Computer-Controlled Machining

The big noisy week in a flash

1. Delay, due to unavailability of 3 axis CNC machine at our lab, we had to fix an appointment at College of Engineering, Pune (COEP) which turned out to be very inefficient, non-experimental and hence I still have to mill my design.

2. Finally came across a much hyped "Shop Bot" at COEP, didn't feel a great deal about it after looking at its squeaky performance, history of bad servicing and unavailabity of parts.

3. Wanted to see how a small(30cm x30 cm bed)and idle CNC machine fares on a 3D relief feature. Though this wasn't big and didn't fit in according to the theme of this week.

CNC Milling


We were received by Mr. Sandeep Anasane of Fab Lab, College of Engineering, Pune, who gave us a brief introduction about Shop Bot. Since the Shop Bot in India has a reputation of breaking down with long waiting periods upto few months, Mr Anasane was very cautious and didn't allow us to experiment with new settings.

He started by demonstrating us the various parts and specifications of Shop Bot:

1. It is similar to a Laser Cutting machine i.e. it works on the same principle of X, Y and Z axis. Shop Bot PRSAlpha is a 3 axis CNC router machine, is numerically controlled and is subtractive in nature.
2. Shop Bot has a bed size of 8 feex 4 feet and the Z axis has a spindle connected to it that has a maximum speed of 20000 revolutions per minute. The spindle inturn is connected to an end mill that comes in various shapes and sizes according to the geometry we want. The illustration 2, above displays the various specification of the ShopBot
3. We next discussed about the various end mills that could be used, broadly they are categorized in three categories:
a. Flat End Mill- They are better for cutting profiles(outlines) and pockets on a plain geometry.
b. Ball nose End Mill- When there are 3 dimentional relief features , two phases are there, first roughing, done by a flat end mill and followed by smoothing using a ball nose end mill.
c. V shape End Mill


The process of machining was very loud and noisy as the step size was very high. Since we had very limited control over the machine as mentioned earlier, we had to agree to the rules set by the lab. The process started from clamping the stock and then uploading the 2D files to the ShopBot software. 12 mm end mill was used during the milling process. The pplywood was not uniform and hence created lot of problems. The major problem was that the stock got scratched at several places by the end mill and led to deterioration. I used one and a half sheet of 4x8 feet for my chair.

Final Assembly and Results

After milling all the individual components we had to take all the pieces back to our fab lab in Pabal and start assembling them, piece by piece. It was a hectic process all together. I didn't use the doggy bones to assmeble my pieces together to form the chair but rather used a milling machine at our fabrication laboratory to assemble the pieces together. I used a steel rod and bolted to hold all the pieces together in place. The final chair came our really beautiful and I made sure it was comfortable enough for the user.