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Tuesday, September 17, 2013

QU-BD Revolution XL Review Part 3

Now that I have had the opportunity to spend a bit more time with my QU-BD Revolution XL, I have learned a bit more about its capabilities and issues that can come up.  I'll begin with examples of objects that I have printed so far.

The first thing that I printed was the single-wall vase, the gcode for which QU-BD provides on the RXL product page:


One thing that I was very eager to print was emmet's brilliant, parametric gear bearing, which, once printed, can be "cracked" and used as a functional bearing.  One reason why this is such a unique and wonderful object to print is because it is a shape that can only be arrived at using 3D printing.  Because its interlocking gears and outside walls use a Herringbone pattern, the piece could not be assembled manually.  This also means that the bearing's parts are forever locked in place:


One thing that I have been unable to figure out is how to get certain shapes to print at high speed.  For example, when using Repetier Host and Slic3r to print sphynx's lovely Koch snowflake vase, I configured slicer and set all speed settings for 400mm/sec but of course configured it to do the first layer at 20% speed.  When printing The first layer goes down as predicted.  The next couple of layers go down lightning fast, as expected, but when the base of the vase has been completed it goes into low speed when doing the double wall of the vase to the point where the print took 6 hours.  This is clearly a Slic3r configuration issue but for the life of me, I have not been able to figure out what setting is holding back the speed.  In any case, the final printed piece was a thing of beauty:


There are a number of things that I have learned about the RXL, mostly through repeated print failure:

Bed Height

The initial distance between the hot-end and the bed is critical and I have found that the Z axis mechanical end-stop to not be perfectly reliable.  On three occasions, it has failed to activate, driving the bed right off one of its Z axis screws before I was able to fumble for the emergency stop.  On a few occasions, it would go off a little late so that the hot-end was so close to the bed that attempting to print would clog the nozzle.  At the beginning, I was a bit frustrated that there was no means of adjusting the end-stop distance other than bending the switch lever.  I am not completely sure but I strongly suspect that the switch's unpredictable behavior may be due to the fact that its lever touches the aluminum bed which may or may not be hot.  It may be that the heat from the bed is being conducted into the end-stop's lever, causing the problem.

In any case, I believe that I have come up with a cheap and easy workaround.  I carefully bent the lever of the end-stop incrementally until it would activate when the hot end was pressed against the bed with no clearance.  I then moved the bed down and began to add strips of clear 3M packing tape to the part of the bed that the end-stop touches.  One can conceivably even use Scotch Tape for finer increments.  The result was that I was able to use this method moth to calibrate Z height and help insulate the Z end-stop's lever from bed heat.

Anti-Ooze Retraction and Nozzle Clogs

When attempting to print several items at high speeds, I found that the print started out okay only to fail a few layers later when the nozzle would clog.  Upon examination of the extruder, I would find that the portion of filament being gripped by the extruder's gears was stripped.  After playing with a number of variables over several days, I found that the problem would not occur if I reduced my retraction from 1mm to .5mm.  This reduction also did not result in any unwanted stringing, as evidenced by this string-free 4-piece printing of MarcoAlici's Recorder that my son is still waiting for me to clean up and glue together:


Conclusions

The RXL is a fantastic printer.  It is super-fast (when you know how to configure Slic3r!), has a great build area and easily puts to shame printers costing $1,000 more.  I think that QU-BD did a superb job.  I am looking forward to pushing this printer much further to see what I can do with a variety of materials other than ABS, namely Nylon and LAYWOO-D3.

Coming Up

The RXL has one notable shortcoming.  It does not have any convenient places to mount a a filament spool on top (where else would one put it?).  I hope to design a spool-holder and use my CNC router to cut it out of some 1/8" Aluminum plate in time to show it to the folks at QU-BD, assuming they will be at the New York City Makerfaire that I am looking forward to attending this weekend.

Monday, September 9, 2013

QU-BD Revolution XL Review Part 2

I have spent hours upon hours putting this machine through its paces under grueling conditions and have much to report, both good as well as things that can be improved upon.  I will start with the good, actually, great.  This thing is as fast as it gets.  Check out the 3D printing of this Samsung Galaxy 4 case (http://www.thingiverse.com/thing:100129):



My adventures have not been without their frustrations and it is only fair that I disseminate them.  I have bathed in frustration for a few days now but I really have nobody to blame.  I have concluded that some of my problems were likely caused by software.  I originally installed Repetier Host on a family computer.  When evidence of Y-axis slippage showed itself, I jumped on hardware, probably mistakenly, but because I had experienced axis slippage in my reprap past.  After loading the software on a new laptop, things went better -- until they didn't.  I had to abort that flashlight-lit Galaxy phone case print when I noticed that the LM8UU linear bearing that supported the right side of my Y axis had shimmied loose:


I can see that a red adhesive had been used to adhere the bearing to its Y-axis parent, but not successfully.  I will ask Nathan, the head engineer at QU-BD what adhesive I should use to make sure it stays put the next time.

The second problem that I encountered is more important, notably the Z-axis end-stop.  The X and Y end-stops are not that important because they do not dictate one of the most critical factors in 3D printing:  how close is the first layer to the bed.  I have found that the mechanical end-stop on the Z axis of the RXL to be finicky.  On a couple of occasions, I tried to home my axes and the Z end-stop did not trigger.  This was bad.  I quickly hit the Emergency Stop and then spent some time re-aligning the bed.  Right now, there is no good way to calibrate the Z axis.  There is a screw-hole at every corner of the bed but only two screws were installed.  This leaves the mechanical Z-limit switch -- something that I have found works differently from one moment to the next.  Home it when the bed is cold, it is a certain distance from the bed.  Try it when the bed is hot, something different.  Right now, the only way to tweak your Z limit is to carefully bend the Z limit switch lever.  My suggestion to QU-BD is that they leave mechanical end-stops on the X and Y axes but that they substitute their Z mechanical endstop with something more precise like a hall-effect end-stop or opto-end stop and that they provide a screw to adjust it.

I don't want to seem overly-critical.  This is nothing short of a groundbreaking machine.  When I look at it, I see a labor of love;  something I would be proud to release to the world.

Saturday, September 7, 2013

QU-BD Revolution XL Review Part 1

I have had my eye on QU-BD ever since their successful Kickstarter campaign last year.  When I visited their booth at last year's Makerfair, I was impressed with the engineering and build quality of their RPM mill/3D printer.  So when they offered their Revolution and Revolution XL printers to customers willing to beta test and willing to wait in exchange for a great price ($800 for the RXL) and for what might be a truly revolutionary new 3D printer, I signed up.  That was in January, 2013.  There were of course delays and I watched over the following months as the impatient beta customers and I slowly transformed into an angry mob.  So it happened yesterday that I was rummaging through my closet looking for my pitchfork and torch when my dog announced with his usual oratory flair that a package had arrived.

The promise of the RXL's revolutionary leap beyond the current landscape of affordable FDM printers was in its speed.  Most reprap 3D printers use an extruder mounted on the X carriage.  This limits their speed.  Other printers, like Ultimaker, speed things up by removing the extruder from the carriage and using a Bowden extruder.  The downside to that approach is that anti-ooze retraction, used to prevent stringing, does not work well with a Bowden extruder.  The RXL was to have the best of all worlds -- a super-light (<6oz) extruder (they call X-truder) combined with 2 X motors and 2 Y motors.  In an early youtube video, they demonstrated 900mm/second travel speeds.  Later, after they tweaked things, QU-BD was able to demo 500+mm/second ABS printing.  For a reprapper like me used to speeds 1/10th of that, it was indeed a great promise.

The first thing I successfully printed with the RXL was a vase for which QU-BD included tweaked gcode to demonstrate the RXL's speed.  That went well.  I then moved on to printing a Filastruder hopper at conservative speeds:


After some success, I became more ambitious and set out to print an over-sized Eiffel Tower at 400mm/sec:



Check out the speed:


It seemed to be working great for a while but something seemed to "slip" somehow on my Y axis, causing the print to fail.  I will investigate and figure out what caused this failure:


Stay tuned as I continue to put this machine through it's paces.