Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 22

Thread: Problems with toolbit sharpening

  1. #11
    Join Date
    Sep 2019
    Posts
    4

    Default

    Ahhh. I read somewhere that you cant run a flycutter fast enuf so gave it the boogey. Ill wind it back to 250 and see how it goes from.there. its just a wee 3inch flycutter and im really only.just shaving the surface. Tha ks.

  2. #12
    Join Date
    Oct 2014
    Posts
    469

    Default

    It looks like you found the problem, too fast! And if it is cutting good at the start it seems you are grinding the right shape tool. I will only add that after grinding you need to stone out the grinding marks with a smooth stone. Look at the edge with a 5 to 10 power loupe and you will see why.

  3. #13
    Join Date
    Apr 2017
    Location
    Kelowna BC
    Posts
    2,565

    Default

    Quote Originally Posted by MattiJ View Post
    HSS doesn't mind bit of discoloration during grinding. Actually up to dull red hot gloving has little effect on temper.
    Tho grinding cracks can be a problem with aggressive grinding and water cooling just makes it worse.

    I'd start from looking from surface speed, HSS quality, steel quality and mill scale on steel.
    A trait of HSS is red hardness, I often made boring bars, by welding 5/16 HSS blanks to a bar to make boring bars. used an arc welder to weld. then grind my tip profile and use them.

  4. #14
    Join Date
    Jan 2014
    Location
    Long Island, N.Y.
    Posts
    2,725

    Default

    Quote Originally Posted by Kiwipaulnz View Post
    Ahhh. I read somewhere that you cant run a flycutter fast enuf so gave it the boogey. Ill wind it back to 250 and see how it goes from.there. its just a wee 3inch flycutter and im really only.just shaving the surface. Tha ks.
    Still a bit fast (~190SFM). Try around 120 to 150 RPM.

  5. #15
    Join Date
    Sep 2001
    Location
    Mountain Brook, AL
    Posts
    1,190

    Default

    As per Mattij and 754, once HSS is hardened there is no simple (non-industrial) way to soften it. To quote someone at Practical:

    "HSS is, generally speaking, not anneal-able. If it were, breaking a drill or tap off would be no big deal... anneal it and drill it out. We all know that just doesn't work. You can actually MELT HSS with a torch, let it cool at room temp and it'll be, for all practical purposes, just a hard as it was before." The main problem with red heat, ie grinding a tool bit is the micro-cracking that can occur when water
    quenched. On one of the alt.??machining?? (dunnoh which since the alt universe imploded in early '00s with flame wars) there was a post by a Carpenter Steel employee to the same effect.
    Steve

  6. #16
    Join Date
    Dec 2015
    Location
    Chilliwack, BC, Canada
    Posts
    5,574

    Default

    Quote Originally Posted by Kiwipaulnz View Post
    Ahhh. I read somewhere that you cant run a flycutter fast enuf so gave it the boogey. Ill wind it back to 250 and see how it goes from.there. its just a wee 3inch flycutter and im really only.just shaving the surface. Thanks.
    I don't know where you read that but it was VERY wrong. And totally skipped the idea that HSS has a maximum cutting speed in linear feet or meters per minute depending on the material you are using. Or it was related to flycutting something very freely machining like certain types of plastic. But for cutting steel with an HSS cutter there is very much a upper maximum RPM you want to stay under in order to get a good edge life.

    Here is a link to a page with a CHART OF CUTTING SPEEDS in both imperial and metric for HSS tool. It is intended for lathe work but speed at the cutting edge is the same for lathe and milling and drilling so the numbers in the table still apply to all cases. It does not matter if the tool or the work is moving to the tool bit.

    It gives a maximum of 80 to 100 feet per minute for working with mild steels. This number range isn't carved in stone. But once you are over that limit tool wear becomes a big factor. And most folks would like to stay comfortably under these numbers in the home shop to extend time between sharpenings. So a good range of values for home use would be 60 to 80 fpm depending on the exact alloy in use.

    Next you don't want to just pull numbers out of the air. That can still get you into trouble in both ways. In this case it's a 3 inch flycutter which inscribes a circumference of just over 9 inches or 3/4 of a foot per rev. And if we're sticking to a conservative maximum of 80 fpm that's 80/.75= 107 rpm And even at the allowable maximum of 100FPM/.75ft= 130 RPM.

    So even your idea of dropping down to 250 RPM is still too fast. Mind you it's highly likely that the cutter will do just fine for this one piece if it survived half a pass at 1200 RPM. But it won't cut too many passes before it wears the end and starts complaining. But if you are trying to learn this stuff it would be a good idea to start with industry suggestions for maximum speeds for various materials and stick with those suggestions.

    Note that these values apply to operations in the lathe and on the drill press. If you were cutting a lump of 3" or 75mm mild steel in the lathe you would not want to use a speed any faster than 130 RPM either if you are using HSS cutters. And if you were drilling a 1" or 25mm hole with roughly a 1/4 ft circumference in that same steel you would want to do so at no higher than 100fpm/.25ft=400 RPM. But since most of us do not like having to sharpen large drills all that often if you stuck to a more conservative 60 fpm you would want to use just 60/.25=240 rpm for that 25mm or 1" drill. Of course this is also provided that the load doesn't make the lathe you have dance around or stall the motor. All of these speeds and feeds are based on big heavy machines able to turn the tools without any stress. On home size machines we may find that the machines are happier and run smoother at less than these maximum suggested speeds and feeds.

  7. #17
    Join Date
    Apr 2017
    Location
    Kelowna BC
    Posts
    2,565

    Default

    IF you don't learn how to calculate rpm for cutting, and it should be done on almost every cut..
    you will either , burn up tooling.. or take much longer to perform the work..... the odd time you get lucky and maybe pic right.
    after a while you will intuitively know for stuff up to one inch being turned.. or drilling.
    but if you are going to try to learn to use a machine by luck or guesswork.. you waste time of break /dull tools.

  8. #18
    Join Date
    Jul 2017
    Location
    Buffalo NY USA
    Posts
    534

    Default

    Was gonna say, I would be afraid to run a flycutter much faster than 200 RPM in any case. Even if everything holds together, I can't afford that much HSS.

  9. #19
    Join Date
    Sep 2019
    Posts
    4

    Default

    Thanks so much guys. Very helpful indeed. Its bviously an area i HAVE to know. Guessqork doesnt work. Iys all so interesting learning this stuff. Thanks.

  10. #20
    Join Date
    Apr 2012
    Location
    NE Thailand
    Posts
    1,226

    Default

    Quote Originally Posted by MattiJ View Post
    HSS doesn't mind bit of discoloration during grinding. Actually up to dull red hot gloving has little effect on temper.
    Tho grinding cracks can be a problem with aggressive grinding and water cooling just makes it worse.

    I'd start from looking from surface speed, HSS quality, steel quality and mill scale on steel.
    This.
    All of it.
    Inc the quality of the HSS, and it's pretty difficult to actually get HSS TOO HOT during grinding to affect its performance.
    Never happened to me yet.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •