MendelMax build: frame part 1
My MendelMax parts arrived! Here’s my beautiful pile-o-stuff from Misumi:
Time to get cracking! I immediately tore into it.
Step one is to tap the extrusions that need tapping. That means the two top extrusions (420 mm), the four diagonal extrusions which will attach directly to the lower vertices (340 mm, which only need one side tapped), and all four of the front and back extrusions on the bottom part (300 mm).
MaxBots was right, the recommended tap really did help things along. It slices into the extrusions like a hot knife through butter. I got all 16 holes tapped in about 45 minutes.
To save yourself some aggravation, for every hole you tap, screw one of your M5 screws into it and make sure that it can go in almost all the way. You want it to be able to thread in so that it’s about three or four millimeters from the aluminum. If you can’t screw it in to that point without encountering resistance, tap some more.
Now you need to drill into the two 420 mm extrusions that you tapped, using the printed jig to guide you. Make sure to wear goggles for this part, because, uh, having aluminum shards penetrate your eyeball is an experience most people want to avoid. My father still has a little piece of metal somewhere in his eye from a decades-ago mishap involving drills, metal, and unprotected eyes. Just do it. If you don’t have goggles, then stop and go get some, even though it’ll kill your buzz and interrupt the build. Srsly.
Next, it’s time to tap the untapped ends of the diagonal extrusions using the self-tapping screws. I bought an appropriate Torx screwdriver but found a ratcheting socket wrench with a Torx bit to be much more efficient, especially towards the end.
After that, you attach the first printed pieces—the lower frame vertices. The tapped end of the extrusions each get an M5 screw to connect it to the vertex. I found it fastest to first stick the screw into the hidden hole in bottom of the vertex, then attach the vertex to the extrusion with its other connection point to prevent it from rotating around, and then finally fasten the screw in the hidden hole. Do all of this four times, one for each extrusion with a self-tapping screw in one end. Don’t forget to use washers! Voila:
Now connect two of the vertices with two 300 mm extrusions, one on the top, and one on the bottom. Make sure to trap a nut in between each of them first.
Do the same for the other pair of vertices. If you’re going to support the Y axis idler on both sides rather than just one, trap two nuts in between each extrusion on this side.
Now you want to connect these two assemblies you just made together with untapped and undrilled 420 mm extrusions, like so:
Make sure to trap two nuts in each side extrusion! At this point, it’s starting to appear more like the frame of a 3D printer. It should look like this:
Next, you need to stick two nuts in each of the shorter 300 mm extrusions that make up the front and back. The nuts should be positioned in the interior slots so that they face one another inside the frame. These are for the interior Y rod holders.
Take one of the two remaining untapped and undrilled 420 mm extrusions and stick four nuts in one side, and then position it underneath one of the already-attached 420mm extrusions with the nuts facing outwards. Do the same for the other remaining 420 mm extrusion. Now you want to attach the printed flats that connect the corner together. Use the nuts you’ve trapped in the 420 mm extrusions. For the holes that line up with the diagonal extrusion, drop two nuts down and fasten those, too. You should wind up with a corner that looks like this:
Now do the same for the other three bottom corners. Lookin’ sharp!
Now for the top. Before you attach the two remaining extrusions, drop two nuts in the each of the diagonal extrusions. They should be in the channels facing the front or back. These are for the printed diagonal stiffeners.
Slide the top 420 mm extrusions onto the diagonal ones and stick your screwdriver through the holes you drilled earlier to tighten the blind joint screws sticking out of the diagonal extrusions. Easy as pie. While you’re up there, insert four nuts into each of these top extrusions, into the front and back, respectively.
If you’re planning on using the attached spool holder, stick two nuts in the top of each of these extrusions for the spools before you attach the motor mounts. Now attach said motor mounts. They go on pretty much like you’d imagine.
The diagonal braces also go on like you’d expect, each using four nuts you’ve trapped in the extrusions.
Almost done! Just a few more bits. First the bottom mounts for the Z smooth rods:
Then the interior holders for the Y rods:
Then the holders for the Y idler. I’m using two of them here since it seems more stable that way, but it shouldn’t be a problem if you only use one.
Then the Y motor holder:
And that’s a wrap. The frame is done. Total build time: 6 hours, 20 minutes. And that’s including the time it took me to write this post, which I was doing throughout the build! If I had been concentrating entire on building, it would have been closer to 3 hours.
At this point I’ll mention that I scaled up my MendelMax a tad—just a tad. Instead of 300 mm long, I made the bottom extrusions 340 mm long for a little bit of extra space in the X dimension (the top ones are 460 mm). Here’s the MendelMax frame, side-by-side with my Prusa:
What’s also amazing is how my larger-than-normal MendelMax is actually barely bigger than my Prusa! It looks and feels larger due to the solid square aluminum extrusions and the greater volume, but objectively, The footprints are very similar. And while the Prusa looks spindly and waif-like, this thing oozes a certain tough seriousness. I’m a fan. A big fan.