So this project didn't really go to plan. Let's recap...
We set out back in August to build a CNC Mini Mill using an old tumble drier motor. There were a few requirements which drove a particular design choice.
- Space - it's got to fit on a tabletop.
- Stiffness - it's got to be stiff.
- Cost - it's got to be cheap.
With these three requirements, especially the one around space, I quickly went back to the idea of reinforcing the Hypercube to be stiff enough to act as both printer and mill. In the previous post in this series, we covered my first attempt at that. Since then, Tech2C published his guide to turning the Hypercube into a milling machine, which inspired a lot of progress...
What was different about his approach?
- More stiffness - He's taken away the carbon fibre X-axis tubes and replaced them with steel rods.
- Less Deflection - The geometry on the milling head in his design is much better, partly through taking away the excess weight introduced by the Dremel tool and offloading that using a flexible shaft, partly through the geometry of that mount, keeping the axis of the bit close to the carriage and reduce the bending moment.
What doesn't quite fit out initial requirements?
- It doesn't use the motor! - Perhaps a slightly circular argument (maybe we shouldn't use it in the first place), but there's another advantage here is the larger motor being more powerful, and also quieter.
- Tip deflection - In the follow-on video to the one above, you'll find that Tech2C found it very difficult to use an angled "V" bit for engraving PCBs, because the flexible shaft attachment had too much play in the end bearing.
So how does this change the plan?
- The flexible shaft idea is really good. It allows us to keep weight off the X carriage, and decouple the drive mechanics from the cutting head.
- Replacing the x-axis rails is going to be important. We need something stiffer than the carbon fibre rods.
- We'll need a redesigned spindle mount for the cutting end, to give us something with less play than the original. Bonus points here for a more flexible collet system such as an ER collet rather than just a standard 3.75mm Dremel collet.
- The z-axis is going to need to be much stiffer on the Hypercube to counter the reaction forces in that direction.
I'll cover the build to the finished product in three separate posts. One for the drive section, one for the milling head and one for the z-axis mods. For a teaser while you wait, here's a view of finished product in action: