Monday, September 3, 2012

Snapping turtle happy time...

While it isn't that unusual to come across strange things every day - walking up upon snapping turtles in the process of mating wasn't something I was expecting...

It was a rather interesting process - mostly slow but determined movement - why they were doing this in the middle of the river not far from a deep drop off I don't know.

Surprisingly there was a lot of interaction leading up to the business part of the episode.  I haven't seen snapping turtles breeding before, but I wasn't expecting a lot of social interplay (especially with jaws that can cause critical damage).

I was also surprised at the flexibility in both the arms and the front legs - watching them it's kind of mesmerizing how much power they can exert.  I'm used to thinking of turtles in the context of the classic box turtles I see almost every day, but snapping turtles are completely different.

Once locked together I figured it was time to just leave them alone...

Just an odd little experience to come across... kind of neat.  Bigger versions are here.

Saturday, June 23, 2012

Unexpected speed -> first tests of the modified printrbot parts...

Before we get to the new part tests, someone asked about bed leveling.  I prefer not to shim between the heatedbed and/or the glass.  What I like is to put the heated bed directly on the platform, place the glass directly on it held in place by tape and not clips (expansion will cause problems).  To level the bed I place a few mm of silicone tubing designed for peristaltic pumps (really springy) between the y-axis bed mounts.  This way 1/4 to 1/2 a turn will cause abount a sheet of paper's thickness change in that corner of the bed.  It's very very stable (no adjustments for hundreds of prints) -> simple, quick, just works (remember to level the bed when it's at temperature).

When I got the three modified parts (see the last post) swapped out and installed I wasn't happy with the way I planned to mount the cooling fan.  While there was a conflict with the standard extruder (there won't be in my upcoming one) making it difficult to put in a nut -> din't matter since the m3 bolts will thread the holes nicely -> I felt it still wouldn't be stable over time...

So I just drilled two quick diagonal holes into the cooling duct through the front two upper holes in my modified extruder mount and fed in two additional m2 bolts -> this solution works really well -> sometime later I will work on updating the design once I finish analyzing the function.

While the fan does work really well for printing small details (I did a bunch of test pieces), once I did the herringbones (came out wonderfully - much better uniformity of detail and alignment) I moved onto speed tests.

Usually I don't print over 25mm/sec but I couldn't find any flex in the new parts (there was a lot in the original parts) I wanted to see what happens whan I increased the speed.  From left to right 50mm/sec, 100mm/sec, 150mm/sec, 200mm/sec and 250mm/sec.  One interesting thing is that above 50mm/sec I have to turn down the fan speed or I get a bit of lift at the edges of some prints -> 50% max speed worked at all the test speeds today -> no lifting.

I really wasn't expecting this to work at all... but it looks like the new designs are better than I expected.  Normally I have slic3r setup for different speeds for lare perimeters/small perimiters/inflil/movement and so on... here I just changed every number at once to the new speed to see where things fall apart.

It seems from the quick tests that I can go to 250mm per second for most parameters but perhaps ought to drop back to 100-150ish for small perimeters.

Over the next days I'll start teasing out what the limits are for the different parameters.

It's such a good feeling to see the little printrbot going at these speeds...



Friday, June 22, 2012

Redesigning some printrbot parts...

Well after getting everything dialed in on my printrbot and adjusted so that I can print parts reliably I decided to start making some changes (partially to fix some problems/limitations and partially to learn how to get sketchup to work best for designing parts for some other projects).

On the printrbot the carriage for the x-axis uses two parallel linear bearings and binds the drive belt from the back of the machine to the extrusion mount.  This is the test fit for my prototype extruder mount and the carriage.

What annoys me most is that the attachment point for the belts is too narrow and effectively acts as a point connection for the belts -> it acts as the center point around which force applied (in this case because of changes in velocity of the entire print assembly) will rotate around.  Couple of ways to sole this -> attach the ends of the belt farther apart so the effective circle of rotation is much much larger -> add a limiter to the amount of rotation possible (longer or multiple bearings).  I decided to do both.

I tried to directly modify the original sketchups of the parts but that didn't go well so I did it over from scratch keeping the horizontal alignment slot concept, the screw locations and the separation distance for the bearings.  I didn't like the bearing compression idea where tightening the center screw adds pressure to the bearings so I didn't include that.  Other parameters I changed a lot to increase the rigidity and strength of the carriage.

The extrusion mount has a wider attachment face for the the carriage and provides surfaces for attaching devices other than the extruder.  It ought to attach to the standard printrbot carriage (but with less surface area than the modified carriage).

I built in a sloped/pinch attachment for the belts - much easier to do the adjustments than the standard design with just a slot.

I'm using Misumi hardend rods and bearings.  One of the companies that never disappoints - really great quality parts.

Quick assembly with some spare z-axis parts to check alignment - slides like butter on a hot pan - no discernible flex at all.  Hopefully this weekend I can swap it into the bot and check it out.
This is just a quick snap of a cooling bracket for the extruder in the middle of printing.  It is designed for the modified extruder mount but should be easy to modify for the standard one.
If you are interested I've put the parts here:modified x-carriage, modified extruder mount, extruder cooling duct.  You may want to adjust the diameter of the bearing holes for the exact type you have on hand (and of course your preferred printing/slicing parameters).  I prefer a nice press-fit rather than adjustable compression since you ought not to need very much force to keep the bearings aligned and working correctly if all the other pieces are properly configured.

The cooling fan attaches with two m3 screws to the extruder mount (surfaces near the top of the cooling duct match the underside of the mount for additional support).

Here's a quick side view of the three pieces plus the 40mm fan all connected together.  When the hot end is mounted the tip extends far enough below the duct that the air flow won't cause problems with bridges but should cool recently placed filament sufficiently.  Lots of testing planned this weekend to make more adjustments.

Monday, June 4, 2012

My first little 3D part...

Well, I finally got tired of being uncomfortable about the stepper temperatures after printing for a while on my printrbot -> so I decided to make my first printable 3D part...

I got a few nice 40x40 fans (Sunon kde1204pkvx -> nice high air flow (1.6W at 12V rated but I'm running them at 5V -> nothing is using the 5V lines on the supply yet).  I got them from a small local computer repair place for a couple of bucks each... (I always try to support local small businesses whenever possible.  There's also something nice about being able to walk in an talk to someone about something you want to do that isn't a product they normally sell -> these little fans are perfect for this -> the guy had a bunch of them in a box in the back, unmarked for sale.)

Now that I had my fans, I needed to make a part.  I decided to use google sketchup... Interesting program -> at first I couldn't get it to do what I wanted, didn't feel comfortable... but after about 1/2 hour suddenly it all just clicked and for whatever reason I could get it to do what I wanted easily.  Strange learning curve, to change so abruptly, but it's a neat little program once you get the hang of it.  I did have to get a plugin to have it export stl files for pronterface/silc3r.

The bracket simply slides over the side of the larger nema 17 motors (for the x-axis just sliding it on is secure enough).  For the extruder stepper I used a couple of M3 bolts to add a bit more strength (but I'm not certain this is really needed).  The y-axis motor is tucked away underneath so I just ziptied a fan on the threaded rods -> works ok but not as well as these bracket/ducts.

There are small panels near the top that stop the fan from getting to close to the stepper.  When it's convenient to direct a few wires under the bracket there are a couple of slots available, but the spacer panels could be snapped off if necessary depending on how you want to route the wires..

It's not perfect, but it works better than I expected.  My gut feeling was that I would need to put a heatsink underneath, but that ended up not being needed at all.  I wanted to put the extruder fan towards the right side and towards the back, but that's going to take more time to design than I have today... perhaps in the future.  I put it on thingiverse here.  Feel free to download it and change it as needed (it's a simple design but I wanted to get a feel for how thingiverse works).




Saturday, June 2, 2012

Begining to tune the printrbot...

Last weekend I got the printrbot built and working, and while it was a busy week and I didn't have much time, I started working on getting better prints.  Once I had passable replacements printed for the parts I thought I would break doing adjustments I started playing with the extrusion and bed temps, the printing speeds, the percentage of fill and most of the settings in slic3r... One at a time of course.  I highly suggest that you do this because the understanding of exactly what each setting does, where it gives valid/perfect/bad results and the tradeoff between printing time and final quality is invaluable (not the same thing to read about these things as it is to see the results in your hands). 

During the process I also found that one of the z-axis smooth rods was a little loose.  I did a short term fix by adding a polypropylene film wrap around the rod before inserting it into the base.  I also tightened the x and y axis belts (I was a afraid to push it as far as I usually tighten belts without replacements).

While printing on blue tape works, printing on kapton tape (poly imide) is a completely different world...  There is no need to check the z-axis height each time - set once and so far it has held over 20 prints without adjustment.  Kapton also makes a much more uniform surface height than blue tape.  But the nicest thing is that it doesn't release during the print (no edge lifting) and as the bed cools down it's very easy to get the parts off.  While most people seem to like really wide tape, I like the relatively thin 1 inch wide tape.  I got mine (the high temp/low static type) from digikey because I was putting in an order for something else anyway.
  
The print here is a simple calibration piece and while I had the settings dialed in reasonably well, I found that the x and y axes were 103% of what they should have been and the z-axis was 105%... not so good.

What I should have done was to check the calibration after tightening the belts, but it didn't occur to me... I calculated the new numbers and added them to the g-code in slic3r and bingo, the sizes were right.

Now the prints come out the right size, I like the internal fill pattern and percentages, the temps are good.  There are still things to work on and fine tune, but I can get reliable of good quality, so it's time to print a set of good replacement parts...

My new filament isn't here yet so I just made the gears, the bed clamps. the belt clips, the x axis carriage and the extruder parts.  Now it's time to start working on the remaining little problems to see how good the build quality can get... 

One important note is that now that I'm looking at the quality I have been printing so many multiple copies of objects -> and multiple copies means that I am beginning to get a good idea of how reproducible the defects/anomalies are and which parts/structures are the sources of errors.  By far the most accurate and reproducible part is the extruder... whoever was involved with the design deserves a nod of thanks and pat on the back - once I got it dialed in it's been very reliable.

While I suspect there are differences in everyone's specific build, a very very good place for information in understanding how slic3r works is here.



Probably not a lot of time this week to work on it, but I am finally beginning to understand google sketchup and design my own things.

Tuesday, May 29, 2012

Finishing up the printrbot build...

The x-axis on the printrbot is driven by a belt.  Rather than having a fixed loop, the ends are attached to the carriage directly (I'm uncertain how it was intended, but it seemed to make sense to loop the ends this way and use zip ties to secure them...  This ends up working surprisingly well (I will probably make special clamps for tensioning later).

The idler on the far end is just a skate bearing between two large washers - works perfectly.  This end (one side of the z-axis) has two linear bearings pressfit (actually works fine) to bind the hardened steel rod and a captive bolt to attach to the threaded rod -> attached itself to one of the z-axis steppers below).  I ended up putting another captive bolt with a spring inside to control backlash later.

The complimentary end holds the x-axis stepper (with a nice printed gear for the belt), another set of bearings for the vertical smooth rod and a captive nut for the threaded rod on this side.  The actual x-axis smooth rods are pressfit.

There is enough space under the threaded rods on the bottom to put the control board.  It's a good idea to only attach one side first or it becomes quite hard to get the connectors for the motors and endstops attached.

I'll look at the quality of the signals later but it's a good idea to check the current limits for the output from the drivers before everything is wired up.    My board was set to send a bit too much current (the stepped got way too hot) so I backed it off to the point where the steppers failed to turn reliably and then gave them a bit more... don't overdrive steppers.

I decided to put a zip tie unter the y-axis stepper for additional support.  this ends up working very very well, but later I will print a part designed to do it better I think...

This is my first print (Mr Jaws #2).  I had to use blue tape (well I didn't have to, but I wanted to try printing and my kapton isn't here yet).  I got a 10x12 piece of 3/8 inch glass at the hardware store (nothing special about it) and just cut a piece about 5x5.5 inches and taped it to the hotbed.

After a bit of not having anything stick at all I found out that making certain the bed is leveled (much more accurately than I expected) and having the limit switch for the z-axis exactly right (piece of paper underneath has light tension no matter where the tip is on the hotbed) -> printing/ticking first layer is 100% reliable and repeatable.

Ok, so it's not perfect but it's not bad at all I think for a first print.

Layer alignements are good, axes are good, flow rate is good.  I can see some artifacts from having the layer height not a nice multiple of the steps/mm... This I don't care about now but will refine later once I have at least replacement parts printed in case I break something.

Yes Mr Jaws is a chip bag clip...

Printing the rail clamps went well, but they weren't ideal - functionally ok but a bit of flare...

The reason for the flare I learned when I failed printing a gear (the one on the points with an x).  It puzzled me for a bit how I could get crazy flare like this... But the answer was easy... so easy (and frustrating to figure out the first time) that it's worth  making a rule...  If you ever change the extrusion temp. or readjust the tension on the extruder you must do the calibration again... the flow rate is almost certainly going to be different.  The gears on the left are correct and all that changed is the calibration for the extruder rate.

Small herringbone gear is good.  The little bot is banging stuff out now with no problems or adjustments at all.

I'm still printing at only 0.4mm layers here and will play with increasing the resolution after I have replacement parts made.  I have not flatted my shafts and I suspect that might be a requirement for higher speeds with might be needed for playing with higher resolutions.

Here's the complimentary herringbone.  Still printing away without adjustments (as long as I don't play with the extruder tension it seems to just work perfectly).

As a side note, the two times I had to rethread the filament were because I hit extrude before the temp was high enough... what happens is that the hobbed bolt shreds the filament and the grooves fill with dust so nothing grabs... Very easy to fix -> heat the extruder -> run backwards to clear the filament -> open the tensioner -> flick out the dust with a needle from the groves in the hobbed bolt -> blow the dust away -> rethread -> CALIBRATE AGAIN -> and you're all set to print.

This is really a fun little bot... once I have replacement parts printed I'll see just what kind of quality I can get out of it.

Monday, May 28, 2012

Building the printrbot...

One of the interesting aspects of building something is that I find myself looking at how someone else designed something and instantly come up with reasons I don't like their solution and start coming up with other ways of doing the same thing... but once I start building I begin to realize why certain decisions were made and why the many ways I would have thought were better would not be in reality.

In the printrbot, Brook attaches the linear bearings for the y-axis with zip ties... I really wouldn't have thought it was a good design, but the zip ties provide enough slack so two bearings can be attached to teach base on the same hardened steel rod.  Since almost all the force is directed downwards in the design this works quite well in practice.  It wouldn't if there were significant lateral forces or large mass differentials across the printbed, but since those are controlled it's a rather cost effective and tolerant design choice.

Four threaded rods are used to connect the two base pieces together.  Straight forward design choice and very adjustable/reconfigurable for design modifications.  Probably would be a good idea to shift the upper rods down a bit since the inside nut will hit the zip tie.  A better choice may be to widen the bases a bit and then there will be no collisions.  The bases work, but are really a bit too narrow for ideal stability of the finished printrbot.

The two z-axis stepper motors are mounted to the outside edges of the bases with two m3 bolts.  Here you can see the y-axis rods through the linear bearings bearings before the zip ties were tightened.  Very smooth movement before and after tightening them down.  The weakness with the z-axis mounting is that there is no support underneath and they bear the weight of the carriage.  I ened up putting another m3 bolt betweent he bottom of the steppers and the base (that works very very well to stop twisting for the mass of the carriage).

The motor for the y-axis is mounted to the inside of one of the bases in the same way.  The belt tensioner (two skate bearings) are attached directly to the stepper (I really like this design choice).

The belts are connected to the steppes with a printed gear.  Having an internal captured nut is a great idea.  I didn't flat my shafts, may have to go back and do that later if needed.

The z-axis uses a two piece linkage for connecting the threaded rods to the steppers.  I decided to use 20mm m3 bolts rather than the supplied screws here.  The limit switch for the z-axis connects directly to one of the base sides.

The x-axis limit switch also attaches directly to one of the bases.   The print bed is attached to the y-axis rods with four clamps, one of which has a hole for the screw that trips this switch.  Interestingly I put it in the wrong place and had to move both the limit switch and the special clamp later.  In the upper left you can see the belt gear on the y-axis stepper.

Bottom side of the y-axis stepper with the belt installed.  A couple of washers lift the bearings to the right height for the belt.

The x-axis carriage rides on two smooth rods.Here the bearings are held directly inside the mount and compressed with a bolt between the bearings.  The screw to trigger the limit switch comes out one side and the extruder mounts on the other.

The extruder is an interesting design. I ended up cracking a part of it (easily fixed with epoxy) while adjusting the hobbed bolt.  The min piece holds the stepper and two bearings for the hobbed bolt.The power is transferred with herringbone gears (in practice it's works really well - I had trouble getting the large gear properly attached to the hobbed bolt (tightening the first time got it in place correctly, but I went to far an cracked part of the arm holding the front bearing.  Tension between an additional bearing and the groves in the hobbed bolt is done with the piece on the left - getting the tension correct the first time was not fun - but when it's right it seems rather stable.

I forgot to take pictures from most of the assembly process.  Mostly straighforward.  One hint I will give you is not to worry too much about having everything tightened down in the beginning, it's not a problem to do later and getting the alignment right before all the parts are together isn't easy.  I don't plan on really locking things down until I have a few prints done and adjusted.

Next time electronics and printing...

Friday, May 25, 2012

Printrbot arrives...

Yay, my printrbot has arrived.  At the end of last year I came across a neat kickstarter project by Brook Drumm for a simple 3D printer.  I was ready to get a Makerbot at the time (which looks quite good and has been refined a lot over time), but there was something about the way Brook wanted to do the project that appealed to me -> so I decided to back him.

The project ended up drawing a lot more interest than he originally expected...  This is a great thing when starting this type of business (more customer interest, more initial capital) but it meant that everything had to be scaled up fast.  Of course this led to delays in the kickstarter rewards, but so what... the goal is to get a business off the ground not to get rewards out fast.  It's been interesting to see how Brook and the community as a whole communicated about the changes in the design, the release of information about business decisions, design files, product revisions, assembling the printrbot, and of course the very few complainers about the delays.  I'm rather pleased with the way things  have developed and think it's likely Brook will end up with a nice little business and a happy community of customers.  There is an unofficial discussion board at printrbottalk.com that has been very helpful.

Opening the box is always interesting... Every company has a different character in how they pack things, and how the quality control is done before shipping.  I knew there would be a lot of light objects and a few heavier ones and that if the packing was wrong lots of damage could occur in transit.  Happily they did a very good job - exactly the right type and size of packing material and positioning of parts - there is no way to tell after opening if the box and actually shipped across the country or just sat on a table... perfect.  So let's see what's in the box...

There are a few lasercut pieces.  The larger one is for mounting the heated build platform (attaches to parallel rails on one axis and drive belt connectors).  The two smaller pieces are used to mount the electronics board.

A standard atx power supply.  Not exciting, but it will be fun to look at the quality of the output later.  Sometimes they can be unexpectedly good, sometimes not.  This project shouldn't come close to pushing the limits so it ought to be fine.

A big spool of ABS filament (about a pound I think).  The motors are off to the left - nicely wrapped in foam.

There are 5 motors in total.  The two smaller ones are wired together (z-axis intended to run in parallel).  All have connecters already attached - connectors look good.  I'll measure the resistances later.  All five turn nicely and the detents feel good.  (with the parallel wired little ones a cute thing is that turning one by hand will cause the other to turn as well).

The heated bed (6 inches by 6 inches) is already wired with a connector.  I'll measure the resistance later - it's a long pcb trace as a resistive heater strategy.  Board is very flat and not warped - mounting holes in each corner.  There are also 3 endstop switches and a thermistor already attached to individual connectors.  Solder joints are good but no heat shrink - not certain why but maybe there is a reason I will discover later.  A couple of extensions for the extruder finish out this bag.

This little bag has 6 bearings (they look like standard skate bearings), 25 little zip ties and 5 pairs of linear bearings for the smooth rods.  The packing list says 11, but there were only 5 pairs.  It's not a problem since there are only 10 needed in the printrbot.

In the white cardboard box we have a jumper (I think for enabling the atx powersupply), a usb cable, a spare extrusion nut, the hot end and the electronics board.  There are two connectors on the hot end - I think one for the heating element and one for the temperature sensor.

There are four 10 inch threaded rods, two 8 inch threaded rods and six 10 inch hardened steel rods.  It's always a good thing to check whether the cut threaded rods are straight (all six were good).  It's also good to run a nut down the threads to see if there are any binding areas (all six were good).

There are lots of little hardware pieces: screws, nuts, washers, strings, tubes and belts.  Everything matched the packing list.  When I have lots of parts I prefer to lay them out on paper with labels - of course as I build things get all messed up, but it helps when making certain all the parts are present.

The printed plastic parts are of a better quality than I expected.  There doesn't seem to be a lot of cleanup needed.  The side that was on the heated print bed is a bit shiny and a few have little bubbles on that surface - nothing to cause a problem. Here we have two base pieces, a mount for the extruder, a mount for the carriage, a mount for the motor (x-axis I think) and a mount for the idler.  They all seem to be both lighter and more rigid than I expected.

This group of printed parts is interesting.  The most complicated piece is the extruder (top center).  There is another piece right below it that helps tension the filament into the extruder.  There are two herringbone gears, two drive belt gears, a bearing mount for the y-axis I think, a mount for a limit switch, two belt clips, two pairs of sandwich clamps (I think for the z-axis) and four clamps (3 the same, 1 with a slightly longer segment and an extra hole, I think for mounting the bed to the rails.

Now we know what came in the box and checked everything off the included BOM (missing one unneeded bearing) -> we can start to build.