Friday, February 13, 2009
Another off-the-shelf linear bearing experiment
Unfortunately, the sliding door rollers have quite a bit of lateral play, so 8 were needed to give the bearing a solid feel. 4 - with two each on opposing sides - allowed far too much play for any productive use. So this linear bearing cost approximately $25, only allows movement in one axis (as well as rotationally), and functions better than any of my other off-the-shelf linear bearing experiments so far.
I don't think the concave surface of the sliding door rollers provides much, if any advantage with this design. I intend to experiment with regular skate bearings as soon as I have some of the apropriate size. As pictured, the linear bearing would benefit greatly from the addition of some lockwashers. I intend to flesh out a full repstrap using this style linear bearing, and more perferated square tube. My goal is a complete repstrap buildable with off-the-shelf parts, and as little tooling as possible, from a local "big box" or hardware store - with the obvious exception of motors and electronics. Suggestions welcome.
I've been playing around with off the shelf materials, but for a CNC build http://flightsofideas.com/?p=377. The funny thing is that I tried a similar approach to yours but couldn't get it to work (using MDF and bad capentry skills). I tried to use square pipe to get rid of the play - have tried your setup with square pipe?
I like Timothy's idea because he is addressing the needs of those (all over the world) who can't afford a kit. Making a repstrap from local materials and without expensive machinery could be important to grow the community.
On the other hand, I suppose that if everyone who could afford a kit bought one and started donating reprap parts then repstraps wouldn't be needed.
Perhaps both approaches are valid?
- I'm working toward an absolutely minimal BOM - tens of parts, not hundreds.
- The entire machine (sans electronics) will be wrench-buildable. I stipulate that the cost of a machine should include the cost of all the tools required to build it, not just materials, and I'm striving for a very low cost.
- The machine should effectively scale from Darwinish sizes to medium-large sizes (4 feet x 8 feet) and be able to handle much more physical stress than a Darwin - suitable for a CNC router, plasma cutter, etc.
- Ideally, all parts (again, sans electronics) should be obtainable from local hardware or "big box" home improvement stores. At this stage in the design (fairly late - most functional issues have been worked out), this does not look at all unreasonable.
All that being said, if I could find parts appropriate to scale the design down further, and make it cheaper, that would be great! I hope some interested RepRap hacker can make a suggestion or two in that direction... The fastest way to scale RepRap dissemination is to leverage the existing mass-production infrastructure - enabling anyone to bootstrap themselves into RepRap development. I'm just trying to lower the custom-fabricated-parts barrier one more notch -- for myself, and others.
Nice idea. Can you post some pictures in the blog? I think you're on the right track. A heavier machine than the Darwin with cnc abilities as well as rdm is what I'm trying for as well.
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