Adding a Bridgeport J-head  -  misc info

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   BP head downfeed dumbell lever
Below is a close-up of the small dumbell pivoting lever that 'knocks off' the BP head's quill power downfeed. (I thought a close-up might be useful for those who've never seen one dismantled.)

The hole at one end of the dumbell is threaded, presumably for a small AF extractor screw as it's very awkward to winkle out without one. I found a BA thread could just get enough purchase. A retaining screw goes outboard of the dumbell to stop it being displaced and falling out. This screw is missing on my setup but the dumbell still stays in place and operates ok without it.

Each end of the dumbell should be a close sliding fit in the two circular housings. As the quill stop collar reaches the top of its travel it pushes the protruding base of the cylindrical pin upwards. This causes the captive dumbell to lever the upper end of the micrometer screw downwards and release the power feed. If the cylindrical stub is 'sticky' in its housing, the micrometer screw will remain in the stuck down position and power downfeed will refuse to engage. Stripping and cleaning these few components will often fix a 'busted' power downfeed. Ditto the corresponding lever components at the lower end of the micrometer screw. Components 'stuck' in this way can be a good sign - an indication that the power downfeed may not have seen much action.   

Neil Fazakerley, 2010.