garageFab.cc

Another attempt to kill several birds with one stone:  

• Test belt-driven mini-router design
• Test solutions for motor coupling backlash (Oldham coupling, pulley on motor shaft)
• Drill the cutting mat in a few hours

The mat drilling contraption is basically the new belt-driven design of the mini-router, with the exception of Z-axis which is also belt-driven (mini-router still uses leadscrew on Z-axis). Dremel flex shaft with the drill chuck and 1/32" bit is mounted to Z axis. The results are rather mixed. 

One problem affecting the accuracy in Contraptor is angular backlash in the motor coupling coming from the rubber spider in between two coupling jaws. While it's not noticeable in leadscrew drive, the error can reach 1/16" in the belt drive because of the low transmission ratio, especially if the stage is heavy. Needless to say, this is way too much. There are several ways to deal with this problem. First, the pulley can be mounted directly on the motor shaft, which conveniently is 1¼" long in Alltronics steppers.

I finally updated the plotter design to use new linear motion components. While at it, I moved few things around, like belts to the outside; and now the plotter has 17"x11" work area. I have not assembled/tested it yet, but I think most parameters from the older version still apply. The BoM is also compete ($290 if built from scratch), the files are at http://contraptor.svn.sourceforge.net/viewvc/contraptor/trunk/contraptions/xy-plotter/

I worked on the plotter contraption pretty much every evening during the last couple of weeks, and here is the result of all that tinkering. I had reservations about several things - I thought it would be too difficult for the motor to move the X stage around at the max speed (150rpm) - not so. To connect the opposite pulleys of the Y stage, I used 17" lengths of 1/4" all-thread rod coupled to 10-24 rod ends - and I thought it would bend too much making the belts too loose. It does bend a bit but the belts seem to be fine.

I've been trying to work on Contraptor despite recent inspiration shortages. They probably have to do with things not working as expected.. which can be frustrating at times. Anyway, I have been able to get the belt drive to work, but there are a couple of issues, one of which seems to be resolved and the other one will need extensive testing again.

It took me a couple of evenings to turn all of the "experimental" angle stock into usable pieces of perforated angle (or trash), since it involved a lot of sawing. To speed things up, I made a starter/sawing template for the angle fed into and made by the drilling contraption. I've also drilled one more 32" length, with couple more to go -