Experimenting With Acetone

After seeing many gloriously polished ABS prints which had used the acetone vapour method for smoothing and hearing of the legendary adhesion achievable on a heated bed with a fine coating of ABS juice, I decided to buy some acetone and see for myself whether it might help me in some way. People had said it could be had from pharmacies, hardware stores or even from the supermarket in little bottles of nail polish remover(though apparently a lot of nail polish removers are now acetone free), so I went to the hardware store where they sell a litre of it for $10 (I don't know if this is good value or not, but it sure won't break the bank anyway).

First up I tried the vapour smoothing method on an ABS model I had lying around - a squirrel with plenty of curved surfaces for the acetone to smooth and polish up. The first thing I noticed was how fast this stuff evaporates; I spilt a bit and it evaporated in seconds, the evaporation also makes it very cold when you get some on your hands. ...and on a note of safety: acetone is flammable and though not a proven carcinogen, it's not something you really want to breathe the vapour of or have on your skin for a long time and especially not in your eyes so be careful. Take care where and what you store it in as well: some types of plastic containers may dissolve and acetone in a hot place = vapour = pressure/expansion. This was the setup I used:

The squirrel before the acetone vapour treatment

A platform I quickly put together to suspend the model above the acetone. It is made from some solid-core copper wire twisted together then bent into shape, there is then a piece of aluminium foil put over the loop at the end for the model to sit on. At the top is a hook which goes over the rim of the jar. This platform is not very effective because it doesn't sit far enough down in the jar to allow the model to get the most of the acetone vapour which is most concentrated lower down. Also, it's not very stable and has a tendency to push the model into the side of the jar under gravity.

The jar sitting in some boiling water with the squirrel suspended, about 2mL of acetone in the bottom of the jar and the lid just sitting on top of the platform's hook since it doesn't allow it to screw down - good for stopping pressure build-up I guess.

The final result of the squirrel sitting in the jar for about one or two minutes. The plastic is definitely a lot shinier, especially lower down, and there are no layers distinguishable lower down. I took it out at this point because the surface at the bottom was starting to get very gooey and liquid-like to the touch, whereas it did not appear that much was happening with the higher layers. The main disappointment is that it has not been uniformly smoothed, with most of the smoothing at the bottom, I think this is because the vapour is most dense in the bottom of the jar and the platform the model was on was already too high up in the jar. When the model first came out of the jar its surface was very soft to the point of being gummy, after about ten minutes, it was hard enough to gently pick up but I easily left a deep gash with a fingernail, in the end it took a couple days for it to fully harden to how it was before the treatment.

After the vapour treatment experiment I decided to make some ABS juice with which to coat the bed to get very nice adhesion (or so people say). ABS juice is just a bit of ABS dissolved in acetone so the liquid mixture can be put on a paper towel and spread over the build platform, with the acetone almost immediately evaporating, leaving a very thin, even coating of ABS. You don't need to dissolve much ABS in acetone for this to work, I put the little ABS pieces seen in the photo above into that half-full tube in the photo. When coating the bed you will notice a quickly evaporating streak of acetone behind the wad of paper towel, I keep wiping the towel over the glass until I very barely see a bit of cloudiness on the glass. I don't seem to need much for it to adhere very well and I don't want parts sticking like crazy and pulling chunks off the glass when the bed is cold. How concentrated and how much ABS juice to apply appears to vary by supplier of filament and bed surface according to people's experiences I have read in the RepRap forums

The colour of the acetone after the ABS dissolved in it.

The bed appears to need to be coated again where the footprint of the part was after each print as each print takes the coating with it. An alternative to re-coating after every print is to "redistribute" the ABS residue from unused parts of the bed by wiping the bed with acetone, though you will still have to apply more ABS juice every few prints to "top up" the bed with ABS residue as "redistribution" takes a lot of the residue away in the process. Also, nophead claims that ABS residue can get baked on after a while of sitting round not being redistributed or printed on, this baked on residue becomes discoloured and is allegedly highly adhesive and thus tends to pull shards of glass off with the part. So even if there are some areas round the edges of your bed which barely get used it may still be worth redistributing and re-coating along with the rest of the bed.

I think I am going to permanently move from using sugared water on the bed to using ABS juice. This is because it saves time and has better adhesion, though it is much more expensive than some sugar and water. With ABS juice I don't have to create a new mixture every week due to stuff growing in it as it sits around, as with sugared water. The coating on the bed can also be redistributed instead of cleaned and re-coated which takes less time. Also I don't need to wait around for the bed to get to 80 degrees C before I can even coat it(this takes about ten minutes): ABS juice is just applied at room temperature because the acetone evaporates so quickly, so now when I click print I can walk away. With sugar water I have to be at the printer on the first layer because when plastic first comes out in inconsistent sputters during those priming loops, it has a tendency not to stick and instead clumps to the extruder. The blobs then begin pulling up good outlines when the filament flow is fully primed, the solution is to wait with a bamboo kebab skewer and push the blobs off the moving extruder and into the bed. Because of this I have to wait the full twenty or so minutes it takes the printer to warm up, stabilise temperatures and begin its first layer after I hit "print". With ABS juice these blobs never form in the first place because even the inconsistent, sputtering priming extrusion loops stick to the bed. On top of this, I save time after the print is done since I don't need "brims" around the base of the part to stop the odd corner lifting a bit since ABS juice has stellar adhesion, thus I don't waste time removing the brim afterwards. As always, parts just detach by themselves when the bed is cooled.

If you use ABS and can find some acetone I recommend giving this a go, especially if kapton of PET are not your thing or too expensive to get hold of.

Filament Feed Tube - a Z-Artifact Fix?

In a previous post I went into detail trying to explain and cure the z-artifacts that I see in my RepRap's prints, though I had only been partially successful, I did mention that there were still more things to test and to try.

Well, a few days ago, a teflon (PTFE) tube arrived in the mail - a guide tube for my filament. Other than possibly being able to fix certain kinds of Z-artifacts caused by filament dragging and pulling the carriage around as the carriage is not 100% solid, the tube allows for peace of mind for unattended printing. This is because it transfers the drag of pulling filament off the spool directly and only to the extruder instead of pulling on the weaker X axis which can cause devastating skipped steps.

THE SET-UP:

The tube with filament in it. It is important to make sure that it will have adequate length to comfortably service the whole range of the machine's motion. Also, the tube does not have to be a tight fit to your filament's diameter, mine has an inner diameter about a millimetre larger than my filament. It is best to try and use a tube with as thin walls as possible to reduce the drag on the machine from having to bend the tube + filament.

Teflon cannot be hot-glued directly so I attached two tightly-fastened zip-ties to the tube and then glued the zip-ties down with plenty of hot glue. Using two zip-ties with a decent amount of spacing is important or the force of the tube being bent will put a lot of twisting force on the first tie and quickly pull it off. The tube only has to be fixed to one structural point; the extruder end of the tube is not fixed down.

THE RESULTS:

 

My first print with this modification on my printer. The layer alignment looks very good but that is mainly due to the shape of the object and lighting hiding still-present Z-artifacts

The layer alignment problems are easier to see at this angle with a different lighting angle.

The bunny on the left was printed with the tube and the one on the right was printed before both the filament tube modification and also before I replaced my Z couplings with super-flexible hosing tube.
You'd be hard-pressed to spot much difference - which indicates that the Z-artifacts weren't coming from the older Z leadscrew coupling or lack of filament feed tube.

WHERE TO GO FROM NOW:

I think I will build a new extruder cold end (the feeding mechanism) as I suspect that the hobbed bolt currently installed may not be perfectly even. Now having access to a lathe, it should be very easy to create a precise bolt. Also, I have noticed that the gears on my current extruder do not mesh evenly and have some problems with eccentricity. All of this could be leading to slightly irregular feed rates of the plastic - it only takes a small irregularity to cause significantly more or less plastic to be fed, which in turn is easily observable as layers having too much plastic and squeezing out. I will post an update when I get around to trying this.

Building a CNC Router/Milling Machine

As my next big project, I am going to be designing and building a CNC milling machine. I am aiming for something that will have a working area of at least 700x700mm, be able to cut steel and still maintain accuracy on small scale objects such as is needed for PCB milling.

For the machine's electronics I am going to use four, possibly three NEMA 17 stepper motors driven using StepSticks on a Sanguinololu. I decided on a Sanguinololu over an arduino and GRBL shield because the Sanguinololu has more memory and came out at the same price (self-assembled) as an arduino and GRBL shield. The Sanguinololu also has a lot of expansion capability with four motor drivers and two fairly high power MOSFETs to name a few. This will all be powered at 12V using an ATX power supply. I wouldn't use an ATX on a 3D printer due to the high-current heated bed which needs a very large 5V ballast to get an acceptable 12V line, but since this one will just be driving some motors which don't need much torque, it won't matter if the voltage dips a volt or two.

I am going to go with a gantry design which moves the X axis to allow Y positioning while having a stationary bed, unlike a 3D printer. As for movement, I am going to use ACME leadscrews, probably only single start to save money at the cost of speed and I will definitely be using some anti-backlash nuts. Once again, single-start nuts are much cheaper and more widely available than multiple start ones. Also, there is a place locally which can supply ACME threaded rods.

The frame will be made of MDF, but once the machine is up and running I will use it to re-create some parts in aluminium if I'm not happy with them. 

The ways will have to be very sturdy to meet the requirements, but linear rails and bearings get very expensive, especially when they have to be thick, so I will create my own linear rail system using 608 size bearings (sometimes known as skateboard bearings) and steel which can be had from local steel suppliers. There is a local supplier in mind that sells in qualities ranging from structural-use to precision-ground engineering metals. The idea will be to get the sturdiness in the rails from  much cheaper, slightly less accurate square tube steel which may not have the best surface finish. Then mounted to this less well-finished square steel tube will be some much more precisely finished flat steel bars which don't have to be all that substantial as they will just act as a good quality surface for the bearings to roll on. Obviously the supporting steel tube cannot be absolute garbage which varies a whole lot over its length (unless I look into a shimming system which can still keep the rigidity). I am hoping that this approach will both save some money and also allow the contact surfaces to be replaceable if they wear out.

As a spindle, I will start off using a rotary tool/Dremel. Later on I will use my lathe to create a much better spindle with a good quality collet and bearings and be powered by a brushless motor and ESC, perhaps an RC car one if I can get away with it not overheating. This may require a power supply upgrade depending on the size of the motor I choose, but regardless has an extra advantage of being able to control the ESC using a spare Sanguinololu pin.

Will I be using the Mendel90 to create any parts for this machine? Probably not anything critical, as the machine has to be as rigid as possible. Perhaps I will use it make some vacuum attachments and an electronics enclosure.

Here is some of my progress so far:

I bought 5 low resistance NEMA 17 motors for about $60 off AliExpress from Wantai motors, shipping was quick (about a week because I chose Fedex IE) and communication was pretty good, but be very vigilant when shopping on AliExpress. For example, always try to make sure, by choosing fast shipping and taking into account a seller's dispatch time, that the item will arrive well before your credit card dispute window closes. If the seller charges an exorbitant fee for anything but default, slow shipping (which can take over a month), don't buy from them. This was one reason I didn't buy a cheap Sanguinololu from some other seller on the site.

A close-up of some StepSticks off eBay, all soldered up and ready for testing. It cost about $30 - 40 for four of them. In the previous photos you could see five, as I had a spare one from a previous purchase.  I will now have two spares for the CNC and 3D printer once done as the CNC will only use three.

The stepper motor and StepStick testing and calibration set up. Every motor and driver worked and there were no problems.

A Sanguinololu from Think3DPrint3D on eBay. I bought it un-assembled to save money and because I wanted to play with a new (budget) soldering station I had bought. I replaced the 2.54mm pitch molex connectors which are supplied for the motors, hot end and bed connections with 2.54mm screw terminals. These screw terminals have the advantage of being able to carry more current (good for a heated bed) and also of removing the need to assemble a connector onto the wires you want to connect. Due to the need of crimping to assemble these connectors properly, which requires an expensive tool, or a painful and slow hand-assembly method, I do not like them. The end-stops were the only ones on which I kept the molex connectors. For the thermistor connections I put headers instead of the 90 degree molex connectors in case I ever have to use this board for my Mendel90 where there is not enough space when mounted for the 90 degree connectors.

The board went together fine in a few hours of soldering (split up over bits of my free time), and I managed to solder the whole thing with no bad joints (yay!), although I soldered a MOSFET a bit wonkily.
I haven't fully tested the board yet, other than having tested the USB and FTDI chip early on during assembly, then later checking for shorts with a multimeter after which I looked for solder bridges, all I have to do now is bite the bullet and plug it in.

Well, that's it so far! As I progress with the design I will post updates.