Review: LinkSprite Mini CNC

It’s a great time to be a hobbyist. No matter how you feel about the Arduino/Raspberry Pi effect, the influx of general enthusiasm and demand it has created translates to better availability of components, a broader community, and loads of freely available knowledge. When people have access to knowledge and ideas, great things can happen. Tools that were once restricted to industrial use become open source, and the price of entry-level versions goes into a nosedive.

As we’ve seen over the last several years, the price of cheap 3D printers keeps falling while the bar of quality keeps rising. It’s happening with laser cutters and carving tools, too. Strolling through Microcenter a few weeks ago, I spotted a new toy on the back wall next to the 3D printers. It was LinkSprite’s desktop mini CNC. They didn’t have one out on display, but there were two of them in boxes on the shelf. And boy, those boxes were small. Laughably small. I wondered, could this adorable machine really be any good? To some, the $200 price tag suggests otherwise. To me, the price tag made it justifiable, especially considering that the next price point for a hobby CNC mill is at least twice as much. I took my phone out and stood there frantically looking for reviews, documentation, anything that was available. It seemed that the general, if sparse consensus is that this thing isn’t a total waste of money. Oh, and there’s a wiki.

According to LinkSprite’s wiki, this little machine will engrave wood, plastic, acrylic, PVC, and PCBs. It will specifically not engrave metal (PCB copper notwithstanding). I’m a bit leery of the chemicals used in the PCB etching process, so the idea of engraving them instead was especially tempting. I pulled the trigger.

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Guide: Why Etch a PCB When You Can Mill?

I recall the point I started taking electronics seriously, although excited, a sense of dread followed upon the thought of facing the two main obstacles faced by hobbyists and even professionals: Fabricating you own PCB’s and fiddling with the ever decreasing surface mount footprints. Any resistance to the latter proves futile, expensive, and frankly a bit silly in retrospect. Cheap SMD tools have made it extremely easy to store, place, and solder all things SMD.

Once you’ve restricted all your hobbyist designs/experiments to SMD, how do you go about producing the PCBs needed for prototyping? Personally, I dread the thought of etching my own boards. The process is laborious and involves messy chemicals and specially sensitized PCB’s — none of which interest me. I’ve only ever done it a few times, and have promised myself never to do it again. Professional but cheap PCB manufacturing is more like it board pooling services such as OSH park have made this both easy and affordable — if you can wait for the turnaround.

So what are the alternatives? If you are really serious about swift prototyping from your own Lab, I put forth the case of milling your own PCB’s. Read on as I take you through the typical workflow from design to prototype and convince you to put up with the relatively high start up cost of purchasing a PCB mill.

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Blob Grid Array Technique Mounts Board-To-Board

[Howard Matthews] mills his own PCBs, and man, does he hate drilling through-holes. Manually changing the bits between engraving and drilling after isolation routing? What is this? The stone age? [Howard] decided to rethink his DIY PCB manufacturing process, and came to one essential conclusion: Only a fraction of these drills are actually necessary.

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FR4 Machine Shield Is A CNC Milling Machine From FR4 PCB

The people behind the PocketNC heard you like CNC PCB mills, so they milled you a PCB mill out of PCB. They announced their surprising new open source hardware product, a pocket sized 3-axis CNC machine entirely made out of FR4 PCB material, aptly named “FR4 Machine Shield”, at this year’s Bay Area Maker Faire.

UPDATE: The FR4 Machine Shield is now on Kickstarter

fr4_thumbWe know the concept from quadcopters, little robots, and generally things that are small enough to make use of their PCBs as a structural component. But an entire CNC machine, soldered together from a few dozen PCBs certainly takes it to the next level.

There is no doubt that 2mm thick fiber reinforced epoxy can be surprisingly rigid, although the Achilles heel of this method might be the solder joints. However, it looks like all load bearing, mechanical connections of the machine are supported by tightly interlocking “dovetail” finger-joints, which may help protecting all the solder connections from the strain hardening effects of continuous stress and spindle vibrations.

As you might expect, most of the wiring is embedded into the FR4 frame construction, and to squeeze the maximum value out of the PCB material, the motor driver boards interface via card edge connectors with the (currently Arduino based) controller board. In addition to the milling head, which features a brushless DC motor and a tool coupler, the team wants to develop heads for circuit printing, microscopy, pneumatic pick and place, hot air reflow, and 3D printing.

With all those cost-driven design choices, from the one-step manufacturing process of the frame and wiring to the dismissal of screws and nuts from the frame assembly, the “FR4 Machine Shield” could indeed become one of the cheapest CNC machine kits on the market. The team targets an introduction price of $400 during a Kickstarter campaign in June 2016. Can they deliver? [Gerrit] checked Pocket NC out at the Faire and ended up raving about how they run their business.

Enjoy their teaser video below!

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Danielle Applestone and the Story of Every Othermill

Many of us may qualify as “makers,” but how about a “maker of machines?” [Danielle Applestone] tells us what kinks to look for whilst embarking on your hardware startup adventure. Co-founder of Other Machine Co, the company that makes a PCB Mill that holds tolerances as tight as a thousandth of an inch, [Danielle] holds degrees in chemistry and materials science from MIT and UT Austin. While she may tell you that the math for running a hardware company is easy, knowing what numbers to crunch and keeping track of them has been part of her key to success. So take 20, and give yourself a moment to take in [Danielle’s] tips from her Hackaday Superconference talk on beating the hurdles ahead in the land of hardware startups.

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Mill Warped PCB Blanks On An Uneven Bed

Milling a PCB at home is a great way to save some time and money if you are making one-off circuit boards. There is a downside though, it’s a little tough. Sure, just export your Eagle design to CNC-Machine-understandable g-code and fire up your mill…. well, it’s not that easy.

The copper on a PCB blank can be anywhere from about 0.001 to 0.006 inches thick. When milling a board the ideal situation is to mill just deep enough to get through the copper but not cut too deep into the fiberglass backer board. Cutting too deep can weaken the board, break a bit, or in an extreme case, cut through the entire board.

Shallow cuts can result in another problem, inconsistent cut depth over the surface of the board. Check out the left photo above. The traces on the left side of the board appears to have just faded away. This happened because the circuit board was not flat. The side where the traces are missing from is lower than the other so the tool bit is not able to reach that part of the board. Since an ideal depth of cut is about 0.010 inches, even a very small amount of waviness or out of flatness can cause a serious problem in the milling process. If you have a hard time picturing what 0.010 inches is, think the thickness of two pieces of paper, it’s not a lot. There are two main contributors to the flatness problem; the PCB board and/or the machine’s bed. If the bed is not flat, the PCB won’t be. Even if the bed is flat, the PCB may be warped or bent.

PCB fabrication enthusiast [daedelus] had this exact problem, and in true hacker fashion, decided to do something about it. He created a software program called AutoLeveller that takes a g-code file and adds a probing section to the beginning before the milling operation. When the modified g-code file is run on the CNC Machine, it first probes the surface of the PCB in a grid pattern and maps the flatness variation of the PCB’s surface. Then, when running the program, it adjusts the height of the tool bit on the fly so that the actual depth of cut is consistent over the entire board, regardless of how flat or not it is. The result is a clean and usable PCB on the first try.

There is one catch: the Machine Control Software has to be set up to accept a probe. This is easy to do if communicating to the CNC Machine via a computers parallel port. An input pin on the parallel port is pulled high with a resistor and connected electrically to the PCB board. The tool spindle is grounded with a clip lead. When the tool touches the board, the input pin is pulled low and the Machine Control Software records the tool height for that specific XY position.

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The Credit Card Sized GameBoy

Think you’ve seen every possible type of Arduino based hand held video game? [Kevin] managed to coax something new out of the theme with a very clever credit card sized console that uses some very interesting construction techniques.

The inspiration for this project began when [Kevin] dropped an SMD resistor into a drill hole on a PCB. This resistor fell right through the hole, giving him the idea creating a PCB with milled cutouts made to fit SMD components. With a little experimentation, [Kevin] found he could fit a TQFP32 ATMega328p  – the same microcontroller in the Arduino – in a custom square cutout. The rest of the components including a CR2016 battery and OLED display use the same trick.

The rest of the design involved taking Adafruit and Sparkfun breakout boards, and modifying the individual circuits until something broke. Then, off to Eagle to create a PCB.

[Kevin]’s experiment in extremely unusual PCB design worked, resulting in a credit-card sized “Game Boy” that’s only 1.6 millimeters thick. The controls are capacitive touch sensors and he already has an easter egg hidden in the code; enter the Konami code and the Hackaday logo pops up to the tune of [Rick Astley]’s magnum opus.

Now [Kevin] is in a bit of a bind. He’d like to take this prototype and turn it into a crowd sourced campaign. In our opinion, this “Game Boy in a wallet” would probably do well on a site like Tindie, but any sort of large scale manufacturing is going to be a rather large pain. If you have any wishes, advice, of complaints for [Kevin] he’s got a few links at the bottom of his project page.