Linear Motor Based 3D Printer 3
I don't like the amount of mass introduced by the direct extruder. I also don't like the problems introduced by the bowden tube feeder. On another printer I used the Zesty Nimble to compromise on this issue, and have been happy with that.
There is a limit to the acceleration the linear motor can impart on the print head. This limit is related to the mass of the print head. Ignoring friction in the linear guide and other non-linear effects, the fundamental factor is F=ma, so half the mass enables double the accelerations. The Bondtech BMG is advertised as 75g without motor (as if it were usable without a motor...). The motor that matter hackers suggests is another 390g!:
https://www.matterhackers.com/store/l/nema-17-stepper-motor/sk/M1C4A52S
So about 500g in mass.
The Nimble, and its competitor the Flex3Drive are lighter. The Nimble is advertised as less than 27g, but that ignores that the drive shaft has to be accelerated too (as if it were usable without a drive shaft...). I weighed a drive shaft with its sleeve and end mounts and it came to 57g. Naturally only part of that gets accelerated. It seems reasonable to estimate 50g or so of accelerated mass. That is an order of magnitude better than the direct extruder.
Aside from increased print speeds, at least theoretically, this should result in less ripple around the corners.
Here a video of a test print with the Nimble:
There are some issues with the Nimble. Many people report seeing ripple effects on the surface of the prints. See here for example:
https://forum.zesty.tech/t/surface-effects-like-ripples-etc/186/255
On the first generation of Nimbles, I had to file down the worm gear inside of it to address the ripple issues. The newest iteration of the product does solve this particular issue, but the unit still seems susceptible to deformation and internal binding when the mount is not 'just right'.
The first mount I used was a modified version of one published by the Nimble creators:
https://www.thingiverse.com/thing:2554334
The nimble did not mount cleanly. The little round spacer between the nimble and the V6 was tall enough so that there was a gap where the screw mounts touch ( See the shiny of the screw).
I did not torque down the screws onto the nimble; just enough to be sure they wont go loose.
This resulted in the ripple I have seen on the previous unit. I modified the model to give more space to the ring, and the ripple went away for the most part. In some layers the ripple returns for short amounts of time. Here a befor and after:
But for the most part it prints beautifully now. And I have a very low mass print head with direct extrusion!
The tech support by the Nimble creators is amazing. They help in their forums. They help in on-line chat. They help with video conferences. They help when the problem is pretty clearly not caused by the Nimble. And they never get frustrated or defensive. That is why - in spite of the technical problems with the first generation - I bought a second one. And I will probably buy yet another for the support material...
One issue I still have is the printing of flexible materials. They do tend to slip in the nimble. If you print slowly enough and there is not too much drag on the feed side, then it works ok. But it is marginal. I had to increase the print temperature of the Ninjaflex higher than usual to get the right extrusion rate, and it was just enough. Increasing the extrusion multiplier did not result in overextrusion.The nimble would just start slipping more. The same is true if I did not carefully control friction on the feed side of the filament. And the same still held true for print speed. I.e. I could print Ninjaflex fine, if:
- The temperature was high enough
- The print speed was slow enough
- The feed side of the filament was carefully routed to minimize friction.
Another issue I came across is with another flex filament that had too small of a diameter for a few feet. That stopped feeding altogether...
I would wish for a way to grip the filament better here. Maybe something like the Bondtech extruders or maybe just a way to increase pressure on the filament to get a better grip...