What You Should Know about RepRap 3D Printer Kits
A kit of ready to use parts can be one of the best ways to start with RepRap 3D printing. You should get all the parts you require, cut to size and ready to assemble. A poor kit includes unlabeled and unnumbered parts all mixed together, and includes no instructions or guidance about what to do next.
A good RepRap kit will include labeled bags of individual parts or fixings; a really great kit will even include the tools you require to assemble the machine — usually open-end wrenches or Allen keys. It's also likely that the kit will include a link to online build instructions, or to a section of the RepRap forum or Wiki where you can find out more about your kit and its assembly.
It's worth taking time looking for a RepRap kit; these come from all sorts of individuals and 3D-printing startup companies, and can have a very wide range of qualities and technical support backing them up. Ask questions about the kit you're looking at; see how long each vendor takes to respond, and whether they provide helpful advice or reassure you with their knowledge on the subject.
A good kit vendor is open about the materials used in the kit, and usually can point you to all the open-source information you need about the design. Some vendors are helpful even to the point of giving you a full list of materials for the kit, so you could make one (or many) yourself.
A poor kit vendor, on the other hand, aims to hide this information from you. He may just state that the kit is for a particular type of RepRap printer, try to convince you that it's a special version, or may omit specific details about the contents of the kit. If the vendor is not forthcoming with detailed information, move on to another supplier.
Kits can vary greatly in quality. Before you buy, know what to look out for from kit suppliers and ask questions if the information is not provided. Some of the questions you might ask include the following:
What materials have been used to produce the 3D-printed parts? and What is the fill density of the printed parts? It's good to know the material; some kit suppliers may choose to provide some specific parts made of ABS if they require a higher temperature on the machine than PLA parts.
In almost all cases, there is nothing wrong with using PLA for the machine construction; in fact, if the 3D printer design you have selected is using 3D-printed gears to drive the extruder or the motion of the machine, these should be made from PLA — they'll have a much longer wear life than gears made of ABS.
Look for suppliers who take care to offer the correct materials for the printer you have selected. You are looking for a minimum of 25 percent infill for usable parts. Extruder parts should be printed with at least 35 percent infill. Ask them to send over a picture if possible.
What electronics are being provided? Are they a RepRap standard or a custom development from the supplier? Electronics may not be provided in the kit at all; it's quite common for electronics to be bought separately from the mechanical kit.
Is the kit based on a recent release of the RepRap 3D printer you're considering?
If the kit has laser-cut parts, what material is being used, and how thick is it? Check with other sources and suppliers: Are they are cutting corners with reduced thickness or flimsier materials?
Are the linear rails provided in the kit stainless steel or just basic carbon steel? It's well worth paying a little more for stainless steel; parts made of it wear better and don't tend to produce as much black oil residue over the rods and bearings.
What motors are provided with the kit? Make sure they are true bipolar 4-wire motors; ask what their current rating is. Another thing to check with the motors that will save you time is whether they have cables with connectors already fitted onto the ends. Most commonly, NEMA17 motors are used for RepRap kits; these have a stated current rating depending on the overall length of the motor body.
You are looking for a minimum of 1.2 amperes (A). A more powerful motor will be rated at 1.7A; the maximum rating for a NEMA17 motor is around 2.5A.
Are plastic parts included? Some kit suppliers may not provide the 3D-printed plastic parts; so do check to see whether that's a separate option.
If you are buying a smaller 3D printer such as the Huxley, it's normal to have smaller NEMA14 motors supplied.
These should operate correctly for the lighter-weight machines, but bigger machines will often require bigger motors to move the heavier axis quickly — most commonly, NEMA 17 motors for home 3D printers. Much bigger NEMA 23 and 34 motors are often used for CNC milling machines and other subtractive manufacturing machines, and thermoplastic extruders almost always require a NEMA 17-sized motor to operate well and quickly.