A simple and tough cnc frame made from low cost hardware store parts and affordable electronics
The project is moving along nicely. In my infinite wisdom I put the sleds in the inner print area, have to flip them around. In real life the work area seems pretty decent, somehow larger than I envisioned. My version of the Peoples CNC Frame won't have much Z height because I want the machine to do mostly cutting and drilling and be as rigid as possible. The Z movement would be ~4-5cm. The Z mount plate could be taller, which would provide more range.
Quick SketchUp modelling really helps in putting all the pieces into perspective. The frame will be a mix of metal and wood. In the sketch you can see a brushless spindle for reference (replace with your weapon of choice). The spindle mounting wheel sleds could be flipped to go inside the Y-axis rails making the setup more sturdy by sacrificing Z height. In fact, this model better illustrates that the frame is great for 3D printing in this configuration because the Z-axis has plenty of range.
I still need to order the Z-axis lead screw setup. I think I'll go with a 20-30cm lead screw for height.
After staring at the 20cm carriages that I had sawed off from the 50x50mm pipe, I decided to split them to make 10cm long pieces.
Each wheel attachment hole is approximately one cm from the edge. The holes should be precisely centered in the vertical axis.
First a mark was punched by hitting a nail with a hammer at the intersection of the scribed lines. Then a small guide hole was drilled with a 3 mm drill bit. Finally it was brought to approximately 8 mm with a step drill. The step drill is a very good tool to get nice round holes without a drill press. The wheels spin nicely when the nuts are a little loose. However I forgot that I need bearing spacers inside the wheel so I ordered those, they should stabilize the wheels and eliminate any wiggle. I'm also ready to expand my 8 mm holes to 10 mm to allow for adjustment when the machine is put together, let's see what happens.
The skateboard wheels arrived! I now have all the crucial components of the frame.
The X and Y axis will be driven by common GT2 belts. I plan on having 2 parallel belts per axis.
With the selected components the Peoples CNC Frame will be both strong and agile!
Buying cheap bearings is a gamble. I've gotten horrible groggy specimen as well as extremely well performing ones. The bearings in this project run very smooth, note that there are two per wheel, this greatly diminishes sideways play.
Two meters worth of 30x30mm tube has been hacksawed to four equal length parts. A 20cm long and 50x50mm wide sled is on top for reference. Maybe the sled length could be reduced, let's see. Below is a picture of the big brother of the Peoples CNC Machine.
I've ordered some SC8UU bushing blocks and mounts for 8mm pipe for the Z-axis. I'm also looking for well priced lead screw sets to move the drill plate. The sideways work area was reduced because the pipe guides are far apart from each other. I think its a necessary sacrifice, it also allowed me to flip the lower central sled up to reduce the height of the gantry. Thanks to everyone following the project, it's encouraging to see that there is interest in such an apparatus!
I've started with 30x30mm rails and 50x50mm sleds. The sleds allow for M8 screw ends to fit inside the square tube nicely. All the rails are 500mm long. The sleds might be too short or I could place the wheels closer to the their edges to prevent rocking. Maybe the 2 on top 1 on bottom wheel arrangement isn't stable enough, if it isn't, more wheels are in order. These are sketches not the final design, the design will transform as the project moves along.
At the Jyväskylä Hacklab here in Finland we've been building a large CNC machine for some months. The inspiration for the Peoples CNC Frame (PCF) comes from the successes and lessons that our lab machine has taught us. The elegance of the PCF comes from its simplicity, ruggedness and availability of parts and tools. Linear motion on the X and Y axis is achieved by using skateboard wheels and bearings. These can be ordered online for quite cheap. The rails are standard hardware store square pipe. Our hacklab version is based on 50x50mm rails, it uses lead screws and covers an area of 1x1m (cutting area is less). The machine is very sturdy and could easily be much larger without losing rigidity. Our hacklab version uses longboard wheels.
The People need a CNC machine for home. I often have a need to engrave a PCB quickly to test a circuit and I wish I had a CNC machine to do the job. I'm sure you have a need for a desktop CNC machine as well, so heck lets make one.
I've ordered some standard skateboard wheels and bearings. While I wait for them I'm going make a sketch of how the Peoples CNC Frame could look like, it'll be smaller than our hacklab version since we don't want to upset our partners, neighbors, pets or our personal zen.