Cin-D LOU EyeLids
So now the task is to make Cin-D LOU's eyelids. The original concept for the working green eyelids was to use cut-up sectors from ping pong balls. Separate R/C servos will be linked to both the right and left side upper/lower eyelid pair to enable simultaneous eye blinking and individual eye winking. Each eyelid needed a stout frame for the actuation linkage. The cut-out ping pong ball sectors will be epoxied to the frames to go along for the ride when the servos actuate the frames. See http://www.youtube.com/watch?v=uYYqycOWH5g. But how do we make the eyelid frame parts that will make that happen? This page tells the story.
Fig.00 - The parts you make are a product of your creativity, raw materials, tools, skills, and time. There is no one right answer. Design is often an iterative process. You start with one idea. You make some test parts to see if it works. You see problems and come up with a better idea. You end up with a plan.
In this case, we first looked at making the eyelid frame parts on the MakerBOT. Initial MakerBOT designs had strength and stiffness issues. We then thought to fabricate these frame parts from brass strip. The first design used 0.020" thick brass strip, but that proved to be too thin and flimsy. The design was then changed to use 0.065" thick brass and that looked more promising. Several trial parts were made to work out unknown details before proceeding.
Fig.01 - This view shows the 'before' and 'after' for the Cin-D LOU eyelid frame parts fabricated from .065" thick brass. We had several sheets of this brass material. Details for the design were first worked out in 2-D CAD. The general idea is to cut the parts out as flat patterns. The relatively thick brass parts would then be periodically notched to facilitate bending them into the eyelid curvature.
Fabrication tools include the band saw and milling machine. Since several HIVERS are interested in learning more about using these tools, the remaining discussion is a 'how-to' that shows the step-by-step sequence for making these specific parts. The techniques and setups can be generalized and used in other parts-making situations.
Fig.02 - We will start on the band saw. We are using a Delta 14" model. It is mostly used for wood, but is capable of cutting non-ferrous metals in some cases. We've had good luck cutting 0.065" thick brass using a particular blade from McMaster Carr; their model 4179A175 Bimetal Band Saw Blade 7'9-1/2" L, 1/2" W, .025" Thk, 14-18 Tpi, Vari/Wavy at $28.95 each. The blade is actually made by Starrett, a very good company. Several associated setup tools are shown on the table. The next few slides show the first setup which will 'rip' nominal 1/2" wide strips of brass from a larger sheet.
Fig.03 - The desired 1/2" strip thickness is first set on the depth of the 6" scale. The scale is then set against the left-side edge (viewed from the infeed position) of the bandsaw blade. The home-built 'depth-stop' tool is then set into the miter slot and extended out to contact the stop on the scale. The hex-screw on the depth-stop tool is then tightened to hold the dowel at this extension distance. The circular face of the dowel is used to transfer this depth to the infeed and outfeed edges of the table as shown in the next figures.
Fig.04 - The home-built 'depth-stop' tool is then slid in the miter slot towards the infeed edge of the table. A C-clamp is used to fasten a straight wood strip 'rip fence' in contact with the depth-stop at this position.
Fig.05 - The home-built 'depth-stop' tool is then slid in the miter slot towards the outfeed edge of the table. A C-clamp is used to fasten a straight wood strip 'rip fence' in contact with the depth-stop at this position.
Fig.06 - The rip fence is now at the right depth (strip thickness) and is parallel to the bandsaw blade. The sheet of brass can be fed into the bandsaw blade repeatedly to cut one or more strips all at the same thickness.
Fig.07 - This view shows several cut strips. We made four, each 9-3/4" long.
Fig.08 - The rip fence setup is removed and the bandsaw miter gage is used in a second setup to cut each of the four 1/2" strip into two smaller pieces. The 9-3/4" length is cut into a 4-3/4" length and a 5" length. The length dimensions at this stage are not critical and are actually 1/16" to 1/8" oversize. These will be our 'stock' (starting) part sizes. These parts will be trimmed to a finish length later.
Fig.09 - For the next setup, we'll move to the mill. It is a 2 horsepower, 3-axis, manual "knee-and-column" type mill; specifically a Powermatic Houdaille Millrite model MVN made in Cincinnati, OH. It accepts standard R-8 toolholders in the spindle taper. A 6" vice is mounted on the table and dialed-in relative to the cutter motion.
- the X-axis (table) moves left to right
- the Y-axis (saddle) moves forward and backward)
- the Z-axis (spindle) moves up and down
Fig.10 - The belt on the step pully setup is set for 430 RPM. This will be a good nominal speed for the following operations.
Fig.11 - The eight pieces of stock are 'ganged' into the vice on the table. We are going to simultaneously mill the top surface of all the parts flat to remove the bandsaw marks. The parts are sitting on a 'parallel' block set between the vice jaws. The exact dimensions of the parallel block are not critical, except for the parallel feature. The vice is 'dialed-in' to be flat to the motion of the cutter. The top and bottom surfaces of the parallel block are parallel (duh...) so the bottom and top surfaces of the stock will also be parallel to the motion of the cutter. The parallel block puts the top surface of the parts at a comfortable height close to the top of the vice jaws (for rigidity) without too much extension. Note the parallel must be a bit thinner than the thickness of the gang of parts so the vice clamps the parts and not the parallel block.
Fig.12 - After milling the top surface of the gang of eight parts, the parts are removed and inverted. The operation is repeated to mill the bottom surface of the gang of eight parts. The stack started at a nominal 1/2" height with rough bandsawn edges. The first cut is called a 'clean-up' cut and was about 0.025" in depth. The second cut also removed about 0.025", but was dialed-in to make the finished parts 'exactly' 0.450" in height. This view shows the 'before' and 'after' height and surface finish on the gang of eight parts.
Fig.13 - Before proceeding, this is a good time to discuss mill tooling. The previous operation used a 1/2" diameter, two-flute, TiN-coated, HSS end mill (cutter). This cutter has a 'whistle-notch' feature and is held in the R-8 collet by a setscrew. This is a good general-use tool for this type of cut. We will now remove this cutter and replace it with a drill chuck that is also mounted on a similar R-8 shank. The next operations will use a sequence of tools clamped into this drill chuck; a large sewing needle (used as a setup pointer), then a center drill, a twist drill, and finally a reamer. This sequence of tools will precisely spot two holes at a controlled 0.250" diameter a set distance apart as shown on the next page.
Continued on next page http://wiki.hive13.org/index.php/Cin-D_LOU_EyeLids2.