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Holey Calibration Expectations

To get an accurate measurement for calibration stick a router bit of the same diameter that you used to do the calibration cut in one of the holes to provide a catch point for your tape measure and then measure to the close edge of the hole you are measuring to. After my first pass at the Holey calibration I entered the measurements and hit accept. The second pass was made and I entered the measurements again and hit accept. For my third pass I was expecting the numbers to reflect an improving accuracy but they were no better than earlier passes, was I not supposed to hit accept until I had made more passes? Have I merely done the Holey calibration 3 times or has the accuracy not been improved by additional passes? How do I tell if things are truly better?

I was the one who created the heart of the Holey Calibration. In my opinion, there should be no need to do the Calibration more that one time.

The only potential value in multiple iterations is if there are nonlinearities in the equations. At the scale of adjustments, a few millimeters, the equations are very linear.

Unless your starting point is waay off, one iteration should be sufficient.

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a good number of people have reported that more than one calibration improves
things. This could be due to inaccuracies in the measurements of the first one
or other similar errors.

if the measurements are very close to the same from one calibration to the next,
there is no benefit in doing more

one round gets you very close, then try cutting something and see if the result
is good enough for you.

David Lang

Thank you for the feedback, it makes sense. So like the worker 3 years on the job who has 1 year of experience 3 times I have merely done my calibration 3 times. Thanks again.

Erik , I concur with dlang. Multiple, succesive Holey calibration exercises seems to result in an improvement in calibration. More than than three seems excessive. Lately, my first calibration run is coming in at 1.25. By the time I finish my third I’m down to .028.

In your case, there was no improvement in your error but there was also no worsening of it. You may have found the balancing point between errors in your measurments and variables in your machine. My point is in theory you could drive your error to 0, however, you will reach a point where your error is just good enough.

One of the things I do is after I finish three calibration cycles is perform another two hole cutting routines. I wont measure anything but I will just observe how well the maslow can dupliocate the hole pattern. In my case, the maslow will drop holes nearly perfectly inside the previous ones.

PRO-TIP:

In between each calibration cycle, cover the previous holes with a small piece of bue painters tape. 3M seems to work well. It will leave you with a crisp clean hole to measure. I dont use the pin method that others use because I bias my Z to cut shallow holes. I just measure from the far edge ofthe first hole to the near edge of the other.

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precision vs accuracy

the maslow, no matter how badly calibrated is very precise (it repeats the cuts
very accurately), with the possible exception of the bottom corners if the sled
sticks

but the cuts are not where you want them to be (accuracy), which is where the
calibration routines come into play.

with a precise machine, you can get what you want, eventually, by modifying your
design to account for the errors you find in the cuts, but it’s accurate, but
not precise, the cuts will vary from run to run and you never know what you get.

so we are starting out in a good place.

David Lang

Right, so to test for both I tell my machine to cut a 10mm circle, 10mm square, and a 10mm triangle in all four corners and the middle of the workpiece. I have the machine begin the cuts at a set XY distance from center home and centered to home for the middle set. I can achieve 0.1mm on the start location of all the cuts in the corners and the center is effectively DNO. I have been getting .25mm on the dimensional tolerances for the shapes in the corners and .125mm for the shapes cut in the center. Not sure what others are getting so I don’t have anything to gauge it against. Then again, this is the11th version of Maslow I’ve built and it is not a standard machine by any stretch. My effective cutting area is only 1680 x 1110. Im also testing in MDF so I am dealing with fairly consistent material.

less than .25mm is doing very well.

David Lang

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