I will reply to my own quote as a means of replying to all and getting it in a single message.
I'll begin by saying that I'm not American, I'm Canadian, and my country is officially bilingual linguistically. French and English are enshrined in law as equal, with all packaging, labelling, instructions and so forth required to be bilingual, all government services available in both languages, etc. We are also "bilingual" in terms of measurements, with metric being the preferred choice of units but imperial being perfectly acceptable as well. Admittedly, old folks have problems visualizing a mm, but youngsters have little idea what an inch is. The reality is that it doesn't matter; young or old, we have no real concept of a light-year or an angstrom, they are just units we deal with.
My problem is that I wish to have a better understanding of the 3D printing process at a LOW level. My Tevo Tarantula turns out quite acceptable parts BUT the first ones were just OK. So over time, I've updated the printer enormously to the point that there's very little left of the original. Of course I've stiffened it substantially, mounting it to a 1/2" thick solid aluminum base, ACCURATELY squaring and reinforcing all corners. I've gone with linear slides, servo motors and ball screws, external heating controllers and so forth.
But even so, there are anomalies in the parts produced that I don't quite understand, and I'd like to understand. To that end, I'd like to do away with the existing firmware running on Arduino boards and go with the same CNC software that runs all my subtractive machining devices (and does so perfectly. When I hear people talking about "missing steps", I just cringe.)
And I want to use the units I'm comfortable with, and experienced with, and in this day and age, that's not too big an ask, especially, as stated before, every other "engineering" like software package allows it.
Now, some of the problems are with the process itself. Cura, for example, supplies extrusion parameters to 5 degrees of precision. That's 100 angstroms! Really? We're asking that cheap Chinese stepper motor to slice to angstrom accuracy? There just aren't enough microsteps in the world to do that.
But others? I'm not so sure. Acceleration, maybe? Could too rapid a direction change (or too slow) affect accuracy? Do we need to adjust extruder temperature based on feed rate? (A directional change almost always results in some sort of speed change.)
Anyway, I'd like to find out.
Now, to respond to just a few of the posters who took the time to write ...
Brulti, let me ask you, do you drive a car? If so, what size are your tires? 16"? 17"?
And if, as you suggest, my country forces me to work in metric only, what about my existing machines? I have four lathes, two big and two very small, two CNC and two manual, two from Europe, two from the US. All have imperial leadscrews. I have three milling machines, one manual, one large CNC, one small CNC (that I use for routing printed circuit boards). All are imperial. Indeed, the PCB machine uses a 100,000 RPM spindle from Germany that takes 1/8" toolbits. Not 3 mm or 4 mm, 1/8".
What would you have me do with these otherwise perfectly functioning machines? Replace all the leadscrews? Of just replace the dials with some that don't stop on an even number?
ahoben, of course I would not describe my nozzle diameter as 0.015748", but neither would you describe yours as .0400000 mm. Six degrees of precision is ridiculous. 0.0158 is a more sensible number, but even that would be foolish as it's just not possible for any reasonable machining process to repeatably drill a hole accurate to a ten thousandths of an inch (or .00254 mm).
Just for fun, I used the good graces (and fancy equipment) of my former employer, a university, to examine a batch of "0.4mm" extruder nozzles. All varied in size, from .35 mm to .45 mm, with most falling between .37 and .43. Our guess was that the Chinese started with a small bit and just drilled and drilled and drilled until it broke, the bit getting duller and duller and therefore drilling larger and larger holes. Without having the means to measure the nozzle on my machine, I could reasonably use any value from .014 to .017 for a nozzle diameter and still be "in the ball park".
(It occurs to me just now to maybe do some testing with ".4 mm" nozzles that are actually a bit bigger and a bit smaller.)
And I HAVE seen a 3d printer based on Imperial units. It was an industrial device that cost half a million Euros, and for that money, you got to pick the units. (You got to pick everything!) That is, for every setting, there was a box to enter a value and a drop down list for the unit. So you could enter .4 and pick mm while I could enter .016 and pick inches; the machine didn't care. (Frankly, for the nozzle diameter setting, I'd probably pick the same as you, but for velocities, I would absolutely pick IPS .. inches per second.)
Yes, the inexpensive little devices we all use in our homes and small shops might be metric, but I bet if Prusa lived in the US and designed his printer there, imperial could well be the standard. Many times, things are the way they are because they started some way, it worked and we just kept on doing it that way.
These will likely be my last words on the subject and indeed my last words to this forum, as the general tone here is more confrontational than I'd hoped; there's other software and other forums.
Thanks to all who responded, online and off, in a positive manner.