PCB Manufacture

Roland iModela desktop CNC machine – review for PCB manufacture

I purchased the iModela in 2014 with the intention of using it to create small Arduino-sized circuit boards, using the isolation milling technique. Some UK based resellers market this device specfically mentioning its capability as a PCB manufacturing tool.

iModela milling machine

This type of “ready to use” consumer electronic device still requires some effort before creating your first milled piece. I think of this a bit like the difference between starting to use a drill and a router (this kind of router, not this kind). For example, I’ve never read the instruction manual for a drill in my life – basically you just insert the bit, squeeze the trigger and start drilling holes (Ok – it’s maybe a bit more complex than that but not much). But a router is a more specialised tool, which is can be pretty dangerous if you don’t know how to use it properly. Sometimes if you don’t get the result you want, that doesn’t mean the tool is wrong – you might not be using the tool right. You need to invest some time to get good results.

Fortunately the iModela gives a really good set of instructions to get you started. Roland creates a workflow which has all software you need to start making things. This is supplied on a disk which comes with the machine, and you can download this software too. My kit was also supplied with a milling bit, some acrylic material and double sided tape, which meant I was able start making an example shape on the same day I received the device.

CNC machines grind material away from around the shape you want to keep, and this usually leads to a lot of dust and particles. The clear plastic shields to the front and rear of the device really help keep this dust in the machine. It’s not 100% dust proof obviously, but the plastic shields help a lot and it does make this device more suitable for using in living areas (rather than in a workshop or garage).

The process of designing PCBs is well documented on the web, and exporting this PCB design to G-code is easy (using PCB-Gcode). The iModela is able to accept G-code, which I’ve blogged about here. To make PCBs, I needed some copper clad board, which is widely available. I also needed a special PCB engraving bit – with a metric diameter of 2.35mm to match the iModela’s collet size.

Using for PCB manufacture

Buying replacement consumables

Finding metric consumables, like bits, is probably my biggest problem with the device, and ultimately the reason why I stopped using the iModela. I found it incredibly difficult to acquire metric bits at a reasonable price. I eventually found metric milling bits that fit the machine available at Farnell here, but these aren’t PCB engraving bits and are not suitable for PCB milling. The only 2.35mm bit I could locate for PCB milling was nearly £27 for one bit. I’ve worn out a couple of these now – the cut through the copper nicely for the first few cuts, but my experience was that they became blunt very quickly, and £27 is way too much for a bit that lasts for only a few boards.

For comparison – I can buy 10 PCB imperial sized engraving bits for just over £4 on ebay (in metric, the shank diameter is 3.175mm). I have not been able to identify an aftermarket collet for the iModela with this size (but United States customers might have be able to acquire this).

Base rigidity

The other problem I found was that the plastic bed (which moves in the Y-axis directions) is not level and is not rigid enough. When the PCB bit was lowered onto the circuit board, it would cut the copper layer fine when the bit was brand new. But after a few cuts, I found bit wasn’t sharp enough to puncture the copper. Instead the plastic bed deformed – this meant that the bit scored the top of the copper, but didn’t break through. I compensated by increasing the cutting depth – this punctured the copper when I hit the limit where the bed wouldn’t deform any further. But it doesn’t solve the problem. The plastic below the copper is much softer than the copper surface, which means that as soon as the copper is broken, the bed springs back and you get an unexpectedly wide cut in the top layer.

Some of this unevenness might be because of how the board is secured to the bed – I was using double sided sticky tape, which is the only option as there are no mounting points on the machine. If even a small grain of material gets trapped under the tape, it will distort the board. Securing material to a CNC machine using tape is very common, but it doesn’t really work for very precise work like PCB milling.

The photo below shows an example of some of the problems with the machine. The engraving process started on the right hand side, and started well. However, as the job progressed, the bit started to get blunt, and it’s possible to see how it hasn’t managed to puncture the copper at times. The width of the cut also varies, and some tracks are completely engraved away. This was unfortunately typical of how most of my boards finished.

WP_20151127_18_21_38_Pro

However, you can see on the right hand side that it is possible to get decent results – other makers have had more positive results.

Summary

I created a few boards, but the experience wasn’t plain sailing, and have stopped using the iModela for isolation milling PCBs. This wasn’t because it was too difficult to use – investing time in understanding how to use a machine goes with the territory (and it’s actually part of the fun) – I’ve put it away because the consumables are just too expensive. If I found a source for metric engraving bits, I’d probably invest more time in trying to make it work.

Advantages:

  • Quick setup time;
  • Shipped with CAD software;
  • Relatively un-messy.

Disadvantages – specifically for PCB isolation milling:

  • Consumables are hard to acquire and very very expensive;
  • Milling surface is not rigid enough;
  • Milling surface isn’t level.

I’ve tried other isolation milling machines more successfully, which I’ll blog about soon.