Introduction

During week 7 we learnt about Computer-Controlled Machining. It basically is all about CNC and the use of what we have here at AS220, a Shopbot machine.

Our particular machine has 3 axis, so it can move with certain precision and a lot of force through the x, y and z axis. What it does, is basically destroying material with a specific shape already designed with a certain software. It uses bits of many possible sizes to achieve this. The software we used depends on the maker's choice until it becomes a PDF. Then, this PDF has to be imported with vCarve which is the software used for some extra editing and finally, the creation of toolpaths.

Assignment

Our assignment this week was to make something BIG. There's many options for this, but I continued with my project from previous weeks, the one that would hold the skeleton of my final project together. This time I'd do a real size version and it behaves as a unit that, if connected correctly with other units, it can become a modular gigantic structure.

So I went back to my sketchup file where I'm constantly correcting and improving the design of this box. Below you can see all the way on the upper right hand side the re-modelled version and the pieces laying flat on the "ground".

Sketchup file is the best for me!

From that Sketchup file I exported a PDF that then I imported using vCarve. The problem with vCarve is that it is only available with a paid license and these are expensive. They do have a free version, but it doesn't allow one to save files, which makes it useless. Despite those restrictions, we have 3 computers at AS220 with vCarve, including the one connected exclusively to the ShopBot machine. Also, it has many features like the easy creation of dog-bone intersections and fillets, very useful when working with round bits that cannot actually reach corners. Below an image of one of the pieces also with some toolpath pocketing information:

vCarve is pretty good despite its restrictions...

The creation of toolpaths is quite easy although there are some necessary arrangements to be understood beforehand. For example, the tool has to be correctly listed with all of its specs and then the parameters are to be considered depending on the job that particular tool will do. There's cutting, pocketing and some others that I did not use.

Toolpath creation can be a piece of cake.

On the software I also defined the material and so I also had to set it up on real life. I was using HDF, also called high density fiberboard - it cuts like butter and if the pieces are small enough, they are pretty rigid for the use I'm considering. I'm using a 1/4'' thickness.

Setting up the board on the machine.

So after calibratin the X, Y and Z axis on the machine I started with the first toolpath I had considered and it was some pockets in order to help me hold down part of the wood. It is very important that the material is held down throughout, otherwise the Z axis will be only precise on the machine but not on the wood and therefore there will be errors. This I find very difficult to do, but I was using screws as it can be seen on the picture. Still, it was far from being a perfect solution. Using carpet tape or double sided tape below isn't a good solution either because if the bit hits the sticky tape then it starts working with defects.

The pockects! They look good but they were not exact.

I also used a 45 degree angled cut, or also named a 90 degree bit to make a miter joint that was very useful. Below the bit already configured to start working on the miter joint.

90 degree angled bit!

After a while, the progress was enough to get ready to cut out the final pieces. It is important to hold everything down very securely tight with something like those wood pressure boards because otherwise the pieces could start getting loose and the machine would move the piece and then the cutting wood be imprecise. Or it could detach itself flying around and that would even be worse because that could hurt somebody.

Safety is very important! And also precision.

Once I had all my pieces cut I had to sand them a little bit and even one of the broke because I used too much strength manipulating it but in the end it was ok. I was ready to assemble!

Just before assembling.

Assmebly part looks very easy but I had some trouble with the first box because the joints where too tight. After this one I made another one with a previous test to be sure that the finger joints would fit.

Assmebly!

The two boxes together did fit and this gave me the motivation to do more -hopefully soon- to make a bigger set up in order to have a better final project.

They love each other.

It's not easy to use the Shopbot and I think if someone is looking more for precision, it is better to use the laser cutter. But the CNC can do things that the laser cutter can't. I just would recommend it with heavy fixed materials and not an excessive detail hunt.

Files

Skethup file download here.

vCarve file download here.