Another mystery object.

[Ian PParticipant @ianp]

This item was in a box of oddments that came with a pantograph engraver I bought many years ago, I have never really worked out what its original purpose was, its obviously not engraving related and seems to be some sort of spindle extension.

The coarse thread is 5/8" OD, 11 tpi and the large end shaft is 1" diameter. The other end appears to be made to accept a collet as it has a taper bore (16mm at mouth down to 9.53mm over 17.5mm) and the closing nut has a 45 degree internal taper, the thread about 20.5mm dia is 40 TPI which seems to indicate it was chosen to ensure best accuracy/concentricity when closing the collet. If this was some sort of extension spindle, say for a toolpost grinder then the lack of a precision register at the coarse thread end does not make sense.

The spindle is drilled through and has a removable/adjustable backstop. Its about 11" long overall

Anyone know what this might be off?

Ian P

[Ian PParticipant @ianp]

Very fine and very coarse threads

[Martin ConnellyParticipant @martinconnelly55370]

The 5/8" x 11 thread is found on the bottom of theodolites. May be something for mounting one on something other than a tripod.

Martin C

[Anonymous]

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[Ian PParticipant @ianp]

Grinding spindle extension is my best guess too, the only thing that makes me curious is how it is meant to accurately locate itself and run run true.

Unlike a lathe chuck there is no register associated with the 5/8" thread, there is only the remains of the 1" diameter face once the spanner flats are taken into account so the slightest burr on the face would throw the far end of the extension quite a long way off. If it is for internal grinding then presumably it would be rotating at high rpm so concentricity and balance are really important.

The extremely fine pitch and the very close fitting thread of the collet nut point to it being a precision made item but its at odds with the mounting thread.

Ian P

[Anonymous]

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