Another update… I spent a bunch of time over the holiday weekend trying to get the calibration working better. Couple things I discovered:
The measurements to Mark 5 are absolutely critical and very difficult to make. The problem is that Mark 5 has to be dead center, directly below Hole 0 (at 0,0). Since calibration requires a measurement from Hole 2 to Mark 5, I have to hang my level on a dowel inserted into Hole 0, get the bubble to level, and then because the level doesn’t have a center line mark, I have to take the average of the measurements from Hole 2 to the left edge and right edge. That’s 3-4 measurements that I have to make and each one has room for error. A plumb bob won’t work because the frame is tilted backwards. The reason this whole thing is significant is that using my painstakingly taken measurements, the lowest Error Magnitude I was able to reach was around 2.0 with some of the inner holes still having errors of over 3 mm (way significant). However, if I shifted the Mark 5 measurement for the outer holes a mere 1 mm to the left and the inner holes a mere 1 mm to the right, my Error Magnitude dropped to 1.0 and most holes were within 1 mm (way better). So having a good way of finding Mark 5 is important. I was thinking of getting an auto-adjusting laser level that will project a plumb vertical line to facilitate the Mark 5 measurement, however, because the frame is tilted back 15 degrees, I have to make sure I’m dead center in front of the thing, otherwise, the vertical line mark will be off… Another source of potential error.
My shed has settled unevenly. I suspected that was the case, but I didn’t realize how much until I measured about a 1-inch difference from the floor to the left motor mount and right motor mounts… The level I placed on top beam seems level, but maybe it’s not good enough. So I ordered an electronic water level since I have to do the leveling without help.
Though the calibration routine is designed to adjust for out of level, it appears that “top beam tilt” value fights against the difference in chain tolerance. As the top beam tilts, the right chain tolerance seems to increases to counteract the effect. Eventually I end up with a 20 mm difference in left motor and right motor Y coordinates, a left chain with a 0.0 chain tolerance, but a right chain with a 0.25 chain tolerance… These are brand new chains from the same spool. It’s hard to imagine there would be hardly any difference in chain tolerance between the two… and again, I don’t think my top beam is so far out of whack that there’s a 20 mm difference in heights.
So what I’ve done so far is to make the calibration routine (newcal-holes-alt0.py) a bit flexible so that you can calibrate to outer holes, inner holes, or both outer and inner. I can get “good” Error Magnitudes (<1.0) with calibrating to outer holes, to inner holes, but not to both simultaneously. I can only accomplish that if I adjust my measurements to Mark 5 as mentioned above.
And as I mentioned previously, just because I have a low Error Magnitude, doesn’t mean they produce good cuts. So my plan of attack is to eliminate as many variables as possible by leveling the frame this weekend, set chain tolerances to 0.0 for each, and do another set of cuts/measurements. If the frame is level, the chains are identical, then Mark 5 should really measure to be half the distance between the two bottom holes. If not, something is wrong.