Milling PCBs?

DNA Robotics

Joined Jun 13, 2014
603
I just finished my second board yesterday. It is for PIC 16F877 & 18F4550 tutorials & development. Designed & layout in Eagle 6.4.0 and used pcb-gcode-3.6.0.4 to generate single pass G-code to engrave & drill with Mach3Mill.

I used a .2mm, .0078" 30 degree engraving cutter and a .8mm, .032" mill/drill at 10,000 RPM and 10 IPM feed. In the future, I will use larger VIA pads.
Nice clean cuts. I didn't even have to sand the edges.


40 pin main board.jpg 40 pin PIC.jpg
 

DNA Robotics

Joined Jun 13, 2014
603
Nice. Is it me or are some of your holes off center? Looks like some are oblong too. Was that intentional?
That was a little accumulated error. I'm glad it wasn't any more. The pcb-gcode drill pattern zigzagged back and forth from one side of the board to the other instead of going down a row of IC pins or header pins.
What might look like oblonged holes, there is a 40 pin IC socket inserted but not soldered in that first board picture.


Drill pattern.jpg
 
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DNA Robotics

Joined Jun 13, 2014
603
Those holes are still better centered than I could possibly do.
The pcb-gcode has an option to engrave the center of each hole after cutting the traces. So when drilling in the next step, that tiny drill falls right into the center mark without wandering or breaking.
 
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Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
That is one heck of a machine! Does the table move? You must have huge stepper motors to move it? How do you think it would have faired at 8k rpm? That is the max on the cheap I am looking. I actually was considering converting a compound table but the one I was looking had only about an inch of travel on the y axis. How much travel do you have?
 

DNA Robotics

Joined Jun 13, 2014
603
The table moves 24" in the X direction & 8" in Y.

I believe in overkill & didn't want any question about whether the motors would move all that iron so I got these motors http://www.mpja.com/Stepper-Motor-NEMA-34-78V/productinfo/17457 MS and these drivers http://www.mpja.com/Stepper-Motor-Driver-5A-Max-Wide-Range-CW250/productinfo/17452 MS

This looks like my interface

DIY Engraving Machine MACH3 USB CNC 4-axis Interface Breakout Board Adapter $15.00
You would have to use slower feed at 8K RPMs. There is a formula to determine Inches per minute to cut 2 or 3 thousandths of an inch per revolution of the cutter.


WT 3-Way Mill & Drill Table $125.20

Thanks guys.

Yes it is held in place with double sided carpet tape. I flexed the board a little to take the bow out of it. When in place there was only .002" variation across the board.
 

DNA Robotics

Joined Jun 13, 2014
603
I actually was considering converting a compound table but the one I was looking had only about an inch of travel on the y axis.
Maybe keep watching eBay & craigslist for a compound table. You may even find one cheap with motors on it. Places that sell used machine tools & tooling may have just what you want. I'll bet there are plenty in an industrial area like Pittsburgh.
 

MaxHeadRoom

Joined Jul 18, 2013
23,393
The main thing with CNC is the leadscrews, most manual machines and tables come with an Acme screw, to convert to CNC it is customary to swap them out for Ball screw, even if the cheaper rolled type rather than the better ground versions.
Also the B. screw nut should be pre-loaded for zero back lash.
Max..
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
Yes it is held in place with double sided carpet tape. I flexed the board a little to take the bow out of it. When in place there was only .002" variation across the board.
Would you mind detailing how this is done in Mach3? I have yet to use it so I am clueless.

Have you tried pc-probe?
http://www.instructables.com/id/Mak...-desktop-CNC-m/step3/Make-G-Code-for-a-Board/

I am not sure what the heck he is trying to describe. The article is not very clear.

I see you are milling on a piece of Plexiglas. Do you drill on that too? Or do you swap out a spoil board? If you swap out the board how do you line things back up?

Maybe you can write a blog on a generic milling procedure? I have yet to see one that is easy to understand. I would be happy to work with you on it. If I could understand it then you would have created a guide that anyone could follow. :)
 

DNA Robotics

Joined Jun 13, 2014
603
It had been over a year since I made my first board & I even had to reinstall Eagle 6.4.0 and pcb-gcode-3.6.0.4 so I had to read the "How to" again.
The Eagle "tuorial-en.pdf " is good & quick with sample projects. These are also good but I didn't need them this time.
https://learn.sparkfun.com/tutorials/using-eagle-schematic/introduction
https://learn.sparkfun.com/tutorials/using-eagle-board-layout

The pcbgcode.pdf User's manual is in their \docs folder. It was pretty much strait forward step by step also. Mine was single sided so I just told it to etch the bottom in one pass & drill from the bottom. Don't check the preview box. You probably don't have the JAVAW.EXE file that it needs.
I am milling on an aluminum plate that was milled flat. I drill .070" into a .062" board so it does drill into the aluminum but using tape, I'm not worried about it. A dial indicator said the board was flat within .002" & I cut .010" deep so I didn't use pcb-probe.

Mach3Mill requires a lot of setup. Their step by step documentation is pretty good. You start by wiring your parallel port cable to your interface / breakout board. DIY Engraving Machine MACH3 USB CNC 4-axis Interface Breakout Board Adapter Some wires you do their way and others, you tell the setup how they are wired. (active high or low etc.) Then set up the machine by telling it how many steps per inch or MM for each axis, then acceleration rate for the stepper motors and maximum speed. Then tell it how much backlash is in each axis. Mach3 compensates for backlash by adding that many steps every time it changes direction. They say it is a last resort but it works nicely on my old machine.
I put a pen in the chuck & had the machine draw that circuit board on paper until it was perfect before cutting the real board.
 

Thread Starter

spinnaker

Joined Oct 29, 2009
7,835
Thanks for the tips DNA. I don't use Eagle Cad but I guess that PDF should still be helpful. It is just a guide on milling PCBs correct?

That breakout board you posted, is it all that is needed for the controller? Because when I see break out board I think of the easy to use boards you might use to interface to a mcu.

Will the USB port on that board work with Mach3 as well?
 

DNA Robotics

Joined Jun 13, 2014
603
This documentation on the interface board that I got wasn’t very clear. When I got it sorted out, I labeled everything on the photo of it. Wherever they use P, as in P10 it refers to that Pin on the parallel port. The USB is only to supply 5V interface power to the board, not data. This board sends step & direction signals to your stepper motor drivers. It does not drive the stepper motors directly.

Product Name: MACH3 interface board BV2
1, new products and that the appearance and size is similar to the
original function has only added to the
5V and 12V output.
This paragraph 2, the upgraded new constant prices, better
features, there are three relays can be used, you can use up to
six axes.
First, the scope
For numerical control software the MACH3 the host computer and
peripheral power control signal transfer and processing.
Second, the characteristics
1, The output and input models by Philips dedicated high-speed chip processing, signal integer, zoom, in addition to the unnecessary interference signals. Operation of the machine is more stable.
2, USB powered with external power supply. Power supply isolation. Computer and machining data is more secure
3, All of the input signal all the optical coupling isolation, of which P11, P12 port for high-speed optical coupling can be used to pick the spindle encoder, or handwheel A equivalent, strictly signal.
4, The ad hoc one off power relay of the power supply automatically when the computer shuts down, turn off all power of the engraving machine equipment.
5, Has a relay switch coolant supply, support MACH3, G code programming (parallel port P3, G code M7 open, M9 off), switch lights on the relay. Convenient to determine the power supply off.
6, Has a spindle-powered relay, MACH3, G code programming (parallel port P2, G code M3 open, M5 off), switch lights on the relay. Convenient to determine the power supply off
7, For the parallel port on the spindle speed control: ad hoc high-speed optical coupling isolation, you can output the PWM signal, the output port P1.
8, This interface board has a PWM converted to 0-10V digital-analog conversion circuit. Output 0-10V level to control there is only analog speed control inverter to control the spindle speed. The output for the parallel port P1.
9, The interface board can be connected to a common cathode or positive output to the stepper drives, servo drives. The output of the 5V level.
10, Wide supply voltage can be 12V or 16-35V two groups choose a
set of power supply. Power input the anti-reverse design.
Third, the Function Description
Input ports
P10 Emergency stop
P11 Alternate
P12 Alternate
P13 3-axis limit
P15 The knife
Output ports
P4 X pulse
P5 X direction
P6 Y Pulse
P7 Y direction
P8 Z pulse
P9 Z direction
P16 4 pulse
P17 4 directions
P2 Relay port
P3 Relay port
P14 An alternate port
The board needs power input in two ways. One is 16-32V input
(the design of anti-reverse function)
There is also a group of 5V is taken from the USB port, which means that
the interface board in this paragraph must be connected a USB cable to make it
work. (Our ship is equipped with a USB cable ). Because to do isolation
protection function, so these two parts of the supply voltage must
be with the USBpower supply voltage is relatively independent of the job
CNCMaker.com E-mail:CNCMaker@hotmail.com

Mach3_USB port bits and pin numbers.jpg
 
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