There needs to be a way to adjust how tightly the gantry is held to the rail. I find that objects that have geometrically complex outer surfaces exhibit very significant ringing, which mares the surface quality in those areas.
The photo I've enclosed below is a 2 X 1 inch closeup of just such an object. (Sorry, this object is printed in black. So the contrast is very high.) The section shown shows a cross-hatch pattern that involves many tight curves. While laying down a bead in these zones so much bounce builds up as the gantry makes the turn that it takes almost an inch of relatively straight travel to settle back down. This results in the entire surface in this section of the print to be completely covered in waves that aren't in keeping with the macro design intent.
The gantry is held in place along the length of the rail by 4 roller bearings. Two of the rollers ride along the slot on the top of the rail, while the other two fit into the slot opening on the rail bottom. The rubber rollers have a 45 degree bevel that matches the bevel of the rail's slot. The contact profile of the bearings seems to be well matched.
Yet the current design doesn't appear to include a means to adjust the spacing between the top and bottom rollers. At least on my rig, the rollers don't pinch or squeeze the rail tightly enough. So there's three types of slop in the movement of the gantry. The first type of slop allows the gantry to move ever so slightly forward (away from the rail) and back (toward the rail). The second type results in the gantry tilting forward along the X axis, like a braking car. Finally the third type is rocking on the X axis of rotation as it moves along the rail. All three forms of slop are most evident when the vector of movement changes (the gantry changes speed or and even more so when it changes direction) and when the vector of extrusion changes (the bed changes speed / direction).
A balance needs to be struck in finding the optimal distance between the top and bottom rollers. Too loose and you end up with the slop that causes ringing. Setting the rollers to pinch the rail too tightly will cause drag, which could show itself in a number of ways including accentuating belt slop. But not being able to adjust roller tightness leaves the current design without a means to manage the inordinate amount of ringing that I'm seeing in my prints.
- Bob
The photo I've enclosed below is a 2 X 1 inch closeup of just such an object. (Sorry, this object is printed in black. So the contrast is very high.) The section shown shows a cross-hatch pattern that involves many tight curves. While laying down a bead in these zones so much bounce builds up as the gantry makes the turn that it takes almost an inch of relatively straight travel to settle back down. This results in the entire surface in this section of the print to be completely covered in waves that aren't in keeping with the macro design intent.
The gantry is held in place along the length of the rail by 4 roller bearings. Two of the rollers ride along the slot on the top of the rail, while the other two fit into the slot opening on the rail bottom. The rubber rollers have a 45 degree bevel that matches the bevel of the rail's slot. The contact profile of the bearings seems to be well matched.
Yet the current design doesn't appear to include a means to adjust the spacing between the top and bottom rollers. At least on my rig, the rollers don't pinch or squeeze the rail tightly enough. So there's three types of slop in the movement of the gantry. The first type of slop allows the gantry to move ever so slightly forward (away from the rail) and back (toward the rail). The second type results in the gantry tilting forward along the X axis, like a braking car. Finally the third type is rocking on the X axis of rotation as it moves along the rail. All three forms of slop are most evident when the vector of movement changes (the gantry changes speed or and even more so when it changes direction) and when the vector of extrusion changes (the bed changes speed / direction).
A balance needs to be struck in finding the optimal distance between the top and bottom rollers. Too loose and you end up with the slop that causes ringing. Setting the rollers to pinch the rail too tightly will cause drag, which could show itself in a number of ways including accentuating belt slop. But not being able to adjust roller tightness leaves the current design without a means to manage the inordinate amount of ringing that I'm seeing in my prints.
- Bob