Problem- Student

[highmikebart]

Hi! I'm having trouble finding the size of an I.D. arc on a CNC lathe. I am using a boring tool with a .047 tool nose radius and am given two lines of code: G01 X3.844 Z-.500 F.015, followed by: G02 X2.500 Z-172 R.672. I am not using tool nose compensation and am asked to find the size of the arc being machined. This is an I.D. G2 radius. I am given a choice of four sizes: .531, .578, .625, and .672. Can anyone please show me how this is done and what the answer is? Thank you.

[holbieone]

R.672 is the programmed radius

or are you looking for the arc length

[dcoupar]

Maybe this will help. On an outside radius, subtract the tip nose radius from the programmed radius (see attached .jpg). On an inside radius, add the tip nose radius to the programmed radius.

[highmikebart]

Thanks for the reply! The question asks for the size of the arc that is machined? I assume that means arc length. Thanks again!

[highmikebart]

Originally Posted by dcoupar Maybe this will help. On an outside radius, subtract the tip nose radius from the programmed radius (see attached .jpg). On an inside radius, add the tip nose radius to the programmed radius.

Hi! Thanks for the help! The question is asking for the size of the arc? Do you think that means the arc length? Thank you!

[cogsman1]

So as the last post showed you.
When you are NOT using tool nose radius comp. and doing a CONCAVE radius you will need to subtract the size of the radius from the radius you want/need on the part to get the programmed value.
If you are cutting a CONVEX radius you will need to ADD the tool radius to the needed radius for the program.

For your example;
You have a .047 tool radius, and the program has .672 radius in it.
to find the size the part will have you need to SUBTRACT the tool radius from the programmed radius (.672 - .047 = .625)

[small_toys]

The drawing in dcoupar's post does not match what he is saying. The outside arc (blue) is a larger radius than the inside arc (red).

[dcoupar]

highmikebart,

If someone asks me the SIZE of the arc, they're probably looking for the radius that is actually being cut. If they asked for the arc length, then they probably want the length.

small_toys,

The blue radius LOOKS larger because it's outside the red radius, but it's actually smaller. Draw it up in your own CAD system if you don't believe me.

[dcoupar]

small_toys

I redrew it with a 0.125 tool nose radius and let the CAD system do the dimensioning. As I said before, the actual radius is SMALLER than the programmed radius.

[small_toys]

dcoupar,
You are correct. I was thinking the center points of the arcs being the same, but they are different. The arc is tangent to both sides. This will put the smaller arc on the outside.

[dcoupar]

Good. I Thought maybe I was losing my mind.