Thanks CNR!
Chapter 17.9 – Link BlocksNext up is the Link Block. This is a teeny-tiny piece that slides up and down in the expansion link. It would appear to be a very simple little item – other than that the link bracket slot is an arc, so the shape of this block needs to be a little arc segment to match the radius of the expansion link.
Kozo recommends that this piece be made from bronze. All the bronze I have is in rods. I just happened to have a 1” piece of round 932 bearing bronze that I’d cut a chunk out of for something else. So, I used that and cut another slice off of it for this. Interestingly, the thin slice I cut (about 0.90” thick was my goal) did an amazing curl.
I carefully bent the thin slice back to a flattish shape. I used the vise some then I moved to this little V-block. Working carefully, I was able to get it quite close to flat.
Then I sticky-taped it to a flat surface and shaved a few thou off of both sides to get my desired thickness (5/64”).
Then I sticky-taped the blank to an aluminum jig that I’ve been using and clamped it to the rotary table so it was positioned with the correct radius.
Next I drilled two holes – one for the center of each of the link blocks. These were drilled #53 (tapping size for 1-72) clear through into the jig block. Then I drilled a clearance hole (#49) just through the bronze. Then tapped through that hole into the aluminum jig, which allowed me to add some additional clamping using #1-72 screws.
This chart shows how I’m planning to cut the link blocks. I’ll be using the rotary table to sweep the arcs, then set specific angles on the RT for the top and bottom edges. I used lots of fancy trig to figure out what the angles would be. I’ve never done this before – using angles on the RT to cut a part to width and length. But it seemed to work adequately. I was able to get within a couple of thou at least!
With the additional clamping screws added I swept the top arc.
Then I did the lower arc.
Next, I set the RT to my calculated angles to cut the top of one of the link blocks. Since I want the edge of the blocks to intersect the center of the arc I had to offset the mill by 1/32” (since I was using a 1/16” mill). And with this offset, I did the top of the other block too.
Now, to do the bottoms of the link blocks I had to offset the axis 1/32” in the opposite direction. Then set the angles and make the cut. With that done you have the completed shapes of the two link blocks.
The only thing left to do is to ream the holes to 5/64. To do this I removed the clamping screws and relied solely on the sticky tape to hold things in place. At this point there’s only a tiny square of tape holding it there. But it worked and nothing pulled up from the table.
And here you have the two link blocks. Guess I need to clean them up a bit. That black gunk you see on the parts is sticky-tape residue. I just need to get it cleaned up. But they are quite small!
I was fairly pleased with my ‘cutting to length by angles’ experiment. The part was supposed to be 0.171” long and in the end, I measured 0.169”. So, a couple of thou short, but it's plenty close for this. The length of this part isn’t that critical I think. The width is more so and that was done using standard DRO methods, so that came out fine. Besides, I’ll be milling the arc in the expansion link to match these parts anyway!
A tough part completed. Now I’ve got a bunch more curved parts up next with the expansion link itself.
Thanks for stopping by!
Kim
