Saturday, March 28, 2020

PCB Mill

PCB Mill Kit
My latest toy is a small PCB Mill, a CNC 3018 Pro, there are many available from Ali Express for the enormous sum of 285 Dirhams or so, which is about 70 Euro.  I thought that even if it didn't work at all, it would not be a big loss.

Assembled CNC 3018 Kit

It will help if you have a little previous workshop experience, but these machines are so simple and relatively slow moving, that any radio-geek can safely experiment.

Carving With a V-bit in a Puddle of Oil

Of course I can have boards made in China by Dirty PCBs, but what is the fun in that?

The problem with making PCB antennas, is that you need to experiment to change the design 1 mm this way or that, to tune it just so and just such and having to wait 2 weeks for each experiment doesn't work.  A few hours playing with a router is more practical.

It turned out to be a pretty nice little kit, made from aluminium and 1/4 inch Bakelite (paper reinforced phenol formaldehyde).  This Prehistoric Olde Fashioned Thermoset Composite is actually pretty good - very strong and stiff.  Assembling the kit was not difficult, but it requires some patience and one has to look ahead to see which nuts need to be slotted into the aluminium pieces for future use, before you bolt them together.  It is also a good idea to put a tiny drop of Locktite on the tips of all bolts, so they don't come undone under vibration (use a wooden tooth pick to apply a very small amount).

Many people don't understand how Loctite/Spring Washers work and why they are very important.  A bolt and nut is normally under tension, with the screw thread pressing together on one side only.  Under vibration, the screw can bounce and become momentarily completely loose, not touching either side of the thread.  Under this floating condition, the bolt can turn very easily.  This effect is used by an Impact Driver.  While the bolt can then turn left or right, Murphy's Law says that it will always turn left (Righty tighty, lefty loosy) and after a while you have little nuts and bolts rolling on the floor.  Purple Loctite 222 is a weak rubber glue that prevents the bolt from turning easily, but it is not so strong that you can never get it apart again.

Use calipers and a triangle to square the machine up as well as you can and once assembled, add a little bit of grease to the slides and worm screws so it will slide smoothly.

Note the anti-backlash springs on the worm screws.  These keep the system locked to one side of the screw thread.  If you stress the machine, then the spring may move and you may get backlash.  You can observe that as a visible jump on the tool tip when it exits a cut into already cut space.  Obviously if you see that, the results will be quite horrible - so slow down - get a mug of coffee and relax.

The step motors are small and there are no end stop switches.  When the mechanism hits the end, the motor magnetic fields will simply slip, which will make a clucking noise.  Don't worry about it - you don't need to add switches.  There is no mechanical wear when a step motor magnetic field slips.

I found only two problems:
a. Two of the three stepper motors rotated the wrong way.
b. The DC barrel plug of the PSU was the wrong size and didn't fit into the socket on the board.

The X and Z axis stepper direction can be reversed using the included GRBL Control software, but I could not find an old enough computer that it would run on (It requires an ancient niche OS called Windows, which was very popular in the previous century), so I cut and reversed the step motor Red/Blue wire pairs instead (reverse only one coil on each motor, else you are back to where you started from).

I could not find a bigger barrel plug in my Junque Bochs and one cannot easily replace the power socket without damaging the board, since it connects to the ground plane (which conducts the heat of a soldering iron away).  I could take the board to my work factory and ask a technician to replace it using an infrared rework machine, but thanks to the Corona virus hullabaloo, I'm stuck at home.  I therefore soldered a pair of wires to the underside of the controller board and fitted an inline socket instead - gut enuff.


Machine Controller
The next problem with these toys is finding usable software to control it with.  I expected this to be a hassle, since I mostly work on a MacBook.  My PCB design software of choice is KiCAD on a Fedora Linux virtual machine.  Hooking Linux via the Mac host USB port to the CNC machine would be very painful and I don't want my Mac to sit in the dust next to the mill - MacBook keyboards do not like dirt.

BTW, the CNC 3018 machine is small enough that one can put a large transparent plastic tote over it to contain the dust and debris.  You don't have to make a special box - just buy one at Carrefour or Ace HW.

I sidestepped the software issues, by ordering a model that includes a little offline controller.  This controller accepts a SD card, so that one can load it with a GRBL file, adjust it to the 0, 0, 0 position manually by rotating the lead screws (Rotate the lead screws when the power is off - best to use white grease or you will get black fingers) and let it go without any further ado.  The only problem then is converting a PCB Gerber file into a CNC GRBL file, which can be done with FlatCAM on Linux.

If you want to be seriously fancy, then you could run GRBL-Web on a Raspberry Pi and access the little CNC machine over your home LAN/WiFi : https://www.instructables.com/id/Control-your-CNC-over-Wi-Fi/

Note that the first time you try it out, it is best to machine something soft, like balsa wood or construction foam, so that if the feed rates are wrong, the machine will not undergo a rapid unplanned disassembly.  I also plan to bolt the whole machine to a sheet of ply wood (Use rubber studs/grommets to prevent noise amplification) to keep it rigid - as soon as the virus scare is over and I can actually find a shop with ply wood.


2D PCB Antenna Carving
Now, I need to fire up KiCAD and design a little antenna to carve out.  That was rather easier said than done.

On Linux, one of the ways to convert a PCB into an outline and Gcode is a program called Flatcam.  This program does exactly what is written on the tin and it wants to have a Gerber PCB layer stack as input.  It can import a SVG file, but then it can be difficult to modify anything, so be sure that the graphic is correct. (Flatcam has an editor function, but it doesn't seem to work and I cannot get the editor to do anything beyond showing a little dot on the screen.  The command line editor does work, so one can add a circle or rectangle at a specidic position when needed, with some effort.).

Flatcam works well, but the UI is a bit confusing to the uninitiated.  In general, first get the red tracks generated, then generate the Gcode.  That sounds tremendously obvious, but it means that you may have to select and do things from the bottom up.  When you try to run Flatcam, you will understand.

Note that for a PCB antenna, you don't need to do isolation milling - simply remove all the non-copper with an end mill and the antenna will be left behind!

The size of the end mill depends on the smallest gap that it has to get through - simple as that - but with a 1/32nd inch or 0.8 mm, you can mill tracks, drill holes and cut out the board - one tool that conquers all.

I can make a Gerber file with KiCAD PCB editor, but while it has very useful footprint wizards, it doesn't have a nice drawing function that can be used for complex shaped small antenna footprints.

I then tried Inkscape and made a neat drawing - then I went on a crazy tour of different CAD programs and file formats, only to come back to Inkscape and the SVG file format.

The trick is that the KiCAD footprint editor can import an outline onto the Front Silkscreen layer.  It then needs some manual editing of the footprint in the library to move it to the Front Copper layer.  

In short: With KiCAD PcbNew, make a new footprint library and a new footprint.  Draw and save a SVG antenna with Inkscape.  Import the SVG file into the PcbNew footprint editor and save the footprint in the new library.  Open the footprint file with a text editor and replace all instances of F.Silk with F.Cu and save it.  Confirm using PcbNew that it is OK by clicking the layers on the right on/off.

Now you can place the footprint on a PCB and carry on as usual, by following this most excellent guide at Inventables https://www.inventables.com/projects/how-to-mill-a-through-hole-pcb

BTW, even with a simple little low cost engraver, you still need to use expensive bits.  The HS sample bits that you get with this toy are only good for experiments in soft wood/plastic - they are not sharp enough to cut copper properly at a fast speed.  Get 1/8th inch shank, Tungsten Carbide 0.8 mm end mills, and 30 Degree V bits for isolation milling (https://www.aliexpress.com/item/32313667075.html).  

Since you cannot easily compensate for board warping and uneven surfaces, you need to cut a little deeper, without making the cuts wider.  Also, don't bother cutting the boards out with a small mill - a jigsaw is much more efficient, but you will need a good 1/8th inch end mill bit to cut out a level work surface and a 1/16th or 1/32nd to mill an antenna.  Cutting a surface with a needle nose V bit, will take longer than the Corona virus quarantine period.

With a larger CNC Mill and larger boards, you could probe the surface and compensate in the Gcode to handle the warping of the board (https://www.autoleveller.co.uk) - you can then save an hour of cutting time, with an hour of probing.  With a small board, the warping is less, so simply cut a little deeper and move slower.

Note that the Gcode is a text file.  You can modify it with a programmer's editor, if you want to change the cutting depth without having to rerun Flatcam for example.  You can also concatenate two or more files so they will run in succession with no further ado, if you don't need to do a tool change in between.  So you can do the copper, board cut-out and hole drilling all with the same 0.8 mm end cutter consecutively, unattended.


Flatcam Parameters
This is a small machine, with small motors, for making small PCBs.  If you stress it, you won't get good results, so take it slow.  The bigger the PCB, the more the warp, so keep them small.

For RF circuits the track width determines the impedance.  For these use a 15 degree needle tip, so that the cutting depth doesn't change the track width significantly - OR - use a 1/32" end mill and take it slow.

Boards are always slightly uneven and warped and the machine is not 100% true and steady.  A cutting depth of 5% to 15% of the thickness of a 1.5 mm board should work, but if you cut deep, the stress on the tool tip is very large, so slow down, else it will go blunt/break, or wander around and chip the copper.  Put several drops of machine oil on the board to lubricate the cutter.  This keeps the bit cool and sharp and also captures the swarfs and dust, so you can just wipe the mess off with an oil rag.  The oil prevents getting itch powder all over your shop.


Levelling Pocket - Made With an 8 mm End Mill

Eventually, I bolted a heavy 1/2 inch board to the aluminium table and slowly (20 mm/min) machined a very good polished 80 x 110 x 0.2 mm pocket, using an 8 mm end mill from my Dremel kit.  Next, I drilled 6 lead holes so that I can secure a 70 x 100 mm PCB blank with 6 small wood screws and washers.  That yields repeatable results.  I sealed the wood with Ye Gut Olde 3 in 1 Machine Oil.

I also made a little jig to locate the zero position, from piece of scrap PCB with little 0.8 mm holes, 7.5 mm deep (as deep as my end mills can go, to be able to return the machine accurately to the origin, in case I had to stop a job midway to change to a new bit and start over.  Four straightened paper clips fit through the holes into the wood base, so I can put the jig in place and zero the machine, then remove it again. It helps to prevent creating many scrap boards.

The important point is that this is not a precision machine.  If you stress it, the results will be worse.  If you don't stress it, then it should last a long time.  For Euro 70, it has certainly exceeded my expectations.


Carbide 3D
The manufacturers of the Shapeoko Milling machine provides a free, online PCB Gerber to CNC outline Gcode converter.  Similar to Flatcam, you upload a Gerber file, select the tool and there you are: https://carbide3d.com/copper/, however, the resulting GRBL code needs some cleanup to actually work - see down below.


Bits and Bites
Engraving V Bits are very strong and can cut very fast (200 to 300 mm/min), but the result is bound to be rough.  This is due to the nature of the bit.  If you need a clean cut, use a Fluted End Mill.  If you want a perfectly clean cut, use a Push Down Fluted End Mill. It has a left hand thread.  A push down bit seemingly goes the 'wrong' way and doesn't lift the copper layer, but then you have to cut more slowly (25 to 50 mm/min).

For cutting copper foil PCB, you need a very sharp bit.  Garden variety High Speed Steel bits are not quite sharp enough - they are OK for wood and plastic - but you should get tungsten carbide bits for PCBs.

The below little SMD board was cut with a new Steel V-bit.  No burrs, thanks to lots of 3 in 1 oil and taking it painfully slow at 20 mm/min.  Cutting in oil looks horrible, but it works. (The double cuts visible below are due to the ground plane fill - I expected the middle left over copper to curl away, but it stayed perfectly and looks like 10 mil tracks.)

Freshly Cut - No Burrs

Cut in a puddle of oil.  Good olde 3 in 1 machine oil works wonders.  Spread it with a tooth pick.  It keeps the bits sharp and cold and prevents burrs.  It also prevents the dust from taking flight.  Wipe up with a rag and brush with a tooth brush and tooth paste under running water - yes, toothpaste works wonderful to clean an oily board!


V Bits need some high school trigonometry
V Milling bit: 0.1 mm tip, 15 degrees
  • Cutting depth: 0.15 mm
  • Cutting tool width: tip + 2 x tan(degrees/2) x depth = 0.1 + 2 x tan(15/2) x 0.15 = 0.139 mm
V Milling bit: 0.1 mm tip, 15 degrees
  • Cutting depth: 0.10 mm
  • Cutting tool width: tip + 2 x tan(degrees/2) x depth = 0.1 + 2 x tan(15/2) x 0.10 = 0.126 mm
V Milling bit: 0.1 mm tip, 15 degrees
  • Cutting depth: 0.05 mm
  • Cutting tool width: tip + 2 x tan(degrees/2) x depth = 0.1 + 2 x tan(15/2) x 0.05 = 0.113 mm
V Milling bit: 0.1 mm tip, 30 degrees
  • Cutting depth: 0.20 mm
  • Cutting tool width: tip + 2 x tan(degrees/2) x depth = 0.1 + 2 x tan(30/2) x 0.20 =  0.207 mm
V Milling bit: 0.1 mm tip, 30 degrees
  • Cutting depth: 0.15 mm
  • Cutting tool width: tip + 2 x tan(degrees/2) x depth = 0.1 + 2 x tan(30/2) x 0.15 = 0.180 mm
V Milling bit: 0.1 mm tip, 30 degrees
  • Cutting depth: 0.10 mm
  • Cutting tool width: tip + 2 x tan(degrees/2) x depth = 0.1 + 2 x tan(30/2) x 0.10 = 0.154 mm
V Milling bit: 0.1 mm tip, 30 degrees
  • Cutting depth: 0.05 mm
  • Cutting tool width: tip + 2 x tan(degrees/2) x depth = 0.1 + 2 x tan(30/2) x 0.05 = 0.127 mm

Default settings for Flatcam that will 'work' with any V tip:
Just remember 20, 20, 20!
  • Z = -0.20 mm
  • Travel Z = 2 mm
  • Tool diameter = 0.20 mm
  • Feed = 20 to 30 mm/min
  • Overlap: 0.15 to 0.25 (15 to 25 percent overlap)
  • Spindle Speed = 5000 (Any number will turn the motor on - no speed control)
  • Dwell Time = 1
The feed rate is related to the spindle RPMs and since this machine doesn't spin fast, you got to feed slow.  Big routers run 10 times faster (25,000 to 50,000 RPM) and they can feed 10 times faster also, but not this dinky toy.

You need to cut fast enough that you get tiny little chips and not a cloud of itch powder, but not so fast that the tip wanders and cuts inaccurately.

Use 3 in 1 machine oil liberally and wipe your tools with an oil rag.  An oiled board lubricates the cutter and makes the dust stay on the board, so you don't get glass itch powder all over the shop and in your lungs.


Handy conversions:
1/64" = 0.397 mm; 1/32" = 0.794 mm; 1/16" = 1.59 mm; 1/8" = 3.175 mm; 1/4" = 6.35 mm
20 mil = 0.508 mm; 40 mil = 1.016 mm; 60 mil = 1.524 mm; 80 mil = 2.03 mm; 100 mil = 2.54 mm


Router tip tips:
  • To clear large areas of copper, use 25% overlap.
  • Use a push down (left handed) end mill for a clean surface cut on a laminate.
  • Use a single flute straight cutter on plastics to avoid melting and fouling.

PCB Fixed with Screws and Bent Washers

  • A straight fluted end mill also gives good results, but 
  • a common right handed pull up end mill is as bad as a V bit.
  • Use a cutting fluid - a puddle of machine oil on the copper makes a huge difference.
BTW, regarding the PCB fixture - one can actually buy bent washers made of spring steel, but I just bent some mild steel washers with a crimping tool...

Table Levelling:
  • Bolt Masonite or other soft wood to the aluminium table and machine a level pocket in it 
  • Pocket depth: 0.5 to 1 mm deep
  • Size: A little bigger than your PCB blanks
  • Use a relatively big end mill to get a polished surface (3 to 8 mm)
  • With a 3 mm end mil, cutting 0.5 mm deep you can feed at 50 mm/min in wood
  • Either use double sided tape, or screw the blank boards down, but screwing can warp them more.
  • Amazing Goop glue also works and it can be rubbed off with a thumb after you pulled the board up. In sheer desperation, I used it for the experiment below and was pleasantly surprized.
Where to get Masonite/Hard Board/Wood during the shutdowns: Buy a clip board, or a bread board at Lulu or Carrefour...


V-Bit Test:
Milling RF parts with a V bit is not recommended and the below picture shows why.


 Yagi Milled with a 30 Degree V Bit

The elements are not of a consistent width.  Cutting this test antenna took about 2 hours, at 200 mm/minute, which is really much too fast for a V bit, if you were wondering, but it proved my mill is working as expected and can keep going for hours without burning out, or falling to pieces.  The quality would be much better with a 1/16th inch push down end mill at 25 mm/minute and will take the same time, since being wider, it will run a much shorter distance.



Yagi Done With 0.8 mm End Mill

Cutting the second Yagi took about 3 hours.  Liberal use of oil resulted in a clean cut with no burrs.  For the next ry, I'll increase the overlap to 25% to get rid of the little left over bits of foil.

See this for antenna details and measurement results:
https://www.aeronetworks.ca/2020/02/phased-array-antenna-for-5-ghz-band.html

One problem is that one has to lower the head until the tip of the mill bit just barely touches the copper - if you drive it down hard, then it will cut much deeper than intended.  A 1 thou contact point is very hard to see for someone my age, even with a magnifying glass.  So I soldered a LED and a 2k2 resistor to a 9V battery and two crocodile clips.

Contact Indicator

Cutting Fluid
I tried using propanol and 3 in 1 oil as as a cutting fluid: Propanol works and is less messy, but it evaporates too quickly.  Oil is more sticky and keeps the dust down perfectly, while preventing kerfs from sticking to the bit.  Wiping it up with a piece of an old T-shirt is also no problem at all.  So my recommendation is to put 5 to 10 drops of thin oil on the board before you start and keep it wetted.


PCB Warp Compensation:
With this little machine, forget about warp compensation.  The machine is not accurate enough to worry about 0.05 mm differences.

For best results, keep the board feature size larger than 1 mm and cut 0.15 to 0.2 mm deep with a 2 flute (1/32") 0.8 mm or (1/64") 0.4 mm end mill, or a 30 degree V-bit at 10 to 30 mm/min.  The bigger the pads and tracks, the better - 1 mm tracks are good, 0.25 mm (10 mil) are not recommended.

If you want to try V bits for very fine isolation milling of SMD parts, the Autoleveller project is here: https://www.autoleveller.co.uk, but I like'em square and prefer end mills and big tracks.  Small tracks will be an exercise in frustration with this machine - it is simply not accurate enough.  You only need one bad track to ruin a board.


Double Sided Boards
It is possible to make double sided boards with Flatcam.  Under Tools, there is a Double Sided Board wizard.  Define a mirror axis, define two guide holes and Flatcam will make two more guide holes on the other side of the mirror line. Then mirror the bottom layer.  The mirror line need not be exactly in the middle, Flatcam will rewrite the Gerber file with an offset.  

When you mill the top layer, drill the 4 guide holes deep into the wood base (7.5 mm with my little 0.8 mm end mills), then when one flips the board, one can locate it fairly accurately with 4 paper clips and then clamp it down.  While doing all this, don't move the mill, to preserve the zero position.

Make the cut-out using the bottom layer, since the cut should always be the last step in the process.


Noise
This little router is not too noisy since the motor is slow.  If you would upgrade it to a faster spindle, then it can cut faster, but the noise will also increase.  Most noise are caused by resonances, so in general, cutting in arcs is quieter than cutting straight, since an arc keeps all the bearings under stress.


Bakelite (Pertinax, Formica, Melamine)
The >100 year old Paper Reinforced Phenol Formaldehyde plastic sheets have made a comeback recently - the modern composites are more stable than before.  Bakelite sheets are dimensionally stable, very strong and much easier to cut/file/mill/drill than aluminium, acrylic or fibreglass board.  It is very useful for making enclosures and panels with intricate cutouts for connectors and it doesn't foul or blunt your tools.

Bakelite is produced in 8' by 4' sheets just like plywood, which presents a large delivery problem. Here are two vendors in Germany for cut pieces of Paper Bakelite, FR2 PCB, Carbon, Aluminium, Lexan and more:
https://www.masterplatex.de/phenolic-paper-brown
https://gie-tec.de/product/hard-paper/?lang=en
https://gie-tec.de/product/phenolic-resin-paper-laminate-fr2/?lang=en

US Vendors:

Radio Spares - World Wide:

I list them here, since it is very difficult to find these type of composite sheet stock vendors.  Google doesn't help, it just turns up page after page of Chinese PCB manufacturers.


Further Information

So What is This Toy Good For?
It is good for single sided home PCBs with parts large enough that someone over 50 can actually see them unaided.  It really does make home brew circuits look much more professional and neat than strip board or blob board.

You can do SMD boards, but you have to keep the pads bigger than 1 mm on a side, such as 1206 or 1812 - the small 0603 (1.5 by 0.8 mm), with 0.5 mm tracks, is probably the lower limit - the bigger the better.  http://www.resistorguide.com/resistor-sizes-and-packages/

If you have to use a little SO8 package for example, buy a little break-out board for it from Sparkfun, so you can make bigger 1 mm tracks.  The secret sauce however, is cutting in a puddle of machine oil - clean the board with a tooth brush and toothpaste.  If there is enough oil, then there are no burrs.

I also had success with engraving plastic, using a V-bit with the same 20, 20, 20 settings and a puddle of propanol as lubricant.  Oil could make plastics craze.  Clamping a small sheet of acrylic down is difficult - it tends to crack - put something under the washers.

I have not had success with cutting plastic panels yet - it tends to melt - even with propanol.  I am waiting for better single flute end mill bits - hopefully that will work. The secret with plastic is that you need very sharp bits and move at a relatively fast rate.  Blunt bits cause friction and melts the plastic.  Once you found one that works, don't use your new found plastic cutting bit to cut anything else.


Enclosures, Brackets and Knobs
If you want to cut panels to make boxes, see this wizard: https://en.makercase.com/#/

To make circles or squares with Flatcam, see the command line reference: http://flatcam.org/manual/cmdreference.html#cmdreference

Flatcam Command Examples:
> add_circle <name> <center_x> <center_y> <radius>
> add_rectangle <name> <botleft_x> <botleft_y> <topright_x> <topright_y> 
> add_polygon <str> [xi, yi <?>]
> add_polyline <str> [xi, yi <?>]

The circle command makes it easy to mill a nice looking volume knob, from a piece of scrap wood and with $50 of effort, save yourself 50c:
  • Click Tool, Command Line to get a TCL shell.
  • Click Edit, New Geometry
  • Double click the "New Geometry" object
  • Change the Name to knob50 <Enter>
  • > add_circle knob50 0 0 26.5
  • add_circle knob50 0 0 0.5
  • Click View, Enable All Plots
And there is the 50 mm cut circle, with a 4 mm hole in the middle!

If you use a 3 mm tool, then the knob radius will be 1.5 mm smaller, so I compensate for the kerf by making the 50 mm circle with 26.5 mm radius.

Similarly, a 0.5 mm radius circle will result in a 4 mm diameter centre bolt hole.

Plot the CNC Job with Multi-Depth, of 0.5 to 1 mm per pass, at 30 to 100 mm/min, depending on the hardness of the wood.

CNC Job for 6.5 mm Wood:
  • Cut Z: -7.5
  • Travel Z: 2.0
  • Feed Rate: 100
  • Tool dia: 3
  • Spindle Speed: 5000
  • Multi-Depth: v
  • Depth/pass 0.75
Stick the wood down with double sided tape, so that the circle won't move when it is cut all around.

Where to get nice scrap wood: When someone tosses away old brown scrap furniture, grab the drawers.

Make two discs, one with a centre hole and one without. Ream the hole to the spindle size and glue them together, sand, linseed oil... La Voila!


Universal Drill Press
I have not been able to figure out how to make an Excellon Drill Object, so I mill out bolt holes with small circles - to make any size hole with only one 3 mm tool.

In the same way as above, you can make a bunch of hole files: 4, 5, 6, 8, 10, 12 mm - a whole series of holes.

The little circle Radius = (Hole Diameter - Tool Kerf) / 2
So a 10 mm hole, needs a circle radius = (10 - 3) / 2 = 3.5 mm
> add_circle hole 0 0 3.5

Save the series of hole files on the little SD card.  

To drill a hole with your new mill drill press, position the mill above the spot and run the hole file.

Note that you can modify these holy NC files with a text editor, so it is easy to make the hole deeper or wider, go slower or faster, by running search and replace, without firing up Flatcam.


Milling Complex Parts
If you want to mill more complicated things, use FreeCAD, the Part and a Path Workbenches, but your machine must have lots of RAM and FreeCAD is a bit complicated to learn for small hobby widgets:

If you have a Mac, then get Carbide Create (Free!), a very nice and simple 2D program for milling things from flat stock: 

With Carbide Create, you could for example, make the cut path for wooden gears:

Involute gears mesh smoothly and I can still remember designing and drawing gears by hand with pencil and paper, during a drafting course - Ugh!


Set the Carbide units to mm, the background grid to 5 mm, the stock size to 100x150 mm by 5 mm thick, open the SVG file from the gear wizard and then it will take you a couple hours to figure it out.  Servos with slow turning gears are rather more kewl than rods, wheels and pulleys!

The reason I haven't cut it yet, is that there is something in the generated GRBL code that trips up the mill controller - it doesn't want to start - so I have some debugging to do...

The Carbide Create code (which doesn't work) looked like this:
G90
G21
(holes)
M05
M0 ;T102
M03S5000
G0X-15.29Y-0.29Z2.00
G1Z-1.00F50.0
X-15.31Y-0.27F100.0
X-15.36Y-0.19
X-15.39Y-0.12
X-15.41Y-0.03
Y0.03
X-15.39Y0.12
X-15.36Y0.19

While GRBL code generated by Flatcam (which works) looks like this:
G21
G90
G94
F100.00
G00 Z2.0000
M03 S5000
G4 P1
G00 X0.5000Y0.0000
G01 Z-0.5000
G01 X0.4976Y-0.0490
G01 X0.4904Y-0.0975
G01 X0.4785Y-0.1451

I edited the Carbide Create code with a few Search and Replace commands till it looked similar and then it worked, except for one fly-over error, which cut a 1 mm deep groove in the first gear.  It actually lifted up to 2 mm, then went down and cut across, instead of flying over and then going down.

The picture shows the gears as they came off the mill.  I need to cut the holding tabs and then sand them a bit.

Wooden Involute Gears

I can fix the fly over error by hand, but it looks like I need to write a GRBL Lint program to fix up messy code to be able to use Carbide Create for projects.  What this experiment shows, is that one can use this little mill to make quite precise fitting wooden robot parts and I can already see that my next satellite tracking antenna system will be all wood, which is a whole lot cheaper than aluminium and stainless steel or even 3D printed Nylon parts and a hobby device doesn't have to last forever anyway.

If your antenna did not blow over during the last hurricane, then it wasn't tall enough.


Square Helical Antenna
Something I would like to try, is to make a quadrifilar antenna on 4 pieces of PCB - a square tube version of this one:  https://www.aeronetworks.ca/2017/12/parasitic-quadrifilar-helical-antenna.html starting with the box wizard above for the outlines.


3 In 1 Oil
Ye Good Olde Three in One is a SAE20 light machine oil.  You can use any thin oil, SAE10 or SAE20 as a cutting oil.  WD40, Q20 and Diesel will also work, while thick SAE40 motor car engine oil may prevent the tool from cutting.  I don't recommend using a cutting oil thinner than Diesel, since thin oil can burn too easily - bear in mind that you probably have a soldering iron on your bench.  When all else fails, you can go seriously 19th century Olde Skool and use soda water, which of course won't burn, but it could cause your wooden jigs to swell. 


Postscript
I can see why people get addicted to CNC machines.  It is quite mesmerizing to watch it go about its job and I will probably build a large plywood CNC machine, so I can make big wood objects just for fun.  There are many things that I would like to explore, which are prohibitively expensive to build from metal, but which can be built cheaply from wood, if you have precision tools and which will then last long enough to get a whole lot of fun out of, before it becomes firewood.  

Speaking of firewood - this is a good reason why to use only natural oils as a wood finish (linseed oil and bees wax).  Polyurethane is poisonous when burned, so don't use old wood finished with urethane in your pizza oven!


La Voila!

Herman

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