2 Sided CNC Testing

Having successfully carried out the first test, we began to contemplate how we might go about creating the 2 sided, complete CNC’ed form. This was a long process with a lot of trial and error on the computer and some external help. However, after 2 days of trying to work out how we create two different reliefs, one back one front, we finally came up with the method-

  • First you much cut the material to be CNC’ed completely square.
  • You much then cut out a matching square piece of MDF to use as a jig when you flip the material to machine the second side. The material being CNC’ed sits inside the corner of the sheet material and when you flip the material to machine the second side the same corner of the material sits against the same corner of the sheet material ensuring it is in exactly the same place so you get a back relief in correct orientation with the front.
  • Then in Artcam you input the material sizes and import the 3D model as if you are doing a normal 1 sided CNC cut, see previous post for steps. The only change you need make is to change the z coordinates to get the model to sit in the middle of the material block. This is achieved by diving the difference between the material height and the 3D model height, by two.
  • Once you have pasted the model down, instead of immediately writing the toolpaths, you click on the ‘back relief’ tab in Artcam. You then simply rotate the model 180 degrees and paste this down. What this does is create a front and back relief of the two different surfaces, treating them as separate objects. What one must do is first CNC the front relief onto the material block and then flip the material over 180 degrees using the pre-cut jig and CNC the back relief.
  • Once you have got your front and back relief in Artcam, you must make supports which stop the pieces from falling out of the block of material. This is done through the use of vectors. You first create 2 outline vectors around the piece. One of them tells the CNC machine to only CNC within that outline meaning it doesn’t CNC the whole block, just the surfaces of the piece. On the second vector you put in points which tell the machine not to cut out, leaving a block of material holding the piece in place.
  • Finally you write all the toolpaths for each surface and a separate one for the supports. For the front surface I decided to test out using 6mm ballnose bit to see what the difference in surface finish would be in comparison to the 12mm. The toolpaths can then be sent to the machine.

Below are images and a video of the process, from cutting out the material to the final finishing stages. You can also view the part where Artcam generate the toolpaths which produces and really cool effect with a mass of lines flowing over the form.

The finished form-

After this successful CNC 2 sided test the only thing left to resolve was the extra thickness of the piece that came out. The piece was an extra 30mm thick than the original 3D model which is something we are going to be working on fixing and should be relatively straightforward to resolve.

I am really pleased with the 2 sided outcome and I think the flowing, undulating surface look really good. I don’t think the 6mm bit actually added any extra quality in finish to the 12mm bit. It also was vibrating a lot due to the depth of cut it have to achieve, which could have actually been responsible for a rougher surface and extra feathering of the material.

I have really enjoyed the process of learning how to CNC a 2 sided model so far and I’m looking forward to having all of my models done. I now need to resolve what material I am going to CNC out of.


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