ChrisA
Well-known member
The CNC machine bed support was delivered this morning. The printer is not fully built yet. But I did have the Kirigami frame installed but no motor yet and could move it up and down by hand. I swapped parts and put on the CNC frame. What a world of difference it makes. It is dramatically better. Yes, it is stronger but that is not the point. It is so much more accurately made.
The kirigami has to be straightened by bending it into shape and carefully checking with a straight edge. You can never get it perfect. It will always be off by a few 0.01 mm. Then you screw it to the linear rails and the rails force the kirigami to be flat. This loads the bearings with the kirigam sheet metal acting as a spring. It works OK and you can make prints.
But the CNC bed is machined to be 100% dead-on flat and has zero spring. When attached the bearings are still unloaded. With the lead screw unattached you can lift the bed and then let go and it simply falls to the bottom of the rails. There is zero detectable play or spring in the cantilevered bed and almost zero friction. The Kirigami would not fall on it's own but could be moved with finger pressure and had enough friction that it would stay in place if you let go of it. There was also too much pressure on the rails so it felt not smooth, a bit gritty.
Yes the CNC bed is heavy. A lot heavier than the kirigami. But with my Moon's lead screw motor set at 0.5 amps current (it is rated for 0.65) the bed moves at 60 mm per second in both directions. 60mm/s is faster than anyone needs to move in Z (I think)
One problem: Formbot did not ship a printed stock T8 nut block because they shipped a special Kirigami t8 nut block. I had to print one in PLA. I hope it lasts long enough to make an ABS replacement.
The kirigami has to be straightened by bending it into shape and carefully checking with a straight edge. You can never get it perfect. It will always be off by a few 0.01 mm. Then you screw it to the linear rails and the rails force the kirigami to be flat. This loads the bearings with the kirigam sheet metal acting as a spring. It works OK and you can make prints.
But the CNC bed is machined to be 100% dead-on flat and has zero spring. When attached the bearings are still unloaded. With the lead screw unattached you can lift the bed and then let go and it simply falls to the bottom of the rails. There is zero detectable play or spring in the cantilevered bed and almost zero friction. The Kirigami would not fall on it's own but could be moved with finger pressure and had enough friction that it would stay in place if you let go of it. There was also too much pressure on the rails so it felt not smooth, a bit gritty.
Yes the CNC bed is heavy. A lot heavier than the kirigami. But with my Moon's lead screw motor set at 0.5 amps current (it is rated for 0.65) the bed moves at 60 mm per second in both directions. 60mm/s is faster than anyone needs to move in Z (I think)
One problem: Formbot did not ship a printed stock T8 nut block because they shipped a special Kirigami t8 nut block. I had to print one in PLA. I hope it lasts long enough to make an ABS replacement.