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.