3D Printer Tolerance Vernier revision 3 by Dan_W_58

Last crawled date: 3 years ago

Revision 1.5 released July 1st 2018.
For status daily updates, scroll down to the Status section.
This is a tool to assess the dimensional accuracy of printed models.
It can measure tolerance range from negative 0.12 mm to positive 0.37 mm, with micron resolution. (Note that I did NOT say "micron ACCURACY"; --the term "resolution" refers to the finest subdivisions of the reading in a measurement. Absolute accuracy, as well as linearity jitters, are a whole different subject, and they'd depend on cleanliness of the print, on the quality of post-print sanding of blobs and "hairs", on the presence of dust on the tool when measuring, on the presence or absence of build bed shifts during printing causing visible lines, and specially on post-printing dimensional stability and/or warping of the material. PLA is notoriously warp-ish and shrink-ful, for example.)
It is not the printers' fault, usually, that prints turn out half a millimeter bigger, or whereabouts, than they were supposed to be; it is more often the slicer program that makes models slightly bigger in X and Y. The reason for this, I suspect, is that the slicer programmers don't want walls thinner and features smaller than the nozzle diameter to simply disappear altogether; --it would look bad on them even if it's technically correct. Besides, it is much easier for them to check for "collisions" of model surface polygons against a line (the center line of the extrusion), than it is for them to check for collisions against the whole cylindrical extrusion around that center line. I'd do the same in their shoes.
Simplify 3D offers you a parameter you can set to compensate this fattening of the prints; but it is up to you to measure the printing tolerance and put the right number in that compensation box. By default it is zero.
When this value is set, the slicer code reads your stl file and internally shrinks the model by the amount you set (in X and Y; --but not in Z); then computes the gcode. Keep in mind that when you do this, features smaller than your nozzle diameter will simply vanish from the printing!
For most models you probably don't need high accuracy; but if you have mechanical pieces that have to exactly fit into each other, then you definitely need to measure your printing tolerance and adjust the compensation. This Thing allows you to get a finer measurement than most printable tolerance test models can offer, and by a very long shot... down to microns; and it does so using only 2 parts, instead of an entire set.
There are many "Tolerance Test" printable models out there, but all the ones I have seen so far consist of multiple pegs and/or multiple holes, on a large base, to fit the peg(s) into.
I thought, "Wait a minute! A tolerance test tool could be made by having a slightly conical or piramidal long peg and a sliding "hole" piece, which has a mark on it, and you read the tolerance from markings along the peg. No?"
So, I was in the process of implementing just that thought, when it occurred to me that I could get an extra decimal of precision by adding vernier type markings on the sliding piece. Thus, this tool gives you resolution down to MICRONS !!!, if you know how to read a vernier... ;-)
Scroll down to the bottom of this page for a measurement reading example.