Next is the Barrel Ratchet.
So I made a 60
o toot cutter using the same process I did in
reply #96 , so I won’t repeat it all here.
Then I sliced off a chunk of 1” diameter 303 stainless and faced it to 3/16” diameter, drilled a 3/16” hole in the center, and cut a fancy ring on one side. And I made a 3/16” mandrel to use in making this ratchet. It will also be used for many of the other gears on this clock.
Here are all the parts I need to make the gear. The cutter is mounted on the arbor on the right. The top arbor is the 3/16” one for holding the gear blank, and the gear blank is the lower item in the picture.
Next, I set up the rotary table on the mill, got it as square as I could, and centered the cutter on the centerline of the mandrel.
Next, I offset the cutter by 0.043”.
Why did I offset the cutter, you might ask? That’s a good question! Generally, you want to cut gear teeth so they are centered on the axis, otherwise, the teeth will come out all wonky. But in this case, Wilding specifies a 5
o back rake on the teeth, to make a more positive latch on the ratchet pawl (which we call a click in clock making, apparently). In order to get this back rake, you offset the teeth. Here’s a picture to help show you what’s going on:
In the top left picture, you see how the triangle tooth will look if you cut it on center. Not too exciting. But if you offset it some, as shown in the upper picture on the right, then you will get some back rake on the tooth, as shown in the lower right picture.
I thought that was pretty ingenious!
So now I had to figure out how deep to make the teeth. I had calculated a number using my rudimentary trig, but I wasn’t absolutely confident in my math. So, I cut the first two teeth to see how deep they needed to be to make them nearly join. And yes, my calculations were mighty close!
After a lot more tooth cutting (only 16, but it still took quite some time!) here it is with all 16 teeth.
I still need to file the hole square so it will fit on the barrel arbor, but it’s looking pretty good.
Interestingly, the ratchet teeth came out looking much more aggressive than they looked in the plans. I went back and checked my CAD drawings, and it turns out, I made this part to look like the drawing in the book, which apparently isn't a very accurate drawing, as it does not match the dimensions shown. Even my drawing doesn't match the dimensions I show! How'd I do that!?!
). The angle at the bottom of the tooth is specified to be 60 degrees, which is what I made. But in the CAD drawing, I apparently just made it ‘look’ like the picture in the book. I don’t know why. That seems extremely silly. But that’s what I did. In my defense, it is one of the earlier parts I drew, but still, not matching my own dimensions is pretty gross negligence. I'm going to have to fire that draftsman!
Anyway, I found a picture in the book of the ratchet, and it looks much more like what I made, and much LESS like the drawing he shows in the book. Go figure.
Anyway, not a big deal, other than I‘m going to have to be careful when making the click to make it match the actual ratchet, and NOT the mythical ratchet that I drew in my plans.
Wonder if I’ll ever go back and fix my CAD drawing? Not likely at this point….
Thanks for looking in!
Kim
