8bit klubben: project: cnc design

the two last days we’ve been working hard getting the cnc mill ready for our final presentation. it has been hard work, and we have to be honest and say that we ourselves are not thoroughly impressed by our own results.

although the cnc has gotten a lot of improvements the last couple of days:

the motor control has been moved into a much nicer housing. we found a cast away pc rack cabinet, and the cnc motor control, power supplies, switches and cables fit very nicely in there. there is even room for a cool little unix machine, should we ever get the money for that.

we added some nice distance pieces to the mill instead of our previous very bulky mount. we produced the pieces in two lengths: 20 and 40cms, so we can change the pieces if we would like to cut deeply on the z-axis

also we made a suction base for the cnc, basically a wooden box with A LOT of little holes in it. attach a vacuum cleaner to the box, and voila: you have suction. we are hoping that this suction will be enough to keep flat objects in place when milling and that pieces of cut-off material will be sucked of the milling subject, but this is yet to be tested.

in conclusion (we have to conclude now, the machine is not done, but the official DTU course is over) we can say, that we have learned a lot about mechatronics in this course. above all we have gained a lot of respect for mechanism designs and the precision of industrial grade equipment. it would have been many times easier to build this machince at DTU, but building it at halfmachine has taught us some cool DIY tricks and has forced us to be creative in relation to materials & design and to think mechanisms trough in a more pessimistic and practical way. it is unfortunate that the frame we bought used for this project was of so low quality, as we think our cnc machine could be OK for small scale projects with the current motor control, had only the frame been more reliable.

the cnc machine is operational, yes:

but in real life there is still a long way to go before this machine is useful for the purposes that we had in mind.

the list of possible improvements is as follows:

hardware:

• the z axis is simply to wobbly to do any real 3D work - we have considered changing the metal rods to hardened printer rods, but we believe, that to properly fix this, the cnc requires a complete redesign of the z-axis mechanism.
• the motor mounting unscrews it self during operation. we need better fastening of the motors.
• we never finished a safety mount which was elegant enough for daily use. we tried building one of wood, but the result was simply too bulky. glasses have gotten us through so far, but we would like to implement a acrylic “cheese bell” which fits over the cnc.

software:

• finding any proper open source (or at least cheap) CAD/CAM package has been very hard. the cam package for rhino looks promising, but we haven’t had time to go into this.
• seemingly simple tasks like transfering an illustrator file to g-code has been surprisingly difficult - we’ve gotten some results with cambam and lazycad (.ai -> .dxf -> g-code), but the workflow is tediuos and the resulting g-code has been extremely dumb; that is, lines and curves divided into very small line segments, rendering any complex pictures (including round objects) super heavy and nearly impossible to process.

mechatronic:

• our milling tools are bad: we use a dremel, which has no feedback mechanism. this means that the dremel is rotating at many thousands of RPM when not cutting, and then dramatically loosing rotational speed when touching the milling subject giving an unwanted difference in milling speed throughout the material. buying a cutting tool with feedback mechanism (or constructing our own) would allow us to cut materials that are more fragile, and materials that might melt or otherwise react in unwanted ways when approached by a cutting tool rotating too fast.
• a general feedback mechanism for the frame/cutting head position would be super nice. with no feedback, even the slightest imprecision will add up throughout a more complex milling operation and result in the final millings being more off target that necessary with our mechanical precision.

we are planning to continue working on the cnc - and so are the people at halfmachine - but first we need some holiday! check back on this blog in a month or two. there might be more news for you.

we’ve taken a lot of documentation photos and bring a little excerpt below. do check our cnc flickr photo pool for the full selection.

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Since the machine performed well on the testrun, we had some minor things to sort out. The motorconnection had to be tighten up, and Nicolas from Halfmachine did a great job on this.

The motors are now held in place by a couple of bolts with machine screws going through them.

We solved the tool mount by attaching a perforated metal plate on the z axis. The holes on the plate allows us to mount milling tools with heavy duty wire strips. The is a quick and dirty solution, which will work for now.

We also began constructing on the machine housing. We found some used wooden plates and made the bottom-suction-room. since we havnt got any plexi-glass yet, we could not finish it. Its larger than first immagined though. The distance from the materialtable to the tooltabel should be about 400mm (so you can get big pieces into the machine) and the z-axis with motor sticks up about 350mm. With a little clearence and 50 mm ind the bottom for the suction we have a machine approximately 1m tall. We will post a picture soon, when it is a bit more finished.

The next step was to actually mill. First of all getting some gcode established for something that we liked. After a few hours Nicolas and Jakob Remin made a first cut-out with CNC:

the text seen on the sign was made using the linux script called “truetype to gcode” which comes with the linux emc package, and allows you to trace any text string and true type font to finished gcode very easily.

Now we can mill, but there are still some things left. We need to build the housing, so the machine can work in a safe environment. We need to figure out a quick way of establishing the gcode. We need to make a more step-by-step guide to the project.

Celebrating the first cut-out is also essential - the machine would be veru dissapointed if we would not appreciate its effort. Having a grill”party” at the boat was neccessary:

We hope to finish the rest in 2 days.

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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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woohoo! we have a new URL and a new layout
you gotta love it

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We have finished up soldering the control-kit, and tested if the voltage was right. Everything seems to work out fine. We really want to plug it to a computer and test if it actually control the motors, but we have just now found the computer to use, and have to reboot the thing and install the ubuntu with the cnc-software to it.

Unfortunately the components for the X/Y mechanism has not arrived yet, so we are a bit stuck in the building process. This makes this day a bit short.

Another task have been to figure out the power sypply. We have decided to use PC power supply, but it (or they) need to fittet to this use. The good thing about PC PS is that they delivers 300W each which is hopefully suitable for the CNC. Jremin have done this before in a 8×8 LED-display project (www.campingsex.org/8×8), and there is also a description about making a PS here. When doing this remember that the green wire (in some PS it has another color!) has to be connected to ground through a resistor. This connection switches the power supply on.

So a little short and unproductive day, but the list for day 3 looks fun:

• Installing the CNC-software
• finishing the power supply
• testing the motor-controller
• building the housing

Well probably not make all of it, but we will see how far we get.

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Day 1 - Planning the project

Intro

This is a project about building a CNC milling machine, understanding the primary functions of the machine and software and using this knowledge to make experimental prototyping of mechatronic ideas. The project is carried out on the M/S Halfmachine (www.halfmachine.dk), whom is also a big contributor to the project. The project is done as a 13-weeks course at Technical University of Denmark (www.dtu.dk), which is set for approximately 8 hours a week for 13 weeks. The course-description can be read here (course-description.pdf). We plan to use every Friday at the M/S Halfmachine.

The components

First we need the different parts and components for the CNC. The first day the circuit for the control is arrived along with the motors (www.hobbycnc.com).
The rest of the parts and components will hopefully be available next Friday. A list of components can be found here: (link not up yet), and we will update it along the way. Also suppliers and prices are included.

Being students at DTU, we have tried to get scrap materials, milling head and milling tools for free at the workshop in DTU. This is needed during testing and calibrating of the machine. The materials seem to be pretty easy, but getting the milling head and tools probably needs some more friendly conversations with the guys at the workshop. Hopefully they get tired of us at a point, and give us some old stuff to experiment with. When the final setup is made we probably need to bye some tools and possibly a milling head.

We need to make a plan for housing and the mechanism holding the milling head. Also a huge concern in constructing the frame is taking safety in to account. Some kind of Plexiglas screen is probably needed, so we can observe the machine at close range without being in danger. We will publish drawings and pictures when we find a proper solution.

First step in the quest for a CNC is to assemble the control board. The kit is pretty straight forward and the guide very good step-by-step instruction. This takes a couple of hours, so day 1 is pretty much over with the planning and the first assembly.

The 4 stepper motors and the control board kit

Specifications of the driver

What you need

Soldering in progress

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