07-03-2012, 07:46 PM
In a shop far away and a long time ago, we made hydraulic cylinders that were relatively thin walled (about 0.040 as I recall). The OAL tolerance was =/- 0.0015, and since they were around 16-18" long, we had to run them in a steady rest. As you all know, parts tend to "walk" out of the rest. Of course, this resulted in oh..one or two of them coming out a wee bit short. It just happened that we used a "bearing on a stick" to roll the first thread of a part we uh...cut too much off. It kept the "no-go" off.....Anyway, this "bearing on a stick" turned out to be a decent burnishing roll too, and we discovered quite by accident that if you burnished the OD of one of our hydraulic sleeves, it grew longer. Longer enough that more than once, we had to face it off a little to get it back to print. These were honed ID sleeves, down to a 2-4 finish, and if you looked inside after burnishing, you could clearly see the distortion from the stresses introduced by the burnishing. A quick pass through the hone, and all was well. The OD tolerance was sufficient to allow a light polish to blend in the burnished area. Sold many sleeves like that.
We did run a couple of parts that we used the Cogsdill tools like Ken referred to. We ended up thinking they were more trouble than they were worth. The size before burnishing had to be held almost as close as the final dimension, and the finish couldn't be too smooth, or we'd get the flaking he talked about. One example of surface burnishing that some may be familiar with is the seal surface of a torque converter for an automatic transmission. Live seal, high RPM seals require fine finish and close size control. Burnishing is an excellent means to that end if you can work out the details. Not applicable to all materials, but most can be successfully burnished.
We did run a couple of parts that we used the Cogsdill tools like Ken referred to. We ended up thinking they were more trouble than they were worth. The size before burnishing had to be held almost as close as the final dimension, and the finish couldn't be too smooth, or we'd get the flaking he talked about. One example of surface burnishing that some may be familiar with is the seal surface of a torque converter for an automatic transmission. Live seal, high RPM seals require fine finish and close size control. Burnishing is an excellent means to that end if you can work out the details. Not applicable to all materials, but most can be successfully burnished.