There are many ways people get their ABS to stick to a heated bed, the most common being covering the bed in kapton, PET or a coating of ABS juice (ABS dissolved in acetone). I haven't used any of them (too lazy to buy any) so I instead use a slightly less conventional choice: water with a tiny bit of sugar dissolved in it which is applied to the bed's glass surface while hot. This has worked perfectly in the past, however I've been having quite a lot of lifting from the bed lately. The solution I currently use is about a 1:50 dilution. I apply it using a paintbrush, painting the mixture on using swirly movements. However I don't think I'm getting the best out of this sugar mixture given how well parts used to stick.
Lots of warping on a BeagleBone case - a recent pritn. Click on the image to see a
larger version and zoom in to see what I talk about below with layer deformation.
This problem seemed to have manifested itself as the ambient temperature fell due to the onset of winter. This led me to blame the lower air temperatures causing increased warping forces on parts(which does indeed happen), but on closer inspection, this didn't make sense. Why? Take a look at the original X motor mount which I printed for my machine (at a time when I had the best adhesion) as an example. Though deformation could be seen in the layers from large warping forces, the plastic never lifted from the bed; it probably would have de-laminated before becoming detached. Compare that to more recent prints - a BeagleBone case - large warping forces too, but not a sign of any such strong bed adhesion. The main reason corners were lifting wasn't to do with a lower ambient temperature creating more warping forces, the main problem was with bed adhesion - something that really doesn't have much to do with ambient temperature since the bed is heated up to the same temperature for every print.
Zoom in on this and see how on that edge all the layers near the bottom curl
upwards but the very bottom of the part still stays flat due to the layers
stretching to make up for this curl and extreme bed adhesion at the
same time.
So if it wasn't ambient temperature, what else had changed since then to produce such drastically different results? A lot, I realised. To list them: my bed wasn't heated to as high a temperature as it used to be, I didn't squash my layers down as much as I used to and the concentration and way I coated my bed in sugar water had changed. All these changes I had made for justifiable reasons at the time.
On my old machine I used to heat my bed to 120 degrees C when measured at the very edge of the bed on the surface. This is the very coldest point on the bed, meaning that I must have reached temperatures of at least 130 on the surface at the centre and even higher temperatures underneath the insulated bed). When I built my second machine I put the thermistor under the bed, right in the centre, like most people do. I also began using a bed temperature of about 115 degrees C (measured from the centre on the underside), this is about the bed temperature most people use so I thought there was no need to go any higher. This translates to perhaps 105 degrees on the top at the centre meaning that the temperature I now use is actually about 25 degrees colder than I used to use. Now I'd just like to get an IR thermometer to check all this rather than estimate.
As for squashing down the layers, on my old printer I had trouble maintaining a level bed (set it, do a print, and it's changed kind of stuff), so what I would do is set the layer height lower than what the slicing software thought(so I at least didn't have too much height if my badly-leveled bed dipped down). At times the hot end even dragged along the bed for parts of the first layer if the bed was higher-than-expected in some places. This wouldn't cause damage on that particular machine because the X carriage was able to pivot easily due to a bodged "floating bearing" on one side which could rotate upwards off the bearing and thus gain some height (though it was normally held down against the bearing due to gravity, quite hard to explain but I don't have any pictures). The end result was absolutely tiny and squashed first layers (0.1 mm).
I had also changed my sugar solution since then to be more dilute even though I hadn't had problems at the old concentration this was because I really wanted to stay far away from having too much which can cause the bed to become all slippery to the plastic and end up creating a big blob on the first layer. I used to use 4:100 but now use 2:100. My logic behind decreasing the concentration being concern about a particularly over-coated patch of the bed becoming slippery (because the solution doesn't tend to come off the brush perfectly). It also seemed that I was getting away with this lowering of the concentration until I really started to think about now vs. back then.
To test these three possible factors I will do some experiments, so far I have completed an experiment on getting the concentration right which is what the rest of this blog post will be about. When I complete the experiments on squashing down the first layer and on finding the best bed temperature I will post some more results.
SUGAR WATER COATING EXPERIMENT
For the sugar solution concentration experiment which this post talks about, I printed three copies of the same object at once, each placed on the bed such that they would be on areas of the same approximate temperature and each receive about the same airflow. The areas on the bed where these parts were printed were coated in their respective number of coatings of 1:100 sugar water to achieve the desired equivalent coatings of 1:100, 2:100 and 3:100, with multiple coats also helping to ensure even coverage on the bed. Printing the parts at the same time had the advantage of saving time and also making sure that all parts were subject to the same conditions (not including sugar water concentration of course).
The spacing and positioning of the parts.
The prints shown here are three Mendel90
vertexes which are small in size for a quick print,
but also high-warp due to high infill percentage.
COATING EXPERIMENT CONDITIONS: Ambient temperature: 12.5 degrees Celsius Print Material: ABS Sugar Solution Concentration: 1:100 Bed Temperature: 105 degrees Celsius Object 1: 1 coat of sugar water Object 2: 2 coats of sugar water Object 3: 3 coats of sugar water
RESULTS:
Here are the undersides of the prints, the blue lines were drawn on
with a permanent marker to indicate the boundary between where the part
has stuck to the bed or come off the bed.
Interestingly, print 2 did the worst, with print 1 coming in at a marginally better second-worst and print 3 with the 3:100 coating being the best. Perhaps print 1 beating print 2 can be explained by a difference in airflow, being that that print was off to the far left - maybe I didn't get the airflow quite equal for all the parts. Though I doubt the airflow explanation since the ring of separation from the bed is so uniform and an airflow in a particular direction would show as a couple corners lifting significantly more than all the others. Also the low profile of the parts and the spacing really should mean that they cannot shield each other. Then again it could have been really minute differences in bed height that caused this(I did take a lot of care leveling the bed before this experiment). Or maybe it is just that a 2:100 coating is really bad, either way it looks like I will use the 3:100 coating from now on, being visibly better.
While I am happy with almost all aspects of my Mendel90 that I built, I have never really been happy with one aspect of the print quality. That aspect of print quality is z-wobble. Or so I thought it was, as I have so far found out, it must be a much more difficult to remedy Z-artifact problem.
This is how prints looked when I first made my printer:
Very typical Z-Wobble - it has the same pitch as the leadscrews of the Z axis and is easily fixed in theory by removing a bit of constraint. However, even at this point in time, the Z-artifacts were inconsistent - they could be horrible one print and then hard to spot on the next.
The first thing I tried was to install a new type of nut trap (pictured below) which transferred virtually no movement except for movement in the Z direction - a desirable thing. Along with this initial modification I then drilled out the holes that the Z rods pass through to give them a bit more room to turn without knocking about, pressing against the X ends and to make up for inevitable misalignments. But if you looked closely there were still artifacts, and now they were looking different and more irregular, I guess the Z-wobble, which was now reduced by a great deal, had been concealing these other artifacts.
I then tried re-seating the rods in the old couplings and not over-tightening them in an attempt to align them more accurately and make sure they couldn't exert too much force in the X and Y directions, but this still didn't grant results I was happy with. I eventually moved to another coupling method - using my lathe to turn down the ends of the rods to 5mm so a flexible section of tubing could be used as a coupling. Alternatively I could have just used 5mm threaded rod.
The coupling system installed. I may have to replace
the cable-ties with hose clamps because the tube
softens up a bit due to heat - no problems so
far though.
The turned down end, I was very impressed given that
it was done using my first home-made/ground HSS
lathe tool. Cutting stainless-steel too!
In the background is half of an old coupling, a nut trap
and also a badly heat-deformed (from the motors) piece of
tubing that went inside the old coupling.
After all these mods, done over much time, I got this print quality on an X Motor End for a Mendel90 - unsatisfactory to say the least:
However, I was now certain that the Z-wobble was gone and that this was something else. This is due to the fact that the misalignment does not happen at regular intervals and does not look like a sinusoidal wave of X-Y layer displacement. Instead it happens very randomly and can go from the displacement varying every layer to happening every 10. The displacement is also very slight - about 0.1mm most of the time, however under certain lighting and angles, and with my highly-opaque white plastic, I can either hide it completely or make it look ugly. I suspect that if I put my plastic into an UP! or a Makerbot Replicator, the prints would come out with a bunch of highly-visible ugly artifacts like this too, but the photos of their parts sure do look nice. Having actually seen UP! prints I can say that the slight transparency that their white plastic has hides a lot, for it is very, very hard to distinguish layers by eye even at large layer heights. Holding hard, 90 degree edges up to light gives away a lot of small, but visible layer alignment issues on the UP! too though.
So, still looking for answers, I thought it could be backlash or skipped micro-steps as per Nophead's excellent article on micro-stepping. So I tightened up my belts and changed a few things with how my StepSticks were set up. I didn't read too in-depth into his article to know how it all related to my motors as they are low-current and high-resistance and I didn't really bother with the maths. So I didn't calculate the off times to get the PWM right for small-current portions of the micro-step cycle given current decay in the windings, let alone how to set this on the driver. But reading through the data sheets and his post, I realised that if I set my current too high with the potentiometer, say 0.4A (hey, I thought having a bit of juice available to them was a good thing) when my motors only draw 0.3A per winding at the drive voltage, the motors would have very bad and uneven micro-stepping. This is because the potentiometer does not directly limit the current to the motor by being in the path of current travelling into the winding, it is instead a user-set way of telling the driver at what current the 100% current level should be. This 100% current level is when all the current is in one winding and the other is completely off - a full step. If you set it above the current a motor can actually draw due to its resistance, the motor may actually reach full current in one winding while the driver is on the 13th out of 16 micro-steps or whatever, causing some really dodgy stepping.
I was in fact able to see and hear this, the motor would, at very slow speeds, change its sound and start and stop when motion should have been continuous. After setting the current properly, movement was smooth and the tone of the motor didn't change nearly as much. I might still only be getting effectively 1/8 or 1/4 micro-stepping for all that I know though, but at least it's smooth. That is something to look into another time. Here's the resulting print, it's still got all the same problems so it looks like the micro-stepping or belt backlash wasn't the big culprit:
Ah well, after all that effort investigating the motors I at least have gained some knowledge on stepper motors and hopefully eliminated that visible artifact on shallow curves and low-angle X-Y lines where it looks like the line is uneven with little bumps due to jerky movement.
There are a few more things to test including an unevenly hobbed bolt and badly-meshing gears on the extruder, my bed changing height as it expands and contracts with temperature swings and also the filament pulling the carriage around a tiny bit - for which I have ordered a PTFE guide tube which will arrive soon for me to test, assuming free shipping from China on eBay is quick.
So, after months and months and the beginning of a whole new year, I have finally finished assembling my second Mendel90, a true RepRap, from parts which were made on my first RepRap, a RepStrap version of the Mendel90. The RepStrap was scrapped for parts which were used in this printer; almost everything - the electronics, extruder, motors, belts, bearings, bed and bars were all saved, the only bit that wasn't was the old frame.
So why destroy the old printer to make this one? Well first of all, I didn't really expect all that hot glue in critical places to hold up for too long, and secondly, I had a mistrust of the old printer's accuracy. The old printer also had a smaller movement area, about 150 x 170mm and 170mm on the Z axis. This new one can achieve 200 x 200 x 160mm, a little less on the Z axis, but much better in the X and Y which is where I wanted the build area. I do however limit this movement area to avoid hitting the bulldog clips which hold down the glass plate to the build platform. Lastly, the Mendel90 provides a very neat wiring solution using ribbon cables, printed cable clips and mounting holes and so on. All this is accounted for in the drilling templates. If you've ever made a RepRap with wires all over the place and a power supply hanging off to the side on your desk somewhere, you'll understand how nice this is.
The wiring at the back, I know it doesn't look neat, but really it is when you're working with it, and none of it can move around so no worries with wires getting tangled, accidentally pulled out of places, etc.
The build went as smoothly as I could have hoped for. Nophead's amazing python script was spot on down to the last washer. However, in the process of building this machine I did modify a few things, and there was a bit of bodging - mainly to do with printed nut traps, but more griping about that later.
First and foremost, I had to modify the OpenSCAD file for the X carriage to fit a Budaschnozzle - the nozzle I already had from the old printer. After exploring the file for an hour or so, you soon figure out the gist of what's going on and can modify it and pray that it's all working out right. This file I managed to keep nice and parametric, though you have to open its SCAD file yourself and manually generate the stl file for it - it's not part of Nophead's python script, though it does have dependencies on many original Mendel90 SCAD files.
... and for more tweaking of OpenSCAD files. I realised that one of my smooth rods on the Y axis was 16mm too short, and instead of ordering a new one, I decided to change the distance between the brackets, of course this means that you'll also have to move the linear bearings inwards a bit on the Y stage. This involved putting "-16" on the end of some parametric value which sounded like the right one when I was looking through the files like so: "Y_bracket_spacing_or_something_similar = something - something + something/2 -16." Assuming Y_bracket_spacing_or_something_similaris actuallywhat you guessed it to be and isn't some value that only gets outputted into the BOM rather than actually changing the model and thus the drill templates, it should work as you intended. However there is one more pitfall - you must hope that Y_bracket_spacing_or_something_similar is a sort of "higher level" variable from which ALL the other Y axis-related stuff is calculated, i.e. bar length, distance between the two Y bearings, etc. is calculated. If not, stuff gets harder and you have to repeat all this guessing and searching for yet another value. Though it should be noted that this approach of "just insert a number here" isn't very parametric - very much a quick fix, in this case what will happen is ANY machine you generate will have 16mm less than what the original OpenSCAD script thinks it has. There must have been an easier way to do this that I missed...
Also, nut traps in the printed parts came out too small, especially the smaller sized ones, however I noticed that this only happened with the ones where the hexagonal perimeter was extruded on the X and Y axes. For M3 sized nut traps, some turned out only just over half the size of the nut! There are a few possibilities as to why: 1. My X and Y axes weren't calibrated well enough, however they can't have been too inaccurate given how everything still seemed to be printed in about the right place, give or take 0.1 mm or so. 2. Corner cutting, probably one of the biggest ones since the corners on the hexagons seemed a bit rounded. 3. Too much plastic - this is probably also one of the main reasons. For one thing, the top layers of some objects came out a little "over stuffed" with infill. 4. See also arc compensation, this also applies to corners, where too much filament ends up on the inside.
Thanks to the shrinkage, I spent a lot of time scraping out nut traps with a small screw driver, or sometimes I even just drilled out the nut trap and instead held the nut with small pliers or a spanner while tightening. I don't know how I'll ever replace the Y belt, or the Y belt anchors now...
For the build platform, I couldn't find any hex pillars, so I came up with another solution. Note the star washers used along with the plain washers, these are very important to stop things coming loose with all the vibration.
The Z endstop set up. Also, on the Z leadscrew you can see a Z screw isolator which was added much later to try and reduce
Z wobble. (Note that this is a very recent photo, it has been
many prints since the machine was first built)
Another place where I didn't follow the design exactly was the Z endstop. Though I printed out the part for the lower endstop I never used it. Instead I used the same method as on the old RepStrap. In what is one of the very few uses of hot glue in this machine, I glued the endstop directly to the gantry, in about the right position, give or take a few mm. To get the adjustability, I glued a couple M3 nuts to the side of the X axis and put a 20mm M3 bolt through them. This solution is more than good enough to allow for leveling, a build surface change, etc. if there's ever a big change I'll just have to pull the endstop off and move and re-glue it.
However, other than a few things, the build went smoothly, whenever I had time that is.
Here is a video of the first print:
The results of the very first print:
Not a great set of parts, barely even usable in fact, but it didn't stop me using them.
Why were these parts unusable? Pretty much all due to the extruder missing steps
because I set the retractions to be too fast.
This was the third print I did - the second print was the big gear for this extruder:
By now I had all the settings well figured out and prints were looking great
except for some Z wobble, which was at least still not as bad as on the old printer.
The first few prints were parts for the Wade's extruder which the Mendel90 uses, I hadn't bothered printing these on the old machine due to time. The machine was at first using Greg's hinged extruder and the ribbon cable was kept in place with a bodge which can be briefly seen in the video of the first print.
All in all, I am very happy with the printer and I can now print reliably and the bed seems to stay level much better so I don't have to worry about re-leveling every time I want to print and it's great not having to worry about hot glue melting.
If you're looking at this blog, I'm guessing I've either told you about it in person, you have a RepRap, or you are looking at building one.
I'll try to keep away from going on and on about how I built my RepRap through the whole blog: there are hundreds of other blogs that do that and are all basically the same but do each have a few new tips, if you are starting out or thinking about it, I would recommend you look at some. Since I have already built my first machine, I'll be able to compact all that I've had to do and learnt into one post. In future, I am aiming to have more projects than just RepRaps (although they probably will remain central to things), most of my projects will probably include some electronics, mechanical and some coding stuff. However, I wouldn't be expecting anything too impressive: I'm pretty much learning all this stuff as I go and don't have much previous experience with any of this.
Before I embarked on the journey of acquiring a RepRap, I had been following and researching the RepRap project for about three years, at the time, I believed it would be much simpler to just buy a Makerbot Cupcake CNC, so I went off and investigated that instead for a year and a half. When I finally did take a proper look at the RepRap project again, it had improved a lot and things were improving even more rapidly, it also now had many advantages over the Makerbot. Confident that RepRaps were now the leading edge and much easier to use, I decided to finally bite the bullet and buy a Makergear.com Prusa Mendel kit. However, a few weeks before I placed the order, nophead, a highly regarded contributor to the RepRap project, posted about a new machine he was developing and pointed out the problems with machines that use threaded rod as the structure of the machine. That really steered me clear of spending a thousand dollars on a machine which had inherent problems which I was also probably going to upgrade from. Nophead didn't release the files and the amazing script which could generate any configuration of machine you wanted for a while after the post which was fair enough: he wanted to get everything perfect and iron out all the problems. I wasn't going to use his exact design anyway because I didn't have access to a 3D printer to make the parts, so that was no big loss or setback anyway, I decided to design and make a RepStrap version of the machine.
I built, or more like bodged the RepStrap together to last long enough to build a more reliable machine. I wouldn't recommend people make one like it if you want a long-lasting, reliable machine: it often requires running repairs. I should also add, that at the time that I'm writing this post, I'm already half-way through making my next RepRap, a Mendel90 made using Nophead's designs, which should be more reliable and precise.
My RepStrap machine
The RepStrap machine itself is made from MDF; uses the weaker, lower current NEMA 17 stepper motors; has a Budaschnozzle extruder; has a PCB heated build plate with glass; uses Sanguinololu electronics; uses M10 zinc plated rod for the Z axis, not the best but it works. The design also uses a lot of hot-glue to fix things together, not an "acceptable" engineering practice, but it makes valuable parts retrievable and it works for my needs, only just. On the axes, I used 8mm "precision ground, chromium plated rod" from VXB bearings which in total, costed about $60AUD. For the linear bearings, I used LM8UU bearings.
The MDF panels I cut for the machine with a pretty inaccurate jigsaw, luckily the original sheet had enough straight edges and 90 degree corners on it to be used where accuracy mattered
The whole frame assembled with screws and wood-glue
The machine is usable enough to create reasonably accurate plastic parts for my next Mendel90, but all printed parts have mainly cosmetic "ribbing" on the surface which could be caused by a number of things. Though I think it is mainly caused by the massive wobble on my Z axis and possibly because the pitch on my threaded rods isn't constant enough, however, I never expected miracles from hardware store zinc plated rod. I got some stainless 8mm threaded rod for my next printer from a local fastener store, which, to my luck and amazement, had every single fastener on the Mendel90 BOM, except for the springs, hex pillars and tiny number 2 size screws for the endstops.
Some printed parts, you can clearly see the "ribbing" on them. I used the "brim" setting to create a skirt around the base of the object to eliminate warping.
In the process of making the machine, there were quite a lot of set backs, the first thing was that the linear bearings have an outer diameter of 15mm, unfortunately, it appears that 15mm spade bits aren't actually made, so I couldn't make the right sized hole for them in the bearing holders. Instead I had to make do with a 16mm bit which left a lot of slop which I had to fill up with hot glue.
Also, as soon as I plugged in the electronics together for the first time, after checking everything for shorts, a motor driver blew up, or more accurately, an SMD capacitor on the driver board.
Here's a slow motion shot of the capacitor blowing up that I managed to film:
After buying a new StepStick, triple checking for shorts and connecting it up, it worked and things were good to go. After doing some calibration, which requires having the motors on for a while, my motors melted the hot glue I was using to attach them to the machine, I ended up fixing them in using cable ties which worked fairly well. I never bothered trying to fix them in using their mounting holes because that would require me to drill 4 holes very accurately with no room for adjustments.
The last problem I faced was that my heated bed couldn't get up to temperature for three reasons, the voltage on the power supply dipped by 1 volt whenever I powered the bed, there wasn't enough insulation under it and the resistance was slightly too high, causing the power to be too low.
The insulation problem was easily fixed by putting some wool carpet underneath. To fix the voltage problem, I tried to put resistors on my ATX power supply's 5v rail, but I was only gaining 0.2v per 5 watts of load on the rail. The resistors were also getting very hot and it was hard to find places to put them safely; it was an ugly solution.
To fix this issue, I bought a so called "Ebay power supply" which are normally used to power LED light systems and security cameras to replace the ATX, it worked great, had good voltage regulation, was adjustable and was meant to power things like this, unlike the ATX computer power supply. However, a couple weeks ago, it suddenly stopped working, there was nothing I could reset, and upon opening it, there wasn't anything that was obviously blown up at all, the fuse was also fine. The only odd thing, which I had ignored when I received it, was that the warranty sticker was cut and part of the metal case was dented. When the power supply stopped working, I went back to the seller and asked for a refund or replacement: according to the Ebay page, it was meant to have a one year warranty, however, the seller would only give me a 10% discount if I wanted to buy another one. A new one is currently in the post from a different supplier, I definitely wouldn't want to support the person who sold it to me by buying another off him. Hopefully the old one was just a one-off dud and the new one will work for a long time: everyone else seems to have no problems with them. As for the problem with the resistance, that turned out to be a fault with my multimeter.
With all these problems fixed (at the time), I managed to calibrate the machine, print a few small improvements for it's accuracy and start printing out my next printer. However, as I mentioned before, things are currently at a halt and only half the parts are printed as I write this.
I sliced the objects using Slic3r, which required almost no fine-tuning to get good prints out-of-the-box and I suspect was much less of a pain than the alternative, Skeinforge. As host software to send g-code instructions to the printer from the computer I used Pronterface. Everything was printed out of ABS plastic, famous for its use in Lego bricks, at a temperature of 235 deg C. I also found a good local supplier of this plastic, their postage was quick and reasonably priced (for a person in Melbourne), the plastic was in good tolerances (less than 0.1mm), the plastic was of good quality and the plastic was also good value ($50AUD for 3mm diameter x 300m or about 2.2kg).
I used 3mm plain old window glass heated to 110 degrees C by the heated build platform as a print surface, all I had to do was clean it and coat it with sugar water before each print which of course evaporated leaving the sugar. One coat of the solution at 2 parts to 50 applied with a brush while the plate was at 70 deg C worked fine for me. However, I did have to spread the coating of sugar (which is impossible to see but possible to feel), by slowly moving a damp, non sugared, piece of paper towel over the surface when it was at about 80 deg C because when the sugar-water is first brushed on, the surface tension of the water causes the solution to not cover some areas.
This sugar-water solution works, as far as I can tell, about as well as the very widely used, relatively expensive kapton tape: like kapton, it has the odd edge that lifts, but since using the "brim" I haven't had any trouble. I think sugar-water is a much better alternative to kapton as it is so cheap and widely available, unfortunately, the plate does have to be cleaned with some glass cleaner and re-coated on each print to avoid spots with too much sugar and to avoid baking it on. Parts also pop right off with some crackling sounds when the print is finished and the bed is cooled, this happens between 40 - 50 deg C.
If you attempt to use this method, one thing to note is that you can apply too much sugar, in which case nothing will stick but instead slide around. The surface, once coated, should feel "dry" and almost feel even less sticky than clean glass, rather than sticky/slippery. I have found that I need to squash my bottom layer down quite a bit to get filaments to stick on the first layer, however, I think this may be down to the fact that I currently cannot level the bed accurately enough on the RepStrap.
Here is my very, very first print:
It took many attempts to get it to stick which is how I discovered that you can coat on too much sugar: each time I tried to put down the first layer, nothing would stick but rather a big ball would form and drag over the surface, taking away some excess sugar till, on the next try, it finally stuck.
If I had to make a RepStrap again, I would definitely do it differently. I would probably scale up a version of the Mantis CNC as they are a lot more suited to being made with simple tools in a home shop and, by the looks of things, would be a lot more accurate and reliable (as a RepStrap). The Mantis would probably only need a few simple modifications, such as belts instead of threaded rods and larger axes.
All up, I spent about $600 AUD on the machine including replacements for defective parts, etc. I now know that, in hindsight, you can get parts much cheaper than what I did: I just didn't look around enough. You can get a full Sanguinololu electronics kit off Ebay, including stepper drivers, endstops and heated bed for a good price and you can also get 5 stepper motors for about $60 including postage, half of what I paid for my motors!
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