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Thread: Radius on TC Cutting Edge?

  1. #11
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    What it comes down to is that a sharp edge works very well for aluminium, a slightly radiused edge has better lifetime with steel (the harder the steel the more robust the edge).

  2. #12
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    Quote Originally Posted by Paul Alciatore View Post
    .................................................. ....................................I ask this because I like to sharpen HSS as sharp as possible but have seen commercially sharpened TC both razor sharp and with a small (0.001" - 0.002") radius. Which is best? Why?
    First, understand that the nose (radius) of the toolbit is related to the "Cusp" height required for the part. When you use a sharp tool , you create a miniature thread more or less. Lets take a perfectly sharp point and say it is pointed at a right angle to the spindle centerline and it has a 45 degree leading and trailing angle (90 total) . If you had a .010 feed rate per revolution, you would create a cusp that would look like a thread about .007 " tall ( seen under a magnifier ). That would really be rough ! so you would , or could do two things...shorten the feed rate ,,say to .001 per rev, but that would increase your time TEN Fold to make the cut, or you could do it with a radiused tool and that would reduce the cusp height . The .001 feed rate would produce a cusp of .0007" , but the same cusp would come from a nose radius of ..25(guess) if you wanted the higher feed rate .

    So feed rate and nose radius directly impact the finish of the part, as well as the time it takes to make the cut. In commercial operations, where they have higher HP than home shops, they can afford to do some hefty feed rates . So yes , the radius affects tool longevity, but it has other effects as well.
    I still love using HS tools with a sharp point as I have lots of time !
    Rich

  3. #13
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    I always prefer dead sharp carbide tooling. I think what you mean by radiused would be more commonly referred to as a honed edge in the carbide insert world.
    Under extreme magnification dead sharp would appear as a radius edge also

    JL...
    Last edited by JoeLee; 02-12-2018 at 08:46 PM.

  4. #14
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    depends on the type of brazed carbide, but I'd say razor sharp edges all round (not talking about nose radius) if you're working with alu. With steel I would just stick to HSS. I had a bunch of brazed carbide way back, sharpened it up with those little HF diamond wheels, each one lasted an hour or two of turning before it chipped for various reasons. Threw them away and got some insert tooling instead, chipped 2 tips in 4 years.

    I know you really want to make this work and good for you for trying, but you are p!$$ing into the wind to some degree. $25 for a facemill and 10 inserts (or $35-40 with an arbor) would get you going in no time with very little on going effort or cost.

  5. #15
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    Great, thanks for the responses and discussion.

    First, I was talking about the cutting edge, not the nose radius. I definitely am adding a nose radius on my resharpened bits.

    I am going to have to think about this. Seems like different strokes for different purposes: there is an argument and a use for both dead sharp and with a radius. The new TC bits that I purchased seem to have come with dead sharp edges so I could reserve them for finish work on steel or aluminum/brass. I bought both C2 and C6 ones. And sharpen the original ones with a radius for ruffing work.

    I did get some HSS bits and plan to grind them into cutters for this face mill. I need to think about what to use them for and how to sharpen them.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  6. #16
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    Hi,

    A long time ago, when I sat at my desk in class, we were taught that the relative strength of the cutting edge of carbide comes from two things - the clearance angle and the size radius of the cutting edge. And that a rounded edge gave good strength to the cutting edge on carbide. But it comes at a price, it takes a lot of power and rigidity to get a plastic flow of material to move smoothly and easily over that edge. This is why old style inserts really suck on light, low power machines.

    Things have changed today. Substrates are much tougher and slippery modern coatings allow material to move much easier and smoother over much "sharper" edges. But few inserts are dead sharp even yet today. Save a few designed for non-ferrous metals. But the edges are getting smaller and smaller radii as time goes on. There are designs that now work a treat on small low power benchtop machines like many of us have at home.

    When it comes to Ye Olde Brazed Carbides, I just run a sharp edge. Even when mounting them into a flycutter or face mill like you describe. I have several I've made over the years. I know the sharp edge is not optimal for long life of cutting, but there is no real good way to put a proper radius on there at home, (or even work). In any case, my machines don't have the power or rigidity to run that type of cutting edge anyway.

    What I can easily control is the clearance angles of my edge. I try to keep the angle as small as possible. I want to keep as much supporting material under that cutting edge as possible without it rubbing. And I try to keep my depth of cut smaller, .010 to .015 deep per pass. But I run my feed rates at near ludicrous speed if possible. To make up for removal rates.

    Brazed tooling, while still available and still having a limited use, is a dying thing. I would switch to HSS for your tool bit mills. Over the long run, you will be happier I think.
    If you think you understand what is going on, you haven't been paying attention.

  7. #17
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    Quote Originally Posted by Paul Alciatore View Post

    When sharpening a TC lathe style tool, is it desirable to have a small radius on the cutting edge or should it be as sharp as the technique and abrasives will allow?

    I ask this because I like to sharpen HSS as sharp as possible but have seen commercially sharpened TC both razor sharp and with a small (0.001" - 0.002") radius. Which is best? Why?
    I sharpen a lot of carbide. I use an accu-finish machine sometimes. I sharpen to a very sharp edge unless I am doing interrupted cuts. JR

    Oh, and for the off topic point that some referenced, HSS and TC are not out of favor. And I have 1000s of new inserts and still grind my own tools also.
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

  8. #18
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    More good information. Thanks!

    OK, I get it. This style of tool is, at least somewhat, out of the vogue. I GET IT. But I have one. I did not purchase it separately, it came with my import mill. I am just trying to get some use out of it. My shop is a home shop. I do not do any production work, at least not yet. But if I purchase a new facing cutter it WILL use inserts. I DO GET IT! And they are so shinny and nice looking. A lot better than this inexpensive, Chinese made one. It would be the prettiest piece in my tool rack. Enough said on that, please.

    I am not just being stubborn; in addition, this is a learning experience. I want to know about using TC and I am sure that much of what I learn will apply to inserts as well. I have wondered about the cutting edges on TC tools, both braised and inserts, for some time. This discussion is very informative.

    The use of a rounded edge has been linked to the available HP of the mill. The facing tool is about 80mm / 3.2" diameter and the cutters are 7/16" square shank in size. It is a gear head mill and the available speeds range from 60 to 1500 RPM. Would anyone care to offer any thoughts if this is enough power to allow a cutter with a radius on the edge to cut in steel. I suspect it would be.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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