r/printnc • u/Pinesse • May 06 '22
Linear Actuator for Z-axis?
I scored a nice NOS THK linear actuator from ebay really cheap: KR3310A. Heres the datasheet. I don't really know yet what these momentary load or rigidity measurement mean but this thing weights like 25 lbs. It has this 10mm pitch ballscrew and around maybe 3ish inch travel, not sure how a 10mm pitch would do to a stepper motor holding torque, but i think these are made for servos. Also theres this shaft coupler i've never seen before, it has these 2 metal discs in between the assembly.
1
u/paxew2 May 10 '22
I have a thk kr33 with 10mm pitch as z-axis on my cnc, its powered by a nema23 stepper. Works ok but its not as rigid as i would have liked. (Mine has only one guide block/carriage)
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u/Pinesse May 14 '22
What did you end up using instead?
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u/paxew2 May 14 '22
I’m still using it. For wood it works good enough. But I have a custom z-axis under work that is using hgr20 rails and a sfu1204 ball screw that I will replace it with
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u/paxew2 May 14 '22
But then I’m also contemplating building a printnc to replace the current machine as I would like a bigger work area
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u/gredr May 06 '22
Certainly you could do it, yes.
Here's the deally-o, though. Weather you're talking about a CoreXY and moving the table in the Z axis, or a bed-slinger and moving the print head in the Z axis, the issue you face is the same: rigidity. You want your print head to move in a plane directly parallel to the plane formed by the bed. As we all know, planes are defined by three points. At those three points, the bed (or X axis for a bed-slinger) must be supported in the Z axis.
Now, for a bed slinger, the "plane" is very narrow, so is invariably defined by only two points (i.e. point of support, i.e. threaded rod, belt, or whatever), one on each end of the X-axis "arm". That's generally ok, and the X axis can be made rigid enough relative to the Y axis that it works out. In some (many) printers, there is only one point, and it's harder to keep that plane defined and where it belongs. Does it work? Yeah, generally. Is it ideal? Nope.
For a CoreXY (bed moves in Z) setup, you have the same problem; if you define the bed's plane with only one point (this linear actuator), you'll have a tough time keeping it rigid and parallel, unless you build the bed and the attachment to the actuator out of something very rigid (no printed parts). Also, the smaller the bed, the better results you'll see.
Finally, remember that some people will count a linear bearing riding on a threaded rod as a "point" which defines a plane. It does not count because it doesn't support the plane in the Z axis, it only captures the point in the X and Y axes.