In earlier posts, I shared why I upgraded (Part I) my CNC, and the sources for the main components (Part II) of it; here I’ll show all the pieces put together and share a bit more insight on the challenges in the process.

The Mundane

Bed & Lift

One key requirement was for my machine to be light enough to hoist overhead in my limited-space workshop. It quickly became clear that though I had weight in mind in each individual system, I was still going to blow through my 220# weight target! Though the aluminum CNC frame weighed in under 100#, the heftier spindle and stepper motors added about 30#, and the larger machine size required a larger MDF waste board as well. That’s before adding in the 4-axis & 5-axis components, wiring, etc.

So I upgraded to a 1000# hoist, secured to the beams in the workshop, which also meant I needed to upgrade the backup earthquake protection for when the lift is in the ceiling. And to give enough headroom for the taller machine, I also cut an access hole for the z-axis protrusions above the gantry.

Frame & Controller

The frame - pictured in this earlier post - was relatively straightforward to assemble with the stepper motors and motor. And integrating all the sensors, limit switches, and with the highly-configurable Masso control, and setting up the stepper motor drivers, was very time-consuming and required lots of adjustments, but not particularly challenging as there were loads of Masso video tutorials.

Multi Axis Capabilities

I wanted to integrate 4-axis and 5-axis capabilities into the CNC bed, and indeed, about a third of the work area is literally cut out of the MDF waste board to give more vertical clearance to these elements. But I wanted to do this in a way that provided that most flexibility for a range of jobs. I can remove the screws holding these 4-axis and 5-axis systems into the T-track so that I can use the full 48” width of the CNC to cut large profiles. Or I can use the hold-downs in this recessed area to mill much into taller items, with an 8” vertical clearance.

The other small customization I did in this area was to reverse the orientation of one of the motors in the 5-axis system; this allowed me to fit the assembly in the limited x-axis space of the recessed area. While I wish it was as simple as just flipping the motor around, I actually needed to customize a stepper motor mount, buy a new motor, and find a longer-but-matching-profile belt to fit into the change in position. While none of these steps was particularly difficult, it actually took a bit of sleuthing to find the right belt profile and a supplier.

Unfortunately, it seems that just as I added the capability to do rotary and 5-axis milling, Autodesk changed their pricing model from including those features in their standard paid subscription (which I have at about $300/yr) to charging an additional $1,600/yr premium! So I’ll be looking into other solutions for this - DeskProto seems like a promising CAM solution. Stay tuned for more content on this in future posts.

Tool Changer Magazine

The automatic tool changer system came with a 10-tool rack; using Mechatron’s design as a template, I built a 16-tool version to leverage more of the space available on my machine. But when I tried to actually use it, it seems I neglected to consider that differences in how deeply the collet can tighten on the tool means that some tool holders will sit higher than others. Unable to detect or handle these differences in height, the tool changer will either collide with or just completely miss some of the tools.

So I had to take a completely different approach to the tool magazine. I found ISO10 ER16 “tool forks” from a supplier in China; they were surprisingly expensive for their size and - perhaps because so few machines of this “small size” have tool changers - there did not seem to be any alternative suppliers or sources for them. But they indeed solved the problem.

The Challenging

Electrical Noise

Once I got all the basic motor wiring in place, it was time for a system test - but the stepper motors were making weird noises and skipping loads of steps, losing their position for even basic “out and back” moves. This one took a while to troubleshoot, and ended up being two problems.

Stepper Voltage

Though I originally was driving the stepper motors with 52V based on the equation 32 * sqrt(inductance) in this introduction, it seemed this was the culprit for the bulk of the motor jitters: lowering the voltage to 20V cut the positional error from about 10% to perhaps 1%.

After a query to ElectronicsStackExchange, I got some guidance as to why a lower voltage was necessary, but I’ll confess that my electrical engineering understanding does not extend deeply enough to fully grasp that explanation. Regardless, my updated settings (lower voltage; fewer microsteps; lower acceleration) seem to work.

Grounding

I was able to isolate the remaining error to the spindle controller VFD (variable frequency drive), a solid state device that converts “standard” two phase power to a three phase signal. Though I do not fully understand the solution here either, I was able to remove the noise by changing the ground wire configuration between the VFD, spindle, and aluminum frame. It seems that perhaps I had created an antenna via a ground loop that removing some of those connections solved - though that loop is probably formed with some non-obvious control wires and is dependent on the VFD being powered on.

Bonus Video

In troubleshooting these issues, I came across this excellent video where James works through some similar issues with his VFD. The two solutions that worked for him - a line noise filter and ferrules around the motor cables individually and collectively - did not solve my problems, though I imagine they may nonetheless help at the margins.

2021 Update

After all these updates, months later, I would still every once in a while get a missed step; I finally bit the bullet and upgraded to closed loop servo motors, which I document in great detail here.

Dust Collection & Tool Changer

Two key elements of my system were initially somewhat incompatible with off-the-shelf solutions: dust collection and the automatic tool changer. In short, if the tool holders are spaced tightly together, the height of the tool holder will hit any dust boot. Only if they are spaced more than 1.5x further apart would the tool holders clear the dust boot, which would mean I’d be constantly swapping tools into and out of the magazine, negating much of the value of the tool changer.

So I created a novel solution here. I used a two-piece dust boot from TiteCNC, where the top portion is attached to the spindle, and the bottom portion with the bristles is held in place via four magnets. That magnetic connection of the bottom portion, however, can be overpowered by an electromagnet grabbing onto the boot from the side. Thus, every tool change is sandwiched by first dropping off the dust boot, and afterwards, picking it back up.

For those interested in the weeds, to achieve this, I modified the Fusion360 postprocessor to inject a line that calls a subprogram before and after each tool change. That subprogram, in addition to doing the movements, also triggered the electromagnet via a relay with one of the customizable auxiliary outputs on the Masso controller.

Fully Integrated System

This whole process took about twice as long as I expected (and still is not complete, what with a probe to still integrate and a few other elements to fine-tune)! Partly because I was waiting for parts as I solved one problem only to find the next. And partly because I was “distracted” by other projects, both paid and personal, not focusing on this 100% of the time. But I’m excited to finally be able to say “done” - or at least, as done as any workshop upgrade ever is!

In future posts here and on Instagram, I look forward to sharing some of the creations that come from this new machine!