Sunday, May 19, 2013

Got my printrbot simple beta... yay

Printrbot did a beta run of the printrbot simple at a little discount and luckily I came across it when it was available.  I was planning on getting a printrboard and an extruder soon anyway for a different project so it was a no brainer (if it wasn't useful then I'd still have useful parts).  Ends up it's quite a neat little PLA printer.

Most of the parts are lasercut wood and designed around a combination of slots/tabs and m3 screws/kept nuts.  I had zero problems with the quality of the cuts, the alignment of pieces, quality of the wood (qc is good here).

The bottom is formed from two pieces, one designed to hold the x axis bearings and the one below it to provide space for the ziptie nubs.  I didn't tighten everything down before all the parts were together later.

The electronics board is intended to fit inside the core of the body.  While I had read that some people swapped it outside the core (apparently there were collisions with moving parts) I decided to go with the original intent.  I didn't end up with any problems at all once everything was assembled.

One thing I should have noticed was that the current settings were too high for some of the steppers -> found that later.

Once logical combinations of pieces could be squared against each other I tightened the frame screws.  I did not lock the z axis stepper in place because alignment couldn't be optimized until the rest was assembled.

The bottom of the build platform attaches to the x axis rods and once caged with zip ties I tightened all of them as much as possible.  Some people don't like zip ties, but from my perspective they work very well and hold up quite nicely -> a very practical solution when used correctly.

The connection to the stepper is fishing line (not certain what it's made of - there was a white line and a yellow line and I liked the feel of the white one better - the yellow one felt like kevlar to me). I was suspicious of the vinyl tube around the stepper shaft/fishing line combination but it actually works very well -> palomar knot on one end and just wrapped a few times around the other screw and tightened on the other (to a high violin C).  I went with fewer wraps around the shaft than suggested because it offered less angular change over the range of motion.

The board with the y stepper and the connection off the back to the z nut... I caged these with zip ties kept them loose for later alignment.
The y axis contains the mounting plate for the extruder and similar strategy as the x axis for the rods.  I botched the side to put the zip tie nubs on and had to reverse them later because they limited the range of motion - silly mistake but I have extra  so it doesn't matter.

I really like the laser cut wood extruder.  I've never had problems with the original plastic printed design, but this version was easier to get the bearings aligned perfectly.  The easy filament changing design is excellent.

The instructions want the stepper attached before mounting on the y axis but I didn't do that because I remember the problem getting to the mounting screw later.

the backing plate design for attaching the large gear to the hobbed bolt is much better than the plastic gear it was pressed into before.  However, I was a bit afraid of the fit of the gears when holding them by hand - they felt very very sticky. The old plastic printed herringbone gears felt perfect moving them over each other by hand.  Once assembled on the extruder the fit was quite good (although a little more slop than the old herringbones).

There were four halfs of what looked like a nut retainer to screw the flat on the stepper shaft and four small gears.  I just used wood glue to bind two halfs with a nut sandwiched inside to one small gear.  That ened up working very well.

The printing plate is mounted on the x platform with four m3 screws and 4 springs.

Once the extruder is mounted there is a slight angular tilt down towards the front from the tension - this is not a bad thing at all, but the angle of the bed needs to be aligned to match this angle.  I guess one could shim or build in an adjustment at the extruder mount point but it's not a big deal to level the bed.

The only thing left to do was find a place for the extra wire lengths...  I just tied them in the space behind the printrboard.  I did wrap the extruder wires in electrical tape as strain relief and to reduce the chance one would catch on something.

When I powered it up and went to print I had a few weird problems.  The suggested software (repetier) would crash after a few seconds when I started a print... Ends up that if I disable the 3D view it works fine without crashing.  I think the osx version (which I need) is different than the windows version (which I can't run).

I was guessing that the built in setting for the printrboard would be in the ballpark of correct and thought I would do the calibration after my first print... bad idea.  The x and y axes were off by a factor of 2, the extruder setting was way way off (got a big pile of goo - it was running 18+mm of filament when told to push 5mm).  I thought that off by around 4 would be a step mode difference on the board but since the values I ended up with for the extruder were not too far from other people with that extruder I think there must have just been some odd glitch.  After calibration everything was quite happy.  After a couple of weeks where I can see how stable they are I'll just burn them into the eeprom.

Not an unreasonable first print.  Because there isn't a fan I had a little warping on the top where the area for the layer was small and insufficient time for cooling.  I went for blue tape since I wanted to stay as stock for now.  I will use glass later.  PLA is interesting, needs a little higher initial height than ABS on a heated bed - seems to have a narrower range of temperatures where is sticks to blue tape well and it starts to string.  Not a good thing or a bad thing.

Just for fun after the calibration objects I tried a rabbit at a couple of layer heights at faster speeds.

As expected the ears got a bit funky without a fan (I'll add one later) but it seems that 0.2mm is better than anything in 0.3 to 0.4 range (probably rounding/achievable steps) in software.  While not that noticeable without the flash there were little black lines in some of the prints.  I looked at the remaining filament that came loosely coiled (I also have a spool but havent used it yet) and there were short regions with little black flecks inside the PLA (not noticeable until I looked closely).  I didn't see any in the earlier prints and it's not consistent along the filament - just some little patches.

Overall it's a neat little printer.  Lots of little design decisions I like - lots of room for improvements and customization.  For the price I think it would be hard to pass up as something fun to build and as an opportunity to get your fingers wet with 3d printing.  It's going to take someone new a bit of effort to research how to troubleshoot and optimise but to me there is far more value in learning something along the way.  (There's nothing wrong with a highly refined (and higher cost) product - but things like this serve a very different niche and the two aren't really comparable).  Get something like this into the hands of kids or adults that want to do something different and much fun will be had and new skill gained.