The Craftmans Shop > New from Old
Boxford back from the dead
awemawson:
You can visually determine whether the pa is 20 or 14.5 by my crude but effective method:
Roll the gear in Plasticine to create the correct meshing rack. Cut longitudinally with a sharp razor blade and look in profile at the flank of the rack teeth which for an involute gear should be a straight line. This flank angle IS the pressure angle. The difference between 14.5 and 20 degrees can easily be determined with a cheap school plastic protractor.
AdeV:
That's not that crude, and sounds effective! If you'd called it "modelling clay" it would seem positively professional!
Looks like there's some Plasticine on my shopping list now!
Sea.dog:
It definitely looks to be 14294, doesn't it? I've asked for any info on these gears on one of the Boxford forums. I'll let you know if there's a reply.
BTW, the large gear is called the Bull gear.
Sea.dog:
Pretty much as expected, the backgear is from a later machine. The PA was changed in the '50s so the 14 is a pretty rare animal. Broken teeth are quite common when chucks get jammed. Since there's no way of locking the spindle until we get to the MKII the usual method is to engage backgear as a lock. Bull gears do come up for sale from time to time and the chap I spoke to does have a set available.
AdeV:
Thanks again for the info - I’m wondering now if the pulley set is original or not - as it is in mesh with the small gear, which is 20pa. It’s possible that the driven gear on the back gear shaft is the original 14pa, as it is pinned to the stamped shaft. Looks more and more like I need to go buy some plasticine at lunchtime :thumbup:
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