Machining the 6-Sided Elevator Bearing Block
Lance Corporal Zachary Geragi, USMC (medically retired) from Farmington, MN, an Iraq war veteran and his team of RC hobbyists are on a historic mission. To be the first to build and fly an AMA flight certified radio controlled ⅛ scale replica of the B1 Lancer Bomber jet aircraft! Because of the technical difficulty, this feat has yet to be successfully accomplished and no easy feat it is. Read the full case study here.
Zach and his team have designed and machined a plethora of components and molds during this mission to date using SOLIDWORKS and VisualCAM for SOLIDWORKS. However, we needed to select one part to take a closer look at for this article. For this we chose the Elevator Bearing Block. This component plays a central role in the actuation and control of the rear elevators on this radio controlled B1 Lancer jet aircraft. The actual elevator bearing block, bearings and the SOLIDWORKS sub-assembly are shown below.
The needle bearings are a press fit into sleeves with retaining compound. These parts form a bearing cartridge which is a push fit into the bearing block. This allows for easy repair & replacement as needed. Between the block, you see two long actuator arms that can move together in the same direction, or the opposite, depending on the radio commands from the ground or from the automatic onboard gyroscope. As much as 2000 in oz of torque is transferred to each of the two pivot shafts by hex sockets on the end of each actuator arm. The pivot shafts are slip fit within carbon fiber sleeves and transfer control to the two rear elevators.
|Watch the actual B1 Lancer elevators in actions here!||In the B1 Lancer, roll control is accomplished with the rear elevators moving opposite each other and together for pitch. In this control mixing, they are referred to as elevons (i.e., a combination of elevator and aileron). On the B1 Lancer, since the “elevons” are smaller, the angle of deflection is extreme to make up for the fact they’re closer to the center roll axis. It is this extreme angle of deflection that makes it look like they are tilting in this video, when in fact the tilting is an optical illusion.|
|“It’s amazing the tight tolerance Zach was able to hold on the elevator bearing block without having to use our boring bar attachment! You guys at Mecsoft have been very open and helpful to us as we expanded our CAM skills, and became adept at designing for manufacturing. We appreciate what you folks do very much!”
Rick Freeman, Engineering,
The 6-Sided Setups
The Elevator Bearing Block requires machining from all 6 sides. Each side includes its own setup and work zero definition. The VisualCAM Machining Job tree here shows each setup in it’s collapsed state. The critical side is Setup 4 (RIGHT) because it includes the Drilling and Hole Milling operations for machining the bearing shaft through hole. This hole is cut through to both sides of the block and requires a push fit with each of the bearing cartridges. The blue Z Axis arrow shown in each setup below indicates the machining direction for that setup.
The Machining Strategies
Shown here is the complete VisualCAM Machining Job for the Elevator Bearing Block. You will notice Drill Set folders for the Top, Right and Left side setups. These can be expanded to show the Drill operations used for that setup. Each machining operation and drill set are also shown graphically in the images below.
Setup 1 (TOP)
The machinable features on the top include two ⅝” daimeter through holes. Drill Set Top (image (1) below) includes a Center Drill operation with a #9 Drill x 0.13 deep followed by a ½” Deep Drill x 0.80 deep at step increments of 0.125. These ½” holes provide access for a 0.80 deep Hole Pocketing operation (image (2) below) using a ⅜” end mill, a 0.125 stepover and a 0.05 stepdown.
Setup 2 (BACK)
This is a 3 Axis Horizontal Roughing operation (image (3) below) to machine the back prismatic contour using 0.5” end mill. It uses an offset facing cut pattern, a mixed cut direction with a 25% setover and a stepdown of 0.05. A bottom Z depth containment is set to -1.7 since it is only roughing half of the cube.
Setup 3 (FRONT)
This contains a copy of the 3 Axis Horizontal Roughing operation (image (4) below) used in Setup 2 (BACK) but with the bottom Z depth containment set to -1.0. This operation is used to machine the front prismatic contour.
Setup 4 (RIGHT)
This is the critical setup that includes the hole machining operations to cut the two 1.098” diameter bearing cartridge holes that require the push fit. It begins with Drill Set Right (image (5) below) that includes Center Drill and Deep Drill operations both for the surrounding hole pattern as well as an access hole to mill the primary bearing cartridge hole. The last operation in Drill Set Right is a ⅝” Deep Drill. This provides the access needed for the ½” end mill to perform the Hole Pocketing & Profiling operations.
Milling the bearing cartridge hole begins with a 2½ Axis Hole Pocketing roughing operation at a diameter of 1.040” +/-0.0005 (image (6) below) using a ½” end mill. The final 2½ Axis Hole Profiling operation (image (7) below) is the 1.098” +/-0.0001 finishing operation that removes the remaining 0.058” of material. To maintain concentricity, these two milling operations cut the bearing cartridge hole on both sides of the part at the same time. The final Hole Profiling operation is shown in the simulation illustration above.
Watch Zach machine and discuss this part and assembly in the video links below!
Setup 5 (LEFT) & Setup 6 (BOTTOM)
Setup 5 (LEFT) performs the Center Drill and Deep Drill operations for the symmetrical hole pattern on the left side of the elevator bearing block (image (8) below). This does not include the bearing shaft hole that was finished in Setup 4 (RIGHT) above. Setup 6 (BOTTOM) contains one 2½ Axis Profiling operation (image (9) below) using the same ½” end mill. This is a finishing and cleanup operation that also removes the ¼” radius fillets left over from the two Horizontal Roughing operations from Setups 2 and 3.
About The Minnesota Giant RC B1 Lancer Bomber Project
Zach Geragi and Rick Freeman collaborate on high-end radio control jet aircraft designs, landing gear, and accessories through The Gear Bunker & The Minnesota Giant RC B1 Lancer Bomber Project. With nothing more than word-of-mouth, they are so busy they get to pick and
choose only the best projects. The AMA (Aeronautical Modeling Association) is the governing body that works with the FAA for RC flight and under which this aircraft will make history and its maiden flight in October 2020 at the EAA AirVenture at Wittman Regional Airport in Oshkosh, Wisconsin.