Week 7

Computer-Controlled Machining
(Mar 9)

Assignment:

make something big

• Note from lecture

  Materials
  - MDF - wood glued with binder. easily machined. 3d.cheap .not good for structure. toxic
  - MDO - stronger
  - OSB - cheap. easy to machine. can be sanded on surface
  - HDPE good to big machine
  - garolite. natural fiber in binder
  
  Tooling
  - 2 flute for cutting 4 flute for finishing
  - flat/ball end : bal end used for curvy angle
  
  speeds and feeds
     chip load: ~ 0.001-0.010" = feed rate (inches per minute) / (RPM x number of flutes) 
     cut depth: ~ tool diameter
     step-over: ~ tool diameter/2
   
   lubri
   - greasing & cooling 
   
   -fixturing matters..
   
   -Dust collection.. small dust 
   
   -OSB can not be curved
   
  - cut air first to test
  - do little cuts to test first
  
  			

• Note from local lecture

  Types of milling : 2-D(2.5D), 2-D V-carve, full 3D
  
  drill bits vs end mills. 
  drill bit : to make the hole. cuts only below (drill) 
  end mills : la punta quadrata
  
  Top: Drill Bit, Bottom: End mill. image source
  
  minimum diameter : the same as radius of the head e.g. head 6 mm => joint 3 mm
  
  roughing with end mill, finishing with ball nose
  
  Chip load = the force that the machine has to make
  
  step-over = distance between passes. max diameter/2
  
  interlocking of 1/3 of the tooth
  
  lines : continuos closed polylines. must be perfect clean
  

Process

Prepare the file in dxf, open it on the machine's pc with Vcarve. Set everything in order to create gcode file 
save a profile, open it with Shopbot. Set the CNC from Shopbot control

0. Prepare file
make sure they are continuous, closed lines 
export as dxf, use 2004 natural profile to maintian the lines contious 
make separate layers for separate profiles of cut (inner/outer/pocket...)

1. Vcarve software
Job setup > tool path > calculate
Open existing file (dxf)
Dimension job size
Select desired pieces and create a profile from Toolpath control panel
Toolpath > set desired profile (cut / pocket etc.. ) set milling type, depth etc.. 
add tabs > Calculate
from Drawing, add fillet : Fillet Tbone ?

2. Shopbot
Fix your workspace 
Turn on the CNC, push Reset button (blue one) 
From control panel, Zero machine (x,y) to make machine go back to its original 0,0 
manually move the mill head to desired position, make Zero, take note the coordinate just in case

00_Inspiration

I started out from Shelga's page which has a lot of refereces : Pinterest 1 | Pinterest 2 | Pinterest 3 | joint references

This chair 's look & feel doesn't look bad

This is my sketch. I wanted to to make a chair with an arm rest

01_3D Modelling

0. after some modelling I gave up the original idea since I do not have enough time for a too complex design : ( So, here's a lot more simplified design

1. with some adjustments, this is my chair model made in Rhino

2. Our material is plywood poplar. The panel size is 2.40 x 1.40 m. with 12 mm thickness. Here is the final drawing that I exported in dxf (2004 natural)

3. At the CNC, I open the dxf file in Vcarve. Set Job setup with plywood size. Do not forget to untick Use Offset

4. On drawing control panel, I click edit > fillet to make fillet. Since there's no way to hide the fillet on my design, I use "Dog-bone Fillet" on snapping part

5. And normal Fillet for angles that don't need snapping.

6. at Toolpath control panel, set the profiles. I use 2 profiles : first one is pocket for the inner cut and the second one is the outer cut.

7. I set 4 passes aas I want the first pass to be only 1mm depth as Nicola suggested. Then I added tabs manually. Now the fie is ready

8. I fixed the plywood panel with screw on the work space. Then set zero to machine, the manually set my zero (x,y) then set zero z. Then I'm good to go !

9. Cut !

10. cleaning then assembly

11. lovely chair ! one problem is that it is not very stable.

Download files :
chair(dxf)

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