Saturday, September 30, 2006


Tommelise sliding thrust collar under construction...

I reached the conclusion that if early generation repraps are going to be made with ordinary threaded studding we'd better get used to the fact that when you buy it from the hardware store it often isn't tremendously straight. I got the piece that I was using for Tommelise's z-axis (horizontal) straightened to a point where over 640 mm it had about +/-2 mm play. There are two ways that I could have dealt with that and kept the accuracy on spec. The first was that I could have had thicker guide rods (I used 1/4 inch) and used full sleeve bushings. That would have let the drive motor straighten the threaded drive rod. That, of course, would have eaten up torque. The other way was to let the thrust collar move freely in the x-y plane. I decided to give that one a go for this design exercise.

I designed a crude thrust collar which would let the coupling nut move in the x-y plane. This consisted of a poplar sleeve that let the coupling nut move freely in the y direction and guides, also done in poplar, that let that sleeve move in the x direction.

The thrust collar had to more or less match the width of the coupling nut (1 in) which entailed me gluing two strips of poplar together. You can see this assembly drying in the first photo.

At that point I carved seatings for the guide rods out of poplar and glued them to the 320x320 mm double strength glass work surface.

In the second photo you can see them glued in place along with the guides for the thust sleeve. Fender washers keep the coupling nut from slipping along the z-axis.

I got a bit overexcited and tried to run it this evening instead of letting the glue dry overnight. The thrust collar appears to do what I'd intended, that is, to keep lateral movements by the theaded drive rod from reaching the guide rods and requiring dissapation as friction heat.

I was able to run it for about a minute before one of the glued joints came loose. I reglued everything and resolved that video clips of the z-axis platform will wait until tomorrow morning. :-s

looks good. cant wait to see the next update. this is getting really exciting.
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