Prusa Mendel RepRap: Calibration Part One

After you finish getting the machine built, what's next? The good news is that you've finished the machine! Take a break. Congratulate yourself. Have a cocktail, or a rootbeer float. My wife and I had a toast to my success with an expensive single malt. Try to resist the urge to fire the machine up and try to print straight away, because the bad news is that now you're just half way to your ultimate goal of a working printer. It needs calibration for you to have any real success at printing.

Calibration, in my experience, takes as long as building the machine. In part that's because you're also learning some new skills and software, and in part it's because there isn't a comprehensive guide to Prusa calibration that I've found and so I had to fumble through it a great deal and get a lot of help from the IRC channel. So let me take a stab at it here. The directions below assume you have succeeded at getting the RAMPS board firmware loaded (sprinter), the print host (pronterface) installed and operational.

Step One: Physical Calibration

1. Level the Print Bed - You may have done this once as part of setting the Z axis end-stop, but you'll need to do it again.
   
   
1. Make sure you have covered the print bed with blue tape so you have an actual working height to level to. With needle nose pliers and hex key wrench, move the nozzle to its home position and adjust the tension screw in that corner to the nozzle height. Notice that even 1/8th of a turn of the screw makes a significant difference in the height of the bed relative to the nozzle.
   
2. It's very important to get this just right. If you're using a .5 or .35 nozzle, you will adjust the height of the bed so that two pieces of printer paper slide under the nozzle without a gap. For the .25 nozzle I used a single piece of newsprint paper (.07 thick) to gauge the height.
   
3. That done, move the nozzle across one axis, 10mm at a time, and adjust the screw across from the screw near home in that direction as you go to get the height just right. When all four corners are adjusted to the correct height, go around the horn again and also move the nozzle to the center of the print bed. Pay attention to the height of the nozzle in the midpoints. 
4. If your bed is bowed a little, like mine, you want the corners to be the same height (regardless of whether or not they're the gauge height and get the nozzle the right height in the center. The center is where the height is most important.
   
   
2. Tighten down the idler on the extruder. For my extruder I needed to swap the springs out for longer ones and tighten them down to near full compression for the extruder to work properly. So, maybe you almost can't get the idler too tight, as long as there is still a little spring compression left for the idler to work with as the width of the filament varies. Test the extruder and feel the filament as it goes through the extruder. Your fingers are very sensitive and you'll feel it if the filament slips in the extruder. If it slips, you either need a better hobbed bolt or to tighten the idler down more.
   
   
3. Tighten the belts. You will be plagued with backlash unless you get the belts tight enough, but not too tight. There is such a thing as too tight, and you'll know it when you see the motors and motor mounts warp significantly out of shape. I added a special Y tensioner feature to the Y belt so I could get it just right. Be sure your pulley gears are well seated on the flat of the motor shafts, and they are tight, but not so tight as to crack the pulley plastic.
   
   
4. Turn down the stepper driver pots -- there are little tiny screws next to the heat sinks on the stepper drivers.
   
   
1. Take a jeweler's screwdriver and carefully, with a light touch, turn the screws counter-clockwise until they stop. They are fragile and it's easy to break them if you try to turn too far. 
2. Turn the pots back up by one 1/4 turn.
3. Try to move the motors. Gradually, in 1/16th turn increments, turn the pots up until the motors move across the full range of movement without skipping. When you find that point, turn it up another 1/16th turn.
4. Include the extruder in this procedure. 
5. With the hot end off, clip any filament sticking out past the bottom of the extruder.
   
1. Measure the length of filament extruded when you set pronterface to extrude 50mm of thread (at a speed of 150). Is it close to right? Save this for firmware calibration in the next step. 
2. Clip off the extruded filament.
3. Hold up the clipped-off filament next to the filament feeding into the extruder and mark the feeding filament at the top of the sample piece. If you are using black filament I've found that red dry-erase marker works well.
4. Put the hot end back on and heat it up to a reasonable temp. I started at 185 deg.
5. Hit the button in pronterface to extrude the same amount of filament.
6. Did the mark made on the filament get close to the extruder or go in? If not, and your filament is not slipping (see slipping calibration above) then you can try to turn up the pot on the extruder's stepper driver a little bit. Try again and see if that makes a difference.
7. It's not crucial that the off/on extrusion measurements match exactly. You'll later adjust the e steps (the calibration in the firmware) to the practical results you get for extrusion. But this comparison process is useful to help negotiate the fine line you need to walk with the pot setting.
   
6. What you want to avoid is running the stepper drivers and/or motors at a high temperature. If you can stand to hold your finger on the heat sink for a couple of seconds without burning your finger, you are okay. If the motors are more than just a little warm to the touch, you have turned the pots up too high. If they wind up being warm at all you should still figure out a way to have a computer fan blowing on the electronics. It will extend the life and safety of the electronics.

In Calibration Step Two, I'll outline how to precisely calibrate the firmware.

Paizo New Products Seminar at Gen Con 2011

Desi and I went to the Future of Paizo seminar at Gen Con. I finally got the video I took, which covers almost the whole thing, edited and uploaded to YouTube. Here they are in neat chronological order for you. The stuff that's of most interest to me is about the upcoming Pathfinder adventure paths up through the previously unannounced Shattered Star aventure path, which takes place back in Varisa.

UPDATE: [part 4 quality and fixed titles]

GenCon 2011: Pile of Awesome

As you can see by our awesome pile of loot, we totally Greyhawk'ed GenCon this year. Yeah, we went a little overboard, but it was just too much fun.

(photo from blondeswan.com)

Some of the best stuff isn't pictured though, including Desi's new leather corset, her fancy new steampunk hat (purple suede with feathers) on order, my red suede fez hat with gold tassel on order, her super-fancy steam punk pocket watch, and a Randovan character Pathfinder metal miniature I got free at the Paizo booth. Oh! And the two minis Desi and I got in the Paint & Take event.

The lady above bought this hat out from under Desi. I found her wandering around the exhibit hall the next day, and I talked to her. I told her about Desi and she told me she'd seen the hat the day before she bought it and initially passed it up because of the price. Then the next day she said to herself, "Screw it, I'm on vacation," and bought her whole outfit. So Desi had to order it. Desi's hat is also from the Blonde Swan.

List of Loot from the Pile of Awesome 2011
1.) Case of Lords of Madness D&D minis (8 boxes)
2.) D&D Beholder collector set
3.) DUST Tactics Core Set (game)
4.) A Game of Thrones Card Game
5.) Lays (2): free at FUDGE game*
6.) Chessex clear vinyl map matt 23x25" w/ 1" grid
7.) Chessex clear vinyl map matt 35x46" w 1" hex **
8.) Q-Workshop dice cup, red leather w/ dragon
9.) Six Castle Molds molds: #164, #84, #64, #87, #66, #83
10.) Leather bullwhip with belt holster
11.) Large hard leather clip-on belt pouch
12.) Battletech RPG core rule book
13.) Battletech introductory box set
14.) Q-Workshop red Celtic dice set
15.) Q-Workshop Pathfinder Chronicles Rise of the Runelords dice set
16.) Q-Workshop fudge dice, two sets, white and black
17.) Q-Workshop steam punk d20 and d6
18.) FUDGE dice, two sets, red and black
19.) Monsterpocalypse (game)
20.) Monsterpocalypse map pack
21.) Random pitcher full of dice w/ yield of 427 dice (breakdown below)
22.) Random cup full of dice w/ yield of 62 dice (breakdown below)
23.) Assorted individual D&D minis (breakdown below)
24.) Privateer Press bandannas, two black, two pink
25.) DDM guild mini boosters for Kevin and Desi (breakdown below)
26.) DDM guild minis from wins: Astral Giant, Giant Centede
27.) Assorted Paizo game books and accessories (breakdown below)
28.) Paizo subscription books I picked up at GenCon (breakdown below)
29.) GenCon 2011 messenger bag
30.) GenCon 2011 blue dragon T-shirt
31.) GenCon 2011 release your inner gamer T-shirt
32.) GenCon 2011 sweat jacket
33.) GenCon 2011 commemorative dice set
34.) Paizo goblin T-shirt
35.) Prince of Wolves Pathfinder Tales novel I won at Pathfinder Society
36.) Cathedral flip mat Desi won at Pathfinder Society
37.) Song of Ice and Fire RPG GM screen
38.) Paranoia: Internal Security, Flashbacks Redux, module***
36.) Rift game from shwag
37.) Magic cards pack from shwag

* I played Mouth of Milu FUDGE module this year and it was a Hawaii themed adventure. The GM had the table decked out as a Tiki bar. Was sweet!

** Disappointed because this one was supposed to be clear. Have emailed Chessex to see if I can get the real deal. UPDATE: Their response: "What's your address. I'll ship you one." Sweet!

*** A Funny Thing Happened on the Way to the Termination Booth

Random pitcher full of dice:
115 d20
102 d6
68 d8
88 d10 (18 d100)
19 d12
35 d4

Random coffee cup full of dice:
16 d20
15 d6
6 d4
5 d8
2 d12
18 d10 (4 d100)

Assorted individual minis:
Cloud Giant
Eldrich Giant
Fiendish Spider
Tundra Scout
Treant

Assorted Paizo game books and accessories:
Area of Effect Templates Miniatures Skirmish Package
Princes of Darkness
Seekers of Secrets
Friends & Foes face cards
Urban NPC's face cards

Paizo subscription books I picked up at GenCon:
Pathfinder Society Field Guide
Goblins of Golarion
Inner Sea Magic
AP #48: Carrion Crown, Shadows of Gallowspire
AP #49: Jade Regent, The Brinewall Legacy
Ultimate Combat (signed!)

Kevin's DDM Booster:
Dutybound Paladin
Stealth Mage
Master Shadowdancer
Human Fighter Lord
Mire Hound
(white d20 and line of sight extender)

Desi's DDM Booster:
Ragnara, Ethereal Hunter
Warforged Juggernaut
High Cleric of Sune
Rot Grub Swarm
Banshee
(white d20 and line of sight extender)

 - Posted using BlogPress from my iPad

"Hains" Prusa Mendel RepRap: Printing!

On schedule, the machine is now printing. The first attempt, as you'll see, wasn't perfect. It was, however, much better than anticipated. I'd been told that especially because of my nozzle selection, starting to print would be particularly difficult. But it worked. In the video I sound somewhat less enthusiastic than the results ultimately warranted, but I really was quite proud of the outcome.

Blue tape goes on to the print bed. Then I put some kind of catch for the leaking plastic, usually I use newspaper, while I heat the nozzle. I clear the nozzle of plastic and load the file into the printer host, called Pronterface. When I hit "print" the nozzle goes to "home" on all three axis, and then moves to the print area. There it goes through its routine until finished, at which point the nozzle is retracted a little bit. I then have to move the Y axis back to home and move the nozzle up a little more.

Peel the part off the blue tape, and there you have it. Looks like hell, but as first prints go it is actually very good, I'm told. It's supposed to be a mustache ring. It's called the Movember Ring and I downloaded it from Thingiverse to be printed on my machine. It's supposed to be a good calibration print because it has something round for judging geometry and something detailed to determine resolution.

Last night I succeeded at recalibrating the machine to produce some better results and changed over to a more simple object, a 1cm high and 2cm around cylinder. The first attempt was somewhat successful (pictured above), but a second try with a little tweak to get the nozzle up off the bed a little before printing started, that helped a lot and I got my best print yet (pictured at top.)

I've started live-streaming much of the activity with the RepRap. You can sometimes catch me live at my UStream channel. You can also follow me on Twitter and I post there when I'm about to start.

So three cheers. I'm printing! Soon I'll have it dialed in and will start printing parts for a child machine (i.e., another machine made by the first.)

But tomorrow I go to GenCon! Next few blog posts will be about that.