I have 3 prusa i3s currently. (Turtle, klunker and snow) Two have been pulled out of service and almost became targets for shotguns. The story of z-wobble is actually quite long and boring.
Here are some things that were tried;
- Out of the box 8mm threaded rod.
- We purchased 3 sets of 8mm threaded and discovered what many know already, threaded rod is not straight.
- Loosen the metal z coupling. This makes sense and helps. The flex coupling which attaches the motor shaft to the threaded rod needs space to flex so the threaded rod should not touch the motor shaft within the coupling.
- Cut a bigger hole in the top of the frame. This also helps as the threaded rod needs to be able to “wiggle” at the top and bottom. If the smooth rod holds the x carriage still and the threaded rod is allowed to wobble freely it will minimize the wobble on the actual x assembly.
- Tighten the x belt and put pressure against the z smooth rods. Again this causes the smooth rod to hold the carriage even while allowing the threaded rod to wobble. All of the above with lead screw vs threaded rod.
- The opposite of all of the above: This is actually the lulzbot solution. Restrict the threaded rod with a bearing at the bottom and top of the frame. The theory is that if the threaded rod cannot wobble it will not.
- There are a few dozen more small things we’ve tried.
The results of all of the above were better prints with less wobble, layer shifting and waves. No where near 20 micron precision for xy on any of them.
Finally after months of tweaking (and using other printers for production prints) a decent solution was found. The pictures attached are of a ~$300 prusa kit. Using aluminum extrusion for the frame. Not steal or even a solid melamine frame.
There are a few upgrades: led lighting, Arctic silver thermal epoxy on the extruder drive, cable chains, custom top plates, and a few more.
The current solution:
We printed an Oldham coupler off thingiverse (after designing a custom one and then realizing someone already did that :). The acme screw/lead screw is free to wobble at the top and bottom of the frame and the Oldham corrects for misalignments during the print. The only restriction is that it can’t move z very fast, currently it won’t print at layer heights greater than 150 micron and z movement is set to 15mms.
I’m certain there are hubs and posts here about z wobble issues and solutions. I’ve seen prints with threaded rod lines and lead screw waves all over the place and made plenty myself. Does anyone have a better solution? Keep in mind this is for cheap diy printers and the prusa is one of the most popular repraps on the market. The photo is of this printer printing parts for the p3steel toolson edition.
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May '16last reply
May '16- 2
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