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COMPUTER - CONTROLLED MACHINING

Assignment: Make something big.

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For this assignment I designed a storage seat that can be stacked and transformed into shelves. I mainly used Rhinoceros for the design and PartWorks for the machining strategy. I used 15 Mm. OSB.

Machines used: Multicam laser, Precix and ShopBot.

//Some notes and recommendations:

Make a parametric design. I didn't and it was tedious to make small changes.

Using Partworks is highly recommended! It has a nice and simple interface.

Measure your material. It might be not exactly what you think it is.

Make a joints test before milling your final design. This is also very helpful to understand all the machining process, understand the material density and it's physical reaction to the milling machine.

Take a look at this 50 Digital joints documentation.

>>3D SKETCHING

My idea was to design modules to be easily transported home.

Design considerations:

Must use complete OSB 2500x1500x15 Mm. OSB sheet.

Easy to carry home: modular + few weight + ergonomic

Should have space for bathroom accesories. Minimum space for toilet paper, maximum space for shampoo bottles or similar.

Should be easy to carry.

The modular characteristic of the design made me think about a double use for this object: Seat and Storage.

Some quick 3d sketches using Rhino and Keyshot:

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>>>LASER CUT MODEL:

To understand the proportion of my design I made a scale model using laser cutting.

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>>JOINTS TEST

I was trying to make "invisible" joints by milling pockets down to 7.5 Mm. (Half of the OSB thickness). I made a joints test using 0.0 Mm., 0.1 Mm. and 0.2 gaps.

What I found is that using 0.0 Mm. offset works, but just because I don't trust at all in homogeneous thicknesses and I wanted to make sure not to sand forever I used the 0.1 Mm. one.

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>>DESIGN

Three modular seat/shelves fitted on the complete OSB sheet, so I decided to cut only one at first in order to see if there were things to be improved, etc.

I modeled everything in Rhino, and I used different coloured layers for every part.

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I created a rectangle of 2550x1250 Mm. and made sure that my first module only used 1/3 of my material. I recommend to leave an internal offset of the osb sheet of aprox 15 Mm. This is useful for future screws.

I used "make2d" command to create each part's path, and edited using "trim" + "join".

Make sure all your curves are closed.

- Export file as as a "dxf" with "R12 Natural" preferences.

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>>PARTWORKS: MACHINING STRATEGY

Before to start, I think it is important for you to understand the steps to follow when milling your designs. This will help you when making the strategy in the software of your choice and deciding which profile toolpath to use.

- 1. Drilling with 3 Mm. diameter drill bit. Toolpath to use: Drilling.

- 2. Put screws by hand using a driller.

- 3. Removing material for pockets. Toolpath to use: Pocketing.

- 4. Cutting. Toolpath to use: Profile.

- 5. Remove screws by hand using a driller.

- 6. Removing tabs by hand using a hammer and a chisel.

- 7. Removing material.

- 8. Clean the machine.

Using PARTWORKS:

Import vectors to Partworks

A window will instantly appear where you'll need to write the size of your OSB or Plywood material which in this case was 15 Mm.

Set the size of the working area and check "Z Zero". This means that the machine will consider the sacrifice surface as the 0 for the Z axis.

If you are not sure about closed or not closed curves, apply "Join Open Vectors".

Select the "Draw Circle" tool. Set a diamater of 7.5, which is the size of the head of the screw that you'll probably use. This will turn into the holes for the screws that will fix the OSB on the sacrificial board.

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Using the "Create fillets" tool, go to every corner of your pockets and create "T bone" or "Dog bone" fillets. For the first module I used both types to see how they looked like.

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Now you are ready to create toolpaths.

SCREWS: With all of your circles selected, generate a Drill Path and select "change tool". You will see a list of default bits, select a "Drill" one, and change it's values to the following: 3 Mm. diamater, 5.0 Mm. pass depth, 12000 r.p.m. spindle speed, 20 mm/sec plunge rate. You can add a name to your tool and save it for the future.

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Click over calculate.

POCKETS: Select all of your desired pockets. Generate a new Pocketing toolpath and select "change tool". Select a 6 Mm. End Mill The values that I used: 6 Mm diameter, pass depth of 4 Mm., stepover of 3.6 Mm., spindle speed of 12000, feed rate 40, plunge rate 15 mm/sec.

Click over "conventional". In my case I applied 7.5 cut depth for "half-wood" joints.

Don't check the ramp plunge moves, this is useful for hard materials such as metals.

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CUTTING PATHS: Select your curves, and generate a cutting toolpath. Select the same end mill used for pockets, check the conventional direction, and the OUTSIDE cutting vectores.

You MUST add all the tabs that your design needs. This is to secure your pieces to the board. I created 8x5 Mm. tabs.

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Calculate and look at the 3d previsualization. This helps to see if there's any missplaced or missing tab.

Create your gcode by saving your toolpaths in the right order: Drilling, Pocketing, Cutting.

>>SHOPBOT

"Home" the machine, by moving it to the 0 position in XY. For this you will have to use the arrows yellow console and move the spindle.

It is important to add a 20 Mm to the z axis, so it can be moved without touching your board.

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Remove the tabs using the hammer and the chisel.

Don't forget to clean the machine using the vaccum cleaner!

>>1st module: FINISHES AND RESULTS

Pieces:

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Sanding:

Start with the roughest sand paper. Make sure it is a proper wood sandpaper. Remove burr.

Dont sand too much, just remove what's necessary.

Sand everything with a medium and then with a soft sandpaper.

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PROBLEM 1! I left a small space between pockets and some little pieces for joints, so my osb broke.

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PROBLEM 2! For some reason my pockets didn't arrived to 7.5 Mm. so I had to cut my joints using the circular saw. ( Thanks to Goriwho helped me to do this! )

Evidence picture: Joints didn't reach the bottom of the wood.

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First module assembled:

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>>2ND AND THIRD MODULE using the PRECIX machine.

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I made some changes to my design and I followed the same Partworks strategy. This time I used T bones which are not visible in the final assembly. :)

Important! Load your file and make sure it appears in the Mach3 CNC software window. I didn't checked and I sent Joao's screws file!

The good thing about Mach 3 is that you can move the speed of the steppers - spindle directly.

At first Ferdi and I put 100% of the speed, but i saw a lot of ugly burrs so I slowed the steppers to 50%. Yes it took more time but I had to sand less and the general finishes were better.

A speed test would be also great to do before milling everything!

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I used again a 0.1 offset (gap) in the joints.

PROBLEM: Althoug I used a 0.1 gap, my joints didn't fit well. I am not sure why did this happen, byt I think it has something to do with the cutting end mill bit.

LESSON LEARNED: Make a joints test for every machine that you use.

I solved this problem by using a Dremel and making the pockets a little bit bigger. ( Not desirable process )

>>FINAL RESULTS:

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Download my files:

3d Model of modular seat/shelf: Rhino .3dm file

DXF of two modular seat/shelves: DXF file

Partworks file with 2 modules: .crv

Citlali Hernández - Fab Academy - 2016