Roland MDX-20

Bit Selection:

1. Contour Milling
2. 1/64 inch end mill is recommended in all cases.
3. Drilling holes for pads and vias:
4. 1/32 inch end mill is recommended.
1. Outline Milling
2. 1/32 inch end mill is recommended.

Notes :

(the terms "end mill" and "bit" are used interchangbly, both refer to the same thing)

• Sacrificial Board:
• You can stack two pieces of FR-4 Copper Clad Paper Board - one on top of other. The upper one would be the one from which the job piece (the are which would form your PCB) would be cutout and the lower one would be sacrificial (to protect the end mill bit from ramming into the hard metallic machine bed below and breaking)
• Over stock on bits:
• In case of densely populated PCB with lots of close tracks/pads/vias of different signals, it is a must to use 1/64 inch end mill. Fablabs in remote places like those in India and South Africa are recommended to overstock on these so as to save on time and money (very high custom duty and shipping charges). Ordering lots of these bits at once is expensive in short term, but then you save on regular shipping charges and custom duty. Also it takes a lot of time for materials to arrive from USA.
• Tightening the bit:
• You will need to change the bit after the contour milling is done. Make sure the 1/32 inch end mill is fit snugly into the collet. If this is not the case, then it might happen that the end mill might slip upwards and after a few drills are done, the mill would just scrap the surface for the rest of the points. If that happens, stop the machine and power it off, close the window/program on the PC responsible for sending the commands out the serial port, then power on the machine and tighten the bit properly this time, reset the bit to Z=0 level and restart the drilling process by resending the drill file out the serial port.
• Bit velocities:
• The velocities have been set to minimum so as to decrease the frequency of bit destruction. Although this means that the machine would take much time to finish the job, but you would end up saving those precious bits longer. While performing the Contour Milling the surface velocity in the X-Y plane of the end mill must be as slow as possible so as to decrease the pressure on the bit and help prevent it from being destroyed. Similarly, while drilling, the velocity in Z axis must be minimum.
• These velocities have been set to minimum by the way of the commands/parameters/code entered in eagle.def file.
• Multiple execution of milling:
• It is recommended to execute the milling atleast twice using the 1/64 inch bit. Milling it again for the second time helps remove all the burrs that were created during the first pass of milling thereby decreasing the probability of short circuits.
• Multiple execution of drilling:
• It is recommended to execute the drilling several times. This is because there is a high probabilty that half way through the drill process the bit might slip upwards and stop drilling the holes located further on in the board. In that case you must wait for the drill process to get over, recalibrate the z axis and strat the drill process again. If you are going to end up doing this many times, you can save your time by opening your .brd file in eagle and switching to "layer 45 Holes" and deleting some of the first few holes (ones towards the lower side of the screen near the origin). This way the machine would skip those holes and directly proceed to drill those which were missed out in the earlier process. This would also prevent the pads around the holes near to the origin from getting screwed up. It is recommended that you drill each hole atleast twice to make sure that the hole becomes pass through.
• Holes for Alignment:
• If you are going to mill out a double side board, you may want to create 2 or 4 holes on the edge (i.e. on the dimension layer) for realignment when flipping the board. In this case do not use eagle's hole function because this would create a "X" mark on the PCB centered at the drill point. Instead switch to Layer 45 called "Holes" and place a dot at the point where you want the holes. This layer contains the locations where the holes need to be drilled. After manually placing the dots (dots can be created using the Draw lines tool or you can just copy one of the existing dots in this layer created by the ULP and place it at any desired point), execute the CAM processor to generate the drill file for sending to Modela via serial port.
• Outline milling:
• You may need to execute the outline milling twice or thrice, each time lowering the bit during the initial setting of the Z=0 level to totally cut out the job piece from the excess material. Use only 1/32 inch end mill for the outline milling. 1/32 inch drill is stronger and can withstand the excess pressure exerted on it sideways as it moves along the edges of the job piece.
• Overlapping contours:
• Make sure that no two adjacent contours overlap in the milling layer generated by the User Language Program (ULP) in your eagle .brd file, before proceeding with generating the .mill, .drill and .dimmill files.
• Dimension layer width:
• Keep the width of the dimension to zero in your .brd file before running the ULP or the CAM Processor.