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Computer-controlled Machining.md 5.46 KiB

Computer controlled machining

This week is about making something big using a CNC milling/routing machine. I want to explore the possibilities of CNC machining - drill, pocket, dogbones, nesting, etc. So I want to make a big jigsaw puzzle with different kinds of digital 2D joints.

Measure material

Material available for use is a veneer plywood of size 1220 x 1220 x 15 mm.

I will check exact thickness with a vernier caliper when in the lab.

Design

I wanted to make a table with adjustable height so after some viewing some references, I decided to make trestle legs for a desk steup. I started by making a 3D version of IKEA's FINVVARD to understand how it works.

Then I started making individual joints so they can be digitally machined in 2-axes or 2.5-axes. I used some details from the 50 digital joints poster to design some details.

![](./images/ccm/joint0.png =250x)

I made some slotted joints, and versions of the finger tennons, lapped finger tennons, throughhole finger tennons to design the trestle.

Here is how the final legs look. I need to make 2 of these and put any flat board on top to make a tabletop.

Cutting file + Nesting

Next, I lay everything flat on the XY plane and did a make 2D. For nesting I used an online service called nestandcut.com to nest all parts in twice the quantity on a sheet of 1220x1220x15 mm. (Half a sheet). I uploaded a dxf file that I export from Rhino and imported the nested dxf back.

I made some changes manually to fit it all in the available sheet. Like I put two parts insode the big board and nest it within to make more space for the missing parts. Here is what that looks like:

CAM

Next, I shifted to the Windows partition of my computer and installed RhinoCAM. I opened the RhinoCAM machining browser plug-in in Rhino6. First I set it to MILL. In the program tab, I set up the material stock - 1220x1220x15.5 mm, the machine details - 3 axis , post - shopbot.

I set the origin at the left bottom corner and the Z at the top of the material stock.

Next I set the tool - Flatmill 6mm, refering to the class notes and some previous documentations:

  • Saved the tool as Flatmill 6mm

  • Holder dia = 50

  • Holder length = 45

  • Shank dia = 6mm

  • Tool dia = 6mm

  • Shoulder length = 30mm

  • Flute length = 30mm

    Feed and speeds:

  • Speeds: 12000 rpm

  • Plunge: 2000 rpm

  • Approach: 2000 rpm

  • Engage: 2000 rpm

  • Cut: 2000 rpm

  • Retract: 2000 rpm

  • Departure: 2000 rpm

    Next, in 2-axis functions there is a list of actions ypu can perform. For my design I needed engraving, profiling and pocketing.

    Engraving

    I set 5 points in the rhino file to engrave markings for screws to be drilled with a hand drill in the correct places.

    Pocketing

    The insides of some parts that needed to be cleared were cut first. 2 parts needed pocketing at different heights, So after making adjustments in 2 different layers I changed the cut depth for both. 15mm for all parts except 2 where it was 10mm.

    Settings

  • Cut pattern: Offset

  • Cut direction: Conventional (Up cut) - standard for plywood

  • Start point: inside

  • Rough depth: 12

  • Finish depth: 3

    Profiling

    To cut the outside profiles of the parts, I set the profiling for 2.5 axis. I also made another profiling - inside for 2 curves that needed to be cut on the inside.

    Settings same as pocketing, set toolpath OUTSIDE the curves

    Simulation

    Then I ran a simulation and found some errors in the settings.

    1. The cutting height did not match the level of the stock. It was cutting in the air. I adjusted this by going back to the material panel and changing the stock thickness to 15mm. (It was 300 by mistake)
    2. The tool path just ran once over all profiles and went in 15mm in one pass. I changed this by making the cut depth 15mm in roughing and finishing at 12 and 3 respectively.
    3. Some parts were creating double paths - so I deselected them from one layer and generated toolpaths again.

    After running another simulation, it seemed fine.

    Machining

    Will do this part when I return to the lab.

    Assembly

    Will do this part when I return to the lab.

    Here's how it should look when done. (w/o the top surface)

    References

  • IKEA Finnvard trestle

  • This CNC wood joinery post

  • 50 Digital Joints

    Design Files

  • Rhino 3D

  • Parts stl

  • RhinoCAM (Got an error while saving this - not all CAM changes can be saved, so not sure if this file works properly)