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Thread: Grinding angles on threading tools.

  1. #1
    Join Date
    Aug 2004
    Central Queensland, Australia

    Default Grinding angles on threading tools.

    I have been trying to grind some threading tools with my recently acquired TC grinder.

    If I set the vise to 30 degrees and then add a clearance angle in a different plane I then no longer grind it at 30 degrees but at a different angle...

    I have looked up Machinery's Handbook for a solution under compound angles but the description given is either extremely vague or I am too thick to understand it..

    Anyone know the formula for this problem??

    Here are the pages from machinery's handbook dealing with compound angles.

  2. #2
    Join Date
    Apr 2009
    Ashburton, near Christchurch New Zealand


    I will be watching this topic with interest, as far as I can see if I want to cut a 30 degree thread and I am going to be setting the compound over to, say, 29 degrees to cut on only one side of the tool it would appear that any practical angle 'sharper' than 30 degrees will be satisfactory?

  3. #3
    Join Date
    Nov 1999
    SE OZ

    Default Compound angles


    Compound angles are a difficult concept and even harder to implement accurately.

    Machinery's Handbook is very vague as compound angles are a big subject.

    Solving for compound angles is usually required for a CNC/NC machine - but can be required - rarely in the shop.

    It is a way of progressing toward a theoretical solution.

    It is easier to work backwards and forget all about compound angles - if at all possible - which it usually is.

    The solution is pretty easy.

    I will address it later.

    In the meantime, here is a sketch in two versions - that I posted some time ago in answer to a question similar to yours - that may assist:

  4. #4
    Join Date
    Jun 2008
    Toronto Ontario Canada

    Default Not so fast at the maths but I still get there.

    I worked as a " conventional" machinist for many years and frequently had to come up with rapid solutions to repair jobs. I have quite often made acceptable threading tools by searching for an appropriate broken tap( Metric, Whit, American etc)grinding off all but one " tooth " and making a suitable holder. I figure that the guys who made the taps( providing they had a real makers name on them) have or had far better equipment to get the tooth form correct than I did in shops with just bench grinders. Certainly , I enjoy working out the maths but not with a broken production line waiting for me to cut some oddball thread and an angry manager asking" how long " every ten seconds' Regards David Powell.

  5. #5
    Join Date
    Sep 2008
    San Diego



    Clamp the tool bit in the vise at a 30 degree angle from horizontal using a sine bar or wedge or ?
    Now raise the vise on your sine plate or ? to the desired clearance angle.
    Grind one angle, reverse the bit and repeat for the other angle.
    Not to worry about compound angles.
    Edit: I probably should have added that the grinding will be accomplished from above as if it were a surface grinder.

    Last edited by easymike29; 08-03-2009 at 02:39 PM.

  6. #6
    Join Date
    Nov 2008
    Suffolk, UK


    Set the axis of the tool at 30 degrees to the wheel face, then rotate the tool axis by the clearance angle, then grind by running the tool across the face of the wheel and Hey Presto. No compound angles needed.

    It's cheaper on wheels if you rough it on a bench grinder first.


    PS: If compound angles where needed machinists would have to be mathematicians, consequently there wouldn't be any machinists.

  7. #7
    Join Date
    Oct 2002
    Bremerton Washington


    I solve the problem by using little top rake in threading tools. So long as it filts the fishtail gage and the tool is on center, no finagleing with math and fancy angle setts is necessary.

    It's an interesting problem to work all these angle but the correct flank angle will appear so long as the cutting edges produce correct flank angles. Also remember there is an angle tolerance for 60 degree Unified thread system. Don't be afraid to use it.

    An optical comparator is an irreplaceable tool to have wherever form tools are being prepared. If you don't have access to an optical comparator, you can make one by gutting an old slide projector. If you rip out the slide carriage there's about enough space to slip in a tool to check its angle projected as a sharp edge shadow on a flat while wall. Make sure the projector's optical axis is perpendicular to the wall so there is no angular distortion to the image. Draw a few lines and work the math to determin the angle. This was my optical comparator for many years.

  8. #8
    Join Date
    Aug 2002


    I have to agree with Forest All the sine a cosine stuff is not needed I don't use it and have ground my own tools for screwcutting easily enough.On top of which you can buy the tips already cut or buy throw away able tungsten cutters why do yoursel brain damage where it is not required.Surely this is taking a sledgehammer to crack a walnut it works but not needed imho as an amatuer machinist myself.Alistair
    Please excuse my typing as I have a form of parkinsons disease

  9. #9
    Join Date
    Aug 2006
    Taylorsville Ky


    What is wrong with experimenting with the angles untill you get it right and then write them down for future use?

    The photo below shows a fixture a friend made years ago and I bought when he retired. It has a single angle ground on the base and I just swap the cutter from side to side and grind it on my surface grinder. I can do HSS cutters with a white wheel or carbide with a green wheel.

    EDIT: In case you failed to realize, there is no compound angle on the fixture in the photo and it produces a perfect 60 deg tip with 10 deg relief on each side of the cutter.
    Last edited by Carld; 08-03-2009 at 11:34 PM.
    It's only ink and paper

  10. #10
    Join Date
    Jun 2006
    Austin, Texas


    Quote Originally Posted by philbur
    PS: If compound angles where needed machinists would have to be mathematicians, consequently there wouldn't be any machinists.
    LOL! Or you could take the modern short-cut of rendering the tool bit in your favorite CAD, aligning the axis however it's going to sit in the tool and cutter grinder, projecting the 30 cutting angles and reading off the resulting 3-space angles.

    Basically, what Brian did on his HSS sharpening jig in Solidworks.

    He probably can do it faster than it took me to type this post
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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