Let’s Print a CNC!

May 18, 2020 - 3D Printing, CNC, Projects, Tools

For more than a decade, I’ve badly wanted a CNC mill in my workshop. I’ve long been a hobbyist CAD designer, and was thrilled to get in to 3D printing about 5 years ago: The concept of being able to take my computer designed thingies and make them real, was just amazing. The next thing was to scratch that itch of being able to actually machine real materials like woods and metals, to make finished objects.

For more than a decade, I’ve badly wanted a CNC mill in my workshop

~ Me. all the time.

Recently I came across Topsie’s TopCNC Project, which is really awesome! The concept is simple: Take readily-available parts  commonly used in 3D printers and robotics projects, such as aluminum V-slot extrusions, wheels, ACME screws, and wrapping those up in a very thoughtfully-designed 3D printed set of components, to make a legit, large-format CNC.

The basic idea is to use these very strong, fiberglass or sometimes Kevlar reinforced, tooth belts to drive the motion on X and Y, and use an idler tensioning mechanism, similar to this:

Idler-tensioned belt drive

As you can see, as long as your belt material is dimensionally stable, you can achieve some really long axes without needing expensive ACME threads. These threads are great, and we will still use this for the shorter Z axis.

Typical ACME thread with linear slide rods

It’s the longer lengths that become problematic, as they need to be thicker, higher precision to prevent any wobble or distortion that will cause binding in your motion. Thicker rods mean heavier rotational mass, requiring larger more powerful stepper motors. More cost, more moving mass on that axis; the whole thing escalates quickly.

Thicker rods mean heavier rotational mass … the whole thing escalates quickly.

~Basic law of diminishing returns

Parts List

Let’s put together a list, starting with the parts deviating from Topsie’s design:

  • (4) NEMA 17 stepper motors: link
  • Stepper motor drivers (3 pack): link
  • 24v 350w Power Supply: link
  • Arduino UNO: link
  • GT2 6mm timing belt, 10 meters: link
  • 6mm toothed pinions: link
  • 6mm smooth idler wheels with 5mm bearing: link
  • (9) 2040 V-Slot Extrusion – lengths are up to you
  • M5 screws for idler wheels (unsure of length yet)

What’s next? This is a quick introduction to the concepts and overall idea we want to accomplish. In the next post, we’ll dive in to the modifications to the TopCNC design, where to obtain the source files, edits. In the Third and Fourth installment, we’ll be going through printing, building, tuning, and also introduce a really cool Raspberry Pi based CNC controller interface. Check it out if you want to preview where we’re going here… check out the CNCjs project on GitHub. Yep, it’s even open source!

Alright, that’ll do for now; check back soon!

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