I was using the universal dividing head yesterday to space the 10 holes and one slot in the brass disc for the old safe. I was tilting it from horizontal to vertical and then back again. It was very hard to move - it had been doing this since I got it. The dividing head was made by the NEWS Yamatokoki MFG. CO. in Tokyo, Japan, in 1968 (inspection certificate is dated 9.9.1968). Today I decided to find out what was wrong. I had figured that it had to do with the tilt locking mechanism. There are two bolts through the casting that each have a brass “shoe” that engages the operator side dove tail (much like gib locks on straight gib lathes and milling machines) except the shoes are pulled onto the dovetail vice being pushed by bolts.
Disassembly revealed some decades old swarf that had found its way into the bottom of the casting - it was mostly aluminum.
Here are some more parts
What was concerning was the deformation of the rotating body and the worn clamping shoes
I stoned and removed the worst of the deformation on the casting. The brass parts were also cleaned up so that they would be a sliding fit into their bores again. I was considering making new shoes - turns out that they were cut in situ during the original milling of the curved dovetail. So I decided against it.
Here was the original problem (a design flaw). When the bolts are tightened to lock the tilt, they slightly rotate in the bore, taking the shoes with them. This results in the brass shoe jamming in the dovetails. After unlocking the bolts to tilt the head, the shoes jam further when trying to further tilt the head (It is like a tapered gib - the harder you push, the more it locks). I was able to duplicate this jamming over and over again. It would explain the deformation as attempts to free the shoes requires a very large force. Also, since the shoes are not making good contact with the dovetail while canted, more force was used in the past to lock the head - another possible reason for the deformation.
The solution: prevent the bolts and shoes from rotating while being tightened. Enter the Scotch Key (anti rotation pin)
I used a 3/16” end mill to make the 1” deep hole for the brass pin. I was concerned that a drill might wander off because it was drilling half cast iron, half steel and half brass. Worked great.
Dressed the original brass shoes to fit the dovetail nicely and reassembled. Testing revealed that there is no more jamming and the shoes release every time, making tilting very easy. You can just see the little brass anti rotation pin on the bottom lock (below the gear)
Sorry for the sideways pictures. Not sure what’s going on...