"Hains" Prusa Mendel RepRap: Building an Enclosure, First Steps

Slowly but surely I'm putting together a box to house the "Hains" Prusa Mendel RepRap machine. The enclosure will have a nesting top secured along the bottom with 20 #6 screws and custom designed (and printed on the "Hains") nut holders. There will be a windowed door on the front with a lock to keep idle hands off it until they can be properly trained. I'm thinking slim windows on the right and left, and a 9" square window in the back. It's all MDF except for the 1" hardwood square dowel used in the frame of the base. The back will have an access port for the power supply, probably with a printed faceplate, and there will be a special on/off switch inside the enclosure. For special effects I'm going to mount some PC lights inside and give it that cool, modded computer look. The finish will be ultra gloss black.

Ran into a bit of a problem last night as I discovered that I'd glued on the wrong trim piece. Had to chisel it off, and I'd done such a good job laminating it to the other wood that it was like carving off a solid hunk of wood -- very hard to do. I did eventually manage to get it reasonably close to normal again and attached the correct piece of trim. I can really only add one piece at a time so it'll be three more days until I get the base finished and can move on to the top.

"Hains" Prusa Mendel RepRap: Goes On a Field Trip

The "Hains" got let out of the house for the first time last Saturday when we attended a meeting of RepRap enthusiasts and makers at the Kalamazoo Air Zoo. That's me stalking around in black, and the "Hains" is there on the table being inspected on the left by the machine's namesake herself. New member Chris is there on the left next to the pizza. In all we had nine people at the meeting. Quite the turnout!

Alan Hollaway (on the right) organized the meeting through the RepRap Michigan Google Group and through the Kalamazoo Maker's Guild Meetup Group. I thought he was so good at putting this meeting together I made him an assistant organizer for the Meetup group. Kyle Mendez (center) wants to build a RepRap the size of a room. John de Longpre (on the left) came down from Grand Rapids and these are his pictures. 

Dean Piper (on the right) also brought his machine. He's sporting a new MakerGear Plastruder and a custom heated print bed under glass. He hooked up to the projector and gave everyone a demonstration of printing and the software.

I printed a whistle (which didn't turn out great and broke) and Dean printed a RepRap Merit Badge.

"Hains" Prusa Mendel RepRap: Printing Prusa Parts

The "Hains" Prusa Mendel RapRap 3D printer has begun to replicate. It's printing parts for the "Desmonda", the second machine I will build. As you may be able to tell from the photo above, the quality is very good, and it's about time!

That quality was hard won and well earned. I've been lax in posting to the blog because I've spent weeks  and weeks tweaking, fixing, modifying, calibrating, and test printing, often putting in 14-16 hours a day. You could say there have been some bumps on the road.

Here are the highlights of the challenges I've been dealing with over the last month and a half.

Temperature

The first prints were such a disaster (see Movember ring first print, above), I now know, because I was setting the temperature too high. I set it to 210 at first, the default temperature for PLA plastic. Then I read that setting it at 185 was a good starting place. Even at 185 deg. Celsius, though, the plastic was oozing out of the nozzle like crazy when idle, and printing a real mess. Sometimes it would even burp plastic, which I came to realize was gas released from the plastic when the temperature is too high. Essentially, it was boiling. Lesson one: the thermistor (temperature sensor) is not calibrated. So, when the computer is set to 185, that doesn't mean the nozzle is actually 185 deg. I started lowering the temperature, and until I got down to 149, the prints got better every time I did a test print. I now print with it set to 152.

Bearing Upgrades and Modifications

The pulley design for the RepRap turns out to be quite problematic. The metal fender washers don't move in the default design, so the belt rubs up against them and causes a lot of friction. You have to turn the motors WAY up to counter it. It also makes things irregular and generally hard to manage. I used a combination of techniques to fix this problem. For the front and undercarriage pulleys I loosened the nuts on either side of the fender washers so the washers could rotate freely, but cemented the nuts in place with loctite. On the back pulley next to the motor I cut a nylon washer in half and glued it back it together  inside of the fenders. They are low friction and rotate when they need to. But that's an ugly hack. The X-end idler could be taken apart, so I upgraded the pulley there. On Thingiverse.com there is a bearing upgrade object, and it comes standard on machines from MakerGear and others. Lesson two: these upgrades will replace the fender-bearing design on every machine I make from here out.

Bad Parts

As I start to print my own RepRap parts, and after having worked with the parts I got from eBay all summer long, I've come to kind of loath them. So much of my trouble has come down to poor quality parts that I couldn't guess how many hours they took up in testing and tweaking. Notice the crack in the pulley gear in the photo above? Yeah, now you start to see why this has taken me so long, right? In addition to bad gears, the X motor mount and X end idler are really quite poor, causing the smooth rods to be out of alignment with each other, and I suspect, not entirely perpendicular to the Y axis. The extruder idler came small and out of shape, and I've had to bore it out a few times to make it so the extruder won't bind. Lesson three: get good parts! The guy I got the parts from is well intentioned, I have no doubt, but I think these Makerbot people aren't the best candidates for producing quality parts. They're the type that are attracted to the instant gratification (or as much as can be had right now) of an easy kit they can throw together in a weekend. The RepRap people, on the other hand, tend to be kind of obsessive about their machines because it takes so much to get them working right. You have to know a lot more to use a RepRap. So, I would say that parts made on a RepRap will tend to be higher quality, as a rule, than parts made on a Makerbot. MakerGear has some really fantastic parts, and if I had to start over again I would have bought their parts. I would have bought their kit, frankly, but that's a point I'll come to shortly.

Wrong Parts

This was probably the biggest problem of the entire project, from start to finish causing me headaches the whole way. First there was the issue with the stepper motors. The parts list I got from the guy on eBay included a link to a supply of stepper motors, except they were the wrong motors for a RepRap. They weren't the right size (dimensionally) and they didn't have enough holding torque. Then there was the matter of fasteners. I didn't know what I was doing, for a start, and then the parts list I got from the eBay seller had parts for an SAE Prusa, but a metric Wade's extruder. I got all confused and now have a large assortment of various screws and nuts that weren't of any use to me in the project. The pulley gears were at the heart of it, in the end. I spent weeks of calibrating after the first print, all of it wasted because the eBay seller included a link to the wrong belt. It's the kind of belt that is used overseas, and is metric. So they didn't match the printed pulleys that came with the parts. I first bought replacement printed pulleys of the same size because I thought the problem was bad parts, and then bought the manufactured pulleys when I finally figured out the problem was wrong parts. Lesson learned: don't believe the parts list supplied by the eBay seller. Do your homework, hard as it is, and understand which nuts and bolts you'll use by walking through the instructions one step at a time and counting it all up.

Belt Tension

While trying to hunt down the backlash problem caused by using T5 pulley gears and XL belting, I learned a lot about belt tension. In the process I managed to pull off a short and messy print I could turn around and put to use right away. It's called a Y-tensioner, and is probably the first thing I downloaded and tried to print off of Thingiverse after the Movember ring and test cubes. It allows me to adjust the tension of the Y axis belt, the most inaccessible one, with a hex key without having to take the print bed off. The X axis belt has to be done the old fashioned way, and boy what a pain that is! Lesson learned: yes, there is such a thing as too tight on the belts. I'll leave it at that. Suffice is to say that you're shooting for a Goldilocks zone when it comes to belt tension: just right.

Z-Constraints

My prints were pretty good, but there was room for improvement. Early on someone had pointed out to me that it appeared that I had quite a bit of wobble in the prints, meaning that the layers didn't stack right on top of each other exactly. That can happen when the leadscrew for the Z axis (up and down) orbits a bit because the motor shaft doesn't line up exactly with the center of the leadscrew and the nut in the X ends. In my case, you may have noticed in an earlier post I mentioned that the Z clips I got from the eBay seller snapped during assembly. Well, they did, and I replaced them with rubber tubing (thanks Tonokip) but the leadscrews definately were orbiting. ScribbleJ, who has helped me a ton via IRC, designed these Z axis constraints that I printed up and added to the machine. Lesson learned: use MakerGear modifications and their design to eliminate Z wobble from the start.

That's a taste of what it took to get to printing well enough to make Prusa Mendel parts for "Desmonda" on the "Hains". I'll tell you about my software calibration journey another time. The test cubes! So many test cubes!!!

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]