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Roland iModela 3-axis CNC Router/Mill Review by NICHOLAS VINEN Looking for a small computer-controlled router/mill? This one won’t break the bank but has quite a wide range of uses, from cutting 3D objects out of soft materials through to engraving metal and making PCBs – not just the tracks but the holes as well. 92  Silicon Chip siliconchip.com.au CNC stands for Computer Numerical Control and is a category that includes 3D printers, routers, mills, laser cutters and other similar devices. The Roland iModela is a new product in their Modela range. It’s smaller and more affordable than commercial CNC mills so will appeal to hobbyists, especially model makers. We think it also has uses in the world of electronics, such as making PCBs. The first thing we noticed upon receiving the demo unit is how small it is – just 214 x 200 x 205mm. That’s tiny compared to most other CNC mills and that means it’s portable, occupies little bench space and is easy to work on. The whole thing folds apart in seconds, giving you access to the milling bed, tool spindle and spindle motor. It’s just as quick to pack up for storage. The small size means the bed (or workspace) is also quite small at 86 x 55 x 26mm – so the largest object you can mill is slightly less than this. Having done some tests, we can tell you that with the right cutting tool and a bit of patience, you can use the iModela to make PCBs, even those with relatively fine tracks (down to about 10 thou or 0.25mm wide); although having wider tracks makes the process easier. As well as cutting PCB tracks and drilling holes for component leads, you can also use the iModela to mill the edges of the PCB, in order to cut it to a particular shape. This involves cutting a lot more material though, so you would probably need to use multiple passes to get a good result, removing the material around the PCB edges in layers. Of course you can also use the iModela for its intended purpose which is to cut 3D objects out of solid plastic, wood and so on. The blank piece, to be cut or engraved, is taped or otherwise attached to the flat bed on the base of the machine. Overview The iModela consists of three basic parts: the milling bed, which moves in the Y-axis (forward/back); the spindle, which moves in the X- and Z-axes (left/right and up/down) and houses the spindle motor and cutting tool holder; and the electronic module which controls all four motors and communicates with the host PC. These are all housed in a plastic case, which also contains the swarf and dust generated while cutting. The tool holder accepts 2.35mm (3/32”) shaft tools only. While they are not the most common size bits, they are commonly used for hand-held engraving machines and for dentistry. There is quite a range of milling bits available – we were able to find and purchase suitable milling and drill bits made from tungsten vanadium, tungsten carbide and high speed steel without too much trouble. Accessories The iModela comes in a sturdy plastic carrying case, along with some accessories. These include the power supply, USB cable, a spare spindle motor, fan attachment for tool shaft (to blow away swarf), Allen key for installing tools, double-sided tape, practice plastic pieces, starter cutting tool, lubricating grease, cleaning brush, software CD and user manuals. The spindle While they call the tool holder a “chuck”, unfortunately it has no jaws. It’s just a 2.35mm hole in a chamfered steel cylinder with a single grub screw to clamp the tool shaft. It relies on the tool shaft being a tight fit in the hole so it doesn’t wobble; while this works, it means you’re limited to a fixed shaft size. It also means that if you are milling a relatively dense material and the tool shaft warps, it can be pretty hard to remove. The spindle motor is a small Tamiya brushed DC job, which many readers will already be familiar with. It simply clips into the spindle housing, making replacing it a breeze. This type of motor isn’t terribly powerful but it’s good enough for the type of materials you can cut with the iModela. It’s certainly cheap and easy to replace when it wears out (or if you manage to burn it out). They say that you should get about 50 hours of operation from each motor but we heard that if you don’t push it too hard, it will last longer. The gears which transfer the power from the spindle motor to the tool shaft are made of plastic but seem to be up to the job. Axis control The X/Y/Z axes are driven by small stepper motors. All three axes have good accuracy and repeatability. The Roland iModela opens out like a box making material placement relatively easy. When in operation, it’s closed up, catching all swarf and milling waste. siliconchip.com.au September 2012  93 The iModela’s spindle is powered by a small hobby motor, which can be swapped in a matter of seconds. One spare is supplied with the machine. The motors are strong enough that if the tool tip gets bogged down, the tool shaft will flex slightly rather than the axis motors becoming jammed. This is one disadvantage of the 2.35mm shaft tools; they are more flexible than the 3.2mm types which can lead to inaccuracy if you’re trying to cut away too much material at once. Repeatability is important since if you are cutting an object in layers, you want to be sure that each layer lines up correctly. Alignment is also important if you want to repeat an engraving pass but make it deeper. The iModela’s precision is good and it seems to be able to return the cutting tool to the same point each time. The iModela axes support steps as small as 0.001mm and the motors can microstep at 0.000186mm per increment! Microstepping helps smooth linear movements but doesn’t necessarily help with absolute positioning. However 0.001mm is very good accuracy anyway, so there are no problems in this regard. Control circuitry The control circuitry is rather clever, especially the way that it adjusts the spindle motor speed. The spindle motor runs at about 10,000RPM with no load. As the tool digs in, this speed drops. The iModela automatically adjusts the motor current in response to its load, in order to avoid the tool jamming or the motor burning out. This appears to work quite well. If the spindle jams or the motor encounters excessive load, the power to the motor is cut and you can rectify the problem before proceeding. It’s important to set the correct feed rate for the all three axes to suit the 94  Silicon Chip Looking up into the business end of the machine, with the routing bit clearly visible. One of the big advantages of the iModela is that everything is relatively easy to get to. material you are cutting. If it’s too slow, the job will take too long to complete while an overly fast feed rate can cause the motor speed to drop, resulting in poor cutting and in the worst case, a broken cutting tool. For milling PCBs, if you use the right bit and use a shallow cutting depth, the iModela can cut both accurately and fast. Shallow cuts are also best for creating fine details. We used a feed rate of around 8mm/ second and with the cutting depth set appropriately, the iModela had no problem removing copper at this rate. The cuts were clean and accurate, as you can see from the photos. In fact you could probably go faster than this. An Arduino shield-sized board (75 x 53mm) of moderate complexity should take less than an hour to mill and drill. Supplied software The iModela is supplied with two main pieces of software as well as the Windows driver. The one we found most useful is the iModela Controller. This performs the two most critical functions, which are manual control over the motors and the ability to process G-code files. Manual axis control is useful for installing a tool, setting the Z-axis height correctly and setting the X/Y origin. These are all important steps before you can proceed with cutting. G-code files contain a set of commands which, when executed, tell the unit all the movements it needs to make to produce a 3D object. For those familiar with Gerber files (used for PCB manufacture), the formats are similar; both are based on the RS-274D standard. Normally, the G-code file commands are relative to the origin at (0, 0, 0). For a PCB, this may be the lower-left corner of the design, with the tool just resting on top of the copper. If you don’t set this correctly, it may cut too deep, or fail to cut the copper at all. Or it may start the design in the wrong place on the blank PCB, possibly causing some of it to go off the edge. So clearly, setting the origin is important. Once the tool is installed and the origin set, you then feed in the G-code file(s) and the iModela starts cutting. During this process, you can see the current position of the X/Y/Z axes, the spindle speed, motor drive power and what line of the G-code file is currently being processed. You can use this information to track the progress of the job but we would prefer to see some kind of progress bar, time remaining and/or percentage complete indicator. It would also be nice to get some kind of preview, to see how the G-code commands will line up with the work piece. Perhaps these will be added to future editions of the software. The other piece of software supplied is called iModela Creator and it’s a “2.5 dimension” computer-aided modelling program (or 2.5D CAM). It lets you cut and engrave a sheet of material into a particular shape. The shape is defined using a set of primitives entered into the Creator program such as text, polygons, circles, ellipses and Bezier curves. It can also import Adobe Illustrator files. Once you have created or imported the 2D outlines of your design, you then have the choice of how to mill them. These are: * “Pocket”, mills out the inside of the shape to a specified depth. siliconchip.com.au iModela Controller gives manual control of the mill’s three axes and the spindle motor. It’s also used to feed G-code command files to the iModela (using the Cut button). * “Engrave”, mills the outline and can be configured to cut inside, outside or exactly on the outline itself. * “Hole”, drills or cuts a hole through the material. * “Cutting”, cuts a shape out of the material (like Engrave but going all the way through the material). Having placed the shapes, you can then move and adjust them until you are happy with the design. Selecting the “Cut” option then prompts you to select the type of cutting bit, the material being cut and so on and then the iModela spins the tool up and mills your design. Preparing PCB files If you want to feed the output of other software to the iModela, your main option is to use G-code files. Generating these from a PCB requires the calculation of an “isolation cut”. This involves computing the paths along which to move a tool of a given diameter in order to remove just the copper necessary to separate each copper “island” (or net). Normally we create a minimal isolation cut, ie, just those cuts required to separate the copper islands while leaving any unused copper in place. This reduces both cutting time and tool wear. For this review, we used a PCB designed in CadSoft EAGLE, as we expect this is what many readers will want to use in conjunction with the iModela. We deliberately chose a difficult board to mill, with 12 thou tracks and 16-20 thou clearances, to see what the iModela is capable of. With EAGLE, the best option for generating the isolation cut and G-code file is a free add-on called (wait for it!) PCB-Gcode. Once it’s installed, it’s siliconchip.com.au quite simple to operate although there are many parameters to set. PCB-Gcode can generate an isolation cut file, drill file, board outline milling file or some combination of all three. The first step is to select which of these you want and configure the tool diameter and the isolation cut tuning parameters (which you can probably just leave at the defaults). We had to choose a slightly smaller bit diameter than our actual tool (21 thou rather than 24) because of the fineness of the tracks and smaller clearance we used; otherwise, the software would have left some tracks incorrectly joined. This is why it pays to check the preview. The next step is to set the spindle spin-up time, feed rates (X/Y and Z), cutting and drilling depth, how high to lift the tool when moving it, where to move the spindle for tool changes (if necessary) and so on. You can then tweak the G-code style the program is going to generate; some programs can be fussy but we found the iModela software handled the “generic” G-code output just fine. It’s then just a matter of telling PCB- Gcode to generate the G-code files and it does so in no time. Having checked the previews (assuming you enabled them), you can then install your tool, set the origin and feed the G-code files to the iModela Controller software and away it goes. Milling a PCB For this job, we used a 0.6mm tungsten carbide spear drill bit. Tungsten carbide does not blunt as quickly as other materials when cutting a fibreglass PCB. Spear drills can be used for both milling track outlines and drilling component holes – there’s no need to change tools. We acquired a set of two such bits (0.6mm and 0.8mm) with the required 2.35mm shafts for about $16 from Proxxon World (www.proxxonworld. com.au SKU 28321). As you can see from the accompanying photos, the outcome was quite good and the assembled PCB (an SMD version of the MiniSwitcher project from February 2012) works fine. The hardest part of milling a PCB using the iModela is getting the board iModela Creator is a simple vector drawing program which allows you to cut, engrave and route various shapes including text. It’s easy to use and appropriate for simple jobs. September 2012  95 At left are the 0.6mm and 0.8mm tungsten carbide spear drill bits we used to create our PCB. At right is a packet of tungsten vanadium general purpose routing bits which also suit the iModela. This small PCB has tracks as thin as 0.012” (0.3mm) and clearances of around 0.02” (0.5mm). With careful adjustment of cutting depth we were able to get a good result. perfectly flat on the bed. This is more due to the blank PCB stock not being flat in the first place rather than a problem with the iModela itself. The recommended method of using double-sided tape to secure the work piece to the bed isn’t exactly a guarantee of flatness (but we found it worked OK). First, we laid the edge of a steel rule along the top surface of the PCB, which made its bend obvious. We then gently bent the PCB in the correct direction and repeated until it was more or less flat. Having done that, we cut out an appropriately sized section (around 85 x 55mm), without bending it too much in the process and filed the edges clean. It’s a good idea to re-check the flatness after cutting and fix if necessary. We stuck one of the flat pieces of plastic provided with the iModela to the bed, using double-sided tape. This made a sacrificial bed and we taped the blank PCB material on top of this and pressed it down hard. It’s possible to use the mill itself to level the bed under the PCB, ensuring it’s perfectly flat (relative to the X/Y axes) but we reckoned it was flat enough to start with so we didn’t bother. The next step was to insert the 96  Silicon Chip 0.6mm spear drill bit in the “chuck”. Ideally, we would then just let it drop onto the PCB surface, tighten the grub screw and zero the Z-axis origin in the iModela Controller software. This sets the unit up so that positive Z-axis coordinates result in a cut while negative coordinates allow the tool to move without touching the PCB. We had already set up the PCBGcode Z-axis co-ordinates to use this system, which makes the G-code files independent of the tool and bed set-up. At this stage, we encountered one minor wrinkle in that the spear drill shafts are relatively short and combined with the limited Z-axis travel of the iModela (about 26mm), they didn’t reach the PCB when pushed all the way up into the tool holder. We had to drop them down quite a bit and even then they only just reached, but we couldn’t lower them any further since they still had to be engaged by the grub screw. In the end it worked OK but this is something for iModela owners to look out for – you will need tools with reasonably long shafts or else you will need a thicker sacrificial bed, to lift the PCB or other work piece up to meet the cutting tool. Having set up the Z-axis, we then proceeded to move the tool to the position where we wanted the lower-left corner of the design to be cut and set the X/Y origin there. If your design is much smaller than the iModela’s working area, this is a convenient way to be able to mill multiple copies (or make multiple attempts). You don’t want the origin to be right in the corner of the cutting area as the tool needs to be able to cut around the lower-left most track (depending on where the origin is in your PCB design). This is a bit of a “gotcha”; if you try to rout a board where the G-code commands try to go outside the iModela’s limits, it simply skips the portion of the commands which it can not execute. This will probably leave you with an incomplete result and you won’t get any warning until it happens. For this reason, it’s probably worthwhile visually checking the G-code text file for negative co-ordinates before you start. Anyway, we’d set up everything as best we could but just to be sure, we re-set the Z origin to be slightly above the PCB surface and then fed in the G-code file. We were then able to watch the iModela go through the motions while not actually cutting the PCB. Satisfied it was all correct, we lowered the Z-axis slowly in increments and re-started the job until it was cutting deep enough to go through the copper layer without going too far into the fibreglass. At that point we left it to finish milling the board. Once it’s finished, you can open up the plastic panels which contain the swarf. Don’t open them while it’s cutting; it may be unlikely but we wouldn’t risk being hit in the eye! It’s then just a matter of removing the PCB from the bed that it’s taped to and cleaning out the dust and swarf. The result is shown here. We have no doubt that it’s possible to mill a full-sized Arduino shield using this method but you would certainly need to be careful to ensure the PCB is nice and flat. Conclusion The iModela is easy to use and can make accurate cuts. It is capable of good results when used with soft materials (eg, plastic) and when milling PCBs. It is compact, portable and cheaper than virtually any other prebuilt CNC mill on the market. It does have some drawbacks; its lack of a proper chuck or collet to hold the tool is unfortunate and the bed size, Z-axis travel and spindle motor power are a bit limited. Having said that, the iModela doesn’t really have any direct competitors and it certainly is a good way to get into CNC machining. For making small PCBs, we like the fact that there are no chemicals involved and once you get the hang of it, it’s a relatively quick and easy process to go from the design stage to having a finished prototype board. Price & availability The iModela is available from Roland DG Australia for under $1000, including GST. They also sell accessories such as cutting tools, replacement spindle motors and wood-based blanks for cutting. For more information, visit their website at rolanddg.com.au and search for “imodela” or call either their Sydney office at (02) 9975 0000 or Melbourne at (03) 8873 3300. SC siliconchip.com.au