Leadscrew stops and starts?

I'm trying to make a cnc plotter similar to this: http://hackaday.com/2013/10/17/unorthodox-home-made-cnc-machine/ I have changed some things though: I'm using aluminum rod with washers super glued to the end, another washer, and two nuts instead of flange bearings (brushings) and two nuts, I'm using 3/8 rod, pololu steppers (#1209), and slightly different conduit clamps.  I'm using a wooden dowel with a half-inch hole, and aluminum and nylon spacers tapped and with a setscrew to act as a motor coupler.  The problem I'm having is that as the motors rotate, even continuously in one direction, the gantry stops and starts moving.  It moves 1/16th of an inch per rotation, as it should, but within each rotation it moves quickly, probably 5/6 of the way within the first 180 degrees, then moves just the remainder in the last 180.  The motors do not stall, miss steps, or change speed, but the gantry does.  There is almost no backlash, and little play.  Any ideas whats wrong?

Asked by jduffy54 4 years ago

How do you make more accurate tools from less accurate ones? Answered

I was wondering, in a general sense how people make more accurate tools from less accurate ones. More specifically, I was reading about reprap and it said it was possible to make components of itself from other previous repraps. However, the errors in them would compound and make less and less accurate/precise models. Therefore there would be some limit to how many times it could replicate. But, for instance. A lathe requires an accurate/precise leadscrew to control x axis motion. Using a lathe it is possible to make another leadscrew however this would be less accurate/precise than the one already on the machine. So for my true question. How do they make more accurate ones than the previous ones. If all the current lathes in the world are +- 1mm then how would you make the next set of lathes that are more accurate/precise than that without a piece of machinery that originally had better accuracy. (sort of a chicken and egg problem) Is there some type of machine or algorithm or something that allows a machine to make something that is more accurate/precise than itself. Thanks

Asked by louey 7 years ago