I am a teacher running an "innovation greenhouse" club -- basically a group that

I am a teacher running an “innovation greenhouse” club – basically a group that encourages middle schoolers to get into programming, technology, design, and electronics through a variety of projects.

I have been looking at a reprap project to get kids into 3d printing, as the process of building the printer is one of my main goals to share with the group.

I took note of +Josef Prusa’s forthcoming RepRap book in the post below, but where should we be focusing our research on this? Which model will give us flexibility and approachability on this project?

In general, the differences in the RepRaps are mostly about number of parts and cost of said parts. So if you can afford it, the most recent RepRap iterations (Prusa Mendel, etc) will give a complex build with good quality results.

If you want something that would be simpler to build, or cheaper, then the RepRap Wallace, or the Printrbot, would be similar builds, with reasonable quality results, and fewer parts with reduced complexity relative to the Prusa.

The Huxley is an alternative path to a simpler, smaller build prior to the Printrbot/Wallace group, so I don’t think I would recommend it at the moment - either build a full size Prusa, or a smaller Printrbot/Wallace if you need a smaller or cheaper bot.

The MendelMax is basically the same as the Prusa Mendel, but easier to build and more stable. It uses extruded aluminum parts, however, and is not self-replicating, so possibly not as much of a learning/teaching opportunity.

The RoStock is an interesting machine with similar properties to the Mendel’s in terms of being constructed from printed parts and vitamins, but is a newer design - might be fun and more interesting to kids that like robotics, but there is less support and experience available out there, and the mechanics of its operation are harder to explain and demonstrate, while perhaps being more interesting and offering more opportunity for experimentation (i.e. you are not dealing with a simple grid anymore, where a simple instruction to spin one motor causes a simple motion in one dimension, as with a Prusa).

Most of the other printers out there involve laser-cut parts for assembly (more akin to building a model plane or the like) and are not self-reproducing and thus not really RepRaps. (Note, this is also true of the non-printed Printrbot LC, etc.)

I would personally say to go for the Printrbot/Wallace - as a smaller, simpler bot to build, it would be more feasible for you to do multiple builds, i.e. have each new class build a new one each year, so that it is not merely the first class that gets the experience of building one, and it would be more within reach for the kids to feasibly replicate one for themselves.

As to deciding between the two, I’m not sure if there are sources out there selling Wallace kits or not, so I guess that might depend on whether you want the kids to have the experience of trying to find and source parts, in which case you can go with the Wallace, or merely of building the kit, in which case you can go with the Printrbot.

Hope that helps!

Tremendously – thanks for the thorough explanation and the in’s and outs of the 3d printing world!

If I managed to scrape together the cash for something like the Mendel, and worked with a pretty savvy group that I have now (some have built their own at home) – can I use that to replicate parts for a Printrbot/Walalce build later on?

Yep, in either direction. A Mendel can print the parts for a Printrbot or Wallace, and a Printrbot or Wallace can print the parts for a Mendel. The difference is that a Mendel can probably print a single plate with all the parts for a Mendel, Printrbot, or Wallace, whereas a Printrbot or Wallace would probably need several plates to print the parts for a Mendel. At least, that is the impression I’ve gotten from various sources.

Build Volumes in mm:

RepRap Prusa Mendel 200x200x100
RepRap Huxley 140x140x100
Printrbot - 150x150x150 (theoretical, in my experience you lose at least a half-inch on X, so probably closer to 150x140x150)
RepRap Wallace - 200x200x140

Note that I just checked, and the printed Printrbot is no longer being sold by Printrbot.com - just the lasercut versions. But as with the Mendel printing the others, a lasercut printer can print the parts for a true reprap - machines that can do this are called RepStraps in RepRap lingo.

Given that, the Huxley may be the cheapest one for which you can get a full kit to build that is a true RepRap, and not a RepStrap.

Your advice led me to a fascinating black hole of new questions and ideas. Maybe you won’t mind clarifying for me one thing?

What’s the difference between a RepRapPro Mendel and a Prusa Mendel or MendelMax?

Ok, let’s see:

The Darwin is the Granddaddy of them all, the big square one, with crossed supports, that they all hail from.

The original Mendel, or Sells Mendel, was the successor to the Darwin, and the originator of the triangular shape, adopted because the rectangular shape was hard to stabilize, I think.

The Prusa is the parent model for the current generation. It is basically a Sells Mendel with evolutionary improvements, and is based on plastic parts linking threaded and smooth rods, bolted together.

The Huxley is a Prusa Mendel redesigned to be smaller, while retaining the basic shape profile - the original intent here was that this should be a faster to build, cheaper printer to increase the speed of RepRap replication (remembering that replication is one of the original design goals and intents behind the RepRap project), while the Mendel itself would evolve to be the flexible, multi-material, multi-purpose machine.

The MendelMax is basically a Prusa Mendel constructed by replacing rods and plastic with extruded aluminum - this improves rigidity and stability, and should translate to better prints. It is supposed to be easier to build and alter, as well as having fewer overall parts and simpler construction.

The RepRapPro Mendel is a Prusa Mendel evolved differently - basically instead of striving for an easier build or more rigid construction, here the goal is greater flexibility. The RRP is intended to support multiple extrusion heads, allowed mixed material or multi-color prints (ala the Makerbot Replicator).

The Printrbot/Wallace is a RepRap descendant that drops the triangle base in favor of an open riser - less stable and prone to wobble at greater heights, but much cheaper to make in terms of parts and vitamins.

Btw, http://reprap.org is the go-to place for discussion of benefits, pointers to places to obtain parts, kits, etc.

Consider me schooled on the evolution of the RepRap projects! I have been browsing the wiki and the forum, but nothing summed it all up quite as well as this comment.

Many thanks!

Highschooler here. I don’t think focusing the class on actually building a printer would work out well. You mentioned some kids already did that at home in your class, which I completely believe. I built a Sells Mendel 2 years ago when I was barely 15 and it only took 3 or 4 weekends to get it to make ugly cubes, and maybe a month on and off after that to make it print pretty nicely. I don’t think you can draw out the build process to anything near a year, particularly because the new designs are so much quicker, and you’ll have a whole class full of hands working on different bits of the bot at once and a few of your kids have already been through it once before. I’m building a second one for my school in a few weeks, and I expect to have it printing within 2 days of when the last part arrives in the mail.

If you want to teach a class around improving the printer rather than doing other cool stuff and using the printer as a tool, I would suggest you let kids develop their own toolhead. The toolhead is the bit that gets moved around over the bed to do whatever the machine does. So on most 3d printers it’s a plastic extruder.

With toolheads you can print chocolate, mill foam or wax, etch simple PCBs, and do just about anything else you can come up with.

Plus, different toolheads require slightly different software to work, since a milling tool has to start from the top while an extruder has to start from the bottom. So it could be a nice segue into the programming side of the machine.

And of course, toolheads are mounted with 2 screws 50 mm apart, so no matter how badly one group’s project breaks, all it takes is unscrewing 2 screws and the machine’s ready for the next group while the first fixes theirs.

You could also work yourself on improving the rest of the machine, and when you find something to improve include the whole class in the process of actually doing that improvement.

I just feel like the actual workings of the Cartesian motion bit of the machine are too finicky to let kids modify all willy nilly.

Nick, I appreciate the feedback – it’s not a class, but a club that meets a couple of times a week – the plan is to break into small groups to work on the printer, but not to drag out the build project over the course of the year or semester.

I appreciate the rest of your ideas, and comments! I am looking forward to sharing what we get up to in the coming months.