Using CNC

Toy Truck – A beginner’s project

A CNC beginner’s project

Toy Truck A beginner’s project day one: While Paul was focusing on designing and delivering the Super Gerbil CNC kickstarter project, I was helping with the testing. Rather than using simple test shapes, I tackled something a little more complex to help avoid boredom !  The result was a toy truck as a beginner’s CNC project. Actually, being made from acrylic, it’s really a model truck, because it’s too brittle for a child’s toy. Yes, it’s delightfully out of proportion… I really just sat down at Fusion 360 without any planning or reference, and ended up with a caricature of an old style truck.

Truck structure

I thought through different ways of connecting the panels at right angles. Most of the joints are tongue-in-groove, but this alone wouldn’t make a stable structure. I discovered parvum blocks, but ended up using stand-offs as a cost effective alternative. Finding and using them was the single biggest learning from the project – I’ll definitely use them again as they’re fast, easy and rock-solid.

The two side panels joined (at multiple points) to the chassis with stand-offs

Wheels and steering

Paul found the wheel design online, and I designed the steering assembly. Yes, it’s simple and far from perfect, but I had fun doing it. Next time I’d design larger wheel arches, so the moving wheels have a greater range of motion.

3D printed wheels and steering mechanism, with brass axles

Workholding

As usual, work holding is a non-trivial part of the project… I used both custom jigs and double sided tape.

Truck profile with workholding

Starting with a rectangle of acrylic, my sequence for profile machining was:

  • Mill the small hole in the middle of the two workholding jig circles. Now screw down the workpiece using screws through these holes
  • Bore out all the small holes for connecting to stand-offs
  • Mill the seven slots as pockets
  • Mill the outside contour of the profile, then clamp the whole workpiece from the outside of the milled profile
  • Contour the inner window shape
  • Remove the shallow surface needed to accommodate the bearing flange using a pocket
  • Remove the remaining material to accommodate the rest of the bearing, again using a pocket

Other learnings

Combining 3d printing and CNC worked well. The fine detail of the wheel tread was 3d printed without a fuss, which was lucky because I revised the wheel size. This would have been a lot of work on the mill.
In future, if I want to get a realistic looking model, I’ll look up real-world objects and pay more attention to realistic proportions.

What’s next ?

This simple model is really just the beginning, as it only demonstrates 3 axis movement driven from the Super Gerbil CNC controller. Rather than beginner’s CNC project, future projects will include 4 and 5 axis control. If you’d like to buy a Super Gerbil CNC controller for your CNC project, they’re for sale at awesome.tech

Just enough details for you to try yourself…

Parts and material

  • 2,3 and 6mm acrylic
  • 6mm flanged bearings (4 OFF)
  • 6mm brass rod
  • 6mm (or 1/4″) collars (2 OFF)
  • 3mm hex head screws Stand offs (10 OFF)
  • Double sided tape (for workholding)

Tools

  • 3D printer
  • CNC machine Super Gerbil CNC controller
  • Fusion 360
  • acrylic scoring knife
  • calipers and ruler

Feeds and speeds (conservative)

For detail:

  • 1.6mm 2FL endmill @10000 RPM, ramp 100mm/min, plunge 75mm/min, DOC=0.35mm
  • 1.6mm 2FL ball endmill @10000 RPM, ramp 100mm/min, plunge 75mm/min, stepover=0.3mm
  • 2mm 3FL endmill @ 8000 RPM, ramp 75mm/min, plunge 75 mm/min, DOC = 0.25mm

For bulk removal:

  • 3mm 3FL endmill @ 10000 RPM, ramp 300mm/min, plunge 75 mm/min, DOC=0.35mm

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