I've been a bit busy lately and mainly working on other people's projects, so I haven't had a lot to post lately, but I have been working on the R3 (RepRap Router) again.  My laser-strap prototype has taken up residence in the new CNC room at Hamerspace and is now sporting new endstops and tool mounts including a boom for its powerful little flex shaft spindle.  I got in a quick test of the tool mount and spindle last meeting and grabbed some video:

Here's some additional pics:

Next on my list of stuff I need to do for this prototype is to get the hold down system in place and mill the sacrificial top flat.  I plan on embedding some extruded aluminum T-slot that works with 1/4" hex bots into the MDF work surface like the bigger CNC setup at the space and using standard woodworking hold down clamps for now and maybe design some milled or 3D printed ones as the project progresses.

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Here's a pic of a quick little dongle I threw together that allows you to power up a PC power supply and use it as a bench supply, or in my case, to power a few stepper controllers for my CNC setup. You can also use the dongle to test potentially bad ATX power supplies.

You can find tutorials on using ATX power supplies outside of PCs all over the net but all of them are pretty much a variant of what I have here.  To get the thing up and running, you just need to:

• Connect the green wire on the 20 or 24 pin connector to ground to power on the supply.
• You'll probably want to supply a load to the supply to keep it up and running, usually just a power resistor on the 5V rail, a 10 Ohm 10W resistor is typically used, creating a 2.5W load.  I've also seen people simply plug in an old PC peripheral like a hard drive to the supply to provide this load as well.
• Attach an LED to the output of the supply OK signal to get a nice "everything's fine" light.

Here's what you'll need:

• 30 Ohm 5W Resistor - Mouser P/N: 71-CW5-30-E3 - This puts a nice 0.83W load on the 5V rail.  Don't worry if this warms up a little bit during operation, that's what a resistive load does.  This smaller load seems to work fine for me.
• 20-Pin Power Supply Connector - Mouser P/N: 538-39-29-3206 - Just the socket we need to connect to the ATX supply where a standard motherboard would be connected.
• 330 Ohm 1/4W Resistor - Just a current limiting resistor, not needed if you don't put a power on light on your dongle.
• Green LED - Just a typical LED for your power good light.

Here's a couple close up shots of the dongle on the inside:

Check out the Wikipedia entry for ATX and scroll down to the power supply section for a detailed pinout of the ATX connector.  Note that I'm using a 20-pin connector and the connector pin numbers on the Wikipedia article are for a 24-pin.  I'm using the pin numbers from the article, so realize they could be different based on which connector's pinout you're looking up, so pay attention to the actual signal names!

Basically I've connected pin 16 (power on) to pin 15 (ground), put a 30 Ohm resistor across pin 21 (+5V) and 19 (ground), making sure that the long exposed lead is connected to ground, and connected the positive lead of my indicator LED through a 330 Ohm resistor (hidden in the heat shrink) to pin 8 (power good) and the negative lead to pin 7 (ground).  After testing, I wrapped the whole thing in a little electrical tape and installed it.  I'm using the switch on the back of the power supply as my power switch, but if you want to have a more convenient switch wired to your dongle, just replace the jumper between ground an power on with a standard normally open switch.

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Basically, FreeMILL can best be viewed as a nice script for taking a 3D model and creating a simple set of toolpaths for reproducing it on a standard 3-axis CNC mill. It has its limitations, and it's a little buggy, but it provides a very quick and easy way to go from a 3D model to a physical part. Plus it's free.

Get it here:
http://www.mecsoft.com/freemill.shtml

There's also a community site for it here:
http://www.freecadcam.com/

First off I'll walk you through the process of generating toolpaths from a 3D model with FreeMILL. FreeMILL supports a few 3D formats, including STL, VRML, Rhino, and VisualMILL (another one of their products). I only used the STL support since it's what my source models are in and probably the most widely used format for the hobbyist user and almost all 3D packages support it.

If you're running Windows 7 or Vista, you'll want to run FreeMILL as admin (right click the lauch icon, select "Run as administrator"). You'll want to do this because the default output directory for the resulting G-code file will be the install directory, which FreeMILL won't have write access to by default.  If it crashes randomly or the preview of your model looks weird you may have to revert to a basic Windows theme and/or disable hardware rendering.  Switching to the Windows 7 Basic theme was enough to make it somewhat stable for me.

After launching FreeMILL, you'll follow a wizard step by step until you generate your final toolpaths.  The first step is to load your 3D model.  I'm using a model of a ceramic mold that someone at the space wanted fabbed. You'll get a nice preview of the part and the determined bounds of the part and you'll be given the option to specify that your part is specified in mm.  I assume the default is inches, as this seems to be the standard for models specified in imperial units.  If your part looks like it's about the right size, click next.

Now you will be asked to specify the cutting direction.  This seems to simply be a way to specify the projection that will be cut (someone correct me if I'm wrong).  If your model is already oriented correctly, just click next, otherwise use the radio buttons to orient it correctly.

Next you'll select the offset of the stock.  This is how much bigger the piece of material you'll be cutting is than the model on either side.  Since this is an offset, if you have a particular piece you want to cut a model out of, you'll have to measure the piece, look at the reported model size and do some math to get the right offset.  I simply left both offsets to zero since I was going to cut the final part out by hand.

Now we set up the parting plane.  Parting plane is a mold making term for the plane where the two halves of a mold meet up.  In FreeMILL, this simply defines the lowest the Z axis will go when tracing the 3D model.  Depending on what you want to do, you may want to simply set this plane to a depth that will get all the details you want to see in the final product as I've done here.  I'll go into some detail on the games you can play with this setting to achieve various things later.  A couple times running through the wizard I got some odd values on this page and the application immediately crashed when I tried to continue even thought the preview looked fine.  Repeating the first couple steps seemed to fix this...

Next we set up our origin.  There aren't a whole lot of options here.  You'll likely want to select top so you can easily touch off on your stock with your mill (this puts Z=0 at the surface of your material).

Next we specify our cutting tool.  Again, this is pretty straight forward, just put in the parameters of the mill you will be using.  I'm 1/4" flat endmill here but on the final part I used a 1/8" endmill with a 1 degree taper since I couldn't get all the details of the model fleshed out with the 1/4" endmill.  You'll see this later in the preview.

Next we set up the spindle and feed rates for the material you'll be cutting.  A feed rate of 40 inches per minute is fairly conservative for the machine this will be running on since we're just going to be using housing insulation foam board.

Now we get to select our stepover distance (the distance between passes) and generate our tool paths.  Tool path generation seems pretty quick and the progress of the processor is updated in the preview window as individual passes are generated.

Here's what it'll look like after the paths have been generated.  We can also simulate the toolpaths and see what the final product might look like.  You can see here that not all the details of the model will be preserved with a 1/4" endmill based on the preview.

Next we select the post processor and save our final output.  I'm using Mach3 (configured to use inches) to drive the CCCKCCNC, so I select that post processor.

When you save, a temporary file containing the G-code for the generated toolpaths will be created and opened for you.  Save this file wherever you want and you're done!

You can look at the generated toolpaths in Mach 3 if you're on Windows or with EMC2 on Linux.  Here's what the generated toolpaths look like in Mach 3:

After regenerating toolpaths for an 1/8" endmill, I loaded the G-code on the CCCKCCNC machine and milled the mold without issue.  You can see that this thing is actually pretty big (the outside edge of the mold is 22"). It's almost  too big to clamp from both sides and not have the skirt run into anything.

And here's the finished product:

Here's some close up shots:

This entire part took about 4 hours to mill with a 1/8" endmill at 40 inches per minute feed rate and a 0.07 stepover distance.

What FreeMILL doesn't do and how to get around that

The simplicity of FreeMILL is nice, but it really lacks a lot of functionality.  Here's some stuff that would be really nice to have but you can't really do:

• More bit options, only flat and corner radius mills are supported (ball mills are a special case which are supported, but not V-bits)
• Depth per pass and roughing passes can't be specified
• Only X or Y parallel finishing available

A lot of these shortcomings can be worked through by generating additional passes manually.  For instance, you can't specify the maximum depth per pass, so if you've got a design that's relatively thick, the generated toolpaths will have your bit plunging all the way to the maximum Z depth of your part and then dragging through your material.  This is a problem for a lot of mills and materials, but you can get around this by setting the parting plane to different Z depths manually and generating toolpaths for deeper and deeper cuts then feeding them to your machine the the correct order.

You can use the same principal to create roughing passes with larger mills then a final detailed path with a smaller mill and smaller stepover distance.  You can create paths for X parallel finishing and then the Y parallel finishing on your final pass as well.

General Impressions

It should be no surprise that MecSoft seems to be releasing FreeMILL primarily to promote its other CAM tools.  I do appreciate that they effectively put out a demo that, while being a little light on features, actually lets you generate usable G-code.  As a free tool, it's annoying that it's buggy but it's still usable and worth the trouble.  Now the catch is that you have to provide some information to download FreeMILL, and I gladly did.  I'm not intimately familiar with their CAM offerings, but I wouldn't mind some additional information or a sales pitch and, as expected, I got an email promotion the day after I downloaded FreeMILL asking me to take a look at their CAM tools after trying out FreeMILL.  The Monday after I played around with FreeMILL I actually got a call from their sales department asking if I was interested in ordering software after using the demo (yes, I do give out my Google Voice number).

Now even if I was interested in purchasing CAM packages, and I am, I don't think that the buggy, poorly maintained (at least since 2003), feature light demo that is FreeMILL would inspire confidence in MecSoft's offerings (especially from a hobbyist's perspective, since their tools are not cheap for that demographic).  I understand that they probably don't want to or simply can't devote resources to maintaining a free utility, but they should probably put forth a little more effort if they're hoping that that same utility is going to help sell their software.

More CAM Stuff

I plan on posting some info and reviews of other CAM tools (and other useful software tools for CNC stuff), including dxf2gcode and PyCAM, but in the mean time, go check those two out if you're looking for other free CAM tools.  I've successfully used dxf2gcode to generate toolpaths that I've run on machines for very simple 2.5D jobs.  PyCAM seems like it needs a little work and didn't load the STLs I was using for the above project but it seems promising.  I'll be keeping an eye on the project and playing with it in more depth in the future.

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Here's a sneak peek at the prototype of the laser cut version of the R3 platform with just about everything but the lead screws installed.  It's based off of the OpenSCAD models for the milled R3 parts with a few modifications, primarily to use T-slot construction rather than 1/4" threaded rod.  I experimented with match drilling as mentioned in the Mantis 9 build page and it yielded some very smooth motion on every axis of travel.  If all goes well, I should have my R3 prototype up and running for demos at the Kansas City Maker Faire June 25th and 26th along with my Makerbot, PE00001, in the 3D printer village section!

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I haven't gotten much done on the hardware side of things lately, but I've been busy with the electronics of the R3 platform I'm working on.  Above is the first draft of the parallel port adapter that will be used for the first round of machines.  This board allows a PC running Mach3, EMC2, or any other G-Code interpreter with a parallel port driver to control up to 4 RepRap/Makerbot stepper motor drivers and has separate inputs for X, Y, and Z axis home, emergency stop, and limit switches, as well as a few additional outputs and it exposes the enable functionality of the stepper motor drivers, allowing you to disable all stepper drivers if needed.  I'm planning on using Mach3 for the initial prototypes and then moving to a microcontroller based G-Code interpreter (possibly based on GRBL) once development is further along.

Other than the main PC breakout board, I've also designed boards for mechanical end stops (seen above) and a stepper signal splitter board (seen below) that will allow two stepper drivers to be controlled by the same signals, allowing for some interesting mechanical drive options.

While designing these boards, I tried to keep them single sided if possible, keep the required part counts low, and use big parts where applicable to make them easy to construct.  The idea is to make them easy to "bootstrap" via traditional DIY PCB etching methods and easy to mill once I've got a machine up and running.

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