Making something big!

Seventh week's Assigment

For this week, the assignments to be accomplish are:

Make something Big!
learn the relationship between Feed Rate, RPM and number of flutes.
learn something new

DESIGN

For this assignment I would like to make a chair for my 2 years old son, so I took some measurements and I started drawing.

The more that I use Fusion360 I like it better.
As it can be seen in the picture on the right, I would like use blind joints.
I used the file to cut a chair (in the laser cutter) in thick cardboard to check the fits.

Once I moved to the CNC the first step was to learn about chip-load and how that range of speed will influenece in the final cut.
Using the information from the Endmill vendor the chip load had a range from 0.0047 to 0.0197. So, I made some number in between to get differents Feed rate to test the tolerance of the cut using the equation "Chipload= FeedRate / (RPM* number of fluts)". I calculate 0,0047 , 0,0067 , 0,0087 , 0,0127 , 0,0147 , 0,0197. for wich the feed rate endup as follow, feedrate|RPM 85|18,000 120|18,000 157|18,000 229|18,000 265|18,000 355|18,000

Note: The tool paths were made for Straight Fluts but we end up using an "Up-Cut" mill because it was broken. therefore, we cut -20% chipload.

Out of 6 setting I choose 4 number (ChipLoads) starting from the second lowes feed rate as 97, 125, 182 and 211 all of them using the same RPM of 18,000.

Now I now how to make fire in the shopbop!!
The problem was that the tabs were too small (1mm) and we changed them to 1.5 and we cut few of them again. After checking the result I choose the setting of 97Feed Rate at 18,000Rpm.

I loaded my file in Vcarve and add the numbers to the setting of the Mill. Starting from the pocketing first

The blind pocketings were clear but for the challenge was where the plywood had press using vertical and Horizontal (where the back support connect with the side of the chair)
the Fix was easy, I used the line (cuts) from the original desing as a guide to create a square using the "create vector" tools, this squares were bigger than the original drawing to allow to endmill to cut more to each side thus creating a super clean cut. (the red lines in the left pictures represent the original drawing and the pink colors lines represent the new lines created in Vcarve.)

If you see closely the blind pocket made (highlighted in red) inside the leg are closer to the center allowing the diameter of the endmill itself to cut up to the desired size.
However, the path highlited on green is wider eating more material but creating a straight line for the fit.

Once cut, I felt really happy that It looked as I expected.
by the way, this chair is all press-fit.

CoolKid ChairMan~

Downloads

Chair_cnc.dxf

Lessons Learnt

What I was not able to do this week:

Make a table for the chair.
Break a endmill
test others woods Feed Rate

What I did but need to get better at:

Make a cute chair for my son
learn the relationship between Feed rate, Numbers of flutes and RPM
I need to pay closely attention to the CNC while is cutting otherwise fire can start at any time.

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