Part 1: Machine Strategy Updates
Strategy 1: "L" Shaped Desk
Following my "Peer Review" session with Professor Slocum, I realised that my analysis of stiffness from last week, was not entirely accurate as I failed to take into account the loading on the legs of the table ( I had drawn my structural loop incorrectly). So I extended my first order analysis to all the members of the table.
I have included the new displacements in my design spreadsheet (see week 3 Brainware). However I am yet to optimize the geometries to obtain the desired structural stiffness and natural frequency of the desk.
With some rough initial inputs for dimensions as well as number of scissor members, I was not able to achieve the desired stiffness for the desk. However, I have not considered the effects of having truss style reinforcements to the scissor mechanism on either side. I will include this analysis in the coming week.
Strategy 2: Scissor Jack Desk
I did some quick 1st order calculation for stiffness of a desk with 2 scissor jack mechanisms on either side of the desk as shown below.
Part 2: Seek & Geek
For this week's Seek & Geek, I inspected the carriage of a lathe machine.
The first thing I noticed was the parallel rail setup for the carriage and tailstock. The Lathe machine has one triangular rail and another flat rail. There is a rubbery material between the rail and the carriage that provides preload. For the tailstock, I realised that it is not fully constrained to the plane of motion when it is not locked. It is possible to lift it up, although with incredible effort. The enormous weight of the carriage and tailstock are essential to minimise errors in tool position while machining. The high stiffness is essential to keep the machines natural frequency higher than resonant frequency of human organs.
The second striking feature I noticed was the two keyed stainless steel shafts that the carriage moves along, when the feed is automated. I was surprised by this feature as flat keyways concentrate a lot of stress.