Milling a PCB

In order to better speed up my prototyping and in consideration of possibly small scale manufacturing I have begun milling my circuit board designs.

This picture should give you a clear idea why this is so important. This is how myself, and many others, make circuit boards at home. By wrapping wire around the back and soldering in place. Its tedious and error prone.

I haven’t mastered it yet by any means but I can tell you about my journey and give you some tips. I’m using a self made CNC machine. Everything I used is off the shelf.

Design

I used Eagle to make the design. Its a popular software and free to use for non commercial. There’s so much to say on the subject of design and using the eagle software. Kicad is another. Not super easy to use and it gets a bit tougher if you want to export to a machine for production. After you make you schematic you click generate your board.

  1. You need to set the net thickness and spacing sizes based on your machine, bits, and personal skill.  I chose 30 mil size and 40 mil space.
  2. The measurements are not millimeters but thousands of an inch. Leave it that way and convert. Otherwise you’ll be fighting the software.
  3. Your origin is at the bottom left. After making you design you need to drag the entire thing to center it over your origin if you want to start your machine off in the center.

There’s a lot more to be said but I suggest you watch some tutorial or do research as needed. Use the cam processor and create your gerber files excellon file for next step

 

Creating G-Code to execute

A free software called flatcam can be used to transform the gerber files and excellon drill files into gcode. For simplicity same I made my project by using only two files the bottom.gerber and the drill.xls

Flatcam creates a tool path to isolate your circuits by using the layout and your input. A few key things.

  1. Your tool size must be smaller than the net spacing you entered in eagle. Otherwise it wont try and cam that area and you will have gaps. I chose .039 as my tool size which is a hair smaller than the 40 mil I put in eagle and is about 1mm for my sanity.
  2. I chose .5 for z travel because I have a floating Z I need .25 inches to lift the float and .25 for clearance. You will see more on floating below.
  3. Speed I use 3.5 and its running beautifully. The project you see above is milled in about 10 minutes.
  4. Flatcam cannot interpret drill files correctly. I’m still not sure why but two things I needed to do. When I imported my drill files they were miles away and huge. First type these two commands into the command line “get_sys excellon_zeros” and “set_sys excellon_zeros T”. Second open the drill file and set each hole size to .050 manually.

The floating Z

When you first try milling a pcb you will find that even the slightest unevenness between your board and the bit will result in all kinds of issues. There are two ways to solve this problem. The first is using a probe to electronically measure and calibrate for this issue over the entire board. The second is to just make the axis spring loaded and let it slide over the board and roll with the waves.

In the video I explain it and give you a good look. Those are just 6mm slide rails and a pack of miscellaneous springs. I now use a makita router due to runout issues from the cheaper router I had in this video.

Here is a video of it running.

I tried small drill bits without success and ended up using engraving bits. I had some really rough experiments where I was snapping bits left and right and making ugly cuts. Eventually I got my machine and software tuned.

Before floating… so much uglyness. Bottom right has tearing. The main line just lifts away
gross!
much better
didn’t have my origin set right
Great!

Finishing them up

Because I use the floating z and an enraging bit I would need to change my set up to drill them out. So for now my engraving bit marks the drill holes just a bit and I drill out the marking on my drill press. One drilled I lightly sand with 1000 grit, then use a steel brush then a nylon brush.

After I use compressed air to blow any dust off and check to make sure there the traces work with my multi meter by doing an audible continuity test.

After my designing and experimenting I can now take a circuit like this from a solder-less bread board to a finished project in about 2-4 hours.

 

CNC milling with router

Here is my video with general info

 

For my milling set up right now I’m using a 2 horsepower harbor freight router with the harbor freight speed control. Its definitely on the cheapest end of the setup but so far I am moving forward nicely.  This whole setup is basically operated with a relay controlled by the mach 3 system. I have to adjust my speed between 18k and 28 manually and I had to make these measurements manually with a tachometer and then draw them into my adjustment knob with a marker!

Wood Milling

Wood working is done on my vacuum table. Here you can see me making some stuff with my new router holder. The vacuum table is super easy to make and I wont go into it. Im ordering some really nice $30 dollar bits from amazon.com and they cut through wood like a hot knife through butter.

CNC Vacuum table

Aluminum Milling

Here is my machine milling some aluminum to make the holder from the video above.

As you can see I have a sump pump pumping cooling fluid onto the bit as it works. Also you will notice that there was massive water spraying everywhere. I have remedied this since then by building walls onto the box containing the vice.

CNC milling Box

The inside of the box is painted with red guard which is a waterproofing for showers. The bit stayed ice cold despite slow movement of tool tip and 28k RPM spindle speed.

Here is the finished product below. Not up to the standards of a large machine shop but that cuts looks fairly decent to me.

CNC milled aluminum

 

 

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Converting a CNC to do 3D printing

Here is the overview videos


There are several parts you will need to convert a CNC to a 3D printer.

Extruder

CNC 3D printer Extruder

This is a picture of my extruder. The bare aluminum is how I mount it to my cnc machine. The orange or copper piece hold my filament. As you can see there is a fan and a little stepper motor driving the filament into the extruder.

Filament Support

3D printer filament support

This is just some abs piping scred on to a little piece of aluminum that is mounted above the exteruder

4th Axis motor driver

3D printer motor driver

Here is the motor driver needed for your fourth axis. On the software side you may need to make some changes to drive your 3D printer, or at least I had to consider that most 3D software will insert an E into the Gcode and mine wanted an A prefix. This hooks up like an other driver with steps and amperage settings.

12 volt power supply

This is a 12volt power supply for the motor, the fan, the extruder heating element and the temperature controller.

Temperature Controller

3D printer temperature controller

Here is my temperature controller. If it is permanently mounted it will need an on/off switch. It will have a screen with an adjustment knob to control the bed temperature. Mine was homemade so I have a plastic food saver as the body right now. If you want to build one check out THIS post.

Print Bed

3D Print Bed

My 3D printer bed is fairly large. I constructed it with aluminum plate. The plate is made stiff be attaching aluminum angle to the back.

Backside of print bed

The top of the bed is 1/4 tempered glass held on with double sided tape. So far I have not needed a heated bed. I put down blue painters tape and sand it with a 40 grit paper. This has held all my prints quit nicely. Some are even tough to get off but most are just right.

Bed Heater or Compartment Heater

3D print compartment heater

Originally I was going to build a heated bed but after trying my bed above I realized it is not needed. However the other issue I faced is delicate parts curling because they cool down unevenly. This heat lamp was a cheap hack and way cheaper and easier to build than a large heated bed. It works great for small prints and at some point I might build an insulation blanket for the whole compartment as well as a temperature control for the lamp itself.

 

 

 

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CNC Motors and Electronics

Check out the video

Stepper Motors

I chose 425 O.Z. inch stepper motors because I wanted to have some strength to perform tougher tasks. They came grouped as a kit with a power supply and motor drivers.

Below is a visual representation of oz inch. It literally means that many oz at an inch away from center.

How does this help you? It probably wont because if you have ever worked with a router or table saw before you know that not much force is needed to push the cutting bit into the material.

When building a machine you have to realize that milling metals will be your most difficult challenge. You also have to understand that these motors could mill through any metal on earth if you use a low enough feed rate. But this low feed rate will depend greatly on finding a proper spindle. Not only that but you have to consider the ball screw break away which keep the machine parts from deforming quickly.

Just for fun consider this formula I found for calculating the force your ball screw might be able to supply.

T = L*P/5.65

T= torque in oz inch you need to provide

L = inches the lead screw will move forward for each turn

P = axial load in oz. Axial load is the pressure

Some common motor sizes for the lazy.

166 oz inch for small 3D printing or engraving

250 oz inch for milling wood or larger 3d printer

400 oz inch for milling non ferrous metal

These of course vary depending on your thread pitch and the speed you want the machine to move.

Wiring Your System

Now I went with a kit but basically each stepper motor needs a DC power supply and a motor driver that can handle the amperage and voltage.

Here is a great diagram of how they should basically work. Your motors are wired to drivers. Your drivers decide which coil to power based on the breakout boards directions.

I used the 18 volt wiring you can get at the hardware store for air conditioning wiring.  The only thing I don’t agree with is the E-stop being integrated into your circuitry. You should have a regular 120v on/off switch that can instantly shut down your motors and spindle without relying on an integrated circuit.

 

Here’s me laying out the board originally. My wire colors mean nothing! Don’t try and figure them

 

Your motors should come with directions explaining which wires are paired. I had a 4 wire motor with Black/Green and Red/Blue. These get wired into the drivers.

My drivers are set up active low as opposed to active high. Active low means that a DC circuit is being switched by connecting or disconnecting the negative wire. Active high is done by controlling the positive wire. So in my active low setup I ran my positive 5 volt power supply into each of the drivers positive terminals and connected the 5 volt power supply to the breakout board which will control the flow of power to these circuits. In the picture above you can see the wires exiting the drivers – PULSE and – DIRECTION port into my breakout board.

Lastly set your resolution or steps per rotation. This will determine how many pulses your driver will need to make one complete rotation of the motors shaft. I set mine to 1600 which is fairly common.

Tips

You can use 28 gauge cat v wiring for your limit switches and 18v for everything else.

A computer power supply is a great way to get 5 and 12 volt power into the system

Never use the relay built into your breakout board. Add another circuit to help isolate it.

Always solder connections after you are sure they work. Wire nuts will fail eventually.

 

 

 

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My CNC setup for small scale manufacturing

In my pursuit of designing and building new things I have constructed a CNC machine of my own design with the help of some parts ordered over the internet. I made a short video explaining what it does as I continue to perfect the machine.

 

Here is the video introduction where I talk about the machine in general and what it does.

 


When planning on building a CNC machine there are a few things to consider which will help you choose the type of machine.

BASICS

A CNC (Computer Numerical Control) machine is a tool used to move a tool tip in a 3D space using computer controlled motors. A tool tip can be anything from a marker to a laser beam. Similar to a person using their own hand a CNC machine can manipulate this tool in space in a variety of ways.

The machine I built is a 3 axis machine meaning there are 3 motors which can move the tool tip either Forward?Backward, Left/Right or Up Down.

 

Here is a picture of mine in the earlier stages. As you can see I chose to build a frame which sits on a table. The work bed is stationary and I have a gantry which rolls up and down the length of the X axis. The Y axis moves side to side along the gantry.  Missing from this picture is the Z axis which will move up and down.

Many people have their x and y reversed to mine to match the perspective of a typical graph but it all depends on where you want to sit in my humble opinion!

However there is another popular set up which is the moving bed set up. In this scenario the gantry is stationary and the bed moves back and forth along the axis.

The advantage of the moving gantry is you can more easily connect hoses,  sprayers, bellows,  dust collectors etc. The advantage of the moving bed design is the bed is usually lighter and smaller. Also the moving gantry will give you a small advantage in how much work space you can use.

If you only plan on doing 3d printing or jewelry engraving you will build a  “weaker” machine in general. This will be an ADVANTAGE because smaller motors and a lighter gantry or movable bed will allow the machine to move quicker.  If you plan on milling wood or metal you will need to use stronger parts. This will however make the machine more difficult to build and it will probably operate slower.

 

Building the Frame and Linear Motion

Here is another video where I run through the major building aspects.

So you probably understand what a CNC is used for so let me talk about some dos and don’t I learned from my project.

Size

The size of the machine is important because most people have space issues. By the time your done the working area will be about 5- 10″ shorter than the table your machine sits on top of. I recommend building a custom table for your machine because there will be lots of parts and wires hanging from it. Better those walking by bang the table than your CNC machine.

Size is also a critical factor because the bigger the machine the more issues you will encounter. One of the major issues people encounter is their longest ball screw sagging. Many builds have a ball screw as long as the builders arm. Hold your arm out and see how long before it begins to sag! Your machine is no different. The ball screws I purchased deflected a slight amount and as the  motor spins it creates a wobbling motion which makes the machine vibrate or shudder. This requires all kinds of custom hacks or more simply a larger ball screw and motor.

However don’t go too small if you plan to use lots of tool tips. My machine takes a variety of work surfaces such as a glass table, a vacuum table and a contained vice table. Each of these tables has to be about 6″ smaller than my CNC work platform width. Some even smaller.

Here is my 3D print table on right. On left is my contained vice. By contained I mean it has wall to contain flying cutting fluid.

Frame Construction

 

Frame construction is a trade off between weight vs strength. The stronger the better as it will resist outside forces. But the bigger it is the more power needed to manipulate the frame, the more weight it will throw around while moving. This will test the limits of your table and the linear rails supporting it.

In my video above you will see that I used 1/4 aluminum and braced is with aluminum angle. Many people choose to use 1/2 aluminum but I made the assumption that the 1/2 aluminum, although strong added more weight than it was worth. So I chose to add the aluminum angles not to add strength but to add stiffness. Stiffness isn’t the ability to withstand a heavy load. Stiffness is the ability to resist deflection even under smaller loads. When attaching these angles it became quit clear how effective they are and this is one modification I would recommend to everyone.

The base I chose to make from steel. This was a naive decision in which I though my machine would be so rugged and accurate that it would need a steel frame to withstand the eventual torture test I would put it through. However the aluminum extrusion people frequently use would probably have been more accurately installed.

Linear Rails

I purchased this kit from amazon.

Cnc Kit
CNC Kit

I can’t really complain because considering the price it has done a fairly good job. However these are definitely hobby kits.  Recommended for your first build they will function quite well.

Now consider how to connect the linear rails. Notice below how my rails are facing sideways. This design is less than ideal because it is putting the weight onto the bearing at a perpendicular angle. Only a part of the bearing is supporting the weight and this will likely reduce machine performance and longevity. Secondly This machine uses ball bearing sliding directly on the rail. This is also a less than ideal situation because these can collect dust which will shorten the life of the machine. Anytime you see linear motion devices with round rails know that you are using the rails I don’t recommend.

Below is a better solution. Its a v bearing on an angles piece of metal. The advantage is that the bearings are protected within and the minor dust on the rail stays outside.

These might come exactly like you see here or the may come in a CNC specific set where there are two opposing angles like a double edged sword with v groove bearing on each side to eliminate unwanted movement.

Construction Tips

If you plan on building the parts yourself you will need to be very accurate. Below is my video explaining the tools

Tools required are;

Table saw  for aluminum

Chop Saw for Steel cuts

Corner clamps for holding two corners square

Drill press

Center punch Set

Digital Caliper

markers

Metal ruler with square

Tap and die set

C clamps

Drill bit set and starter bits

Wax or oil for drilling tapping and cutting

Safety gloves, goggles, masks and ear protection

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