Machining Steps:
- Stock cut with bandsaw down to 9.25"
- Faced both ends in Tod shop
- Turned down to 6"
- 18 thou passed
- Feed rate 1.5 in/m
- Spindle speed 180rpm
- Note it was extremely non-concentric
- Machined live center on waterjet
- 6" OD
- 0.5" ID
- Turned down motor casing end OD, base emulator used for slip fit
- 600 RPM w/ live center
- Centered in chuck using contact between live center plate and faced edge of piece
- Bored out motor casing end ID
- Please fill in
- Turned down mission package OD
- Please fill in
- Attempted to bore out motor casing ID - see below.
Manufacturing Incident:
Setup:
- Adjusted boring bar bit to be 6.5" extended beyond tool assembly
- Charlie centered the piece in the chuck using a dial indicator - final concentricity no worse than +/- 1 thou
- Initiated boring at 800 RPM, piece and boring tool chattered excessively, lowered to 600 RPM
- Slow but somewhat variable feed rate used
- Note the material "felt" different (surface finish) between the area immediately surrounding the cut face (from the bandsaw) and the deeper stock material
- Began a deep pass into the piece, the desired ID of 4.5" (supposedly the stock ID), zeroed against the end of the piece, which measured to 4.515"
- The piece continued to notably chatter, but this was judged inevitable due to the cantilevered end
Incident:
- At a depth of about 4", the bar suddenly caught on the piece
- The piece was torn from the chuck
- The boring bar tore several gauges within the interior of the stock
- The tool stuck was rotated about 40 degrees
- Spindle off button was immediately triggered (closer than E-stop to my hand)
- See below for pictures of the damage
- Note the bar was being moved only along the Z-axis - DRO confirms this after triggering of stop command
Causes:
- Unknown. A few theories:
- Resonance between the boring bar and the stock
- Discontinuous surface of stock, potentially in excess of 15 thou
- Jerk induced due to lip from previous boring attempt.