Things people told me which I wish I had listened to more attentively when I started building a RepRap 3D Printer
My RepRap is a 1st-generation Prusa Mendel http://reprap.org/wiki/Prusa_Mendel_(iteration_1) which was pretty much the bee's knees in affordable DIY 3D printing back in August 2011 http://julianh72.blogspot.com.au/2011/08/first-post-inspirations.html.
I bought a kit of plastic bits and "vitamins " (nuts and bolts etc) on eBay, and self-sourced all of the other components (stepper motors, electronics, etc). The buy-and-build process was itself instructional (and fun!), and about two months after construction commenced, I had a workable 3D printer in operation. http://julianh72.blogspot.com.au/2011/10/cheers.html
The Prusa Mendel and its predecessors truly embodied one of the core philosophies of the RepRap Project: RepRap is short for Replicating Rapid-Prototyper; that is, the 3D printer can (almost) build itself. To this end, the maximum possible number of components were made from 3D-printed plastics, right down to the z-axis couplers and axis bushes.
These days, if you start a similar adventure, you are more likely to try building a 3rd-generation Prusa i3 http://reprap.org/wiki/Prusa or similar. To the uninitiated, it is hard to see how the Prusa i3 is directly related by just two generations from the Prusa Mendel, but for those of us "in the know", the family heritage is obvious.
- You NEED proper mechanical linear bearings on all axes - 3D-printed PLA bushings are a nice philosophical concept, but realistically, the motion will be MUCH smoother and jitter-free if you install linear bearings (LM8UU or similar). Do yourself a favour, and buy a kit which uses them (most modern kits do), of else, print yourself some replacement carriage parts which are designed for LM8UU bearings instead of PLA bushings, and install them as soon as possible. http://julianh72.blogspot.com.au/2011/11/smooth-operator.html
- You NEED a heated print-bed. Yes, it is possible to print on painter's tape etc, but life is MUCH easier when you have a heated print-bed. http://julianh72.blogspot.com.au/2011/12/hotbed-of-intrigue.html And this leads us to ...
- You need a power supply with heaps of capacity. I started off with a hacked ATX power-supply http://julianh72.blogspot.com.au/2011/08/my-parts-list-power-supply.html which I thought had enough capacity (16 amps @ 12 volts), and while it did work, it turned out that it had trouble maintaining full supply voltage under heavy load. I have replaced it with a more robust true 15-amp sustained (18-amp peak) power supply http://julianh72.blogspot.com.au/2015/10/powertech-mp-3800-0-24-volt-power.html , and it runs much better now.
- Get rid of the 3D-printed Z-axis couplers, and replace them with engineered metal shaft couplers. You can pick up 5 mm x 8 mm aluminium couplers for a couple of dollars on eBay, and I have found that they grip the smooth stepper motor shafts much better than a plastic clamp - of which, I printed and installed quite a few design variants http://julianh72.blogspot.com.au/2011/11/smooth-operator.html. (This is particularly important for a machine like the 1st-gen Prusa Mendel where the X-Axis is suspended from the Z-Axis motors; possibly less of an issue on the Prusa i3, where the motors are at the bottom, so the couplers are in compression, not tension.) They also run MUCH smoother, as they are able to take up the angular and offset errors between the motor and the threaded rod with a more reliable spring stiffness than the plastic clamp couplers.
- Get yourself an LCD Controller, like the RepRapDiscount Smart Controller http://reprap.org/wiki/RepRapDiscount_Smart_Controller - this will allow you to print without a computer attached, freeing up desk-space, and also removing one link from the failure chain. These can be bought very cheaply on eBay - highly recommended.
- If you are running an old-generation plastic-bodied print-head (PTFE and / or PEEK), replace it with an all-metal print-head with a heat-sink and fan. These run MUCH more reliably than the old PTFE-bodied print heads, and are also much more physically robust, and are able to withstand the occasional (and inevitable) print-head crash.