Both components have practically zero material cost. Packing strap can be found for less than 4 Euro (US$5) per 100 meters, and rubber hoses can be aquired for very little cost. The straps are connected to the carriages with links of bicycle chain. So don’t throw away old bike chains; they’re extremely useful for QuadRaps!
The Carriages The friction of sliding carriages will always be several times higher than rolling carriages, no matter what high-tech sliding bearings you use. Sliding bearings are also very sensitive to asymmetric application of forces, so you’ll often see people in RepRap forums lamenting lost motor steps due to belt misalignment or insufficient lubrication. For the QuadRap I chose to go with mini-rollers which cost about half a Euro (US70¢) each. They can be adjusted from all four angles to get the most ideal alignment. These carriages roll gapless and without resistance regardless of the force applied to them, and haven’t yet caused any noticeable wear on the aluminum tubes, and when they do I can just swap the bars up to 5 times.
The elevation of the printing platform is adjusted with screws at its corners. Adjustable plastic plates at the corners prevent the platform from moving in the horizontal direction due to imperfections in the threads. The threaded rod is suspended on the stepper shaft using the same rubber tubing as the belt drives so no exotic coupling from CNC shops is needed.
No Endstops Pick up some wine bottle corks and connect them with a rubber band as bumpers and alignment guides. Nothing will get broken when the carriages hit the limit positions. Of course, if you want to embellish your QuadRap, feel free to use any endstops you like. I’m doing fine without being near the printer when it starts or finishes, and checking the GCode to remove the “home axis” commands.
The Z Platform The printing platform in QuadRap moves in the vertical direction. This maximizes the usable area of the printer and reduces printing problems associated with accelerating the printed object. The vertical movement is achieved with only a single threaded rod at one corner. The other three corners are suspended on fully-tensioned packing straps connected via pulleys from the driven corner. The straps are connected to the platform with bike chain links. QuadRap extruder REPRAPMAGAZINE