The first project for designing accessories to mount on the extrusion beam, a holder for ER11 collets, turned out well enough I wanted to continue. Apply some of the lessons learned to create more nice-to-have accessories for the CNC project.

One accessory is a holder for a 5mm hex wrench. This is the size used by the fasteners bolting our gantry’s extrusion beams together. There are a set of four bolts, two on the left and two on the right, that we loosen to adjust the height of the gantry. Lowering the gantry lets the cutter cut through our work surface to cut holes for threaded inserts, raising the gantry gives us more Z travel for the work piece. Or we might deliberately trade off Z travel to use a shorter and more rigid gantry for more challenging pieces. We’re not sure what the viable combinations are, but we do know we’ll need this wrench handy for experimentation.

The other accessory is a wire management clip. Wiring is a perpetual challenge on this project, from finding appropriate component placement to isolating electrical noise. I’m sure electrical challenges will continue to vex us as we proceed. We’ll figure out the problems one by one as we go, but one thing is for sure, we’ll need a lot of ways to route wires and keep them in place, hence the clips.

Unlike the previous accessories, the wiring clip may be mounted in any orientation. To hold themselves in place, each clip will require additional holding force. To get this force, they are printed slightly more open than their installed configuration. Installation would then require compressing the ring and this tension in the plastic will provide friction against extrusion rail to hold it in place. And while I’m not entirely sure it will be necessary, I added a small flap to keep the wire from sliding out of the ring into the rail slot.

There will be more accessories along the lines of what’s been printed so far, but I’m eager to get back to the primary exploration of cutting material.

While I was in Onshape CAD designing our goose neck work holding clamps, I also tackled a few other to-do items on the 3D-printable accessory list. The top of the list was building a way to keep extra collets accessible on the machine. Our CNC spindle came packaged with a 1/8″ ER11 collet, which we swapped out for a 1/4″ collet when we wanted a stouter cutter. We didn’t have a good place to keep the temporarily unused 1/8″ collet and, rolling around on the tabletop, we were constantly at risk of losing it.

I thought it was a good project to practice designing plastic’s flexibility to my advantage instead of constantly seeing it as a disadvantage. I’ve had several projects along these lines before, but my interest was renewed by Amy Qian’s demo board she brought to show off at Supercon.

There are two ways I wanted to apply this concept. First, I wanted a holding mechanism that can snap into an extrusion rail and stay there without use of tools or fasteners. Second, I wanted a way to hold the collet so that it is held securely by default (not fall out or be dropped easily) but can be removed easily on demand. Again without tools or fasteners.

Here is the first draft of a flexible clip for installation into extrusion beam, this design was too flexible and fell out of the extrusion rail easily. More iterations followed, hunting for the most secure hold possible while still making it possible to insert into the rail.

Separately, I started designing a flexible cover for the collet. The test piece for each mechanism evolved separately until I was happy with both designs, then they were integrated into a single piece incorporating both mechanisms.

With the success of this holder, I took the lessons of a flexible extrusion beam mount and applied the concept to a few additional 3D printed accessories.

Once we have metal threads securely inserted into our MDF work surface, we could bolt on clamps to hold our work pieces. These clamps are 3D printed because we fully recognize our CNC beginner status and, while we’ll do our best to avoid crashing cutting bits into fixtures, it’s realistic to plan for the probability that crashes will occur despite our efforts. If we use commodity metal clamps and our carbide cutting tool makes contact it will break our tool. But if our carbide tool contacts a piece of 3D printed plastic it might survive our mistake. We have the luxury of this provision because we’re starting easy with scraps of MDF, which requires less forces to hold and to cut than cutting metal.

We started by copying standard step clamps. We weren’t sure if the steps could be accurately replicated with 3D printed plastic so it was worth a bit of experimentation to find out. They look very promising but we probably won’t use them, because the reason step clamps exist is to have a few set of them that can adjust to various sized work pieces. 3D printing gives us the flexibility to print project-specific fixtures that don’t have to compromise for flexibility. This advantage can make up a tiny bit of deficiency inherent in using plastic instead of metal. Hence the second iteration: a single piece clamp shaped like an L designed specifically for the thickness of our test piece of MDF.

Once that was printed and eyeballed on the work table, we moved on to the third iteration: a low profile goose neck clamp tailored for the height of our scrap MDF. Low profile design reduces chance of cutter collision, and it allows us to use shorter and stouter bolts to fasten them to the table. This is what we will use for our first real cutting experiments, alongside other 3D-printed accessories for our CNC project like a collet holder.

We now have a small G-code program that we can call upon to cut holes for self-tapping threaded inserts. We’ll cut them as needed for work fixtures on our CNC work table. However, cutting the hole is only part of the process, we had to install the metal insert as well. In order for the resulting threaded hole to be vertical, the inserts have to be held perpendicular to the work surface as we install them. However, the coarse exterior thread makes it difficult to maintain the orientation, made more challenging by the fact the shallow hex socket allows the insert to rotate around the tip of a ball-end hex wrench making it even harder to hold vertical.

We originally had the hypothesis that, given the geometry of the wooden hole, our metal insert will self-align as we start turning it. This may be true for some types of wood but it didn’t work for our particular sheet of MDF. If the coarse outer self-tapping thread starts biting at a bad angle, the insert did not self adjust in our experience. It just jams partway down the hole ruining the MDF hole in the process.

To solve this problem, we designed a small 3D-printed plastic tool to help maintain vertical alignment for installation.

The bottom part of this tool helps keep the insert vertical, and the top part keeps the hex wrench vertical. The bottom is mostly flat for the work table surface. I tried adding a small lip to help with hole alignment, but that turned out to be unnecessary. These metal insert can align itself in the XY plane well enough. And once these inserts are in place, we can bolt down our pieces of scrap MDF using custom gooseneck clamps.

The first thing I wanted to address after a wobbly (but successful!) first run was placement of the control console computer. I didn’t have a good place to set the tiny laptop down. The machine may not look like it would take up the entire table, but once machine’s range of motion is accounted for, there’s not a whole lot of space left. During the test run, the laptop was literally on the ground next to the table. It would be useful to have a dedicated computer shelf.

The shelf was designed in two parts. The right side could be bolted to the end of an extrusion beam, but the left side didn’t have that luxury. I thought I would design it to clip on to the extrusion beam, but the first draft hooks were far too aggressive. I had to trim them back with a saw before I could fit the piece around the beam.

Both hooks installed and ready to host the computer. The right hand hook was printed with the final filament from one spool and start of another spool of PLA. Even though I ordered from the same vendor (Monoprice) they have apparently changed vendors or specification and the new spool filament is visibly different.

At first glance this design may appear to be heavily cantilevered, with most of the weight on the front of the hook placing great stress on the mounting points. This is only true when the laptop lid is closed. When the lid is open, where this shelf mounts on the beams is actually very close to the center of gravity of the laptop.

It still needs to be able to accept some weight, though, since there’ll be physical forces as I type on the keyboard and use the trackpad. But PLA is plenty strong for this application, with very little flex even when I rest my wrists on the computer.

This shelf is probably not permanent, but it is nice to have a convenient shelf to hold the laptop while I figure out how to work the rest of this machine.