Looking for a 'good' kit for my school's limited budget

I'm a teacher who wants to do two things with a 3D printer:
1) have a good starting project for our new robotics club
2) soon make trouble-free parts for robotics and for a class that will be sending an experiment to the ISS.
As we searched for a printer, we soon found that RepRap was the way to go.
Then the Prusa i3 seems to be the most actively used and constantly updated design. This has pros and cons - the pros are of course a very active community of user/builders for my students to join who can help them get it running and keep it running, and even update it over the next several years. The cons are that there is no 1 Prusa i3, and the kits are all over the map - so it is hard to figure out what exactly we should look for in a kit, IF we should go with a kit, and if a kit will do it, then who makes one that is worth the money?

Can I ask, on behalf of my students -
what are the list of features this community has learned are the most important to focus on in a Prusa?
what kits are the highest quality for the lowest price?
if not a kit, then how do you source all the parts to make the best Prusa i3 for the lowest price?
(ideally finishing under $800 USD after buying the parts and all necessary build supplies. We have a good soldering iron, but not much more.
should we look at another design entirely?

So far I'm learning that for any 3D printer, the biggest goals are: quality electronics and motors and moving parts; as rigid a frame as possible (steel, but other materials can be good depending on the design), the best possible extruder assembly, (Wade?) and a good quality (how to tell?) heated bed. With the Prusa, there are z axis issues that can be addressed with a quality frame and good quality long-shaft motors, (not sure what else to aim for there)
I know there is no one answer to these questions, but there is likely a range of answers we can learn from? I thank you in advance for your generosity, and for this vibrant group that I've learned so much from already!

Take a good look at the steel Makerfront kit. It has a full steel frame, which makes it very durable and easy to keep in spec and printing.

Hi,

I understand schools don't have a lot of money.
These days low price and quality does not often match...

You worry about price but not about safety.
I'm affraid safety is important when kids are around.
Most of reprap kits does not care about safety.
There's many ways to get an electric shock
or to get burnt with repraps,
because nothing is out of the touch,
neither the electrics or the heating stuff.

The I3 Berlin is probably the most "covered" printer,
because accent is made on design first.
A box type printer like the SmartRapCore can be safe too,
if you plan to add any door.

The kits :
I3 Berlin
SmartRapCore

You can save money following what we call a BOM (bill of materials).
Most of open source printers offers a BOM,
building instructions, and parametered firmware.
The components can be bought through the web,
and sometimes you can home made some.

Sources (BOM and information)
I3 Berlin open sources
SmartrapCore open sources

++JM

Edited 1 time(s). Last edit at 09/16/2015 06:17AM by J-Max.

I've found auto bed leveling to be an important factor in my projects. It makes running it much easier and less time consuming starting a print, which has a chance of one in 3 to fail using manual bed leveling, certainly at first couple of weeks.
I've also converted the 2 stepper motor design for the z axis to a single one using a looping timing belt and works very well. I've heard it can happen that the motors go out of sync, this will put one end higher than the other, no longer square to the print bed.

I like to print at a higher speed than what a non bowden setup can handle. So I use bowden to print faster and similar quality. This also opens up the possibility of adding a second nozzle so you can print with two materials in one print (two color, flex & ABS, soluble filament and ABS, electrically conducting & non conducting etc)

You could consider getting a cheap sunhokey, geeetec whatever and upgrade the parts that you think are important. It'll be a great learning experience, you'll definitely run into things you'll need to resolve. If that's not what you need/want, get a solid printer and pay the extra.

I'd go for a printer using Arduino/Rams 1.4 as this is the cheapest to run and easiest to maintain, though can be less easy to setup without the option of setting motor current programmatically. If one of both boards should break, you can replace them (some integrate both, with stepper controllers soldered on board). You can also easily replace stepsticks, which die easily if a motor is disconnected while the board is powered. During the first setup phase this can be a real pain.

If you want the option of ABS (better resists higher temperatures than PLA), HIPS, PETG, PA (nylon, great for strong gears and sleeve bearings) etc you need a heated bed. I can recommend a 24 PSU exclusively for the heated bed, it will heat up much quicker. RAMS 1.4 allows you to use a separate PSU for the heated bed.

If the only thing you have is a soldering iron (very important though!) I can highly recommend the following things, and don't be fooled it can add up quickly:
- Digital caliper for measuring the filament, calibrating e steps, x y and z printed lengths etc. It's also very handy to take measurements to interface parts to existing parts during design.
- A good LED swan neck light clamp to direct towards your prints. I love looking at my printer during prints, also looking for possible printing problems like backlash. I can stop the printer to prevent it from wasting filament if I can already see something is wrong.
- 0.05 to 1mm feeler gauges in steps of 0.05 increments. Useful to level the bed, unless you intend to use auto bed leveling.
- A (couple of) sorting boxes full of nuts, bolts, washers of different lengths and diameters. I use M2, M3, M4 and M8 most in my projects. Another for the 3D printer spare parts, stepsticks, bearings, thermistors etc.
- Buy spare parts. Most notably, stepsticks, spare motor, z rods, idlers, couple of meters of timing belt, thermistors, heater cartridges, nozzles, fans (only use maglev type fans, these can run vertical, sleeve bearing can only run horizontally), spare bearings, end stops. Especially the LM8UU seem to wear out quickly, and some may not fit snugly enough so get 5 or 6 more and compare which ones are tight. Other bearings that can come in really handy: 608ZZ, 623ZZ, 624ZZ.
- Buy different kinds of bed adhesion. Most used are: extra strong hair spray, PVA glue (normal school glue, water soluble), blue painters tape 3m, vinyl table cloth on glass plate (I'm really fond of this stuff, PLA and ABS stick to it very well). Find out what works best for you and a school environment.
- Buy some lithium lubrication grease for bearings. Also rub it on smooth rods to protect them from rusting. Don't use oil based lubricants on bearings. Grease will dissolve in oil and oil runs out of the bearing easily leaving too much room in them making them resonate more. It's noisy and may cause artifacts in prints.
- glass cutter to cut your own glass plates. You can also buy borosilicate plates of course, but cheap picture frame glass or mirror also works well.
- Tools like micro (nail) and normal files, drills, screwdrivers, pliers, needle nose stainless steel tweezers (really useful for removing stray filament from prints while the printer is running).
- A drill press also comes in handy to drill out bolt holes which tend to print out smaller than designed.
- If your printer comes without pre-crimped/soldered connectors, get some heat shrink tubing of different sizes and a heatgun. For projects with stepper motors and/or servos I'd get male and female SIP connectors. These can get expensive quite quickly depending how much you'd need. A crimping pliers and crimping connectors can also be costly.
- Some flat cable for making connectors/cables. Useful for arduino/robotics type of projects to interconnect stuff. It's a great practice to make connectors on everything instead of direct soldering. It's great for trouble shooting.
- double sided velcro cable ties, infinitely reusable and easy to add more wires as and when needed while keeping things tidy and out of the way.
- couple of 8mm Threaded rods, as a construction material, I used it for a filament spool holder with 3D printed parts and 608zz bearings, spring for a clamp, a great first project
- Rubber mat for reducing vibrations of the 3D printer.
- Network IP camera for monitoring the printer during its long print runs (ie during the night). Also fun to forward this toward a live video stream service for people to watch and share.

Some more tips:
- When you can print, first thing to do is print spare parts for the x carriage, x idler and x motor if you go for a printed version of the printer. This has saved me many times
- Don't let the kids print with the printer, there are many steps in the procedure to get prints started properly, kids may not have the patience to follow the necessary procedures.
- Expect about 20-40% of the time spent on the printer to be maintenance. Belts may stretch a bit and need tightening, bearings need replacing, calibrating and adjusting the bed level (that's where auto bed leveling comes in handy) etc. Nozzles can clog up, hobbed bolt eating into the filament etc. Printed parts may fail and needs to be replaced etc.

Sorry for the information overload