Presentation on theme: "Set-Block Design Issues August 12 th, 2008. Frederickson Skin and Spar MBU Background Set blocks are used to verify the distance between the bed of."— Presentation transcript:
Set-Block Design Issues August 12 th, 2008
Frederickson Skin and Spar MBU Background Set blocks are used to verify the distance between the bed of the machine and the cutter is 2.100”. Skin Mills have dual spindles, which need to be set as close as possible to eliminate miss-match between cutters. Even though cutters are set on presetters accurately to +/-.0002, changes in temperature and the machine cause slight variation. For many years the cutter height on the Skin Mills was set using a cube with brass surface on the edge that contacts the cutting tools. This was replaced around 2003 with the current dial indicator block designed in the mid 70’s for other Boeing areas.
Frederickson Skin and Spar MBU STP Situation- Current plunger design binds when side loads are applied from tapered cutters, causing the cutting edge to chip. The dial is small and difficult to read under the low light conditions where it is used. Reaching under the vacuum shroud and trying to see the small dial in the shadows makes it difficult to get accurate readings. Several vendors offer solutions, but none have met our needs. Target tall block that can be set to master and gauge and repeatably measure to within +/ of gauge. Features would include digital gauge that can be zeroed in master, back light, lever to depress plunger, linear bearing plunger guide. Proposal-Work with University of Idaho to develop this device as a Senior Design Project for the Mechanical Engineering Department.
Frederickson Skin and Spar MBU Frederickson Skin and Spar MBU Current Boeing Designed Setpoint Block (ST 8738C-4SG gauge ST 8738C-3MG setup block, Federal 2X dial indicator) 2”cube Zero indicator to certified gauge
Frederickson Skin and Spar MBU Frederickson Skin and Spar MBU Typical Skin Mill Machine and Use Cutter height set to above bed of machine. Small dial and shadows makes it difficult to accurately set cutter to +/ Plunger binds when slid under cutter and give inaccurate readings, or possibly chip the carbide cutter. Additional travel will eliminate the majority of accidental over travel destruction of gauge Cutter SetPoint
Frederickson Skin and Spar MBU Skin Mill Mis-Match If cutters are not accurately set, the areas must be sanded to remove the variation
Frederickson Skin and Spar MBU Cutter height is checked off from top of spar to verify dimension Gauge is used by several areas throughout Boeing Spar Mill Use
Frederickson Skin and Spar MBU Digital Prototype Not accurate over range of travel, and not enough travel Metric Dial Plunger motion not smooth, not enough travel Separate Transducer Plunger motion smooth, very accurate, but not enough travel, handle gets in way of measurement Gauges Already Tested
Frederickson Skin and Spar MBU Dial Smooth motion, not enough travel, to tall Metric Dial 4” tall, not enough travel Dial Plunger motion smooth, very accurate, but not enough travel, 4” tall Dial Plunger motion rough, inaccurate, not enough travel, difficult to read Gauges Already Tested
Frederickson Skin and Spar MBU Frederickson Skin and Spar MBU Revised Boeing Designed Set Block 2”cube Plunger does not have smooth movement, indicator has.020 backlash which causes gauge to be inaccurate. Overall size and weight larger than original.
Frederickson Skin and Spar MBU Frederickson Skin and Spar MBU Plunger slides in green pushing and is attached to blue ring. Red finger from indicator follows ring movement. The problem is that even if there is not any gap between the ball on the end of the finger and the blue ring, the finger has about.020 backlash from upward to downward travel. 2”cube
Frederickson Skin and Spar MBU Digital indicator with.500 travel Easy to read LCD with back light Smooth travel on plunger, prefer linear bearings Gauge can be zeroed or set to true height of set gauge (2.100) Resolution.0001, repeatable to +/ when inserted in set gauge Overall accuracy +/ Replaceable plunger Lever to depress plunger instead of dragging measuring surface across cutting edges Design Preference
Frederickson Skin and Spar MBU Frederickson Skin and Spar MBU Proposed Modifications Replace analog gauge with digital gauge, preferably with analog bars similar to Mitutoyo B Resolution.0001, accuracy needs to be.0002 Preference would be to have replaceable plunger in case accidental machine over travel occurs. Plunger needs to be very minimal resistance even with side loads produced from pushing under cutter. Suggest Thompson Precision Ball Bushing Bearings
Frederickson Skin and Spar MBU Frederickson Skin and Spar MBU Proposed Plunger Support Thompson Linear Bearings MarMotion Rotary stroke bearing