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Thread: Manual tool comp on partial radius (Lathe)

  1. #1

    Default Manual tool comp on partial radius (Lathe)

    I've been trying to figure out on my own how to manually calculate the tool nose compensation on a partial radius for a while now and i just can't seem to get it. However, I can get it right when i use the formula for tool comp on a straight line. So basically my question is: Is the formula for figuring out tool nose radius compensation the same for angles as well as for radii?

    Here are the formulas i am using:

    z axis comp= nose radius-(nose radius x tan(angle [divided by] 2))

    x axis comp= 2 x [nose radius-(nose radius x tan(45- (angle [divided by] 2))]

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  2. #2


    The answer is no to your question. You are going to have to do some trig to figure the values out.

    Care to post an example?

  3. #3


    Ok, this is what i've been practicing on. I started off at the radius on the nose of the part and thats where I've been stuck. By my calculations, the point diameter at the nose is 2.4544. I've also figured out that the coordinates for the beginning of the radius are: x2.3408 z0 and that the coordinates for the end of the radius are: x2.4643 z-.0566. I was able to correctly add tool comp to the beginning of the radius (x2.3408 z0) with the formula i posted in my original post, but when i try to use that formula for the tool comp on the end point of the radius, it gives me the wrong coordinates. Any help would be greatly appereciated.

    Attached Thumbnails Attached Thumbnails -practice-part-bmp  

  4. #4


    Also, i am using an insert with a .031 nose radius

  5. #5


    The tool compensation (your tool radius) is applied at a TANGENT to your precise position on the curve. You basicaly increase the radius programmed by your tool radius for convex and decrease it for concave by your tool radius value. An easy way to do it is just to increase the radius you program by the tool radius for convex CW cutting and decrease the radius you program by the tool rad and set NO COMPENSATION, it's a cheat, but isn't all engineering

    Say you're cutting a 4 inch dia part with a start flat of 1 inch then a convex for 1 inch (in X) then a concave for 1 inch then a flat to X0.

    Your tool (say it's 0.1" rad) would need to move back in Z by 0.1" Z for the first X 1". It would then need X compensation to the right by 0.1" and it would move into the part in Z as it tried to place itself rightwards and to the start of the curve.

    Stick a 1.01 fillet betwen the flat and the first radius to stop this.

    Think about it. Think about the centre of the tool, THAT is the path without compensation think how much you need to move it back in Z and left for concave, in in Z and right for convex.

    The above two conditions are, of course reversed for CCW cutting rather than CW. But they remain the same even if you got the tool upside down.

    Think about it.... draw a simple shape on graph paper. Get a penny and drill a hole in it- that's your tool (essentialy a circle). Trace the shape with the centre of the penny (tool path without compensation) and THINK how much you'd need to move it and where to get the edge of the penny to cut the surface... then the penny will drop

    [Edit]Personaly, I'd just cut them radiused conrners without compensations but tell the prog the radius was the design rad plus the tool rad This has a problem if you change the tool though. you need to re programme.

    I love deadlines- I like the whooshing sound they make as they fly by.

  6. #6


    Soz, just looked at the part. Easy way- the radius is 1/16"? tell it to cut 1/16" + 0.031" (your tool radius) with NO COMPENSATION.

    I love deadlines- I like the whooshing sound they make as they fly by.

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