hardware, because I know funny things can happen when you push hardware to their limits.
I also know that the other issue that could arise from raising the feedrate is acceleration planning. With all the other awesome tasks youâre handling, the last thing Iâd want to throw into the mix is adding that to the firmware. When the time comes, I would gladly do some of the testing on my machine. Until then, I found that Fusion360 will handle that before post, so I will program it into my G-code.
Not that exact test, but I have detailed a pretty thorough bed accuracy test here. This test is actually still a HUGE priority of mine, as it will tell us much about both the machine and the linkage systems. It actually supersedes any feedrate tests. I need to finish cutting my test sled, and then I will be running them.
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In the usual moosely tangent this suggests a âhigh performanceâ mode for projects where youâre willing to trade accuracy for speed, or have a project where you use roughing and (slower but full depth) finishing passes, perhaps by limiting speed by max motor RPM.
It also suggests a phase II super Maslow with more powerful motors, lower gear ratio, and more PP motor R encoders, and an accompanying higher current motor driver. Ties nicely into a 32b faster clock processor too. Add me to the prospective upgrade kit wait list
My numbers are right, I am just reading them incorrectly. On the minimum chart, when it says 3mm in the lower left corner it is correct that the left chain only needs to move 3mm for a 50mm move to the right. However, moving the left chain 3mm by itself wonât achieve that result the right chain needs to move nearly 50mm as well.
So I am going to remove the minimum chart as misleading and correct some of my statements above.
Yes, but again I really canât stress enough how badly things mess up when the machine canât keep up. It isnât just a case of a few rounded corners. An inability to hit the desired feedrate causes a cumulative error. So longer cuts, particularly those in a single direction could be an inch or inches short. And so on.
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