Weekly Brainware
Week 11
Bottom Bearing Block Redesign
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Last week, when designing the bottom bearing block, I had only considered overlapping stress cones in determining the number of screws required to create the L bracket from 2 plates of Aluminum. I assumed that 4-40 screws would be most suitable given that I intended to machine the plates of the block from 1/4" Aluminum plate. While my spreadsheet helped me determine the number of bolts & spacing needed to secure the block to the wooden backplate, it did not calculate the number of 4-40 screws required to bear the load. My understanding was that as long as the stress cones overlapped, this would be sufficient. However, this week I decided to do the calculations to ensure that the screws don't fail. An important consideration as pointed out by Professor Slocum was the screw preload force.
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With the inclusion of screw preload force, the number of screws amounts to 10. This is an unacceptable number given the limited area of the plate. Hence this approach is not the right way to go!
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Instead, an extruded aluminum L bracket should be used! Noting this, I redesigned the bearing block and machined it in the LMP shop.
The updated spreadsheet can be downloaded below.