shootnride wrote: ↑Wed Dec 02, 2020 9:03 am
Harold_V wrote: ↑Tue Dec 01, 2020 4:07 pm
I've used his guidance for turning the corners off square stainless plate by tailstock pressure holding the piece in a lathe. By plunging straight in, the corners simply evaporate without issue. A lesson I've never forgotten.
H
Harold,
This is pretty interesting. What type of tool are you using to do this ?
Ted
Imagine a HSS right hand turning tool, or a tool ground such that it can be mounted so the end cuts, much like a parting tool. The right hand tool would be mounted parallel to the spindle, while the end cutting tool would be mounted @ 90° to the spindle. Either one would work equally well. The difference being you don't create a slot, but machine the width of the plate in one pass. My experience was with plate about 1/8" thick, and was about 5" square. If one has wider plate, two or more cuts may be required, but the process would work equally well.
The tool is ground with extreme positive rake by grinding a chip breaker that is deep and wide. It is important that the chips flow easily. The breaker isn't intended to break the chip, and it most likely will not. If it does, it may be too narrow. The cutting edge may be in the neighborhood of an 18° angle, and appears to be fragile. The feed rate (it should be used with power feed) is quite slow---something like .0015/.003". Surface speed can be surprisingly fast (considering the alloy) because the shearing action, along with the light feed, produces far less heat than one would generate using a coarse feed with less rake. The light feed, accompanied by the high rake, reduces cutting pressure, almost totally eliminating any hammering of the cut. The cutting edge does undergo degradation, but it appears to continue to cut reasonably well.
I had the opportunity to see the difference because I had started the project with conventional tools, and was beating the tool mercilessly. I was almost offended by the suggestion to use high rake and to plunge, but I was to the point where I'd try just about anything, as I was struggling getting the corners off.
I have used this method on my Graziano on occasion. It's a medium duty machine, 12".
H