Archive for the ‘ Uncategorized ’ Category

Building the C-Bot 3D printer: Part 29 : Rearranging the Leadscrews

Jump to C-Bot blog index to see all the posts.

The C-Bot build instructions have you create a cantilevered build platform, with two rear leadscrews to drive it up and down.  Other designs have modified this to have a triple-leadscrew system where two screws are in the back, and one in the front:  This provides for better stability for the cantilevered build platform.  I’ve noticed on my larger prints a bit of “bounce/vibration” that happens on the platform as it drops over the lifetime of the print.  It would make sense that attaching the front to something would reduce this.

I seriously contemplated going to a triple-leadscrew system, but this would involve buying more hardware, cutting another leadscrew, etc.  Not the end of the world, but I’d like to work with what I already have.  I got to thinking:  Why not just take one of the rear leadscrews and put it in the front?

That’s what I did this afternoon, and so far, it’s worked out really well:  I had a long enough 20×40 cutoff I was able to put across the front of the build platform, and some spare printed corner-brackets to mount it in-place. From there, I took the right-rear leadscrew and moved it to the center.  Then I took the left-rear leadscrew and moved it to the new front location.


Things noticed so far:

  • Build platform is much more rigid.
  • It’s easy to raise\lower the front\back for bed leveling by just twisting the leadscrews.

Jump to C-Bot blog index to see all the posts.

Building the C-Bot 3D printer: Part 20 : Electronics Day 3: Swapping stepper drivers

Jump to C-Bot blog index to see all the posts.

Update:  Since authoring this post I have switched my electronics to RADDS, and my firmware to Repetier.  See the “Part 31 post” for the latest on it.

Total time:  about 3.5 hours.

My Rumba board originally came with 6x A4988 Motor Stepper Drivers that have a 1/16 microstep resolution (I won’t pretend to know that that really means.  Sounds small).  Their ‘continuous current per phase’ is rated at 1A.  I’d had previous problems trying to drive both my Z-steppers off a single driver, so I switched to a driver per stepper.  In the meantime though, I ordered a five-pack of DRV8825‘s:  They have 1/32 microstepping resolution (ooohh…) and their ‘continuous current per phase’ is 1.5A (which I figured may be enough to drive two z-steppers, which is how Mason does it).

My thought was go back to the ‘single stepper driver controls two steppers’, but since I’ve already got my paired steppers and drivers working, I’ll just leave it that way for the time being.  I may only never need to change if I decide to go to dual-extrusion.

Removing the A4988’s and swapping in the DRV8825’s was seamless: I didn’t even need to flip any of the dip-switches living under each driver, on the Rumba:  In both instances, {on,on,on} was exactly what I needed set.  However, it’s VERY IMPORTANT you mount them the correct direction (see below pic):  The trimpot on the DRV8825 mounts 180 from the A4988:  Towards the ‘top’ of the board, rather than towards bottom.  I figured this out my checking the silkscreen on both the boards and (luckily) realizing the difference.  DRV8825:  Trimpot over capacitor.  A4988: Trimpot away from capacitor.

Like before, I needed to tune them.  Previously I tuned them by adjusting their resistance (rather than voltage) values while they were un-plugged from the Rumba.  Later I found these values to be off, and ended up manually tuning them via the trimpot while driving the steppers back and forth.  Second time is always better, and I grasp the whole process more fully:

This post from the RepRap Wiki spells it out pretty plainly:  To set the reference voltage,  you take 70% of the steppers current, and divide by two.  So the maths:

How to actually tune it?  They have a nice pic on the above link, but the steps I went though were:

  • Turn on the Rumba.  I then energized the stepper drivers by manually driving the x\y gantry from the LCD.
  • Once energized, I set my multimeter to volts, touched the positive probe to the trimpot, and the negative lead to the negative pin on the driver itself.
  • From there, I’d adjust the trimpot slightly until I got to around .58v on each.
  • drv8825 tuning

    Checking the DRV8825’s reference voltage: One probe on the trimpot, the other on negative.

When that was done I thought I’d try and print the calibration cube again:  Suddenly everything started printing 2x as small.

AH!  A4988 drivers have 1/16 microstep resolution, but the DRV8825’s have 1/32 : You need 2x the steps to go the same distance.  So it was back into Marlin’s Configuration.h file to retune the ‘DEFAULT_AXIS_STEPS_PER_UNIT’ variable.  By default I doubled everything to: {200, 200, 800, 300}, then individually started tuning them via the process I used before.  My final numbers:

#define DEFAULT_AXIS_STEPS_PER_UNIT {199.7403,  200.5415,  804.90995, 300}

Noooow, I can get back to final wiring and tuning my print settings…

Jump to C-Bot blog index to see all the posts.

Building the C-Bot 3D printer: Part 12 : Assembly Day 6

Jump to C-Bot blog index to see all the posts.

Today I righted some wrongs of the past, and got nearly all the hardware assembled:


  • Mason updated the ACME block holders and I reprinted both of them for install:  Now the z-steppers and lead-screws line up perfectly vertical.  Nice!  Unfortunately I ran out of the pretty ‘soulful blue‘ filament I’ve been using, so I had to print them in a different color blue.   A nice blue as well, but I was hoping to keep this all the same color.
  • Mason gave me the shim I was missing, so I was able to finish installing the X-gantry/hotend bracket.

New stuff:

  • Got the E3d Volcano mounted to the x-hotend gantry.
  • Mounted the Bowden extruder to the frame & connected the PTFE tube to the extruder.
  • Installed the heated build platform.
  • Printed and installed end-caps for the Z-gantry.

Notes on the HBP install:

  • I’d just eyeballed the location of the paired cantilevered 20×40 extrusions (the ones along the Y axis, which I will now refer to as the ‘Y-extrusions’) that hold the HBP and attach perpendicular to the 20×60 z-gantry:  Of course this wasn’t close to how the HPB wanted to be mounted.
  • The process I used to get it mounted is as follows:
    • I measured the distance from the mounting holes on my HBP:  It’s 12″ square, and the mounting holes happen to be exactly 30cm apart.
    • Starting on the left Y-extrusion, I measured 1cm back from the front to bolt in the first mounting bracket to:  I based this on eyeballing how far forward my hot end could move.
    • From there, I measured back 30cm, and installed the other bracket.  I then repeated this process on the right Y-extrusion.
    • Laying the printer on it’s front, I loosened the bolts holding both Y-extrusions to the z-gantry allowing me to slide them left and right:
    • First, I got them spaced 30cm apart (based on the holes on their previously installed mounting brackets).  Then I centered them by measuring how far away they were from either side of the gantry, and slowing shifting them until they remained 30cm apart, but an equal distance from either side.
    • Righting the printer, I then loosened them up again, and made sure the two end brackets were 30cm apart from hole to hole.  Tighten everything up.
    • From there it was easy to install the mounting springs, bolts, and thumbscrews.
  • Finally, I found a level spot in my house (which is surprisingly hard actually, considering it’s on a hill and built in 1938), and used a bubble-level to “level” the rear z-gantry by twisting the lead-screws.


  • I ended up cutting up one of M3x25mm bolts to help attach the swinging arm to my Bowdwen extruder:  As it turns out, I needed that to install my HBP:  I only had 4 left.  So I’m short one, but luckily Mason has a spare he can get me.
  • When installing Mason’s new ACME block holders, they were about 3mm deeper than before to compensate for the previously-mention misalignment issue.  The problem is, the bolts I custom cut to attach them were now too short:  More bolt cutting ensued based on the new design.

The only thing left hardware-wise is running the belts:  I’m still waiting for my pullys to show up, but I hope to have them this week.  So the next stop will be electronics!

Time spent: About two hours.


Day 12 progress

Jump to C-Bot blog index to see all the posts.

Printing PLA with the Replicator

I’ve been printing in ABS since receiving my Replicator last year.  Today I finally made the switch over to PLA.  The ‘why’ is mainly to try something new… see how a new medium prints.  But there are other benefits:

  • PLA doesn’t need to have the HBP (heated build platform) heated to 110 deg Celsius like ABS does :  I read it dosen’t need to be heated at all, but many people find success at around 40 deg C.  What this means is the HBP heats a lot faster…. meaning things print faster.
  • You don’t have to affix kapton tape to the HPB:  ABS sticks really well to kapton tape, and that’s why it’s used.  But it’s difficult and time consuming to get the tape applied to the HPB:  PLA can print on ‘blue painters tape‘, which is much more forgiving when being applied to the HBP.
  • PLA is biodegradable:  More ‘green’ than ABS.

First test run successfull, pic below.  Some notes on the process:

  • Extruder temp set to 210 deg C.
  • HBP temp set to 40 deg C.
  • Purged the ABS by ‘loading’ the PLA for 5 minutes straight, per online docs.
  • GCode compiled via ReplicatorG 0040, Replicator firmware 6.2.
  • Used ‘natural’ colored PLA, it’s semi-transparent.

I’m still getting a ‘bug’ where when during the pre-heat, filament ‘leaks’ out of the extruder nozzle.  On the ABS it would happen slowly, but with the PLA, I can physically see it leak out.  The side effect is the ‘anchor’ it first builds on the corner of the HBP doesn’t always fully form… which can screw up the start of the printing session.  But this first print tured out a-ok.

Tiny PLA vase : Success!

Merry Christmas

Wow, not much posting lately.  And not even a fancy picture to go along with this one.  Amazing how doing non-digital work (household plumbing, wiring, lighting, etc) cuts into the digital 😉  But the posting will pick back up here soon, I’m sure.

A merry Christmas and a Happy New Year to everyone out there!

— Eric

UPDATE:  This is a complete lie:  I’ve already got a newer post.  After the movie we went to was sold out I suddenly had a few hours to myself before our dinner reservations.  So, Merry Christmas :)