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  • RLWP
    replied
    Originally posted by Evan View Post
    The sharpest edge obtainable by any process is the edge of broken glass. The actual edge is one molecule wide. The standard for cutting exceedingly thin sections of tissue for microscopy is the broken glass microtome.
    You can make some splendid scrapers for wood that way too

    Richard

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  • Boucher
    replied
    Adequate Sharpness

    The cutting edge left from finishing with either CBN or a fine Diamond wheel is very good (almost like a mirror finish). If one is set up with guides and the table is left at the correct tilt, it only takes a second to refresh an edge. Try it , You will like it. The fact that the Tangential tools cut so good is related to the simple accuracy of their sharpening fixtures.

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  • Evan
    replied
    The sharpest edge obtainable by any process is the edge of broken glass. The actual edge is one molecule wide. The standard for cutting exceedingly thin sections of tissue for microscopy is the broken glass microtome.

    Leave a comment:


  • Dr Stan
    Guest replied
    Originally posted by vpt View Post
    Many times I hear the best possible edge is from snapping a bit in half. Like when you shatter a endmill or break a bit off in the lathe. The edge of that break is normally razor sharp.

    I know nice formed angles aren't possible this way but has anyone ever tried making cleanish break and turned with it?
    Sounds similar to the process of napping flint for spear & arrow heads. I just do not know how one could control it enough to create the necessary clearance angles.

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  • vpt
    replied
    Many times I hear the best possible edge is from snapping a bit in half. Like when you shatter a endmill or break a bit off in the lathe. The edge of that break is normally razor sharp.

    I know nice formed angles aren't possible this way but has anyone ever tried making cleanish break and turned with it?

    Leave a comment:


  • Doozer
    replied
    Originally posted by Boucher View Post


    .
    O.T. -- But,
    I had the same problem fitting a box end wrench on the compound nuts
    when I had my Nardini. Nice fix.

    --Doozer

    Leave a comment:


  • customcutter
    replied
    Originally posted by Dr Stan View Post
    The good ones do not. They use a stone or a steel just like my Dad the meat cutter taught me.

    Or even better yet, a leather strop like a barber uses or a leather wheel like a wood carver uses on a chisel.
    Or a paper wheel loaded with buffing compound. Or a 3M belt in the 5-10micron range.

    Ken

    Leave a comment:


  • Evan
    replied
    At school the instructor says since hss is pretty much out dated, and we wont be covering it.
    That is a ridiculous statement. HSS tools are a part of the arsenal and will address cutting problems that cannot be solved any other way. You should print out this thread and take it to him, privately.

    I use everything from carbon steel tooling to diamond, ceremet and CBN cutters. They all have their advantages and disadvantages, uses and limitations.

    I'm just waiting for the Russians to start producing tooling with the trillion carat stockpile of superhard diamonds that they just declassified. The diamonds are a different crystal structure created by a meteorite impact and twice as hard as regular cubic diamonds.

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  • lazlo
    replied
    Originally posted by Boucher View Post
    Freehand grinding is good but simple guides produce better-looking results without a bunch of facets. This is one that I made from some HDPE.
    Nice job Byron.

    Leave a comment:


  • Boucher
    replied
    Grinding HSS

    Freehand grinding is good but simple guides produce better-looking results without a bunch of facets. This is one that I made from some HDPE.


    John Stevenson’s recommendation to use the diamond wheel on HSS and view it as an expendable has improved the quality and sharpness of my tools.

    With these grinding guides I Don’t use the overhead water pot but I do wet the table and guide which removes a lot of the heat and prevents the bit reaching a troublesome temperature.

    I rough out the bits on the 2X72 belt sander and finish on the grinding wheels.

    For grinding good threading tools using HSS cutoff blades I copied this setup from over on the PM Gunsmith forum.


    The wheel shown is CBN that Evan’s wife got for me.

    Leave a comment:


  • lazlo
    replied
    Originally posted by sch View Post
    that dipping really hot HSS into water to cool it can induce microfractures at the thin edges, a POV supported by metallurgists at Carpenter Steel, a tool steel specialty company.
    We've discussed that rec.metalworking thread here many times. My recollection was that when he asked the guys at Carpenter Steel, they told him to dip the tool steel.

    The amusing part was when several folks pointed out that all grinders have dip pots, and that most machine shop books, including Moltrecht's Machine Shop Practice, tell you to dip the HSS to cool it between grindings. He said he was going to track down Dr. Moltrecht and ask him why -- the thread stopped there

    I agree with the point about HSS having red hardness in the 1200°F range, that should make it immune to as much heat as a bare hand can handle.
    Last edited by lazlo; 09-21-2012, 10:54 AM.

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  • Mcgyver
    replied
    Originally posted by sch View Post
    There is a school of thought, bolstered by a reviewer on the old rec.crafts.metalworking site that spiralled into oblivion >10 yrs ago, that dipping really hot HSS into
    water to cool it can induce microfractures at the thin edges, a POV supported by metallurgists at Carpenter Steel, a tool steel specialty company. .
    I remember that, and while he didn't seem to have a lot of support it also seemed an informed and well reasoned view, and he carried on despite the mob reaction it generated.

    .....perhaps we would be better to hold the bit with vise grips and let it turn blue...and maybe dunk the other end to draw off heat but not shock the business end

    I've not embraced the well reason view into practice because 1) its so much easier to sharpen the bit hand held and you need to cool it to hold onto it and 2) if I was inducing micro cracks I can't say I've noticed it in performance. hss bits last a long time in my experience...then again I don't how long they could last without the quench....or maybe these micocfractures are so shallow they get stoned out.....or maybe i'm cooling it before it gets too hot and avoiding micocfractures.

    good to be aware of in any event.

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  • sch
    replied
    HSS does not mind being ground hot, so some color change in the bit will not damage the steel. It is designed to cut at 1000F without loosing its hardness, not that you would want to grind it
    at any where near that temp. There is a school of thought, bolstered by a reviewer on the old rec.crafts.metalworking site that spiralled into oblivion >10 yrs ago, that dipping really hot HSS into
    water to cool it can induce microfractures at the thin edges, a POV supported by metallurgists at Carpenter Steel, a tool steel specialty company. YMMV, but be not concerned by a little
    heat induced coloring near the tip. Another consideration is that smaller bits are a lot easier to shape, ie 1/4 to 3/8" is easy compared to 1/2" or above, especially for threading cutters.
    It helps to have a threading gauge and a set of ID/OD radiuses for shaping tool bits for same. A good sharp cutting wheel of high quality ALOx, reduces cutting heat significantly and can make
    short work of shaping a bit. A bad or inappropriate wheel will cut slowly and burn your gloved fingers. A tool holder is a nice thing to have along with an easily calibrated angled tool rest.

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  • darryl
    replied
    I've wondered also about how to identify a sodium filled valve, without grinding into it. I have some stellite valves that I've used for making custom cutters. Seems to work as well as some of the hss cutters, maybe better. With this kind of thing it takes time to prepare a cutter, since there's often a lot of slow grinding to do.

    Leave a comment:


  • michigan doug
    replied
    Why do you suppose there are companies still today, who make high speed steel inserts?

    Because sometimes, hss is better for the application. Under some circumstances, you can get a better finish, etc.

    Please carry on,

    doug

    Leave a comment:

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