I've decided to call it a day with my Lego based RepStrap (but not on making a RepStrap). It has been interesting to experiment with but I ran into too many problems and have decided that a more substantial steel-based solution is in order. The machine has been sitting there for a few months not doing anything now, this is the short story of my change in direction over the last few days after being inspired by some recent blog posts.
First I decided to give up on screw driven axes as they are very so slow to move and make printing painfully slow. With this in mind I ordered some new more powerful motors to drive the axes directly. I received my new stepper motors today. I got four NEMA 23s from Astrosyn for £49 including postage.
They are not the most amazing spec motors but I think they should be perfectly sufficient.
I also bought some 608 skate bearings the other day with the intention of using them to make a new Z axis for my Lego RepStrap. I started playing around with them, and tried bolting two up close together like James did here and running it along another [threaded] steel rod. I was impressed that it even ran pretty smoothly even along a threaded rod. I then tired covering a rod in heat-shrink plastic to make it even smoother.
This gave a very smooth run, and also moved incredibly silently due to the dampening from the thin layer of heat-shrink plastic. A quiet machine is an important goal of mine [this is why I also plan to move to a stepper driven pinch-wheel extruder].
At this point I became decided that abandoning my Lego RepStrap was in order and started looking around for other parts.
I saw the post Ikea Design and remembered that I had seen the very same chain and gears available from Rapid Electronics.
I found a company selling M8 300mm threaded steel rods on eBay for £3.37 for five + postage and was unable to resist the temptation of nicely pre-cut rods. I ordered 20 M8 300mm rods today and a whole load of nuts and washers.
My plan now is to make some corner pieces from wood and construct the steel frame, then put the motors, gears and chain on. The four rods that have skate-bearing runners sliding along them will be covered in heat-shrink plastic.
I am also thinking of trying and modify my generation one PIC electronics to run a stepper driven pinch-wheel extruder.