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.