There are four stages to the PCB design and manufacturing process:
We will be designing single sided PCBs with copper layer on the solder side (bottom).
Here are some considerations for board layout in EAGLE.
If you've accidentally placed some parts with finer grid, you can run a ULP (user language program) to reposition everything on the grid. First make sure you've set the 50 mil grid per above. Then choose File:Run, and select cmd-snap-board.ulp from the file dialog. Run the program, accepting its defaults.
EAGLE's default libraries have pads that are too small. I recommend pads 70 mils across.
In the Engaging Computing Lab, you won't have write permissions to EAGLE's libraries. So you should copy needed library files into your own directories, modify them, and then use those libraries. Please make sure to give the copied library a different name to distinguish it from the stock factory libraries!
From EAGLE's Control Panel, open your copy of the library. Click on the Package tool:
This will bring up an Edit dialog. In the example below, I have chosen the "LED3MM" from the led.lbr library.
Next, use the change tool (the little wrench). Select Diameter -> 0.07. Then click on the LED's pads to change them. (You can also specify change parameters at the command line, e.g., CHANGE DIAMETER .07 or simply CH DIA .07.)
Click on the pads to change their diameter. I have also changed the pad shape to mark the cathode with a square pad. This is a standard convention for diodes (cathodes marked with a square pad). It helps you when you go to stuff your board, especially since there will not be a printed silkscreen component guide.
Here is how the LED looks after the changes:
Save the library. Now you will have to go back to the schematic program and tell it to use the new library (Library:Use ... menu choice). Finally, you may have to delete parts you are using from the factory library and replace them with the same part from your newly modified library.
Here's how my sample board looks after routing. Notice the two unrouted air-wires. One of these, from the pin labeled Wh of the jack in the lower left, to pin 17 of the IC, will actually be implemented with a jumper. Each of those connections has a trace leading to via hole. When stuffing the board, I'll use a jumper wire to make the connection. (For the other air-wire, the signals are connected but EAGLE doesn't realize it.).
When your board design is done, we move on to the File Preparation Stage!
T01 0.024in T02 0.032in T03 0.040in T04 0.047in T05 0.066in
You won't need this file directly, but it's used in the very next stage.
The engraver is now installed.
From GCPREVUE, look at the "Absolute mm" coordinates. The design is at an offset of X = ~50mm, Y = 2.5mm from the real 0, 0 origin.
So what we are going to do is:
In other words, we must set the Roland's XY origin so that when the tool moves 50 mm to the right, it will hit the PCB mounted on the table.
Move the tool to the front left corner of the PCB, and set this as the XY zero. (From the XYZ position display, hit Enter, then Enter again over Position Set XY-Axis, then Enter again over the absolute XY position display, then hit Left-Arrow and Enter to make it happen.)
Calculate the offset required. We are looking for 50 mm in the X coordinate. Each Roland step is 0.025 mm. So 50 / 0.025 = 2000. Move the X coordinate to -2000 ticks. Similarly for the Y axis, we are looking for -2.5 mm, which is 100 ticks, so set the Y for -100.
Now repeat the process for setting the XY origin.
You may wish to write down the coordinates in case the tool head gets jarred and you have to re-zero. For the job I'm photographing, the absolute Roland coordinates are X=406, Y=2694.
IF THERE IS ONE DIAGRAM YOU REMEMBER FROM THIS
WHOLE DOCUMENT, PLEASE LET IT BE THIS
It is critical to set all three of these Z origins before any tool run!
For now, we'll set all three to a position where no harm can be done. Using the Z+ and Z- keys, move the Z axis so it is higher than the top of the jigging apparatus:
Now use the keys to set the Z0 origin there. Hit Enter, choose Position Set Z-Axis, etc. First set the Z0 workpiece origin. Then set the Z1 DOWN and Z2 UP positions. When you are done, still in this menu area, Z1 and Z2 should both show zero!.
For the photograph, I have a Z0 setting of -1207.
When you are done, hit Menu to go back to the XYZ display. Z should now show 0, with the tool high up above the jigging.
From the PC controlling the Roland, bring up an MS-DOS shell. Send your engraving file to the machine by copying it to lpt1, e.g.:
copy yourfile.plt lpt1:
Watch the trial run! Make sure the tool head doesn't move over anything bad.
First, move the tool head over a portion of the board that won't be used (e.g., near the right edge). next, move the z axis down until the tool tip just touches the board. Establish this as the Z0 SURFACE origin.
Use piece of paper to tell if the tool is down. Or use ohm meter.
Move the tool head up about 200 ticks. Establish this as the Z2 UP position.
Hit Menu to go to the XYZ position display, and move the tool head over beyond the edge of the PCB. Move Z down until it's just below the surface origin, at position -10.
Now determine if this is going to be a good depth for engraving. Close the safety shield and press the button to turn on the spindle. Turn the speed knob about 2/3 of the way up.
Now manually move the cutter into the board, engraving about a 1/4" long groove. Move the cutter up, then turn off the spindle and move the tool head out of the way.
Examine the groove! It should be just under the depth of the copper. The copper should be fully removed, but you don't want to be digging too far down into the phenolic substrate, or the cut will be too wide and too much of the pads or lines will be removed.
If the cut is too shallow, move the Z axis down (say to -15) and try again.
If the cut is too deep, move the Z axis up and try again. If you need to go "above 0" to get a good cut, then the Z0 point is set too low, so you'll have to re-establish that. If you change the Z0, make sure to re-establish the Z2 UP position also.
When you have a good depth for cutting, establish it for the Z1 DOWN position.
Make sure to watch. If anything goes wrong, please be ready to hit the red EMERGENCY STOP button.
If it all works out, you should be rewarded with a nicely engraved board, all of the traces isolated but not cut too deep:
First unscrew the engraver. The knob turns clockwise and the wrench goes counter-clockwise, backward to how you'd expect. use the wrench to hold the top of the tool hand, and your fingers on the brass knob:
Please put the engraver back into its plastic tube.
Get the drill. Be gentlethey break easily! It looks like this:
The red plastic shield protects the cutting end.
Now at the engraving machine, position the tool head over some unused area of your PC board. Move the Z axis up so that you can get the drill into position. Now, still holding the drill, lower the Z axis so that most of the drill shank is up into the collet. You have not tightened anything down yet! It should look like this:
Now, tighten down. This is the only time you have to really apply elbow grease.
Next, before moving the tool head, establish the Z0 SURFACE as here.
I get a Z DOWN value of -300. Establish this via the menu keys.
Next, move the tool up and tighten the drill some more. You have to really crank it.
Note: if the drill is not sufficiently tightened, it will get pushed up into the collet!!! If this happens, stop the job as soon as you notice it. Follow the procedure below (for drill changes without recalibrating). Then re-run the drill job.
First, move the tool head over an unused portion of your PCB, and move the head up. Loosen the collet. Remove the old drill and put it away.
With the collet still loose, insert the new drill. Move the tool head down to exactly the Z = 0 position. The drill tip should be touching the PCB surface as the tool head slides down onto it.
With the tool head at Z = 0 and the drill tip resting on the PCB surface, tighten down. Now the Z0 tool surface position is re-established, and Z1 and Z2 don't need to change.
Move the tool head up and tighten some more. Then send the plt file for your new drill!