Different readings for the 3 different blocks?

I printed the 3 blocks with holes, as well as the long part with posts. The 3 different blocks fit on 3 different posts. How do I interpret these results? BTW, the picture turned upside-down. Sorry. So 0.23 is on the left, 0.25 is on the right. The block with the arrow pointing down fits on the 0.240 post, the one with the arrow pointing up fits on the 0.230 post, and the one with two holes fits on 0.234.

I printed on my Ultimaker Original+ with PLA, after slicing in Cura 2.5.0. No supports or raft. Layer height 0.1 mm.

Picture of Different readings for the 3 different blocks?
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JON-A-TRON7 months ago

That print looks really good. The whole point of this is to get a sense of the offset distances you'll need to use to get the right results. If you want two parts to be able to move freely when interfaced (like the hinge on the bottle lock from the next lesson), you'll want to pick an offset where you can feel the cubes moving freely on that post. If you want something that's press-fit and won't come apart once you put the pieces together, try a tighter offset that makes it difficult for the parts to come apart.

pillaleitner (author)  JON-A-TRON7 months ago
I do understand the purpose of the test assembly, but don't know what the difference between the 3female parts is, and which one I should use. You say they are for different settings on the designer's printer. Any idea which to use for 0.1 mm layers? Thanks for creating this lesson series, Jon, and especially for answering questions!
pillaleitner (author)  pillaleitner7 months ago

After studying John Edmark's Instructable on Ojet 3D Printer Fit Tests, I think I see. The arrow on each female piece points toward +Z when printing. So if I want to print a male and female piece with comfortable fit (not snap together fit), and want to print the two parts with the post and hole on top (+Z), I would use the block with the arrow pointing toward the hole. That has a 0.01" offset in dimensions so I would design the two parts with a 0.01" tolerance. So exciting to figure this out!

You got it! Excited to see what you come up with-

You might want to check out John Edmark's original instructable for the fit tests, it will explain in detail.


This model was made specifically for a DLP machine which is part of the reason there are three mortises, but it's still useful for FDM machines. The only one I use regularly is the mortise with two holes. The holes are on different sides of the block because there may be a difference in the way your machine / material handles layers made in the X, Y, and Z directions. This is probably overkill for most work, but it's a good tool if you want to get really precise.