New & Reviewed

New To Our Desk: Bantam Tools' Desktop PCB Milling Machine

DIYODE Magazine

Issue 8, February 2018

This powerful mill makes light work of prototyping, with simple software and great accuracy.

I recall in high school messing about with PCB etching, using etch-resistant pens for hand-drawn circuits, and achieving mixed results with exposure-methods. It was always treated as something that was trial and error, or you really had to have more experience to achieve success. Of course, some of that was probably equipment error or user error, but likely a combination of the two, since the processes themselves are reliable. For the most part, we were purchasing kits with pre-made PCBs when it mattered, so there was little thought given to it.

Fast forward a few decades to a world we barely dreamed about then, and we find ourselves with 3D printers, and CNC machines that are just about as accessible as all other electronics.

SETUP AND CONFIGURATION

This is about as easy as it gets. Barely five minutes since running a knife through the tape on the box, and we’re ready to start milling.

It’s supplied fully assembled, and the case is made from thick HDPE, with aluminium and precision ground steel for the rails, bed, and other parts where the structural strength is required. Large clear acrylic windows are part of the design, so you can easily see what’s going on. The acrylic windows are held in place by magnets, so they’re very easily removed to assist with tool-change access, material insertion and removal, and even to get a vacuum in there to remove dust and debris.

This machine is well built. Just enough of everything, so you’re definitely getting your money’s worth. It’s all slide rail/slide bearings taking the weight for smooth action. Motor to gantry/head connections are all leadscrew driven, so there’s no belt-wear to worry about. This is especially important when 1/100th inch tolerances are sometimes required.

They’ve also thoughtfully added some consideration to the mounting of the slide rails to allow for some tolerances, which is needed when temperatures fluctuate, and we suspect also provide an amount of shock absorption for any vibrations. We also notice anti-backlash fittings (backlash occurs in machines like this when the motors stop, and the part moving can move in the opposite direction briefly, like a recoil). Anti-backlash fittings help the moving parts resist the urge to recoil, increasing positional accuracy of all moving parts.

The print bed is made from an aluminium t-slot, with precisely located threads for bolting down the wasteboard, and bracketry.

Great safety features are included too. Software can pause/stop the job at any time. There’s a large emergency stop button on the side, and reed switches in the windows also stop the machine if they’re removed. This magnetised window design provides premium safety, without creating a major hurdle for access, which you will need regularly for tool changes, material changes, and just general cleaning. This is a milling machine after all, so keeping it clean is going to keep it running well for many years.

Being a machine designed and developed in the USA, you may need to get used to working in imperial measurements to some degree. Sure, everything can be converted to metric, but you’re using 1/32” tools for instance, which is 0.79375mm. You can’t always round that up to a clean 8mm. The software will operate in imperial or metric units, just be conscious of both and be careful with any conversions you may have to make. Many imperial measurements can result in many decimal points in a metric unit, especially when working at tolerances such as 0.001” (one mil), which is 0.0254 millimeters. For us, we’re comfortable with either, so stick with the imperial measurements in this instance, purely for consistency and ease of conversion.

THE CONTROL SOFTWARE

Installation of the software is clean and simple. We use Macs here at DIYODE. Though we do have a few PCs around as required, it’s about 95% Apple hardware. So we were glad to see Bantam’s own milling software is cross-platform.

Really, there is no substantial configuration required at all, it’s really very plug-and-play, even if you haven’t used any type of CNC machine before. There are some test-projects included in the box, to help familiarise yourself with everything too (more on that later).

The software is very straight forward to use. It really couldn’t be easier. It is dedicated to the Desktop Milling Machine, so there’s no configuration of machine limits, and there are built-in selections for using Bantam’s genuine milling bits. This means you’re just a dropdown away from the correct selection. There’s no math converting steps to distance, or any of the other related challenges that exist with generic software.

Importantly too, there’s automatic detection routines to set the Z-height, and detect bracketry. These detection routines look for electrical contact between the head and bed in order to confirm where the physical limits are. This takes the guesswork out of calibration, further ensuring success with the job. If there’s grime or dirt on the fixtures and electrical contact can’t be made, the software will ask you to retry. A little cleaner to remove any debris or grime will help, but we didn’t have any difficulty anyway.

While all the setup is taken care of automatically, the software provides you all the flexibility you need. You can also load up multiple jobs at once, so if you are milling multiple PCBs (same or different pattern, it doesn’t matter); you can easily load them up onto the one blank, and position them to optimise space and reduce waste. If you’re milling double-sided PCBs then it will compensate for “the flip” by milling the opposite side automatically too, which makes handling this process VERY easy indeed.

top-side layout
Our top-side layout.
bottom-side view
The bottom-side view for the second side.

We would perhaps like to see drag-and-drop capabilities for positioning boards on the bed, but with numerical controls available for each axis it’s not a difficult process anyway. Once your jobs are loaded, the preview provided is very detailed, with the option of a flat or 3D preview, which you can rotate, zoom, and pan within, just as you’d expect. This is also great if you want to double-check your board design has imported correctly too. You can see all the toolpaths and previews very cleanly, and clear warnings are given if your selected bits are too wide for the milling precision required. Provided you read the feedback in the software, it provides fairly foolproof operation. Of course, if you fail to heed the warnings given by the software, you can still proceed at your own peril.

navigating the boards
You can navigate the boards in 3D.

When milling, the software provides real time tool location and timing. It also supports automatic pause for tool changes, so you can easily use high precision bits where required, and larger bits where the same detail isn’t needed. Overall this results in a faster output if you’re removing large portions of material, in combination with fine details.

We were originally a little surprised that PCBs are held in place by double-sided tape. However after using it, we can see that it’s more than enough to secure a PCB and most objects to the surface. With the mill running at suitable speeds as the software dictates, there are minimal lateral forces on the material. So it makes sense that massive bolts or other things aren’t really required.

top-view
Top-view is also provided when preferred.

THE SPINDLE

The spindle itself is a powerful, brushless motor that runs at between 8,500 and 26,000RPM. This is the noisy part, and while you certainly don’t require hearing protection, it’s probably not going to help you make friends in an office environment. That said, we have a large 3-phase 2.2kW spindle on a large CNC machine, and by comparison, this thing is whisper quiet. The motor itself is attached to the rotating head by rubber O-rings (and plenty of spares are included too). This helps reduce vibrations through to the tool head, and also provides some emergency slippage should the tool-head bind for some reason (though it’s unlikely, unless a grave miscalculation has been made by the user, and all warnings about collision have been ignored).

The spindle is provided with compatible collet and chuck to suit all provided bits, which use a 1/8th” shank, regardless of tool size. This provides maximum interchangeability without having to completely remove the chuck when changing tools.

There is a high precision collet available also, which may prove useful for extremely precise milling, such as when using the 1/100th bit. We used a 1/100th bit with the standard collet and didn’t really notice any tool run out, but at this level of precision, every bit helps. The precision collet holds the tools with about twice as much metal contact as the standard collet. We haven’t tested this yet, but hope to get our hands on one, to do so soon.

Tool changes are made easy thanks to two small spanners provided as part of the toolkit. They definitely fit inside the confines of the machine’s enclosure better than regular spanners, so we’re glad to see them included.

The Test Projects

First of all, there are a few test projects included in the kit, which are designed to familiarise you with basic operations and functions, and they do a really great job.

engraving dog tags

ENGRAVING - DOG TAGS

The first project is some basic engraving of a dog tag. This is a great, simple project that helps you familiarise yourself with basic processes of the machine, with step-by-step instructions on how to successfully complete it too. We had some fun with this project.

aluminimum ring

MILLING - ALUMINIUM RING

This project demonstrates the Desktop PCB Mill’s metal milling capabilities, by milling an aluminium ring from flat aluminium plate. This project also takes you through modifying the ring design in Autodesk Fusion 360 too, which is some great additional skill-building for newcomers to CAD design.

tools badge kit

PCB - BANTAM TOOLS BADGE KIT

Included is the PCB design itself, and all components required, for a cool PCB badge kit. This is a great way to test out the capabilities in a PCB context, even without having any PCB files to mill yourself. Once complete, you solder up the handful of components to create a Bantam Tools badge, which has LEDs that illuminate when you push down on the battery holder. Awesome!

pcb

Milling Our Own PCBs:

Finally, we get to the part we were really waiting for. After all, the test projects are fun and great to familiarise yourself, but we wanted to make some PCBs!

We tried using PCB’s design in Altium, and Eagle. We didn’t really care too much what we milled, we just wanted to make something! But we had some PCBs from various projects that were suitable. The milling software supports Eagle BRD files, Gerber RS-274X, G-Code, and SVG files. This is quite versatile and provides scope for most vector and PCB files too.

The Eagle file is a PCB from our Mega Digits project. The Eagle BRD file loads quickly and cleanly, and this compatibility is great since many people use Eagle at a hobby level. Our first Gerber export from Altium wasn’t too happy, but fortunately, Bantam provide a profile to ensure Altium appropriately exports everything. Once we followed this, it imported precisely as expected. The lesson here? Read the instructions!

Once we got the hang of things, milling PCBs has to be the easiest thing ever! It used to be that getting the board layout done was the easy part, and etching it was the difficult part. Now that’s turned on its head! This machine produces reliable, repeatable, and highly precise circuit boards without missing a beat.

We only used the Bantam Tool’s genuine PCB blanks. It’s entirely possible to use other PCB blanks if you have them, just be conscious of the 4 x 5” (10 x 12.5cm approx) maximum size. You can stretch to the full 4.5 x 5.5” (11.5 x 14cm) workspace for single-sided boards, however double-sided boards require the use of the positioning bracket (so the bottom side can be lined up precisely), which costs a small amount of working surface. Material thickness can be easily custom-configured in the software.

ACCIDENTAL DAMAGE...

From time to time, you’ll miscaculate something, or enter a value somewhere that’s going to cause a problem. In our case, it was during one of the test projects. For most things, a few gouges in the wasteboard doesn’t really matter. The milling bits are more than capable of milling the wasteboard itself, but in our case, the gouges were interfering with the bracket detection.

gouged wasteboard
We gouged our wasteboard, but it's easily fixed.

Fortunately, there’s a procedure for resurfacing the wasteboard, and a working file that can be loaded into the software, to automatically take care of it. We ran this file, following the Bantam guidelines, and it worked perfectly. Of course, the software warns about collisions, but since we’re resurfacing, in this instance it’s actually what we want.

Resurfacing complete
Resurfacing complete - looks great!

The surface was quickly restored to pristine condition. The team at Bantam Tools have obviously considered this well, since the bolts holding the wasteboard in place are well-recessed. You could perform this operation a good number of times before you got anywhere near them.

OTHER CONSIDERATIONS

With the PCBs produced, it’s important to remember that there are differences between these PCBs and commercial prototypes. The most notable and obvious, is that there’s no solder masking or pre-tinned pads. This isn’t a deficiency in the milling machine at all, simply a difference in the way the board is created.

With double-sided PCBs, it’s also necessary to create your own vias. A PCB via is a link between the top and bottom layers (or between any of the layers when there’s more than two). Commercially these are often tube-lined or electroplated (as are the pads), which creates an ultra-reliable connection. However with a milled PCB these processes don’t exist. The solution is simple however. You just need to solder a link wire from the top-side to the bottom side. It’s quick, reliable, and is a small imposition when you’ve just gained a world of protyping flexibility.

Obviously no PCBs, single or double sided, will have solder masking or tinned pads like a commercial prototype. But these are prototypes after all. Twenty years ago, solder masking was something of a luxury, on commercially produced boards anyway! A skilled constructor will have no difficulty at all, it just takes a little care.

We haven’t really scratched the surface of the other milling capabilities of this machine, far beyond PCB milling, and of course the included sample products. However the mill is very powerful and highly accurate. We’ll be getting our hands dirty with some general milling soon though. In particular, we’d like to try milling moulds for silicon pouring, which is a great way to create flexible objects in many shapes. Bantam also have a chocolate mould making kit which, let’s be honest, is probably the best way to test that out!

For best operation, you’ll need a set of digital vernier calipers. Accuracy of your measurements will help reduce waste, and getting your material thickness more accurate will help reduce instances of the wasteboard being milled by accident.

FINAL THOUGHTS

This machine carries a cost that you’d expect from any precision piece of hardware. It’s not a throw-away machine. Appropriately looked after, it’ll probably last until we have hologram-to-reality printers or some other fancy future technology we haven’t thought of yet. The Bantam Tool Desktop Millling Machines are really well suited to light commercial prototyping, or heavy hobbyist use. For someone with a once-a-year PCB requirement, the cost may be hard to justify.

For us here at DIYODE, the mill will provide us rapid prototyping at a speed that we cannot get anywhere in the world at a comparable cost - no matter how much money we’re prepared to spend! In a rapid world of technology (or publishing!), days and weeks matter. It can mean the difference of a deadline, a successful sales pitch, or perhaps just absolute flexibility to get it right.

If you’d like to know more about this amazing piece of hardware, head to: bantamtools.com

In Australia, our friends at Core Electronics are the best place to find one, so visit core-electronics.com.au or call them on 1300 334 338. They’re extremely knowledgeable about this hardware, using it themselves, so they can answer any questions you have.

Bantam Tools Desktop PCB Milling Machine is available at Core Electronics: