Plaster of Paris? That is going to be very abrasive to your milling bits. Wood or wax is a better media to use for test cuts.
Well I just tried testing with MDF. Now the mill doesn’t work. I think I’ve either damaged the Powerbrick or the motor. Best case is that the motor has overheated and just needs to cool.
On another note. Is there a way to make an RLP function call back managed code?
RLP can raise an event, which NETMF can handle, is that what you are looking for?
@ Errol, yes events cool. Is there a delay in the event handling or is it real time?
I would expect it carries the same 1ms delay as all other interrupts etc.
The moment you cross over to NETMF then there is no such thing as “real time”
One of the hardest things for newbies to CNC to get a handle on is the correct feeds and speeds, type of bit to use and the correct depth of cut (DOC). There are formulas, based on empirical evidence and the theoretical chip load for a particular bit, but these will only get you in the right ball park. There is still a lot of trial and error involved at times trying to optimize the feed/speed for a particular job. Feeding to slow just creates more heat from the friction of the bit just rubbing the material, feeding too fast can over load the machine and break bits. In general though it is best to error on the side of feeding too slow and then increase the feed while keeping an eye on the quality of the cut. A good rule of thumb for DOC is 1/2 of the bit diameter. This is very conservative but a safe starting point.
@ Jeff, that would be the Max DOC right?
Methinks that I’m going to move on to PCB plotting with the CNC for a while; at least I can get the handle on the feedrates and DOC stuff (and get a new power brick).
Stay tuned for a new video of the Mini CNC!
Max DOC is the maximum thickness of material you can cut with a bit. In other words a bit with a 1/2" Max DOC can be used to cut all the way through 1/2" material. ‘DOC’ is the amount of material you remove on each pass. For example with the 1/2" material you may only want to cut 1/4" deep and make two passes.
DOC = Depth Of Cut?
Yep
The current Status of the Mini CNC. The video was still processing when I posted the link so HD may not be ready yet.
EDIT: HD is ready.
I checked the machine this morning and it seems that all is well. The problem must have either been heat or my area may have had some under voltage (brown out).
Either way it seems that there is nothing wrong with the machine 
Hurray
Seems to me that plaster was a very odd choice. I am sure there is still a lot of things can be done to improve the machine, boot looks great!
That jerky X axis problem is my next challenge. I can’t even move forward with the RLP code until the thing moves correctly. I’m thinking that the lead screw isn’t tight enough.
So I figured out what is wrong with the spindle: At initial start up the motor draws to much current from the power supply. The power supply then shuts down before it the motor starts turning which stops the motor.
I’ve abandoned the SD card in favor of flash drives: So now the machine will load and execute commands from a flash drive text file.
And on the down side: It seems that the machine is slowly falling apart! There might be a limited amount of time left in its usable life 
Picture of a cut from text file
Which part(s) of the machine are falling apart?
I know you wanted to basically create the pieces for the miniCNC out of scrap then upgrade itself and the FEZ with parts cut from this mill, but my offer stands to cut anything you need out of HDPE so that your mini can live it’s purpose to cut out pieces for itself the bigger FezCNC. Definitely want this project to succeed!
The problem child is that joint which is holding up the entire Z axis; it is giving way ever so slowly (bad design). The nut on the bottom there used to be higher! I will have to take apart the machine to solve these problems. I should just buckle down and do it, however that would mean taking off the electronics, and risk damaging the X axis (as it too is not the best of setups.
I’m not entire sure I understand what I’m seeing but it if the problem is the tilting wood on rollers in the first picture then you might be able to solve it by sliding in a piece of aluminum channel for the wood to slide within. It looks like there may be enough clearance to do this w/o disassembly.
If you want to take it apart and send me dimensions, will be glad to cut more precise versions of whatever you need, just let me know!
Along Ian’s line of thought, McMasterCarr has C channel HDPE as well, so maybe we can figure out something there if you don’t want it out of aluminum (mainly due to cost I would assume).