Mendrel Cutting

This post provides a step-by-step guide to cutting and some of the issues that arise.

First, Get a 3D STL model or 2D SVG model for PyCAM. Convert the model to g-code following the PyCAM post. Remember where you saved your g-code file (/pathto/model.ngc).

Second, mount the styrofoam that will become your object onto the sacrificial piece using double-sided tape. You should only need 3 or 4 pieces of tape. Line up the piece with the marked line. This line represents the origin for cutting.

Turn the kill switch to ON; a red light should turn on.

Turn on the Dremel. Put on dust mask.

Open a terminal (ALT + CTRL + T). Type:

cd cnc_mendel

python controller.py /pathto/model.ngc

The Mendrel should begin moving. Its first command will be to home (move to the origin). After that, it will proceed to cut the styrofoam. During this time, gently hold down the board as it cuts from a safe distance. Do not put your hands near the drill while it is ON. If something happens, turn the Dremel OFF then flip the kill switch OFF. Wait until the Dremel bit has stopped spinning before putting your hands anywhere near it.

When the cutting is finished, the Mendrel carriage will move itself upwards in the Z-axis above the Styrofoam and return to the X, Y origin where it will remain. At this point turn off the Dremel. After the Dremel bit has stopped spinning, remove your object and the sacrificial board. Separate the cut piece from the sacrificial board.  Remove the leftover tape.

Vacuum the Styrofoam particles on your object, the sacrificial board and the Mendrel as best as possible.

If everything went well, your cut object should be ready to go. If things did not go well, some known issues are discussed below.

Styrofoam Melts to Dremel Bit

This tends to happen if the object or sacrificial board are allowed to move while the Dremel bit is cutting. To avoid this, make sure the piece to be cut is secured to the sacrificial board with double-sided tape at all times of the cutting process. Ensure the sacrificial board remains in place by gently applying downward pressure to it while cutting takes place.

To remove the hardened Styrofoam around the Dremel bit, cut at it with a box cutter knife / utility knife / X-Acto knife. It is an arduous process, but eventually it will come off.

Resolution

If the Dremel bit’s diameter is thicker than a fine detail, the detail cannot be cut, or at least not very well.

Accuracy Errors

The cut piece may have some inaccuracies. This is an issue that is very difficult to correct. As described in the background post, the Mendrel is derived from the Mendel — a 3D printer. After a lot of work and testing, we came to the conclusion that the Mendel has some design issues that introduce some inaccuracies in odd ways. For its time, these problems were acceptable, but a lot of work has been put into creating 3D printers with better resolution, consistency and accuracy. As a result, we decided against putting more effort into fixing these issues in favour of building a cutter in the future.


  1. Mendel Background
  2. Hardware
  3. Electronics
  4. RAMPS
  5. PyCAM
  6. G-Code
  7. Cutting
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