Scottie sensor-pcb design and Bits of Trouble
I've been making PCB's for the Scottie Project for some time now, and recently i've started to make a board that contains all the sensors and actuators we're using.
The sensors it contains/connects to are an accelerometer and four touch sensors.
The actuators are six high brightness RGB leds and four solenoids.
From this board a long cable runs to the 'brains' of the scotty, a GPRS-modem. Power and communications must go from the brains to the sensor-board, so a thick multi-core cable was chosen to do the job. Originally I was also running the output from the touch-sensord trough this cable, but there seems to be too much desturbance in this signal over this long distance.
Currently only SPI, I2C and power are routed trough this cable.
The top-layer of this board is exported to png at 500 dpi so it can be processed by cad.py.
I used GIMP to clean up the board before I let cad.py make the final contours (10).
As you can see in the above picture, the result is still pretty messy.
The tools that we are using are Garr tools 13550 (a four-flanged 0.010" dia. carbide end mill)
A problem that i ran into is that at higher xy-speeds the traces get all mangled up (rough edges on a 10 mil trace is not nice). But the biggest problem is that i can't get the board finished because my mill-bits keep snapping...
It always happens while milling a trace, so not while plunging into the material.
I tried lowering the xy-speed, but this seems to only enhance the problem. (as we are using the modela mxd-200, we can't do anything about our spindle speed wich is at 6500 RPM)
I also tried milling in liquid to prevent the bit from overheating, but this also only seems to enhance the problems.
At a speed of 1 (didn't dare to go faster yet) it manages to get to about 70%, but at 0.3 it didn't really get beyond 10%.
I'm really at a loss at his moment..
.edit. 17-4-09
Problem solved. Lessons learned.
Problem appeared to be the slow movent. it seems that the bit would bite into the material pulling itself forward, with the result that it snaps off.
