RepRap RAMPS Build

I’m building a RepRap Mendel because one bot just isn’t enough.

The brains of my new bot will be a RepRap Arduino Mego Pololu Shield (RAMPS) because it’s a design that manages to be small, powerful, and line-replaceable. The biggest plus I can think of over the Makerbot electronics is that RAMPS fits the same functions into a much smaller package. That’s not entirely fair, because the MBI Gen 4 electronics are designed to be more flexible in potential applications than RAMPS, but I’m not looking for flexible at the moment. The biggest plus over the RepRap Generation 6 electronics is that the most important pieces are easily replaceable.

So, lets get to it. I found the Arduino Mega (2560) on Amazon, got the DIY RAMPS kit (v1.2) from Ultimachine and found some Pololu stepper drivers in stock at Robot Shop.

[update: I can confirm that this build works for running steppers from the Repsnapper control panel, but I'm still waiting for endstops, so I haven't tested that function yet.]

[update: I can confirm this build works for running steppers, using min and max endstops, and sensing/controlling the extruder temperature. I don't have a heated build platform, or a build cooling fan, so I can't test those features.]

1. Get out two 4.7K resistors and seven 100K resistors.
2. Solder them into place.
3. Get out the 10nF 100nF capacitor and LED.
4. Solder them into place. The LED’s polarity is not marked on the board, but the RepRap wiki instructions say the short lead goes closer to the bottom of the board.
5. Get out several double stacked headers.
6. Cut them into seven 2X3 units.
7. Place them in their respective locations.
8. Use tape to hold them in place. Now solder them drama free. 
9. Get some single headers.
10. Cut off a single 1X4 unit.
11. Place it in the T1-T0 location. Use the tape trick to solder it in place.
12. Get out four 1X16 female headers.
13. Place them in the appropriate locations.
14. Use a couple long strips of headers to keep the female connectors aligned and in place while you solder them.
15. Get out the power terminals.
16. Also, the little push button switch.
17. Solder them in place. Be generous with the solder.
18. Get out the Arduino Mega and associated headers.
19. Cut one 2X18, one 1X6 and 5 1×8 units (it doesn’t matter if some of them are made out of multiple pieces).
20. Insert the headers into their respective locations on the Arduino Mega board.
21. Put the RAMPS shield down on top so that it seats nicely.
22. After you’ve soldered all the headers in place, they’ll be perfectly lined up with the Arduino Mega.
23. Get out one 100uF capacitor and two 10uF capacitors.
24. Solder them in place. The polarity is marked on the board.
25. Get out the three N-channel mosfets.
26. Solder them in place. The proper orientation is marked on the board (a thick white line).
27. Get out the fuse and diode.
28. You have to install the fuse, but the diode is optional. According to the RepRap wiki the diode connects the RAMPS power terminal to the Arduino mega board. Without the diode you can theoretically run 35v through the steppers (more torque). With the diode you are limited to the 12v the Arduino is happy with (theoretically 20v, but don’t push it).
29. Make yourself four 1×4 header units.
30. Insert them in the appropriate locations next to the female headers.
31. Grab four Pololu break out board kits and make two 1×8 header units. Hopefully you don’t end up with 3 out of 4 kits containing 1×15 strips of headers instead of 1×16 (like I got). But, if you do, you should be able to make up the difference with some scraps from the RAMPS kit.
32. Insert the eight 1×8 header units into the 1×16 female headers on the RAMPS shield.
33. Set the four Pololu breakout boards on top. Now you can solder everything together with the correct alignment.
34. Remove the four stepper drivers and get out twelve jumpers.
35. Install three jumpers underneath each stepper driver for 1/16th stepping (default).

The Search for a COTS Nozzle

For anyone interested in improving existing 3d printer designs, or creating new ones, the extrusion nozzle is a real issue. The biggest problem is that the nozzle can’t be made out of the same material the bot prints in; it will either liquify at extrusion temperatures or bond with the material being extruded. Additonally, the nozzle has to meet very particular standards of size, shape and strength.

It’s entirely possible to machine a custom nozzle that does the job quite well. That’s what everyone has been using so far. But the level of machining required is prohibitive. Just try drilling a 0.5mm hole if you don’t believe me.

What we need to find is a Commercial Off The Shelf (COTS) nozzle that is already being mass-produced for some other purpose. It doesn’t necessarily need to be a drop-in product, a little light machining (like tapping threads) would be fine, but it does need to be:

• Resistant to heat. ABS is extruded at around 220*C, and some people run a little bit higher.
• Rigid. It needs to resist quite a lot of pressure from the extruding plastic.

Also, it would be nice if it was:

• Cheap. Duh.
• Interchangeable. Some preexisting threading or method of attachment.
• Doesn’t stick to molten plastic. Infrequent, if any, need for cleaning.
• Variety. A range of nozzle inner diameters would be great.

I don’t think anyone’s found anything like this yet, at least not with an inner diameter under 1mm, but here are some ideas that might work.

• Graphite Ferrule. These things are used in gas chromatography. They’re described as “soft” but they are manufactured with a range of diameters in appropriate sizes and are made out of pure graphite, so they don’t melt until 450*C.
• Capillary Tubes. These things are used in liquid chromatography and other advanced stuff. They can be made out of all kinds of different materials.
• Ceramic Tubes. More of a range of things. What’s important is that they tend to be manufactured in sizes down to and below 0.5mm inner diameter.
• Needles. Again, a range of things. But a few examples for different purposes like veterinary medicine, dispensing materials, and inflating balls.
• Flow Control Orifice. These are used to control the flow of liquids or gases through pipes. They’re all made out of brass or steel, they’re tiny, and they’ve already got pipe threads.

If we can’t find anything that works as-is, then we have to move on to additional steps that take a COTS nozzle from almost right, to totally right. Some examples might be:

• Solder. High-temperature solder (usually lead free, possibly with silver in it) could be used to close up an overly large inner diameter, and then an appropriate hole could be drilled through the solder.
• Cement. Some sort of fireable clay, mortar or concrete type stuff could, once set, resist the temperatures (and maybe the pressures) involved. Maybe it could even be formed around a wire of the appropriate diameter, so when it sets the hole remains and no drilling is necessary.
• Multi-part. Perhaps machining appropriate grooves (.25mm-1.5mm) in two matching surfaces, and holding them together, would work.
• Tapping. Threads are great for attaching one thing to another, particularly if you might want to detach it in the future.