Last week we needed some extra seats
for a discussion meeting In order to keep the cost low, we decided to make them.
Using our own DeskProto software of course. This proved to be easy, as many nice CNC plans
for furniture are available on the Internet. We bought this “banquette stool” at
CNCrouterDesign.com As you can see the DXF-file
still needed some editing, as in the original file the three
parts were not efficiently nested. Here I’m gonna show you how to create
the toolpath in DeskProto. As you will see that’s a very easy process.
We’ll be using one of the wizards which makes it easy. We want to use the Basic Vector machining
wizard as that’s what we want to do: basic vector machining,
and the first step obviously is to load the DXF-file that we want to use. It is on the desktop.
Here we are: this is the file that we bought. Here are the three parts to be machined. The total size is about 1 meter by 50 cm,
so scaling is not needed, rotation is not needed. Z-settings are needed:
the milling depth needs to be a bit more than the 15 mm thickness of the board.
I will make it minus 15 and half. On the machine we will have a spoil-board
below our board, so this half mm extra makes sure that our board will
be completely machined. Next: the dimensions of the material block.
As said one meter by half a meter, but we’ve cut it a bit larger:
to make sure that even if the board is not correctly aligned with the true X-axis on the
machine it won’t be too small anyway so we have made two cm extra on all sides. And obviously the correct thickness needs
to be entered as well: 15 mm, here we are. Location of the zero point here on the corner of
the material block and on the top of the block is OK, so we can press Next and these are the most
important settings: the actual machining parameters. We want to use a six mm diameter cutter, a flat tip. Feedrate can be a bit higher:
say 2000 mm per minute. Spindlespeed can be a lot higher:
10,000 rpm – Rounds Per Minute. We want to use Profiling,
so the cutter will follow the curves, the profile. Here on the outside,
and DeskProto is smart enough to realize that for these holes the cutter needs to move on
the inside of the curve, it will do so automatically. So that is OK.
We want to use support tabs: A support tab is a small piece of
material that keeps a connection between the part and the rest of the board, otherwise
while machining the part would be completely loose and would move while machining.
We use custom support tabs as default will be a bit too many,
and we simply click a number of times and on each blue point a support tab
will be added, as you will shortly see. Here we are, and I also want to change
the dimensions of each tab. Now it says the height will be half of our board,
but that’s far too much: 20% (so 3 mm high) is enough to keep the parts fixed. OK, I’ll close with the OK button (you have to trust me:
it’s outside the screen now but it’s here: the OK button). So now we’ve set the support tabs
and the final step is roughing: the layer height. I want to go down in 3 layers:
the wood is a bit too hard to do it in one go. So 5.2 mm makes nice three layers. So we can calculate.
Here are the toolpaths: you can zoom in a bit. Here you see the support tabs at 20% of the total height. Here the toolpaths are on the outside of the curve,
here they are on the inside of the curve. So it all seems OK.
Estimated machining time is 12 minutes. OK, I will go to Next,
and the final thing we … no, what I can do first is show a Simulation:
this is what we will machine. Here you see the support tabs.
So it looks OK. So, the final thing to do is to write the NC program file. Yes, it goes a bit below the block, I know that. We call it “Stool”, and then we have an
ISO-file that we can send to the Machine. Our own milling machine is too small for these parts, so we were happy that we could use
the large CNC router of our local FabLab. As you can see it’s called ProtoSpace. You can find it
in a building of the University of Applied Sciences. Their router has been made in China,
and it works with the Mach 3 control software. The first thing to do is to fixture
our slab of plywood on the machine. We did so by simply screwing it down onto the
spoil-board, using one screw for each of the 4 corners. The next step of the process is to set the zero point: on the Top-Left-Front corner of the block.
Here you can see the Z=0 being set. And then the milling process can be started:
first the holes then the outer contours. We found that on this machine we could
increase the speed to 4000 mm per minute, with a theoretical machining time of 6.5 minutes. In real life that proved to be 8.5 minutes, as the
machine can’t always achieve the prescribed speed. Remember that three layers (or three
passes) are machined to reach the full depth. The third layer creates the support tabs. After removing the four screws the result
can be seen, with all support tabs clearly visible. These then can simply be removed using a chisel,
with some sanding for a smooth result Assembly – as you can see – is very easy: our compliments for the
designer of this elegant small stool. With the four stools that we machined
the meeting could now be done while being seated: much more comfortable. Feel free to download the DeskProto software
to create your own furniture. Or in fact to create any other parts that you need.