Chapter 17.5 – Combination LeversThis week I’ve been working on the Combination Levers. These are the short levers that connect the valve rod to the rest of the valve gear (the Radius Rod and the Crosshead) and produce that combined motion that is characteristic of the Walshaerts valve mechanism.
Just so I don’t confuse people who may be following Kozo’s book, this is NOT the method he shows to use for this part. I charted my own process here. I did use some of his techniques though, as you’ll see later. But he did most of this part in a completely different way.
To start with, I cut some 1/4" square 12L14 bar then did some stress-relieving. Not sure if 12L14 is as prone to go banana as the 1018 CRS is, but I figured it was easy to do. The two short pieces are for the Combination Levers. The longer pieces are for the Radius Rods which will be coming up shortly. Figured I’d just do the stress relief at the same time.
After shaving the 1/4" square down to 0.200” square I drilled some #49 holes in the right place. These will be reamed out to 5/64” eventually, but for now, this size will allow a nice close fit for some 1-72 screws to use to hold the part in a jig for shaping.
Next, I made a jig using some 1/2" aluminum. I drilled & tapped holes in the right locations to hold the rod in place. This jig will be used in both horizontal and vertical positions for various operations in the making of this part.
Here I’m using it horizontally to mill the neck of the ‘small end’ of the combination lever. Hopefully, this will become more clear later. I milled this 1/4", but if I were to do it again, I’d probably use 3/16” instead. I think 1/4” was just a tad too big for this radius.
With that done, I turned the part sideways (sans-jig) and drilled a #45 hole (0.082”) as the termination for the slot.
And then proceeded to cut the slot from the end to the hole just drilled. I did this by using an 0.040” saw, positioning it to produce the right with of the upper fork. After slicing the upper side, I flipped the part over and did it again to get the other side (which was now the upper side again of course, since I flipped the part). This way the slot was centered and I had the same with of tines on both sides of my fork. This operation was surprisingly satisfying. I would have normally just gone to a 1/16” end mill for this operation, but Kozo showed doing it this way and I decided to give it a go. I was super impressed with how well it worked!
Back to the jig, where we mount it vertically in the mill vise and use a 5/32” mill to narrow the bulk of the lever. The just-completed one is mounted in the jig, and the second one is sitting on the vise below, waiting his turn.
There’s a notch that has to be cut into the small end of the lever, so I did that next. I wanted to make sure and get that done BEFORE I cut the taper on the rod (which would make it a lot harder to hold! I also did a double and triple check before doing this operation since the lever is no longer symmetrical - Wouldn't want to notch the wrong side!
And now, the taper. This is a very shallow taper. I calculated that it was around 1.5
o. To do this, I drilled another hole on the right side that was 0.048” thousandths lower than the centerline. I had to use the second hole from the right. If I’d used the first one, the hole for the taper would have overlapped the hole for mounting it straight. By using the second hole, I didn’t have that problem. But I did have to make sure I did my trig calculations for THAT hole and not the other one. It’s hard to see here, but the taper has been cut on the topside, but not the bottom. To do the other side, I had to flip the part over. This jig only cut the taper correctly on one side.
Here’s a better view of the part in the jig, post tapering. It’s hard to tell, but the part is at a bit of an angle, and after the tapering, the top is now flat/straight.
And finally, I made some 0.200” filing buttons and rounded the ends of the combination levers.
Here they are completed!
Oh, wait! I forgot to ream the holes out to 5/64”!
Guess I’ll do that tomorrow. But they are essentially done!
Thanks for taking a look,
Kim