Fab Academy 2018 - Jun Kawahara

Week 8. Computer-Controlled Machining

Assignment

group assignment: test runout, alignment, speeds, feeds, and toolpaths for your machine
individual assignment: make something big

group assignment

I've done with this week assignment aside from two other lab members. So, this is not a group assignment but a test result of the machine I used. See "test my machine" page.

see other members' group assignment page.

computer-controlled-machining/computer-controlled-machining_index.html

make something big

something big... surfboard

I waited to decide whether to make a surfboard or just put sensing components onto my existing board. On the second thought, why did I enroll in Fab Academy? Wasn't it to learn how to make almost anything, right? I made up my mind to make a surfboard.

something big means a surfboard

surfboard material

Surfboard materials are usually polyurethane foam (with polyester resin) or EPS (expanded polystyrene) (with epoxy resin). I chose ESP because it was readily available. The XYZ size is 600 x 2000 x 150 mm.

big EPS blocks

machine and endmill selection

FabLab Kamakura doesn't have a Shopbot like big CNC machine. Mr. Takemura Takashi, director of FabLab Hamamatsu TAKE-SPACE, was kind enough to let me use his equipment.

The machine is CNC Router 1325, and its XYZ axis working area is 1300 x 2500 x 200 mm.

CNC Router 1325

Commercial surfboard makers use a big ball-like endmill (picture below). Its price tag was ¥33,449 JPY ($313USD), which I cannot afford.

Credit: SHAPERS / too expensive

I tested a tiny endmill to cut an EPS, and it will take years to make a surfboard.

too small

A bit bigger one...but it's pretty much the same.

still too small

We bought a ball-like endmill because its shape similarity might work and the test result was greater than I expected. It was a rust remover and looks like this product. It seems that it is made of a flexible non-woven nylon fiber disc and rigid material. Its size was 50 mm in diameter.

I can cut a lot and fast!

preprocessing

cutting a styrofoam

A big endmill compromised Z axis working area, and I have to slice EPS block by 30 mm thickness.

Mr. Takemura helped me with cutting a foam. He immediately made a hot wire foam cutter from what he had in his lab.

Cutting speed was slow, but it was sharp-cut.

Done!

CNC machine and EPS block was ready for machining.

I fixed styrofoam onto the working table with double-sided tapes. The location of tapes was bottom and outside of the foam. I change the position at 2nd trial which I'll explain later.

3d modelling

I used a surfboard CAD software, Akushaper, as I did in week3/computer-aided design. I modified surfboard dimensions (shorter length and lower rocker than the original size) to fit the CNC table.

shorter in length

lower the rocker

g-code preparation

CAM software was cut3D(Vectric). It was my first time to use it.

I opened an STL file of a surfboard.

I have to select an endmill. There wasn't 50 mm endmill in option, of course. I copied square-shaped endmill settings and changed its diameter.

Here is a roughing toolpath of a top side. I added tabs to check the location after machining the top and flip the board.

A roughing toolpath of a bottom side.

This is a finishing toolpath of a top side.

and a bottom side.

Then, I saved roughing toolpaths on both top and bottom.

Then, I also saved finishing toolpaths of both sides.

CNC software settings

CNC software was Mach3.

Before I start machining, I have to set a reference position. I moved an endmill to the table.

and press "zero Z"

I moved an endmill to the edge of an EPS block.

and press "zero X" and "zero Y"

Now, all set and ready for machining.

machining: first trial

Spindle speed and the feed rate was 10,000 rpm and 3,600 mm/min (as 100%), respectively. First I set the feed rate of 50% (1,800 mm/min) to see if conditions were right. As the machining looked beautiful, I increased the feed rate to 100% (3,600 mm/min). Roughing and smoothing cut used the same machining conditions. Machining was smooth and fast.

Tab dimension was not appropriate. As a top part of the tab was machined, the reference point was compromised. I gave up machining the bottom side.

Even though there were a few problems, machining was pretty good.

machining: second trial

Based on the previous test, I changed the setting as follows

Double-sided tape location should be center of the EPS block. Because the tape was machined when it was outer side of a foam
Tab's Z dimension should be the same as the initial EPS block thickness not to be machined.
I draw a center mark on an EPS block.

the location of tapes and the center position maker line