If you are going to the effort of putting the leveling probe on the head, you might as well use it to its fullest. Plywood does change as it dries out. Variable warp with time is not at all an unusual thing. The biggest issue for probing is space in the middle of the printer. Here's a possible solution:
1) Right now all the arms meet at a single vertical pivot point directly over the hot end. That makes for simple(r) math. It also means we have a hollow shaft in the middle of the printer.
2) You *could* replace the single vertical center pivot with three pivots (one for each arm). Mounting them around the edge of a round disk would give you room for this and that in the middle of the printer. (Could be a probe setup, a compact extruder (yea!), a rotary tool, ...). The hot end would mount in the center of the disk.
3) The added pivot points mess up the math in the pre-processor. You have one more angle to figure. Since that's code on the PC, I don't see it as an issue. You would have one more variable into the pre-processor (vertical offset maybe) that would be zero for the normal LISA. It will tax a Mega a bit more. Fast ARM’s with FPU’s better get here soon!!!! Fast stepping and lots of math do not sound like a good combo on the Mega.
4) The three hubs would use the same number of bearings as the center hub. They could easily be 608's with 8mm blots in them. Hollow bolts are no longer a constraint. Cost to build is same / less with this approach.
5) The center disk would be < 4” in diameter on a normal sized LISA. How much smaller depends on clearance issues. Even at 3” you have a lot of room for stuff. On a scaled up printer you (obviously) would have even more room.
6) Print area / print height would not be directly impacted by the change. (At least that’s my guess). The arm “reach” at the full extension points is not changed. That assumes the distance to the inner horizontal pivot in the arm is not changed.
7) A practical implementation might lose you a bit of build height (maybe an inch) simply to get everything to clear. A lot depends on the distance from the vertical pivot to the inner horizontal pivot.
8) I believe that accuracy would not be impacted by this change. The disk could be pretty heavy duty.
9) Ideally I’d put the pivot arms *under* the disk. That way you don’t lose build height. That puts some constraints on the design in terms of bumping. I’d have to do a bit more work on this to see how severe those issues are.
10) We already have one printer design and one set of math that does not fold into Marlin. This would add a second set of math to that pile. Having that math variations grow faster than the number of printers built may not be a good thing.
Yes I know, it would be a lot easier to work out what the heck I’m talking about if I did a sketch ….
(Truth in lending --- I'm mostly thinking about doing this to put a compact extruder and probe on a scaled up version. The post here is simply a sneaky attempt to get the alternate math folded into the main core of the project. Also to get somebody other than me to do the math…).
1) Right now all the arms meet at a single vertical pivot point directly over the hot end. That makes for simple(r) math. It also means we have a hollow shaft in the middle of the printer.
2) You *could* replace the single vertical center pivot with three pivots (one for each arm). Mounting them around the edge of a round disk would give you room for this and that in the middle of the printer. (Could be a probe setup, a compact extruder (yea!), a rotary tool, ...). The hot end would mount in the center of the disk.
3) The added pivot points mess up the math in the pre-processor. You have one more angle to figure. Since that's code on the PC, I don't see it as an issue. You would have one more variable into the pre-processor (vertical offset maybe) that would be zero for the normal LISA. It will tax a Mega a bit more. Fast ARM’s with FPU’s better get here soon!!!! Fast stepping and lots of math do not sound like a good combo on the Mega.
4) The three hubs would use the same number of bearings as the center hub. They could easily be 608's with 8mm blots in them. Hollow bolts are no longer a constraint. Cost to build is same / less with this approach.
5) The center disk would be < 4” in diameter on a normal sized LISA. How much smaller depends on clearance issues. Even at 3” you have a lot of room for stuff. On a scaled up printer you (obviously) would have even more room.
6) Print area / print height would not be directly impacted by the change. (At least that’s my guess). The arm “reach” at the full extension points is not changed. That assumes the distance to the inner horizontal pivot in the arm is not changed.
7) A practical implementation might lose you a bit of build height (maybe an inch) simply to get everything to clear. A lot depends on the distance from the vertical pivot to the inner horizontal pivot.
8) I believe that accuracy would not be impacted by this change. The disk could be pretty heavy duty.
9) Ideally I’d put the pivot arms *under* the disk. That way you don’t lose build height. That puts some constraints on the design in terms of bumping. I’d have to do a bit more work on this to see how severe those issues are.
10) We already have one printer design and one set of math that does not fold into Marlin. This would add a second set of math to that pile. Having that math variations grow faster than the number of printers built may not be a good thing.
Yes I know, it would be a lot easier to work out what the heck I’m talking about if I did a sketch ….
(Truth in lending --- I'm mostly thinking about doing this to put a compact extruder and probe on a scaled up version. The post here is simply a sneaky attempt to get the alternate math folded into the main core of the project. Also to get somebody other than me to do the math…).