The Meticulous Z-Axis

[MeticulousMaynard]

@Joshua

We might want to understand the sensitivity here. I don’t think it is too sensitive; raising the z-axis by a few inches might raise the center of mass by 1/2 inch. Has anyone done analysis to understand the consequences of 1/2" of CG height? If not, I would like to test it before it is eliminated as an option.

Another idea. We might be able to switch the motor to the bottom of the lead-screw. That would lower the CG a little.

To be clear, I’m not as worried about the extra weight of the plywood/linear rails. Those will have a very minimal effect on the center of mass. I massed the entire Z-Axis kit and it only came to 326 grams, or 11.5 oz (0.72lbs). My major concern is with the router. That masses almost 3kg (6.6 lbs), and when it’s at the top of the axis it will push our center of mass up significantly.

Personally, I don’t like mounting the Z-Axis motor at the bottom of the lead screw. That means we have to put a hole in the back and there isn’t a lot of clearance for a pulley down there. That’s not to say that it isn’t possible, more than I like the motor where it is.

In my model I’ve raised the linear rail mounting blocks 40mm from the original position and I think I’ve found a position I’m happy with. It’s tight, but not problematically so.

This is the view from behind the router, with the back hidden:

And this view is from in front of the router, with no parts hidden.

The first view shows us that the current configuration gives us a hard “stop” at the bottom of the axis, just before the router plunges through the dust hood window. I like having a hard stop there to prevent the machine from breaking a linkage member or the plexi window. I would also like to add a limit switch to add a soft stop just before it hits that hard stop, though. Does anyone know how difficult it would be to implement limit switches into the firmware? Luckily, the belt will most likely slip before something breaks, so we should have a good failsafe in case we hit the hard stop.

@Joshua

Another thought. I am sorry for inundating you. Sometimes I cannot help it. I was thinking about the motor mount. In the current design, correct me if I am wrong, there is no ability to tighten or loosen the belt. This would be some kind of horizontally movable piece, a horizontal degree of freedom in the motor’s mounting position, so that the belt could be installed then tightened. This would take the form some horizontal slots that have a bolt or screw going through. In the current design, this is present in the vertical direction, due to the slots in the metal motor mount.

This is a good point and it’s something I’ve been thinking about on the back burner. Ultimately, yes, I would like to make up a bracket with horizontal adjustment rather than vertical. I drew in the bracket that comes with the kit for the prototype and until we have a more final version, I don’t think it’s worth putting the time into making up a separate bracket.

Also, the advantage of timing belts over a serpentine or v-belt is that it’s much less sensitive to tension. At least for the prototype, it should be relatively easy to screw the Z-Axis motor with the belt on it to tension it.