Want a CNC mill, but only have a 3D printer? Well, if it’s sufficiently overbuilt you can convert it for less than $100!
So i’ve always wanted a CNC mill, arguably my interest in automated manufacturing in general was what got me into 3D printing in the first place, since 3D printing is sorta the same thing from a technical standpoint, just way more accessible. But i still wanted something that could machine materials and not just extrude them, even if it was only for the educational value and less so for actually opening up a job shop and running the machine 24/7 to produce parts. Essentially, it should just augment the 3D printers i already have and be able to occasionally machine a thing or two from aluminum, acrylic or wood. So i set out to do what i had planned for a long time with the MendelMax 3: I converted it into a CNC mill.
Now, even though the MendelMax 3 is a fairly sturdy 3d printer, it’s not quite up to the task of machining materials out of the box, at least when it comes to my basic understanding of the cutting forces and resonance issues involved with milling. So my padawan and I started replacing a few essential parts that were originally only made from relatively flimsy 1mm steel – which, surely, sounds like a lot, and actually is the same ballpark thickness that a large part of your car’s chassis is made from, but the geometry plays a huge role, too, in how easily a part will bend. For a lot of applications, a chunky, 3D printed plastic part can actually be way stiffer than anything that’s just a flat sheet of metal. So after removing the parts that made this beast a 3D printer, we grabbed some aluminum flat stock and replaced the Z and Y-axis motor holders and the X-axis carriage, since that’s where the new toolhead will go. The great thing with these OpenBuilds wheels is that you really don’t have to work precisely at all when it comes to the positions of the mounting points for the wheels, since you’ll adjust the pretension of the wheels anyways. We also stiffened up the print bed, since, again, that was simply sheet metal from the factory and didn’t come with any significant stiffness. To make it less prone to twisting, we spaced out the openbuilds wheels a bit more, which does make the Y-axis a bit shorter, but that’s ok. What also helped was adding a two-story MDF top-plate. The thicker bottom part was screwed to the original sub-bed and is going to stay there, forever, and the 10mm thick top plate is essentially a waste plate that will get screwed, milled and drilled into and is just something that is going to be replaced on a regular basis.
Electronics-wise, we didn’t change anything. The motors, drivers, control board etc are still the original parts, but the firmware is now running slightly slower maximum accelerations and speeds as well as slightly higher current for the extra weight on the X and Y axis as well the cutting forces themselves.
So the original idea was to use this Proxxon rotary tool, because it came with a nice mounting flange, has a collet chuck and a wide range of adjustable RPMs. And it worked great for a while, using these cheapo 3mm two-flute bits, it milled happily through MDF and even aluminum with, like, super reduced cutting depths and feeds. Engraving into acrylic also worked beautifully, but it didn’t last long. The bearing in these tools aren’t great, well, at the very least they’re not made for machining like this, and after replacing the original Proxxon tool with a newer that supposedly had an extra bearing for that exact purpose and still having it fail in almost no time, the MendelMax sat unused for quite a while.
I was frustrated, after spending so much time on modifying the machine and buying two of the Proxxon tools, it was almost all the way back to the start. But thanks to the internet, you now have access to an almost infinite catalogue of parts, and eventually i found this 400W, 48V spindle motor with an ER11 collet. Sure, it’s technically only a large-ish brushed motor with a collet chuck on its shaft, but if it worked, i’d have a more powerful tool, a better chuck and still pay less than buying yet another Dremel. So after getting that and a matching 48V power supply, the machine was back in business really quickly, and it turned out that the spindle motor was actually quite solid. I can adjust the RPM by just tweaking the output voltage of the power supply, but i still want to add something like this DC motor controller to make it a bit more elegant. Right now, the surface finish can be tweaked to be, i think, fairly amazing, it definitely needs a finishing pass on any surfaces you’ve machined and tricks like trochoidal milling won’t hurt, either.
Now, the converted MendelMax isn’t perfect by any means. It’s still a 3D printer frame after all, never intended to be used for these heavier applications. For example the Z-axis nut holder are still way too weak for this and will be replaced by printed versions, also the electronics and the Y-axis rails for the openbuilds wheels could use some extra protections from the chips, with electronics, obviously, for not shorting stuff out with aluminum flakes, but the OpenBuilds wheels are also extremely prone to just picking up chips that sit on the rail and then end up rolling everything but smoothly.
I also sorta want to replace the regular GT2-2M 6mm belts, which are often just called GT2, with something maybe at least a bit wider to make it stiffer, maybe even a leadscrew or a ballscrew if the little MendelMax doesn’t present me with any more severe issues. Though that would probably also warrant stiffening up the frame significantly.
And obviously, both 3D printing and CNC machining are very heavily dependant on what software you use to prepare your jobs, and while CNC obviously has a ton of options when it comes to high-end CAM packages, the equivalent of a slicer, there’s not that much great software out there that is somewhat powerful and still easy to use. Sure, Autodesk Fusion is an incredibly powerful too, but the “free as long as you’re a tiny startup” and the learning curve involved kept me looking for simpler options. I personally can program something like a Haidenhain CNC controller directly and use a five-axis CAM like TEBIS, but neither of them apply here, obviously. What i found to be a nice middleground was the shareware-like ESTLcam, which is a fairly simple, 2D or 2.5D-centric cam that does just about enough for me without having to relearn the entire tool whenever i want to machine something. It also does picture engraving and 3-axis 3D milling, and while that’s good to have, it’s not a major selling point for me. What i want is just a simple, visual tool, ESTLcam is just about ok enough for this. It even creates Marlin-compatible gcode out of the box!
So yeah, that’s the first part of my adventure with turning a 3D printer into a mill. While it’s not perfect and was a lot of work, it has most definitely turned out better than i expected. I mean, it mills aluminum, that’s a success whichever way you look at it! I’ll definitely be making a few more mods in future, but at this point, it’s already an awesome little conversion, i think.
If you want to try something similar, i’ve linked the spindle, power supply and milling bits i’m using in the description below. I hope you learned something in this video, if you liked it, give it a thumbs up, consider subscribing to the channel, and because Youtube is still being weird about it, remember to also click that bell next to the subscribe button or you might end up missing some videos altogether.
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