Continued musings about building a large-format 3D printer …
(Continued from yesterday)
taking your challenge and am starting by cloning the M2
That gives you an existence theorem: you know exactly what you want to end up with.
AFAICT, few of the M2’s parts bear standardized numbers you can simply order from a reputable seller. Makergear knows what it’s buying (obviously!), but they’re under no obligation to help out: you must reverse engineer the requirements, find a suitable part, find a supplier, then buy one item.
Let me know how that works out for cost & performance; “cost” should include a nonzero value for your time and “performance” should have numbers you can verify. I (obviously) think the build will be a dead loss on both counts (*), but good data will be interesting.
(*) Albeit useful for educational purposes, which I’ve used to justify many absurd projectst!
How the heck do you read out the current (estimated, obviously) X Y Z position absolute to the machine coordinates?
Perhaps M114 or M117?
My overall list may be helpful, although the RepRap Marlin reference has more detail on their command set:
https://softsolder.com/2013/03/14/g-code-and-m-code-grand-master-list/
The LinuxCNC (and, perhaps, Machinekit) G-Code languages give you access to built-in variables and extend G-Code into a true scripting language. Marlin evolved differently and doesn’t support that sort of thing.
G-Code is pretty much a write-only language, but you can do some interesting things:
https://softsolder.com/2013/07/18/makergear-m2-cnc-platform-corner-clips/
I use the gcmc compiler whenever I can for actual CNC machining:
https://softsolder.com/2014/02/21/can-opener-gear-rebuild/
Works for me, anyhow, although I don’t do much CNC these days.
move my nozzle up .01 at a time
Stiction / microstep errors / command resolution prevent that:
https://softsolder.com/2014/03/06/makergear-m2-z-axis-backlash-numbers/
The only way to measure the nozzle position is to measure a finished part with a known height, because any variation comes from the first layer offset. That’s if you have Z=0 at the platform, of course, rather than whatever offset you get by defining Z=0 at some random height based on jamming business cards / feeler gages / special Japanese rolling papers under the snout. [ptui & similar remarks]
For example:
https://softsolder.com/2015/09/14/makergear-m2-platform-stability/
You need numbers. Lots of numbers. [grin]
strip basic tools out of the control interface
Yet another reason I don’t use S3D: that “Simplify” thing gets in the way of my obsessive need for control.
(Continues tomorrow)
The Smell of Molten Projects in the Morning 
“How the heck do you read out the current (estimated, obviously) X Y Z position absolute to the machine coordinates?”
Short answer, “you can’t”. At best, you can read what the software thinks is the current position. If your stepper motors do anything funky, as unregulated control systems are wont to do, the estimate is less than useless.
If this person is interested in expanding the state of the art, he should be encouraged and shown some of the unsolved problems. But there is no way he is going to produce anything better than he can get for about $600 from Printerbot for less than $2000 all in (and probably much more after trial and error take place.) One thing that you get from most of these commercial printers is all the tuning the makers have already discovered for getting adequate results.
There’s a lot to be said for learning-by-doing (and I’ve said and done my part!), but that’s not how to design a marketable system, even one for the DIY market. Worse, the real challenges seem to be in the firmware end of the biz and aren’t amenable to becoming Kickstarter projects.
Slightly longer answer: “You can, but at a cost.” A shaft encoder would work; HP had some up to 1000 counts per rev, or a strip encoder (commonly found on HP inkjet printers in the ’90s. I have no idea if they’re still in use).
Going way up the price points, there are commercial DROs with readouts in any accuracy you could pay for. The metalworking tool places sell packages good to about 0.5 mils or better at almost affordable prices. [Depending on one’s definition…] (I saw one unit demonstrated at Semicon in the late ’90s that was good to a few microns. Didn’t ask the price.)
After HP Semi closed, the product lines were sold off. I don’t know who has the original, but US Digital was offering products that were a match. (Might have been value-added from HP components.)
They told Elon Musk it’s stupid to start a rocket company. And a car company. Now “they” mostly keep quiet :)
To be honest, I don’t expect his project will be anywhere near that kind of success but that really shouldn’t stop him from pushing forward. My self sourced Ultimaker clone clocked in around 500€. As Ed mentioned that figure doesn’t include my time on the project but if you label it as a hobby it’s all good :)
Absolutely. It largely depends on expectations.