Taylor and I have been working on a DIY 3-axis CNC mill over the last few months. I’m posting this mostly to brag :), but also as an excuse to do some documenting on the process that might be useful to others. We’ll keep posting as things progress.

Some video of testing

The original plans use 1/2″ MDF for all the panels. We decided to go with with clear acrylic for the visual effect. Also, we were able to use a laser cutter for most of the cutting to the edges are nice and clean.  The downside is the brittle nature of acrylic, which likes to crack when drilled from the edge (and this design requires a lot of that).

CONTROLLER & CONFIGURATION

We’re using linux-based Enhanced Machine Controller to run the mill, with a modified version of the standard stepper configuration. Here’s our EMC configuration files. So far, I’ve been really pleased with the performance. It was trial-and-error figuring out the scaling– I ended up attaching a pencil to a dremel collet, then manually jogging each axis until I could draw a one-inch line in each direction. The scaling factors I came up with are: 520 for X and Y, and 16000 for Z, and that’s with quarter stepping set on the hardware controller board.

We kept getting a “Joint 2 Following error,” indicating that the z-axis was losing its position. I found that this was happening only when using  G00 (rapid-positioning) codes. I’m still a little unclear as to whether we need to even worry about positioning in this case, but for now I’m just replacing G00 codes in my toolpaths with G01 (linear motion). It’s a little slower, but for now the error is not happening anymore. See Feed Speeds for the permanent fix.

TOOLPATHS

We use Rhino3D and RhinoCam to generate our toolpaths. I’ve found that a number of different post-processors to work just fine, but mostly we’re using .NCD’s out of habit.

FEED SPEEDS

There doesn’t seem to be a way to directly set the feed and plunge speeds in EMC. The NCD post-processor defaults the feed speed to 3.7 and the plunge speed to 7.3 and the units are inches per minute. So we’ve been doing a search and replace in the post-processed files setting plunge to 14 and feed to 10 (this is easier than going back to RhinoCam to re-generate the toolpath with new feed speeds). We also then modified the MAX_FEED_OVERRIDE setting in the stepper_inch.ini file to 3, meaning we can increase the feed override up to 300%. We now limit the max override to 150%, and more deliberately set feed and plunge speeds in RhinoCam, under the Feeds & Speeds tab — these vary depending on material.

ERRORS

We kept getting a “Joint 2 following error” while testing, and found–after consulting the EMC documentation wiki–that changing the FERROR setting to 5.0 and the MIN_FERROR to 1.0 (that’s percent) for all axes in stepper_inch.ini alleviated this error. There’s the potential with increasing the FERROR settings of losing some accuracy, but that’s not our main concern at this point.

The situation: Steve* a former roommate of mine moved out, and left a box of things in our basement storage unit, including an old Apple iBook laptop. Even though our other three neighbors had access to the storage room, I wasn’t too worried about any of his stuff; the laptop was old, the battery & ‘Y’ key were broken, etc. Plus I know all of my neighbors, they are all women in their mid-to-late 30’s and I had no reason to suspect any of them of doing anything… let’s just say ’strange’.

At one point Steve sent a friend to pick up some stuff, and I assumed he had taken the laptop, because I noticed later that it wasn’t there any more.

I didn’t think anything more about it, since I never heard anything more from Steve. Until about a month ago, when I noticed that Steve’s laptop was connecting to our wireless network. I contacted him and confirmed that he did not have the laptop, nor did his friend. This pretty quickly led me to one conclusion: one of our neighbors had taken the laptop from our storage room, and was using it. On our network.

I found this situation to be pretty mind-blowing: that one of our adult neighbors would be so ignorant and unscrupulous as to take something and use it so flagrantly. It wasn’t so much the value of the computer that bothered me. The laptop, let’s face it, was a piece of shit. Beat up, old, and not containing any sensitive data, I would have had no problem loaning it out until Steve wanted it back. The principle of the situation was what really got under my skin: you don’t steal stuff from your neighbors, and if you do you certainly don’t advertise it to them!

Whoever had the laptop was basically waving a huge red flag saying, “I’m ignorant. Please take advantage of me.” At least that’s what first flashed through my mind--­­visions of vengeful data-mining, FBI raids, etc. But after the initial shock wore off, I realized what a delicate situation this was. I certainly could not go about blindly accusing each of my neighbors in turn–this would only offend the two who were innocent, and produce a denial from the guilty one. I did consider calling the police, or using a packet-sniffer to maybe track down the email address of the culprit. But even that seemed a little harsh; pressing charges or going to elaborate lengths to embarrass the guilty neighbor would also probably lead to an awkward living situation.

I decided that my ideal approach was to let the thief know that I knew about the theft, and that they could return it to the storage room with no questions asked. And I would let them know in a firm yet polite fashion. By remotely breaking the shit out of that laptop.

Luckily I was able to get the login information from Steve, giving me pretty much unfettered access to his machine over our network. This was my plan: to put the machine into kiosk mode, disabling all other applications and interfaces save for one–a never-ending popup loop with a [polite] message commanding the return of the laptop.

To do this I needed to do a few things:

• Disable the Dock
• Disable the Menu Bar
• Replace the Finder with the popup-loop app

I decided to start with the Finder-replacement App. I used Apple’s Script Editor to cobble the code snippet into an application bundle.

The bundle part is important, since it bundles an info.plist file with the script, which allows us to take control of the Dock and Menu Bar (We’ll get to that later).

Now to tell OS X to auto-start Stealer.app in place of Finder (which itself is an application), I placed Stealer.app in Steve’s Applications folder, then modified his com.apple.loginwindow.plist file (usually located in the Library/Preferences folder of the user’s Home directory) by adding the following lines:

<key>Finder</key>
<string>/Applications/Stealer.app</string>

This code causes Stealer.app to automatically launch in place of Finder. This makes it basically impossible to quit Stealer.app or navigate to and start any other applications.

Next was to hijack the Dock and Menu bar. This makes it very hard to launch any other applications besides Stealer. I did this by editing Stealer’s info.plist file (control-click on Stealer.app, selecting Show Package Contents), adding the following lines, and keeping the tags in alphabetical order:

<key>LSUIPresentationMode</key>
<integer>4</integer>

Since all these changes were taking place as the computer was running, and pretty well depended on it being restarted to work fully, I also took the precaution of moving all the Applications to a separate folder, then duplicating Stealer.app in the Applications folder, and renaming it iChat.app, iTunes.app, etc. This way the message would still appear without a restart. (I figured the surprise of realizing someone was remotely messing with your stolen computer would be enough to scare the thief into returning it.)

Two nights later, the laptop was back in the storage room, safe and sound. And later the same night, our upstairs neighbor coincidentally dropped by with a gift basket full of snacks, which she ‘just happened to have laying around, and thought we might like.’ She just moved out today. :)

Disclaimer: The solutions I came up with to deal with my situation are extremely specific and jury-rigged, and nowhere near foolproof. They are by no means the best solutions, they just happened to work in my situation. I wrote this post mostly because the situation was very weird, to the point of being comical, and it presented some opportunities to do some fun pseudo-hacking and learn a few things.

The only downside to this setup is having to reboot every time I switch OS’s. Boot Camp only allows one partition to be the default startup disk. I keep my default set to OSX, since that’s what I use most. But if I want to reboot in Windows or Linux, I have to sit and wait while I hold down ‘alt’ and the Boot Camp bootloader comes up. I would rather spend this time staring out the window, or getting up for coffee.

That’s why WinRestart is awesome.

WinRestart is a [painfully] simple two lines of Applescript (thanks to Taylor for the code) that passes a shell script to the Terminal, using the bless command. This sets your Windows/Linux partition to be the boot disk on the next restart only. WinRestart is saved as an application, which means you can keep it in your Dock. Just click to launch, and you’re on your way to automatic restart heaven!

After downloading and extracting WinRestart, open it up in the Script Editor (Applications -> AppleScript -> Script Editor.app) and change the name of the boot volume to your alternate partition. For example, if your Linux partition is named ‘linuxpartition,’ you would change the default Untitled:

do shell script “bless -mount /Volumes/Untitled/… privileges

to ‘linuxpartition’ (no quotes, though):

do shell script “bless -mount /Volumes/linuxpartition/… privileges

UPDATE: Andy writes with this tip about using WinRestart with an NTFS partition:

I just wanted to thank you for your WinRestart post on rainbowlazer. It was pretty much exactly the information I wanted — however, using a NTFS partition for boot camp did cause some problems with using bless.

Bless seems to require statfs, when you use it with the –mount option, which apparently isn’t supported with MacFuse/NTFS-3G. Instead [of bless -mount /Volumes/Untitled/ -legacy -setBoot -nextonly], the following bless command worked great for me:

bless –device /dev/disk0s3 –legacy –setBoot –nextonly

Thanks for the input, Andy!

UPDATE: Tim writes with this tip about adapting WinRestart to work with System Events to prompt saving of open documents before restart:

Thanks for developing the WinRestart application. I wanted to comment that I have used it a lot and have found it really helpful. I made a version of the script that might suit most users a little better though, maybe you would like to post it as an alternative.

do shell script “bless -mount /Volumes/Your_Volume_Here/ -legacy -setBoot -nextonly” password “Your_User_Password_Here” with administrator privileges
tell application “System Events”
restart
end tell

It doesn’t ask for a password and lets you save unsaved documents/close programs.

For users of this, I also recommend turning off the startup screen in the WinStart File menu.

Many Thanks Again,

Tim

Thanks for the tip, Tim!
The addition of your password in plaintext is a little iffy in my opinion, but if you’re not worried about it then it’s a good time-saver.