Week 8. Computer Controlled Machining

Go to:
  1. Group work
  2. Model
  3. Manufacture
  4. Machining
  5. Results of the Week

1. Group work

Task: Test runout, alignment, speeds, feeds, and toolpaths for your machine.

This week the group was all Oulu Fab Academy students together. The pictures are taken by Jobin.

Eino showed us the CAM operations needed to prepare nc-file for cutting. He also showed how the machine works and gave the safety instructions. You always need to have safety glasses on when using machine. Also hearing protection is needed.

Group work design created with Fusion 360

We went through following issues:

We used Fablab CNC machine and NC Studio software.

We opened the design file that supports CMC machine (NC file). We connected the flat milling bit of size 8 mm, the feed rate was 80% of the maximum 6000 mm/min to 4800 mm/min. Spindle speed is 80% of the maximum 15000 rpm-12000 rpm. We chose the board for cutting and fixed it on the table with screws. We set the Z origin both manually and automatic to the learn the process. XY position was set to zero avoiding screw region.

Cut piece and measuring.

The measurements

We easured the average milling length for 2 squares is 20.14 mm while the average milling length for the 2 circles is 20.16 mm. Both values are close and error is minimal in comparison with the 3D design file.

We also documented the engraved area from the square, and circular engrave thickness measured before and after milling using digital screw gauge. See the results and difference in thickness from the square area and the circular area from the below table.

2. Model

Task: Make something big on a CNC machine.

A few different designs in AutoCAD.

The idea of this project appeared about six months ago. The design was made in collaboration with my good friend and talented engineer Mikhail Lebedev. It is a press-fit guitar stand. I even cut a test version on the laser cutter from 6mm plywood. But to cut through 6mm plywood I did about 10 passes with the laser. So the kerf was terrible. I assembled it anyway, but 6mm plywood wasn't enough to make the whole construction stable. So the project was waiting for this week for a while.

The original design was made in AutoCAD but I don't have a lisense anymore. So I imported side part into Fusion 360. I used Find Features command trying to edit the geometry. But I failed to get a sketch from it. So I Extruded geometry up to 11mm and using the Move command adjusted all joints to 11mm. We measured the thickness of the material earlier and I wanted the joints to be as stiff as possible, so I have not added any kerf number. Then I sketched a hook and a slat. Then I copied elements and Aligned them first into a model and then on one plane. And then I moved to Manufacure part.

3. Manufacture

Choose working space in Fusion360

In toolbar SETUP/New Setup

Orientation: Select X & Y axes (X as Y and Y as X), axis X is flipped. Bottom-left box corner is defined as origin point.

First I created paths for all pockets

Select a tool

I downloaded a Tool library and imported it to Fusion360. I used 8mm flat milling bit

Then I selected all pockets on my design

Model Top as Top height and Model bottom as Bottom height

Marked Multiple depths and Use even Stepdowns

Unarked Lead IN and Lead Out

Pocket toolpath on the model

The smallest pockets (d15mm) will not be cut. Not a problem. They are just decorative thing. Next pocket is d20mm and it will be cut. Actually, it's easy to fix. In Ramp/Ramp Type: Plunge (last tab on 2d pocket set). Nice!

Then select 2D Contour. The tool should be already set.

All contours selected. I created Tabs. But I decided to make them smaller so it will be easier to cut them after. I was a bad decision.

Model Top as Top height and Model bottom as Bottom height

Multiple Depths, 3mm, Use Even Stepdowns

Unarked Lead IN and Lead Out

Outcut taces on the model

Simulation of the process. Looks nice!

Final step is to set the path to Postprocess file and save guitar_stand.nc file.

I did all the same the next day and cut another piece. I used leftovers from the material so I rearranged details on the plane. I increased tabs width a little bit.

4. Machining

The Machine

The 8mm Flat milling bit was already installed so I just made sure that everything is ok.

Moved the jog to Mechanical Origin

After screwing the Stock material to the table I moved the jog to the start point.

Set this point as WP's origin for X, Y.

To get a zero in Z I turned on the rotation on 7% speed and moved the jog down until it started make sound like it touches the surface. Then I stopped the rotation and set this point as WP's origin for Z axis.

Then I ran a simulation

And started the job on 80% of the Feedrate (4800 mm/min) and Spindle rotation speed (about 10000 rpm). After the start I lowered the rotation speed to 70% (about 9000 rpm) because it sounded wierd.

The tabs I created were too small. Because of the material structure on some parts the tabs were cut trough. So for a few times I paused the process and removed parts with a carpet knife. Pockets were cut perfectly.

After belt-grinding the thickness of the material varied from 11 to 12mm. So I sanded all press-fit pars carefully.

After sanding.

First assembly Fits nice and stiff

5. Results of the week

I used pipe isolation material to make a soft bed for my guitars.