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Fundamental Newbie Questions on position Resolution

Posted by mars bonfire 
Fundamental Newbie Questions on position Resolution
April 28, 2011 02:11PM
Newbie alert. If I need to read some faq or other source, please kindly direct me to such.

With that preface, I am starting a reprap machine, using a unique 3D mechanism that I got out of some hi tech junk...one of kind but three nice orthogonal axes and a positional envelope that is pretty darn appropriate...and built like a brick root cellar. 3/4" hardened rods, recirc ball slides, ball bearings in idlers, all cogged belts, 1/4" aluminum plate machined frame.
Only small issue it is now equipped with encoded servo motors, not steppers. So, swap in some steppers... but...

Simple question: what are the step resolutions that I need for a good hobby 3D printer? I know this question starts to get into microstepping etc. but my question is the step size resolution I need **as delivered** in inches (or mms) at the extruder tip for X, Y and Z axis?

I would like to not count on the stepper motor beyond 1/2 stepping for "real" resolution...so working backwards, let's say I use a 200 step/rev stepper and use a cog pulley with a *circumference* of 2 inches (so, something roughly a little bigger than 1./2 diameter)...that gives 2 inches of belt travel per rev....or, for 400 1/2 steps per rev, 0.005" per step (5 thou per step). My guess is that is OK but even with a real extruder, something more like 0.001" per step is more comfortable.

I have seen some 3D kits claim 20 microns resolution (double yikes) but I am guessing they are doing some heavy microstepping (which is, IMHO, fantasy beyond 4 per real step).

Anyone one know what the Mendel step size is per axis (and what degree of microstepping is used to give that number)?


Re: Fundamental Newbie Questions on position Resolution
April 28, 2011 03:29PM
0.005" = 0.127mm. Since the *goal* of accuracy on this project is 0.1mm, and it's not that accurate yet, I'd say a .005" resolution would be fine.

The Mendel uses a 8 tooth pulley and a 5 teeth per inch belt. Ok, the spec is for 5mm per tooth, but 5 teeth per inch is only a smidge off of that anyway. With a 200 step/rev stepper, that gives 1 full step = 0.008".

I'm building it with Baling Wire
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