3D Printer, Extruder, SCARA 3D Printer

The Cold End, Bowden Style

The idea behind this cold end is that it too is well placed behind the sheet metal. Here is the inital concept. Because this printer will eventually have two extruders, it was important to build them in such a way that fillement could be fed from either side. This is because the extruders will be mounted on each side of the printer. This can be best shown in the Solidworks rendering below.

Assem1.3

 

Note the location of the light gray stepper motors to each side of the main geared stepper motors. These are the locations for the extruders.

Assem cold end2

 

The hobbed gear is purple in the rendering above. The bearing carrier is green and the main block is the brown part. Notice the small hole in the main block. This is where the filemant will passes through. There is an identical hole on the other side resulting in the feed direction being reversable. This cuts down on the number of different parts that must be designed and machined.

IMG_0267

Machining the bearing carrier.

IMG_0268

The stud and the bearing carrier are all one part. This decreases complexity and also the number of parts made.

IMG_0271

The main block with the bearing carrier installed.

IMG_0274

Resting on the stepper motor. Note that the bearing carrier is upside down in this picture to better illustrate the assembly.

IMG_0275-002

This is the proper orientation for the cold end. The carrier is pushed from right to left against spring compression in order to load filament. There is a spring pushing against the central post which returns the bearing carrier and maintains compression on the filament. It is adjusted through the use of a set screw. The NEMA 17 stepper motor is mounted using an L bracket purchased from Phidgets.

IMG_0283

And finally, here is the cold end mounted to the sheet metal. Four 4-40 bolts are used to hold it in place. The compression adjustment set screw is more clearly seen in the picture above. The other cold end will be mounted in the mirror position on the frame. Though the holes for the filement to pass through  have not been drilled yet, they will allow the PTFE tubing to pass behind the geared stepper motors and come around from the opposit side, maximizing lenght so that the filament does not experience too sharp of a bend on its way to the hot end.

Advertisements
Standard
3D Printer, SCARA 3D Printer, Sheet Metal

Front Facade

A bit more sheet metal work is in order. The front facade is necesary for both aesthetics and functionality. It helps to stiffen the frame in addition to enclosing the electronics. Made from the same 22 gauge mild steel used for the frame. Liberal use of machinist blue was needed for scribing the lines for the sheet metal brake.

IMG_0246

The front is then marked with a Sharpie for the area of material needing removal in order for the arms and platform to operate. Holes were drilled at each corner, then a nibbler was used to follow the lines.

IMG_0247-001

 

Finished with the sheet metal. The facade neatly encloses all the electronics.

IMG_0249

 

Standard
3D Printer, SCARA 3D Printer, Sheet Metal

Sheet Metal Frame

A large part of making this 3D printer portable is the ability to stow all the components in a protective shell. The frame also must be rigid enough to mount the components within. Starting with a sheet of 22 gauge mild steel, machinist blue was applied and the dimensions were scribed on the surface. A few minutes with the electric shears and the basic shape began to emerge.

IMG_0191

Using the sheetmetal brake to form the sides. The depth of each side is 2.5 inches.

IMG_0192

Holes for the arms to rotate through were cut into the back. This will give the arms a larger range of motion so that more of the platform can be utilized.

IMG_0203

Laying the all the parts in the sheetmetal frame to check the fit. The Arduino Mega and RAMPS 1.4 board will sit along side the power supply unit. In the picture below the platform is shown in its stowed position.

IMG_0196

Platform in printing position. The Z axis motor is sitting in its eventual orientation. The bracket holes have not yet been drilled for the stepper motor mount. The Z axis will ride on a 5/16″ x 18 allthread rod.

IMG_0194

Holes drilled throught the sheet metal and arms mounted to the frame.

IMG_0204

Standard
3D Printer, SCARA 3D Printer, Uncategorized

Build Platform

The build platform must be as rigid as possible yet still retain the ability to fold for storage. Two bearing blocks each hold two linear bearings for the 5/16″ diameter stainless steel rods to pass through. They are machined from 1 inch 6061 square aluminum stock. The platform is held in place perpendicularly by two arms which pivot on 1/4” bolts. The arms are in turn held with removable braces. This allows the platform to rotate down and lay flat for storage when the braces are removed. The aluminum plate for the build platform can be seen in the background of the following picture with a caliper resting on it.

IMG_0144

The build platform consists of a 1/4 inch thick 6061 aluminium plate. The bottom was machined to lighten yet retain stiffness.

IMG_0181

Because this milling machine only has 6 inches of travel in the Y direction and the final build platform is 8″ x 9.5″, the machining process was broken into two operations. First one side was machined as can be seen above. Once this was complete, the plate was then rotated 180 degrees, and taking care to square up and index the part using a dial indicator and an edge finder, the plate was reclamped securely and the operation was completed using a 3/16″ three flute carbide end mill.

IMG_0182

IMG_0184

And finally a view from the bottom, all bolted up. Four 8/32″ bolts are used to secure the plarform to the arms.

IMG_0185

A cross brace can be seen in the photo above reaching from one bearing block to the other. The hole in the center is where the threaded rod for the Z axis will pass.

Standard

First to be machined are the upper and lower arms. The Solidworks files were converted to STL and ran through MeshCAM and Gwizard to generate the Gcode necesary for the CNC milling machine.

IMG_0114

The arms are held together with 5/16 inch stainless steel bolts. Each elbows uses two 608 bearings to provide silky smooth motion.

IMG_0318

IMG_0113

The all important spring. This spring pretensions each arm. This in turn pulls the backlash to one side of the gear train. The spring is sufficiently powerful that when the arm changes direction from clockwise to counterclockwise, no slack is introduced into the system. This in turn assures that the end effector which in this case will be the hot end, moves in a precise and predictable manor. The threaded hole contains a set screw which holds the arm to the stepper motor shaft.

IMG_0117

 

Each stepper motor is a Bipolar Nema 17, with 51:1 gearboxes attached. They were sourced from a company called Phidgets, along with the brackets.

3D Printer, SCARA 3D Printer

The Arms: Let the machining begin

Gallery

After looking at what is currently for sale on the market, it is clear that what I wanted in a 3D printer is simply not available. Because of this, I set out to make the best possible 3D printer to match my needs. My criteria for success was as follows:

  • Portability- The machine must stow itself in as small of a space as possible, yet be quick and easy to setup.
  • Large work volume- A standard Reprap printer uses a 8 x 8 inch build platform. This machine must be able to accommodate an equally large build platform.
  • Speed- print speed must be as fast and as accurate as the best consumer grade printer on the market.

To this end, I settled on the SCARA arm configuration. SCARA stands for Selective Compliance Assembly Robot Arm. The configuration has long been used for pick and place robots. It is typically much faster than a cartesian robot of similar working volume, yet utilizes a smaller foot print.

A lot of research and Solidworks time later, a basic outline of the printer began to take shape.

 

Assem1.4Assem1.3

Notice how the platform layes flat when stowed. This saves alot of space when not in use. Additionally, the printer has a very small footprint when in use, making it perfect for sitting on a desk without getting in the way.

There is one rather large, glaring problem with SCARA robots however: cost. The stepper motors that drive the arms must be geared down in order for the movements to be fine enough for high resolution printing. The typical SCARA robot uses harmonic drives to accomplish this and in here lies the problem. Harmonic drives tend to run into the thousands of dollars apeice which puts them out of reach costwise for a project such as this. A normal geared steppermotor has backlash wthin the gear train resulting in up to 1.5 degrees of play in the shaft. This results in a significant amount of movement if used to drive an arm, resulting in a serious loss in accuracy. A cheap and simply cure was devised. By spring loading the arms in one direction, all the backlash would stay to one side of the geartrain and thus not manifest itself in the print. The cost savings by doing it this way is enormous. What would have cost over $2000 to do is now done for less than $100! This simple modification is what makes this printer affordable.

3D Printer, SCARA 3D Printer

SCARA 3D Printer, The Dream

Gallery