Kevin, could you please post a photo of a cutting edge both pre and post radiusing? I'm pretty sure i know what you mean, just want to be certain. I use HSS most of the time. Keith
I don't know if my camera would pick it up, but I'll draw you a pic. On the left, when someone sharpens a tool, they try to get it as sharp as possible. But with almost any feed and speed combo, the tool will not coincide with the diameter of your stock, your feed, and your speed. So in turn, it will give you a rough "furry" finish. If you look at the tip of the same tool on the right, there is a very slight radius on the nose. It would actually take something like an electron microscope to show what a surface finish would actually look like, but with a very sharp point, under a microscope, it would show a very rough jagged surface. With even a .002 to a .005 radius, under a microscope would show a smooth but wavy surface, although undetectable by the eye or not able to really being able to measure.
In the second pic is a highly exaggerated sketch as to what I am trying to convey. You can never get an absolute smooth surface, but a slight radius can give you a mirror finish vs. a zero radius tool.
Also if you are using a HSS toolbit, you can use a standard India stone, or a fine stone on your bench grinder to break the edge. If you are using a
carbide insert that has Zero radius, you need to use a diamond hone to break the edge. A diamond hone can be bought for $10 or so. Also if you are using carbide inserts instead od an insert silver soldered on to a toolbit, you can order inserts in a variety of radiuses, from .005 on up.
On thing you have to remember though that the larger the radius, the more the tool pressure there is, and depending on the material, you can generate a lot of heat, possibly work harden or put hard spots in the material, and the larger the radius, the more chance of chatter. So you have to find that fine sweet spot that you are looking for yet not distort the tool or the workpiece.
A lot of boring bars you buy will have zero radius ad will give you a ****** bore. Breaking the tip with a slight radius will eliminate the ****** finish, but with a boring bar, and with one not being as rigid as a turning tool, the larger the radius the larger the chance of flex. When your boring bar flexes, you will get a tapered bore. The sharper the radius, the less the flex, but again, you still need a couple of thousandths to get the sweet spot you need.
I've have always told everyone that I have trained to run a machine....."Become one with the machine, become one with the material". You have to envision in your head what is going on. Envision what the cutter is doing if it was running in very slow motion. See with your eyes, and see with your ears. Sometimes you can see more by sound than you can by sight.
Also, like you learned in school years ago....heat expands, cold contracts. If you have ever worked in a factory with a dedicated Inspection Room, the room is kept as a consistent 70-72 degrees. Some factories will let a piece of work set for an hour for it to acclimate to the temperature of the room before inspecting the part. For the average person, it may not make a difference, but to highly precision parts for medical, aerospace, outer space, it is highly important. In machining some parts, you can make a cut, the part is hot to the touch, but if you mic it, the part is right up to size. Later on, when you go to assemble that part to another part, they won't fit. You check your part again and it is .003 smaller than before. That is on a solid part. But if you were turning a part in the lathe and boring out the center, depending on material, the bore may end up being large, or the bore may end up being too small. So if your part is hot, you ALWAYS want to let it cool before making your final cut, and for your final cut, you only want to take a few thousandths.
Hopefully I answered your question and probably made it as clear as mud with all the other rattling on.
Hopefully it answered it though, and if you have any other questions, I'll be more than happy to try and answer them. The only thing I love more than machining is my wife and my son.
