3D printer test

New users moving first steps here.

I’m software engineer, with some basic experience of operating traditional (i.e. non-CNC) lathe, which I don’t have a the moment. Instead I have 2 3D printers (Anycubic Mega S) and I am interested in building a Primo (will take my time), potentially adding a 4th axis for both making it a CNC lathe (which I guess we can still call it 3-axis) and for making slightly more complicated parts without having to reposition them, which I think can be a pain.

In fact I have questions if Primo would support a 4th axis and what you would suggest for holding pieces in a way that’s easy to hold them, reposition them, and (most importantly) making sure that the tool does no hit the clamps! But I’m getting far ahead of myself, and I will take my (long) with with this, so no hurry. Instead, a question about this quote

If your 3D printer is of questionable quality it is best to run a quick basic frame test to make sure the parts will print as intended. If the test indicates that your frame is not square, then carefully check the frame and adjust, and retest.

What do you mean by “square” here? Of course it’s not square, there will always be a tolerance and if you have an accurate enough instrument you will measure that. In my case, the two sides of the large square and the diagonals of the small ones are between 14.5mm and 15mm: a caliper set at 15mm was able to “get” them all, some with a bit of wobble. I am pretty sure (but not 100% certain) that the most wobbly (one of the diagonals) was dialed in at 14.5mm – and at that setting the caliper could not get any of the others (certainly not the other diagonal, but not even the sides). I wanted to measure them with better, but while I was attempting to do so, they detached from the printer bed and now they are too floppy to measure.

So, advice: is that printer accurate enough? Yes, no, or print again to be sure?

Also, do I need the advanced frame test or something else to test the z? That test is big and I’d rather spare me the effort to run it if I can (or maybe I can scale it 50% in all dimensions? or 50% in x/y and leave it as is in z?)

Also, I noticed that some of the features of that test are round holes parallel to the bed. In my experience with this printer (and the settings I run it with, and the brand of PLA I use, and the plethora of details that make a 3D print different from another), these sort of holes come out “sagging”. Not that I printed many of them: I try to slice it in another position. But the ones that I did print it horizontally were not round (I compensated that a bit by making them ellipses in the CAD, so the sagging made them closer to round than otherwise). And to complete the information, the ones I printed in this position were at most 3mm in diameter, all the larger ones I printed either with support or horizontally. So will this be a problem?

print a small part and see how dimensionally accurate it is. The “squareness” indicator is the calilantern print measurement that allows you to caliper xy, xz, and yz to see if you have significant skew and it scores your printer. If you run a newer firmware, you can incorporate the skew and offset for it. This dimensional accuracy will only stop error from cascading from the printer to the printed part and hopefully with your build skills you can stop the printed parts from skewing the CNC and not let it run into to the CNC’d part produced. the drooping holes is something I had to deal with. That turned out to be more of a slicer issue. Are you using orcaslicer?

Thanks!

Isn’t that what this square test was already? Are you saying I should print a smaller cube instead?

Indeed I am! But I thought it was a widespread issue, since a friend using a Bambulab printer with its proprietary slicer has it almost identical…

I’d recomend the used of this for dimensional calibration:

Calilantern Calibration Tool – Vector 3D

I wasn’t meaning a cube, but the lantern. as mentioned in the video above.

That test is nothing compared to at least 3 of the parts you are about to print. Would you rather take a few hours now to make sure your printer is accurate, or find out you have wasted many hours and lots of filament later because you didn’t? Seems to me you would be much better off just running the test and knowing for sure.

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I know and I am not saying that I don’t want to print it.
To be clear: I still am not sure if the test that I did print is a pass or fail. What sort of accuracy do I need? Is half a mm (which I achieved) good enough? If that’s for just making the holes of the screws/bolt align, I assume it is. If that’s for making sure the pipes/rails align correctly with small friction but not looseness/wobbling, than 0.5mm is definitely too much and I would need at least 0.1mm accuracy if not better.

So is what I did print a pass/fail (or marginal)? If it’s a fail, it’s moot point to print something more stringent.

Thanks. I’ll take a look (but then why it’s not on the instructions…)

Dimensional accuracy is only part of it. The main thing you will get from the calilantern is skew. That is how you know when you print your core that it prints straight and square. You are never going to measure skew correction from a cube.

Is half a mm (which I achieved) good enough?

If you mean you are at + or - 0.5mm then that’s probably good enough.
If you mean you are at + or - 0.25mm then that’s definitely good enough.

The truth of the matter is most people won’t actually know as they don’t have the equipment to measure it properly, which goes beyond just having a set of vernier calipers.
Which is one of the reasons it’s difficult to get responses on this type of subject.

The lantern comes with a spreadsheet as far as I know. Putting in all the values there and posting the results might be easier than to guess.

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A key question about how close is good enough, is “over how much distance?” As explained in the video linked above, being off by .25mm over only a 20 mm distance (small cube), is a variance of 0.0125. But on a part that is 165 mm tall, that 0.0125 means screw holes near the edges will be out of alignment by over 2mm on at least one side. So measuring against a larger lest model is helpful. The Calilantern model is not only larger, it’s larger in ways that allow measuring that compensates for over-extrusion and under-extrusion (and for elephant’s foot), and that allow for measuring not only dimensional accuracy in X, Y, and Z, but also for measuring for skew problems. I seldom buy a 3D model, but I bought that one, and it was well worth the price. The accompanying spreadsheet is an active calculator document that not only scores the printer but also spits out exact code for correction in a variety of firmwares, with clear instructions for how to apply the code.

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Thanks everyone for the explanations.

I’m trying to wrap my head on what you all have written, which of course makes sense in theory, but then it needs to become something practical, over the distances of the test I ran and over the distances of the parts for Primo (which is all I care here, in case it wasn’t clear, I’m not asking if my printer is good enough to print replacement parts for a high-end SLR shutter!).
To me what you guys have written here somewhat contradicts the instructions at MPCNC Primo Parts list - V1 Engineering Documentation which I quoted at the beginning of this thread.
I’ll think hard to resolve this conundrum and decide if it’s me being completely dumb (most likely), you overkilling/overengineering or Ryan being overoptimistic or dismissive in his documentation (least likely).