this is a amazing project that i have started looking at trying to build.
looking at all the extrusions mainly with the gantry main beam.
whats the reason for using 20x60 instead of 20x40? is it to stop it from bowing? if it is wouldn’t the track have more wight on it then the gantry will ever have?
I would love to know this answer as well.
Great question! We used to use the 20x40 (look at old docs) but recently switched to 20x60 for two reasons:
- Having the larger main beam means that the wheels on the cross-slide are spaced farther apart (contact points with the main beam go from 40mm to 60mm apart). This helps with torsional resistance between the cross-slide and the main beam. So for example when FarmBot picks up and puts away tools, the z-axis/cross-slide is more securely attached to the main beam and it prevents flex and wobble when moving in the x-direction.
- Aesthetically it looks better because the main beam fully hides the driveshaft and cable carrier when looking at the bot from the front. Small detail, but it makes the bot look “cleaner”
Second extrusions question.
You are using a V-slot extrusion, yet it appears that you are running the wheels on the “core”, rather than on the V slot. If that is the case, would this extrusion (http://us.misumi-ec.com/vona2/detail/110302684350/?Inch=0&CategorySpec=00000042730%3A%3Ac) work as well? It is a bit cheaper per meter, but has the added advantage that it can be ordered I 4 meter lengths. This eliminates the joint between the 2 pieces (although you would probably still want a support at around the 1.5 meter position. (If you went the full 4 meters, I would put a support every 1.33 meters, rather than stretching out to 2 meters. You would want to reduce the potential for damage if an accidental weight (playing kid) happened to “fall” between support.
For those that have read this: Never mind. In looking closer they ARE using the V groove to keep the wheels centred. However, it would STILL be nice it the extrusion could be purchased in longer units.