12-01-2012, 06:50 PM
(11-21-2012, 11:09 PM)f350ca Wrote: [ -> ]Jason, post 19 shows the mechanism. i think its called a Scotch yoke. The slider can be adjusted out from center on the rotating disk to vary the stroke length. Neat mechanism, it cuts with the pin on the top half of the disk and returns faster with the pin on the bottom half.
Hello Greg,
In the interests of accuracy, I don't mean to offend by contradiction. The quick return shaper mechanism isn't really a scotch yoke, there are similarities with the sliding block running in a slotted component, but the big difference is that a scotch yokes number one claim to fame is it's perfectly even sinusoidal speed profile where both the return and forward strokes are the same, and the actual correct name for the shapers mechanism is the "Whitworth Patent, quick return shaper stroke" Catchy, isn't it?
In reply to another post, Yes the shaper is credited to James Nasmyth in 1836, however there are examples of shapers and planers that predate the Nasmyth version, and I believe that the Nasmyth didn't have the quick return mechanism which was applied to the shaper by that hero of machine tool designers Joseph Whitworth, who was a student of Nasmyth as well as Maudslay, My memory doesn't stretch to the Patent date of the QR mechanism. but it should be noted that the original QR mechanism didn't use the vertical/near vertical slotted link with the sliding block, but rather was less effective using only a crank disc and conrod that was mounted above the ram rather than in the column, the column style shaper like Gerrards, with the internal QR mechanism, came some time later, the earlier versions had a table that moved up and down but not sideways instead the ram complete with QR mechanism traversed sideways in order to cut plane surfaces.
This traversing ram style can often be seen when older hand shapers find themselves on EBay.
Best Regards
Rick
