A small, precision milling machine for prototyping circuit boards. It can also be used for engraving of faceplates and other items if the proper bits are used. This unit was made in approximately 1999 by the German company LPKF Laser & Electronics AG. It uses standard 1/8" shank bits, 38mm for cutting the board and 36mm for cutting and milling the copper. The 38mm length is pretty standard, but the 36mm bits are more specialized.
Before using this machine, you must meet with someone who is experienced in using it. The bits are expensive and easily broken, and you must be careful when using the machine as there is a risk of injury if it is not used safely.
The toolchain for making a PCB using the ProtoMat is: schematic design (e.g., Eagle) -> board layout (e.g. Eagle, FreePCB) -> CircuitCAM (build the tool paths from the Gerber files) -> BoardMaster (cut and drill the board)
Shortening 38mm Bits
Since 38mm cutter / scoring bits are much cheaper than the required 36mm bits, some members have ordered 38mm bits with the intent of cutting down the shank length. A jig is available to help with grinding, since they are small, brittle, and get very hot during grinding. Place the bit through the two holes so that about 3mm of the dull (non-cutting) end are exposed. You may need to expand the gap by placing a screwdriver blade in the edge and twisting lightly. Place the holder with the bit on a bench surface so that the bit is nearest the surface. This will ensure that the washers that clamp the bit are flush with the bottom of the jig. Use two 7/16" wrenches to tighten the bolt / nut so that the bit is secure. Use the "Carbide Only" wheel on the grinder in the metal shop. Move the bit across the face of the wheel to ensure that it wears evenly. It will get very hot as the jig pulls the heat out of the bit. The bits are solid carbide, so it will take about 40 - 50 strokes across the wheel to remove 2mm from the shank. Use a caliper to verify the length. Once you've cut it down to 36mm, let it cool and remove it from the jig. Remember that the bits are brittle and will shatter if dropped. Also, be very light with the caliper to avoid dulling the point on the bit or damage to the caliper!
Some things we've learned
Support Material: Use a backer sheet under whatever you mill. For PCBs this should be 2mm. Do not use anything thicker or you will break bits. Do not use anything thinner or you will drill into the machining bed.
PCB Content: Bits, especially the cutter / engraver bits, have a limited life and they are expensive. If you're working with a harder material like copper or aluminum, minimize the amount of cutting. For example, avoid text. Text does not contribute to the function of the board, it takes a long time to cut, and it wears the bits out faster.
See machine manual, linked below.
- Why does the ProtoMat make the final cut to separate my circuit board from the PCB stock offset from where it mills the circuits?
- If you are making a bottom-layer-only board, the CircuitCAM software still puts the cutout milling layer on the top. In BoardMaster, pick Configuration / Phases and choose the cutting phase. Check the "Reversed side" box to put the cutting paths in this phase on the bottom. The cuts, drills, and mills are all assigned to "phases" which roughly correspond to the layers in CircuitCAM. Each phase works on one side of the board. What it's doing in your case is that it is expecting you to flip the board over so it's cutting from the top side, so it's cutting where your board would be if you flipped it over. Since you're making a single-sided board, you should not need to do this. (You remembered to add in bridges so your board doesn't fly out, right?)
- Why are some of the pads for components on my board missing? The area where they would be is milled out and the trace that would connect to the pad just stops there.
- If the missing pads are octagons or some other non-round shape, then the problem is that these are special "flash" element codes in the Gerber file that CircuitCAM does not seem to render. There are two options. One fix is to go back to your PCB design application and change the pads to circular pads. In Eagle, you might have to edit the symbol for the component(s) in the Library file that they are drawn from. The other alternative is to fix the pad sin CircuitCAM. Pick Config / Format Configurations / Gerber - Aperature list ... from the menus; double-click the configuration(s) that has it's Used check box checked (do NOT use the edit button!). Find the flash aperatures (e.g., D13, marked with a * instead of L), edit each one (click the name and then the edit button - do NOT double-click the name!). In the edit window, choose the correct shape and make sure the size is correct. You may have to go back to the board view, or the board design, to determine the correct size. Make sure to save your work.
Procure a full set of the mill, routers, and drills.