Category Archives: printrbot

Calibrating the Printrbot Simple

printrbot calibration fails

As a barebones 3D printer the Printrbot Simple needs a little bit of software love before you can reliably print stuff. You’ve gotten your printer together, the X-Y fishing lines are tight, and it’s plugged in. You’re satistifed that despite your hamfisted build process, the bot won’t catch fire, and it’s time to get it calibrated so you can get started on your adventures in 3D printing.

First things first, download and install Repetier-Host. I’m using Version .56 on OSX, but the clicky points should be pretty much the same no matter what OS you’re on. If you’re a TL;DR type, skip to the starting gCode settings at the end of this post and proceed from there.

Repetier-Host desperately needs a name change. In the hierarchy of 3d printing software names, MakerWare is clearly the hep cat, followed by ReplicatorG. Pronterface sounds like a schoolyard insult, and Repetier-Host is the foreign exchange student who eats his own scabs.

Connect to the printer with the button on the top left of the screen. Assuming you get something cryptic in the log at the bottom like:

5:37:47 AM: FIRMWARE_NAME:Marlin V1; Sprinter/grbl mashup for gen6 FIRMWARE_URL:http://www.mendel-parts.com PROTOCOL_VERSION:1.0 MACHINE_TYPE:Mendel EXTRUDER_COUNT:1

You’re connected and ready to go. First, let’s calibrate the X-axis.

The plan here is to find the difference between how we’re telling the bot to move in software and how it’s actually moving in hardware. Variance in motors, line tension, humidity, gear slippage, localized tachyon concentrations, sunspots, Lindsay Lohan, all these things contribute to unpredictability in the Simple’s motion.

Once we find the difference we’ll write a little bit of simple gCode to correct for it.

The first thing you’ll do is set a default value for the X-axis steps per mm. I’ve been using 114.20, but any number in that neighborhood will work for this step. You’ll likely change this value later, so don’t worry too much about it.

Go to the Print panel and enter the following gCode in the G-Code field (inside the Print Panel tab) and then click Send:

M92 X114.20

Not much will appear to happen, but Repetier-Host has silently told your Printrboard to set the steps per mm of the X-axis motor to 114.20. We’re off and running with the calibration process.

Now move the print head all the way to the left. I do this by disconnecting the power supply to disengage the motors and physically sliding the print bed to the right, as if it were an old-style typewriter carriage.

warningWARNING: It looks like physically moving the X-stepper this way generates a current, which you’ll see lights up the status LED on the Printrboard. I’ve done this dozens of times with no apparent damage to the bot, so I’m assuming there’s a diode in there somewhere protecting it. Manhandle your bot at your own risk.

Once you have the X-axis homed, move the Z-axis up just enough that you can slide a ruler under the print head. I’ve covered my print bed in painters’ tape to help prints adhere, which also makes a handy writing surface. Record the start position of the print head with a mark on the tape.

marking the first line

Remove the ruler and click the X +10 button 5 times, for a sofwtare move of 50mm. Record the position of the head again and measure the distance between the two points, in millimeters. Mine was 46mm in this case, but yours may be different. In the unlikely event that your hardware move already matches your software move, congratulations! You’re done with X and can skip on to calibrating your Y-axis.

If your print bed doesn’t move or moves haltingly, there’s a good chance that you don’t have enough tension in the X line. Tighten it up and try again. The first few times I adjusted the line I was being way too gentle and got unpredicatble movement in the print bed, especially before the motor took up the slack on one end. Really pull hard on the line, like you’re trying to land a walleye.

A note to our international readers: a walleye is a type of North American antelope traditionally hunted with tethered harpoons.

We need a little bit of math to figure out our steps per mm. The Magic Formula is:

(old steps value * software move) / hardware move = new steps value

So plugging in our values we get:

(114.20 * 50) / 46 = new steps value

Which evaluates to 124.13 for my bot. Put your value into the gCode field like this:

M92 X124.13

And hit Send again. Test your X calibration by moving the print head back to the left with the X -10 button and recording the position. Repeat as needed until you’re satisfied that the print head is moving precisely enough for your needs. I’m OK with a little slop in my calibration because I’m trying to have fun with this machine and not get obsessive about print quality. It’s not like I’m printing jet engine parts here.

Repeat this process with the Y-axis, except swap the X for a Y in your gCode. I calculated a Y-value of 114.58 this time.

M92 Y114.58

The process is very similar with the Z-axis. Measure the distance from the top of the leadscrew to the extruder head, Z-move the extruder in software, and measure again. I’ve got one end of the ruler resting right on the plywood, sandwiched between the leadscrew and the head of a hex nut.

UPDATE 6/3/13: Read Bill Owens’ comments below on Z-axis calibration.

measuring the leadscrew

Plug your measurements into the Magic Formula and calculate. Calculate like the WIND!

After you’ve got the motion motors moving the way you think they should be, the next thing to do is calibrate the extruder motor. You need to make sure that the motor’s feeding enough filament to the hot end, but not so much that you spaghettify your print bed during a print.

The process is pretty straightforward: wrap a piece of tape around the filament, 10 centimeters up from the extruder.

filament

Set the extruder temperature to 220°. Repetier-Host won’t let you extrude with a cold hot end, so while you’re waiting set the extrude distance to 10mm. It shouldn’t take more than two or three minutes to go from room temperature to 220°.

If your hot end gets up to around 80° and stalls, check to make sure the power supply is plugged in. USB power will get you to 80° without the power supply, which can be deceptive.

After the extrusion is done, measure the distance to the tape again, and use the Magic Formula one more time.

Once you think you’ve all four motors calibrated, it’s time for a test print. You’ll want something simple and small, so that you can iterate quickly through test prints and really home in on the correct settings for your printer.

I’ve been using a 2x2x0.5cm test lozenge, which you can download right here if you’re not into 3d modelling yourself. The lozenge is nothing fancy, no bevels or geegaws. I keep the gCode for it handy so that I can quickly calibrate after a mishap or hardware adjustment. Do not suck the lozenge.

I’ll be exploring Slic3r and test printing in a subsequent post. For now just accept the defaults, hit Slice with Slic3r, and cross your fingers.

Before I print, I put my calibration setting into the Start gCode dropdown. If you’ve never done this before the dropdown can be a little hard to find:

start gCode

Here are the values that have been working well for me lately. They’ll be decent default settings for a Simple, but more than likely you’ll be tweaking them for your own bot. Note that these are a little different from the values I calculated above– there’s been some adjustments done to my bot since I originally started measuring things.

M92 X112.20 ; calibrate X
M92 Y112.58 ; caibrate Y
M92 Z2387.0719 ; calibrate Z
M92 E450 ; calibrate E

Assuming your print bed is mostly level you should have a printed lozenge in short order. Check the dimensions with a pair of calipers and adjust the print settings repeatedly until your OCD is satisfied.

Once you’re reliably printing lozenges, head on over to The Forge and grab a more complicated model to try out.

Also! Pledge fealty to The Horde to receive the latest Zheng3 models along with assorted other useful giblets like this calibration guide.

printrbot calibration fails

Printrbot Simple: First Impressions


Lao Zheng's Printrbot Simple

In mid-May I got all hopped up on endorphins from 6AM yoga and BAM! right there in my Twitter feed was an offer. The first N users who bought a Printrbot Simple would save $50 off the already low, low price of $300. My impulse control weakened by the flush of healthy qi, I had one in my shopping cart within two minutes, or roughly the time it takes me to huff and puff four sun salutations.

Two-fiddy plus shipping isn’t a budget breaker for a 3d printed squirrel magnate, and the gnomes at Interdimensional Bank of Zheng say we haven’t skimmed anything off the upgrades fund in a while, so why not, indeed.

A quick note for anyone thinking they might purchase this printer once it’s out of beta in June and available to folks other than the lucky N.

if (eval(‘yourTime’)>=eval(‘yourMoney’)):
     buyADifferent3DPrinter()
else:
     thisIsThePrinterForYou()


If you’re a high school student with a few hundred bucks and a weekend to burn, grabbing the Printrbot Simple is a no-brainer. If you own a complete set of matching stemware, look elsewhere for your first 3D printer. Especially if your only exposure to 3D printing so far has been the SkyMall catalog.

Make no mistake, even more so than the Replicator1, this is a hacker’s 3D printer. You’re like two steps up from a homebrew RepRap when you get into the Printrbot Simple. If tweaking and calibration and watching prints fail while you dial in gCode ain’t your thing, purchase a different printer.

On the other hand: right after I made my first successful print on the Simple I was mobbed by Brazilian bikini models. Your mileage may vary.

On the gripping hand: as an instructional tool, the impact of the Printrbot Simple can’t be overstated. Anyone who assembles, calibrates, and prints with this bot is going to learn buckets about the ins and outs of 3D printing at a granular level.

Best of all, at $299, it’s relatively inexpensive. I’d be disappointed if hundreds of these bots don’t find their way into high school STEM clubs.

Well-to-do techie parents looking to build a 3D printer with their tweens might be the sweet spot for this bot, but Mom or Dad should be prepared to sneak back to the basement after bedtime to put in an hour or two of extra build time.

The Build

warning The Simple is a beta, so there are guaranteed to be some bumps along the road. It ships as a kit, so you’ve got to put it together yourself. You’re also paying someone else for the privilege of beta testing their hardware, which is a genius business model if ever there was one. Fortunately Printrbot is up front about that fact; “BETA” is laser-etched onto the build platform. You buys your ticket, you takes your chances.

Printrbot describes the build difficulty as “moderate.”

I am reminded of the time I went to the Thai place across town that isn’t my usual Thai place and I ordered the larb with a 7 on the 1 to 10 spicy scale which is where I like it but they use a different hotness scale and hoo doggies that’ll burn tomorrow on the way out but I could still mostly finish it. Ach, mein ass.

So maybe Printrbot’s definition of moderate is different than mine.

I’m not a complete idiot. I can read English and make logical deductions, I’ve got a well-stocked toolbox, I have an amateur’s burgeoning knowledge of electronics, and I’m not afraid to jimmy-jim-jim a part to get it to work. Surprisingly, given my pyrotechnic proclivities as a pup, I still have all ten fingers. I have a SparkFun wish list, for the love of Pete.

Even with my bona fides, I still find Printrbot’s estimate of one to two hours for assembly of the Printrbot Simple wildly optimistic. I’m sure there are wizards from the Printrbot community who can wham-bam-thank-you-ma’am this printer into a finished state in that time, but coming at this build cold I’ve probably got 8 hours put in over the course of three days. Keep build time in mind while you’re salivating over that $300 price tag.

Printrbot’s marketing claims that you can put this together with only a screwdriver. Maybe, if you’re the Last Son of Krypton or you have vise grips for hands. There are a few tools that will make this process much easier:

  • you’ll need super glue.
  • it amazes me that my kit didn’t include an Allen wrench. Maybe Printrbot figures that IKEA has acheived such market penetration that the probability of an Allen wrench being within reach is approaching 1.0 for a given location in the Western hemisphere.
  • a cordless drill with an Allen bit will speed up the assembly considerably.
  • a metric/Imperial ruler so you can tell the different bolts and screws apart
  • scissors or a hobby knife– you’ll be cutting fishing line.
  • an adjustable wrench, and maybe an M3 socket.
  • needlenose pliers
  • zip ties. You’re going to need a lot more zip ties than are included with the beta to manage all those cables.
  • painters’ tape for the print bed. No sense in marring that nice birch any more than you have to.

Most people willing to tackle this process are going to have this stuff in the toolbox anyway, I just include the list because I’m a huge fan of deflating marketing hype by emptoring my caveats.

There’s a point during assembly where one must gently fit two steel rods through laser cut plywood holes; these are the rods that stabilize the extruder arm as it traverses the lead screw. The holes are cut to very fine tolerances, so much so that it can be difficult to push the rods through.

I recommend that you put your steel rods in the freezer maybe an hour before you get started on the build. Thermal contraction will temporarily shrink them just enough to get them through the plywood. Once they warm up again they’ll be nice and snug.


rods in the freezer

Be prepared to slightly modify some of the parts that came with the kit to get them to fit. The laser cut plywood all fit together perfectly, but I had to file down the plastic edges of my hot end so that it fit into the extruder assembly. I accidentally stripped the wood around an M3 nut and had to super glue the nut in.

Not a big deal for your average maker geek, but someone expecting a snap-together 3D printer is going to be sorely disappointed around hour three. You can see where my file chewed up the top of the hot end in the closeup below.


hot end

Suggestions for Printrbot

I’d like Printrbot to etch more directions onto the wooden parts of the printer. Etched labels like “this side faces out” would be very helpful in determining orientation during the build. I got turned around a few times and ended up dismantling and reassembling the previous two steps of my build.

At the end of each step, a photo of the entire printer from multiple angles could help a lot. I kept getting disoriented and had to backtrack or skip ahead to find out what part went where.

Once you get the bot together the first print is very satisfying, but along the way there is likely to be some gnashing of teeth and rending of garments. Here’s a test print of a small cylinder that I did, just to make sure everything was put together properly.


first print

Calibrating the Printrbot Simple so that your prints are the right scale is a whole other can of worms. I’ll get into that in a subsequent post sometime in the next few days. Watch this space.