Chapter 18.10 – Reach Rod Arm and Reverse ArmNext up were the Reach Rod Arm and the Reverse Arm. These arms will go on the reverse shaft (just made) and translate the forward/backward motion from the reverse lever, to an up/down motion for the radius rods (which move up and down in the expansion links).
These arms are grouped together because they are very similar. The main difference is that the Reach Rod Arm (of which there is only one) is shorter than the Reverse Arms (of which there are two).
I started with some 1/4" x 3/8” 1018 bar stock. First, I shaved it down to 0.200” in thickness, taking a little off each side to reduce warping. Then I sliced it into 3 parts for the 3 arms.
Next, I drilled the holes in the ends. These define the arms. I made one hole #49 (clearance for 1-72 screw) and the other 1/8”. These will both be opened up and reamed as the last operation. But for now I want these sizes to make monting it in a jig easier.
The bigger end has some additional holes. First, it needs a 1/16” hole through it for an eventual pin which will lock the arm to the reverse rod.
Next, I put a 3-48 tapped hole in the end. This is for a temporary set screw to help in setting the location and angle for the arms on the reverse shaft.
For this step I made a little jig that holds the arms at the appropriate angle for tapering the sides of the arms. There are two different holes – one for the shorter Reach Rod Arm and one for the longer Reverse Arms. Using this jig I tapered one side of the arm:
Then I flipped the part over and tapered the other side of the arm.
For the final shaping I used filing buttons to round off the ends.
Finally, I cut the slit in the small end to accept the mating part it will be moving. These cuts need a little additional clearance so Kozo has you cut the slit at an angle (different angle for the two different types of arms). The Reach Rod arm shows an angle of 60
o. I used angle blocks to set this. It’s hard to stack up multiple angle blocks like this – they always slide around. So I used a thin strip of double-sided tape to hold them together during setup. Now, the angle I made here was actually 64
o. The additional 4
o makes up for the slope of the side.
I removed the angle block stack once the vice was tightened down. The little strips of brass are just spacers to prevent the angle blocks from being the things that get clamped. The angle blocks are 1/4" wide and the part itself is only 0.200” wide. With the packing it makes the part wider than the angle blocks so I’m getting the clamping force where I want it (and it allows me to slide the angle blocks out of the way during machining).
Finally, I reamed the holes to 5/32” and 5/64”, respectively. And here are the completed arms. The longer two are the Reverse Arms and the shorter one is the Reach Rod Arm.
Just a few more parts to go to complete the reversing assembly.
Kim
