Yes I agree. Like I did to confirm some of my findings you should test your method at extremes, anomalies will always be more visible that way.
In math yes, on a printer with a crooked Gantry no…
Correct, that gets to the nature of my point. This thread gets a little messy, but there are a couple observations I’ve been trying to express that are relevant (I’m sure these are things you may already be aware of)
- Regardless of what we might want/like M1005 skew comp to do - it doesnt do anything else than compensate for the physical angle the gantry sits at relative to the Y axis of the machine.
- The comp is only adjusting Y position relative to where the print head is in its X travel (there’s no axis scaling or coordinate rotation going on)
- This means that a square physically printed will most likely measure smaller in X than it will in Y (Becasue X travel is happening at an angle)
With that last point in mind, I’ve got another sketch to share that I think gets to the heart of what I’m trying to express about the difference in measuring method (measuring the “square” directly vs. measuring a Octagon and backfiguring the “square”). And the potential for error when the print isn’t at nominal dimensions.
Looking for a different way to visualize the error I started with a regular Octagon and the translated all the points up to a skewed version of shape as it would be physically printed, per the kinematics of the machine (all the X coordinates remain in the same place and only Y coordinates shift/move).
- In the example on the left I make the sides of the square equal length and everything works out. It retains the relationships you’d expect from an Octagon. Angles are 90 and diagonals of the square evenly bisect the sides of the octagon
- In the Example on the right I make the Y dimension of the skewed octagon (and thus the square too) slightly bigger and things get complicated. Angles stop being 90 and diagonals no longer evenly bisect the sides of the octagon.
Both skewed shapes are translated up from the normal shape the same way. The example on the right is just showing how things are more likely to be in the physical form.
I believe, how this relates to the method of doing the math, is that: Using the octagon to backfigure the square width doesn’t allow it to be anything other than a square. In physical form the measured diagonals are likely a going to be from a rectangle - so calculating the “squares” width and treating those diagonals like they came from a square (equal length sides) leads to an error.
Using the direct measurement of the square width for the math does allow for the possibility that the diagonal measurements were actually from a rectangle and still calculates accurately.
I understand the idea behind your efforts is ease of use and reducing error - but I really think that the foundation of the math should be bulletproof even if the difference in the error this makes is small, let the error come from the measurement rather than the math.
People can learn to use calipers correctly and measuring accurately with them isn’t hard once you spend some time and learn how, it’s just a skill that takes some practice and coaching (thumbwheels aren’t evil, and you learn to never put more pressure on those than you do up on the thumb rest - your thumb should be able to slide over both of them with a little drag when the caliper jaw stops). The people who use calipers are invested in getting an accurate print, and those who aren’t won’t bother in the first place, which is fine too.
EDIT: Sorry for deleted post below, was trying to redo with direct reply and then deleted wrong one (now can’t repost again to correct because its “too similar”)
