A 3D Printer for rapid prototyping is an expensive purchase with retail models beginning at $15,000. Going the DIY route in creating a 3D printer can save tens of thousands of dollars while creating a machine that's capable of building high resolution 3D objects out of a variety of easy to work with materials - all for a price that falls well below the $1000 mark.
3D Printer Basics
The process of 3D printing is heavily based on 2D printing flatbed methods. In fact most DIY 3D printers are made from converted flatbed printers with the addition of an additional axis. Because of this, the print process is much the same as with an unmodified 2D printer.
Like a 2D printer, the horizontal X and Y axis motion of your printing element can be moved using the flatbed's printer belt drives and motors. By using the flatbed's equipment, you should be able to print each layer of your 3D object with the same level of detail of a 2D print. The vertical Z axis which gives you the 3D print capability will require most of the conversion work for your DIY project.
The printed object itself is created by binding print media material together through a series of separate layers. You design your object using 3D modeling software like 3D Studio Max or Maya, and then send it through a 3D printing program like ZPrint. The program slices the object into layers of uniform thickness for printing a single layer at a time. The more you can control the movements of the various elements of your printer the higher resolution you can print a 3D object in gaining in object detail.
Z Axis Modification
To convert a flatbed printer into a 3D printer you need to do is adjust your printer bed. Making the bed mobile in a tightly controlled downward motion is necessary for printing the multiple layers. This has have a stop and start ability, controllable in extremely small increments. Each downward movement enables the printing of an additional layer which in turn builds up your 3D object.
Use a microcontroller to provide the vertical movement ability, programmed with high precision servo PWM code, like that generally used in remote controlled models. The Z Axis will be controlling a motorized bin for holding your materials, and depending on the size of your created objects this materials bin can be quite heavy when filled. Design your Z axis accordingly, using a strong stepper motor for movement.
Once you get the flatbed moving along the Z axis you'll need a system for providing a new layer of print media for each print run. Print media used in the 3D process tend to be either powders or granular in nature and must be spread across the previously printed layer evenly and thinly in order to print the next layer of your object. You'll need to create a mechanism for spreading a new layer of media to print on. This new layer must be applied quickly so the process of printing can create connected layers building a single object.
Choose from a variety of plasters, sugar, or even low melting temperature plastic for your media. The media you use for your printer is largely determined by the printer design. This includes the way you've chosen to extrude each layer, as well as the way you've chosen to bind layers. The more detailed you want your object to be, the finer the material you should use as a print media.