Week 7 : Computer-Controlled Machining
This week is BIG week. BIG projects, with BIG machines, with even BIGGER ways of messing up! Our goal was to make (design, mill, and assemble) something large on the meter scale. So naturally, for our group assignment, our goal was to go through labs safety training for the CNC and test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for our CNC.
Buildign Something BIG with the CNC
For this week’s project, I chose a design based off a few work arounds I needed to consider and even with the amount of preventative planning, I still had challenges to face. At AMRoC Fab Lab we currently didn’t have a wood bit available in the shop and we have a decent amount of scrap polycarbonate, so the chosen material would be polycarbonate. Also, our CNCs in the shop are on the smaller side, the largest with a cutting size of 39inx23in. This means I would need to divide my file into more pieces and consider connections.
I decided to make a standing cutout structure of the Forest Spirit from the Studio Ghibli film Princess Mononoke. A friend of mine will be getting married and she will be having décor that is Studio Ghibli themed. This Forest Spirit is intended to be uses in a photobooth scene.- To create the files, since it is more of an organic but distinct design, I wanted to draw it out. I used Photoshop and a Wacom tablet to draw the main design and shapes.
- I used two different colors for my own indication of which pieces I want to cut all the way through versus which I want to be pockets.
- Then I transferred the photoshop file to Illustrator. I imaged traced the design to turn it into a vector file. I cleaned up edges and imperfections.
- I sized the design to the desired dimensions. Here is where I divided the design into four separate pieces. Once I divided the pieces and cleaned up what are attached pieces and split up pieces, I added in the slot connections.
- I measured the thickness of the material and made the slots accordingly. We will add in parameters after when we transfer the file into Onshape or Fusion360. I added in dogboning.
- Once I completed the file in Illustrator, I exported the files as DWG files to open them into Onshape.
- In Onshape, open a sketch page and choose the Top face. There is a button in the top menu bar to import a DXF or DWG file. Here is where you import the file.
- The file will show up on the sketch page. Extrude the main face/surface to the thickness of the material.
- To create different thicknesses within the file (which shapes I want as pockets, pieces that are thinner but not cut all the way through), create a second extrusion. Click on all the faces(shapes) you want to be the same pocket thickness and type in the desired depth.
- Now the file is set to the correct setting. We need to open our file in Kirimoto to set up the toolpaths and other CNC settings.
- Click the plus sign at the bottom left of Onshape and go to applications where you can connect to Kirimoto.
- In Kirimoto, the operations list is to the right menu bar. You choose a toolpath (like pocket, trace, rough, etc.) Here you set the spindle rate, feed rate, plunge rate and other specs depending on which toolpath you are working in.
- Set the rates and then click the select button to click on the corresponding parts on the 3D file. If you are doing a trace cut, that cuts completely through the material, you want to select the bottom edge of the file material verses the top edge of the material. For pockets, you select the inset surface and not the edges of the file.
- Once you select and set up all your paths, you can preview the toolpath both in “slice” where you can see the layers and animation with a video running it intended cuts.
- Now that everything is ready to go, save your file as a gcode.
-Open your CAM software. At our shop for our machines we use Mach3Mill. Load your gcode into the software.
- Before running any files, you are going to want to make sure the spindle/bit is out of the way of you loading your material onto the CNC bed.
- To fix the material to the bed, we use brass screws to screw our material into the spoil board. Make sure to fasten down all corners of the material so you don’t get material lifting during cutting.
- If the material is fastened down well, then we want to set our Zero for the X, Y, and Z axis.
- With all our previously set code, we should be a to press play and watch the magic happen…SHOULD. When I hit play and it started on the first pocket, it looked very deep on the first pass and was getting instant material build up on the bit and even minor material chipping. The grove was about 1/8in deep when I had set the step down to be.025in. I triple checked and trouble shot everything I could think of. Was the step down set correctly? What about spindle rate? Well that shouldn’t affect the depth of the cut? Its not a down cut. Is the material getting stuck on the bit? Maybe I didn’t set my zero position correctly?
- I started the cut over multiple times and still same result. I was stumped. After hours and actual days I have come to find out it was something simple that I that I had accounted for but didn’t in a certain aspect. The material was bowed/warped.
Group Assignment
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