Scotch Yoke Mechanism



Squaring up the Yoke Block

A good way to fall asleep at night when you drank caffeine late in the day is to lay there trying to plan how to machine an irregular casting....

I decided the best surface to consider the reference was the the bottom face.  I clamped the part in the vice with the small top-not against the movable jaw and the bottom against the fixed jaw and a parallel to keep it level.  I machined the top face in this view and then flipped the part and did the corresponding face. 

I then put the part in the vice with the bottom face on the parallels and flattened the top-not.  Flipping it now with the bottom face up a machined the bottom face.  Belive it or not the machined faces are square to each other!

Blind danged luck......


Cuttingthe Yoke Block to length

The part has been mounted vertically after trimming the other end to the prescribed location and is now being faced to length.

Boring the shaft hole in Yoke Block

I rolled the yoke block and then drilled the hole for the file shaft.

Cutting transfer block groove

Cutting the slot for the bronze transfer block.  I used a 7/16 end mill to cut to depth and then made two passes to bring it out to 0.500"

Yoke Parts I

Yoke parts, view one.


Yoke Parts II

Yoke parts view II.  I have yet to cut the slot in the yoke block to allow the pinch bolt to tighten the clamp on the shaft.

Parts Test Fit

Dry run of the parts, the hole through the yoke block is tight enough to allow it to be turned by hand to see how it all functions.



I clamped the part in a machinist's vice so I could saw the slot for the pinch in the horizontal bandsaw.


Cutting the slot

Cutting, making sure I have a grip on the head to keep from marring the bore of the part.


Scotch Yoke Parts

Parts all polished and ready for the final test fit.


First assembly of final parts

Final test fit, everything fits and runs smoothly.