Thanks, I'll try that, really like the concept! John
I like to think of it as a pressure equalization. When you first start out, the cutter is resting on the 90 degree corner of the cage. Although the cutter weighs only a few ounces, the pressure (lbs per sq inch) is very high. The cutter is driven by gravity into the cage and shears metal away to form a uniform seat as you spin the cutter with your fingers without applying any force (or pressure) of your own. The width of the resulting seat is dependent upon a couple metallurgical properties of the metal which for 544 bronze happens to come out to .005" to .007". This seat width is the point where the resulting pressure of the cage pushing back on the cutter equals that of the cutter acting under gravity alone. The cutter stops shearing metal from the seat under gravity alone, and this is where I stop.Thanks, I'll try that, really like the concept! John
???which for 544 bronze happens to be .005" to .005"
oops... I meant .005" to .007". I edited my original post. I guess people are actually reading my texts after all. Thanks. - Terry???
.005 to .006"?
The valves were machined from 3/8" diameter 303 stainless on my little Wabeco CNC lathe without using the tailstock. For coding purposes, they were divided into five overlapping zones, each about .2 inches long. Five g-code programs, each capable of fully machining a valve inside just one of the zones were compiled and combined into a single operation. Machining began at the stem end and, with less than .2 inch stick-out, part deflection wasn't an issue. Since it wasn't necessary to reposition the workpiece in the chuck during machining, all the valve's features came out precisely concentric. A small downside to this technique was the numerous non-cutting movements at the zone boundaries more than doubled the valve's machining time. But, the 20 minute operations ran hands-off, and the long unwieldy stems came out virtually perfect.
Excess stocks of .001" were left on the stems for final polishing with 600g paper. A spare valve cage repurposed as a go-no-go gage verified the final fits while the parts were still on the lathe. The stem's upper end has to pass through its guide during assembly, but during operation there's no contact. This portion of the stem was turned three thousandths under for a later helpful clearance inside a shop-made collet. This collet was used to hold the valve for two secondary operations: 1) facing the valve's head after band sawing the valve free of the workpiece, and 2) turning the stem's lock groove.
Leak-down measurements were repeated one last time on the fully assembled valve train. Vacuums were pulled through the port liners, but stoppering the valve stem leakages with the springs installed wasn't practical. The dry stem leak-down times were on the order of 15 seconds, but with oil dropper'd on them through the springs they typically improved to 20-30 seconds. - Terry
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Beautiful work, as always.
When you've got a minute, I've got to say I've never seen the use of epoxy like you're doing here. What does that do? Does it add strength to help it resist the machining forces from the other side, or is it cosmetic?
Bob,Beautiful work, as always.
When you've got a minute, I've got to say I've never seen the use of epoxy like you're doing here. What does that do? Does it add strength to help it resist the machining forces from the other side, or is it cosmetic?
Bob,
It's just like kvom said. The Devcon keeps the already machined side of the part connected to the workpiece so the other side can also be machined free of it while still being held in place. A strong epoxy is needed, but also one that gives up at a reasonable temperature. JB Weld continues to hold on at temperatures that are too high to be useful and isn't useful in this application. Devcon 5 minute epoxy used to give up at a much lower temperature, and I could get it to release with a heat gun. I think they changed their recipe a few years ago, and now an oven bake is needed. I may try one of the high temp glue sticks. The low temp stuff might melt under the heat of some machining operations without sufficient coolant. - Terry
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