The new MendelMax 2.0 has been announced!
The new MendelMax 2.0 has been announced!
Could we expect this version to be good as a first 3D printer acquisition in a few months ? (that would be my case)
While, it’s an improved design, it still uses way too much aluminum extrusion. Take a look at the bukobot, or the ORD bot for something which is a little lighter on the wallet in regards to framing.
Extruded frames look nice and solid, but are expensive and raise the price of the printer. I feel like unless they are used along with lead screws so the user can add a cutting tool to the printhead, all that aluminum is kind of wasted.
@Olivier_Jolly , it is very easy to assemble and tune, so it will make a good first 3D printer.
@ThantiK Those two additional bars add a trivial amount to the BOM.
This is what the Mendelmax should have looked like from the start. Unfortunately, the Mendelmax still isn’t what an extruded aluminum printer should look like.
What should an extruded aluminum printer look like?
An extruded aluminum printer using the mendel-style axis order should be rectangular frame with all four right-angles braced for the X/Z plane (this is where the forces of printing motion apply torque to the frame) with a fifth beam (or pair of beams) attached to the one at the bottom of the frame to support the Y-axis linear guide (like the Bukobot and Ordbot).
An early sketch of the Bukobot design looked a lot like the new Mendelmax, but it was changed to the current layout on my advice.
Actually, whosa whatsis, the MendelMax 2 (and earlier versions) are quite well braced in the directions of the loads. The X axis is braced with triangular attachments at the top. They are considerably smaller on the MM2, but still plenty rigid. If you wanted to increase the rigidity even further on a printed version, adding additional tringular bracing to the back side of the gantry would be easy and would not interfere with the movement of the bot. The weakest link in all this remains the unsupport Z shafts, but with the recommended 10mm shafts, flex is really not a significant issue, and extrusions are really not precise enough to be used as a bearing surface on a high performance machine.
Interestingly, you cite the Bukobot as an example of a better design, but it provides no obvious bracing of the X/Z from the motion that will be induced by the moving Y axis. That is fine as long as your print speeds are low, but rapid speeds and particularly rapid infill will introduce problems with that design. Adding the two additional extrusions to turn the gantry into a triangle (as the MendelMax does) makes the whole machine substantially more rigid. It costs a few dollars more, but not really much. The total cost of the extrusions for a MendelMax is under $30, hard to stress about adding one or two more.
-Mike (AKA Maxbots)
How is his printer going to shear in XZ with those massive brackets holding it together?
Billy- is your question directed at me or Whosa?
It was at Whosa. I posted at the same time you did.
@Mike_Payson the motion of the Y axis transmits force to the legs of the machine. The inertia of the platform’s mass (which is kept lower than most other designs) works against the mass of the entire machine, which is bottom-heavy (with the Z motors and other heavy components mounted at the bottom). Because the platform is so close to the base, its motion imparts a linear force that, if anything, moves the whole machine, which only becomes a torsional force if there is significant mass at the far end of the Z axis. As it is, any slight movement of the fram imparted by the inertia of the Y axis is distributed throughout the frame so that it all moves together if at all.
The X axis is different because, besides carrying much more mass with the extruder motor, it is much further from the base of the machine. The inertia of the base works against the inertia of the extruder to impart a torsion force that makes the square of the X/Z plane want to turn into a parallelogram. The Bukobot and Ordbot overcome this with right-angle, metal-to-metal joints at the top and bottom of the frame. The old Mendelmax lacked these joints, and the new one has them only at the top. The bottom extrusions join at the wrong angle, making it possible for them to twist, so that it relies on the metal plates (which are neither off-the-shelf nor printable) to resist bending in that direction.
I’m not arguing that it’s not structurally sound. What I’m saying is that it doesn’t achieve structural soundness in an efficient way.
The Z frame is a long arm, if you introduce any linear motion into the frame, you will necessarily introduce a load into the Z frame. Directing it to the legs will help, but not eliminate the problem. While I agree with your reasoning that it should be minor, addressing it with the triangular bracing we use was cheap and effective.
As for the lack of lower bracing on the MendelMax, your point is reasonable for the 1.5 and before, though the loads involved do not seem to create a problem. On the MM2, it should not be an issue. With metal plates (granted, non-standard but easily DIYable) you do not need the bracing you refer to, and if you use printed plates I recommend a blind joint that accomplishes exactly what you are talking about. The loads involved are nowhere near enough to actually flex the extrusions, so a blind joint is a cheap easy way to get the rigidity you need.
All that said, you make good points, and I will absolutely keep them in mind on my next designs.