8bit klubben: project: cnc design

yay!!
our machine is moving! it is now possible for us to control the cnc machine with linux cnc … we simply forgot to apply jumpers to the motor control board defining the microsteps that we apply to stepper motors (we thought applying no jumpers meant standard setup, but it turns out, that you had to apply at least one jumper to have an acceptable motor configuration)

setting up the motor control:
setting up the motor control board with EMC2 is really easy — it comes with a setup wizard which allows you to assign specific pins in the paralel port to specific home switches, motor steps etc.

on homing difficulties:
we need to set up the cnc machine so it can always find its absolute position — this is done with home switches on the X/Y/Z axes, and should be a simple task, but alas, quoting from the manual:
“Homing seems simple enough - just move each joint to a known location, and set EMC’s internal
variables accordingly. However, different machines have different requirements, and homing is
actually quite complicated.”

so we need to read up on: homing setup: chapter 5.4 homing in the EMC2 manual

also the connection between our motors and the driving shafts are too loose — this can be seen our the first test drawing made with our wonderful machine:

the letters are written mirrored and on top of each other — they should be like the vector layout below

the connectors are simply not tight enough to withstand the rotational torque when the machine is moving fast between letters (when drawing the letters are “milled”, so the machine is moving much slower)

but hey: this is all minor tweaks and mechanicals — all very fixable! yeah! what a nice way to start a weekend

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Even though we were hoping it would have been to much to ask, if all have just been perfect in the first run. But nothing really happened.

We have connected all the hardware to the controlboard, and followed the configuartion of the system in the software, but we cant get the motors running yet

We will call it a day, go home and read the manual (here) and hopefully come back next time and start running.

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So now we need to connect it all to the controlboard. The two motors controling the x-axis is going to be connected to the same terminals, so those we have found a connector for on the ship.

The motors are now ready to be connected to the controlboard

along with the swithes, the power-supply, the emergency stop and the computer, the machine is now a mess:

We have considered along the way how to connect things in a way, that makes it possible to do a better design in the end - soon we will clean up the mess, and hopefully get a nice little machine.

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Before running the machine we have made the limit- and homeswitches. Most of the configuration can hopefully be done in the software, but the tool used is probably not always the same. Therefor we have decided to make one limit-switch were there is a risk for the tool to hit the frame if not configured right. The rest of the limits is not changing, and therefor should we have chosen to configure these in the software.

The home switches are mounted in all axis, and provide a point in the space for the machine to calibrate (0,0,0). It is worth considering where to mount the home-switches so that the point is suited as a starting point. It depends on wich direction is front of the machine. The home of the z-axis should always be when it is at its highest. The small switches is wired together on a board, for convenience when we shall connect them to the controlboard.

The swithes are powered by 5V when not opereated, and when pushed the power is cut. This makes the power fluctuating in the air not affecting the terminals.

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we have now mounted motors in the X, Y and Z direction — all wires have been soldered neatly to parallel port plugs — so we are basically ready for the initial testings, just need to figure out to cable the stepper motors to the motor controller with no motor datasheet (we threw that away )

we have mounted the motors on pieces of standard metal U profiles found in the dump. for practical reasons the motors for the y&z-directions are positioned skewed in a 45 degree angle.

to transmit rotation from the motors to the shafts we have used flexible hose with the right diameter - they actually fit so tightly, that we can use them as they are with no further tightening — this will also provide us with a mechanical clutch, securing the motors and frame, if we do faulty programming in the initial testing phase. using flexible hose as connectors has the advantage of compensating for minor imperfections in our homemade motor mounts.

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After measuring a bit, and cutting out the frame piece here is some details on the frame:

The important thing is to do a little thinking about the movement of the z-axis. The other dimensions is pretty straight forward. Everything depends on how the XYZ-table is, but I just wrote some of our most important specifications.

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As mentioned we want to start out by making a test by drawing, since this should be pretty safe compared to fast rotating milling tools.

We want to test both XYZ-axis, so we made a little SpringPen for this purpose.

its a plastic tube with springs in the bottom as well as in the top, so the pen can flex up/down easy. We will mount this in a foam holder to the z-axis…. Its gonna be fun fun fun.

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a design specification for the cnc project is now available: click here

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Since the X/Y-table has arrived, it is time for some thoughts about the frame and housing. There is both functions, dimensions and safety to take into considerations when making the design. We have started out with some rough outlines of the housing, which will be followed up by actual drawings with dimensions later.

There are a few very important things to consider. First of all it is necessary to make a safe work environment, so the frame should hold all the pieces inside a box. Next the distance between the tool and the plane, where the material is fastened is very important. Together with the length of the Z-axis it determines the possible size of the object milled. Also it is worth considering how to hold the material on to the plane. We have talked about doing both tension and suction, so there should be made room for this. One of the most important considerations is how to level the plane and the X/Y-axis. We havent made this yet, so we will get to that later.

So here is a few sketches on the housing.

As you see on a previous post we have begun cutting out the frame from an old scrap thingy. We found that this piece of scrap had the right dimensions for our project, so we saved some time there. Maybe it is not quite tall enough so that the z-axis can move up, if we put on a top. So this may force us to do another design for the top and sides, but we will see.

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this week the x/y frame finally arrived - weee! - talk about feeling like a little kid at xmas again!

the build quality of this used frame is pretty good: x and y axis is rock solid, with only a slight flexibility in the z axis — we’re thinking we might work on the bars holding the z axis, maybe change the material used to metal rods from printers, as they are about the hardest metal rods we can get our hands on within budget and also the size seems just right.

knowing the dimensions of the x/y frame we started (de)constructing a base for the cnc machine, so we can obtain full use of the z-depth.

jakob sindballe made some truly heroic metal cutting efforts and sparks were flying!! who said engineering isn’t sexy

see more info on base design considerations in upcoming post

also today we experimented with installing linux cnc on the pc that we found for the project — unfortunately the pc only has 256MB of RAM so the process was painstakingly slooooow. and finally we gave up. so now we are on the lookout for some extra RAM blocks.

we have started wiring the motors to standard parrallel port plugs — this way we can connect and reconfigure the motor setup any way we want to in the future, and also we can disconnect the x/y table and motors from the control unit, which will be very practical later, when transporting the cnc.

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