Week 7, Computer-Controlled Machining

This week assignment task is to Make Something Big



Coming out with the design

I have completely no idea what to built for this week assignment on Make Something Big. My course mate, Hendra gave me this idea on builting a fishbone chair concept. I did a google search on it and found some the were quite intriguing. I noted some of the designs and started conceptualize on them.


Concept Chair Drawing

I am a novice in Autocad and Inventor but I'm more familiar with MasterCam X8 because my job required me to use it often. But my mate Hendra gave me a big helping hand and used Inventor to completed the design with a new twist.
Inventor Chair

From Drawing to Tangible

Sequence of operation, at least in general;

1) Launch the MasterCam application and open the inventor file. Remember dont import the file.

2) Add square tab on the contours so that it wouldn't break your mill bits.


MasterCam Work Page

3) Select Machine Type - Mill (Default)

4) Select Toolpath - Contours

5) Start Chaining the lines in MasterCam

6) Ensure the Clearance, Retract, Feed Plane, Top of Stock and Depth have their Absolute ticked or checked. Very Imporant !!!


MasterCam Linking Parameter Page

7) Click G1 to generate gcode in MasterCam Code Expert and saved the file as xxx.NC into your flash drive

8) Next launch JG application to convert your xxx.NC into xxx.JG

The reason for this seemingly illogical step is because this Router only understand "Japanese" and knows no other languages whether in writing or speech.

9) Now prepare your plywood stock onto the router and clamped it down properly

10) Set the router XYZ to the workpiece zero position.


From Drawing to Tangible

The milling operation cannot be overlooked because the type of the cutter, number of cutting flutes, cutting speed and feed rate will determine the quality of routing. The formulae can be found on this web site Mill Cutting speed calculation

It gives an excellent illustrated explanation of the milling operation.
There is an app that can give you a quick solution to feedrates and spindle speed and downward feeds. It can be found here on google PLAY store, CNC Machinist Calculator.
The thickness of the plywood varies slightly along its entire length averging about 1 mm and warp at certain sections of the plywood . Therefore it is important to note the thinkness of the plywood determined the size of the slots or joints.

For this routing operation, I used a 2 flute 6mm carbide milling bit, spindle speed at 21000 rpm, feedrate at 350 mm/min and 50 mm/min plunge rate. The formulae could not be strictly followed but as a general guide because the router had limitations and cutting speed is predetermined and cannot be easily altered.

Another good way to quickly help you calculate the feed rate and cutting speed is to download an app called CNC Machinist Calculator. It really saves a lot time.

Generally from here you are good to go.

The results

The end results of the layout after routing.


Layout of the Chair

Finally the the chair after assembly.





The working files can be downloaded here:
Concept Chair in AutoCAD
Inventor Part Drawing
Inventor Assembly Drawing

My comments

Given such a short time, it was a tall order even to learn properly a CAM software. As such the design started with high inspiration but ended doing a frustrating simple design. If not the help from a fellow course mate, the end result would not have tasted sweet.