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# Taper/fillet calculations

#### CNC1970

##### Plastic
Hi, guys, I need some help! Since we don't have CAD/CAM software anymore, we have to write all progs for our turning lathes manually... Recently we've got tons of parts with tapers and fillets, so I really need to figure out the way of calculating this stuff. This is an example of what I'm talking about:

Here's isometry:

And actual dimensions (in mm):

Now, I'm more interested in formulas and sort of step by step guide than in getting only results for this particular part because I'll have to do many other variations of this part, I mean same type of geometry but with different dimensions, angles, etc. Can someone help me? Let's say I use outer turning tool with a tip radius 0,4. So my G-code starts like this:

G0 Z10. (safety distance from face)
G0 X-0.8 (moving to the center point of part considering my tool tip radius is 0,4)
G1 Z0. F0.05 (moving to the face of the part)

Errrr.... that's it... How can I calculate the rest coordinates of this radius and taper manually? Any ideas?

#### SIP6A

##### Titanium
How can I calculate the rest coordinates of this radius and taper manually? Any ideas?

Take a Trig. class

#### Booze Daily

##### Titanium
Yep. You’re going to have to draw a bunch of triangles and use trig to solve for the endpoints you need.

#### CNC1970

##### Plastic
Of course I know it should be somehow calculated via triangles and tangents but I'm really in trouble with calculating compensation for tip radius and this fillet, considering it's not a full radius 12,5 but just a part of it. So I'm really need a proper guide

#### BoxcarPete

##### Stainless
Of course I know it should be somehow calculated via triangles and tangents but I'm really in trouble with calculating compensation for tip radius and this fillet, considering it's not a full radius 12,5 but just a part of it. So I'm really need a proper guide

Since you know the radius of both the form on the part and your tool, you can calculate the endpoints of your toolpath by drawing lines from center of the part to center of the tool tip. Here's a circle calculator tool which will come in handy. You know the radius and arc angle so you can solve for the x and y coordinates of the endpoint through the chord length.

#### Booze Daily

##### Titanium
Just use TNR comp.

#### SIP6A

##### Titanium
Of course I know it should be somehow calculated via triangles and tangents but I'm really in trouble with calculating compensation for tip radius and this fillet, considering it's not a full radius 12,5 but just a part of it. So I'm really need a proper guide

When I said "take a trig class" I wasn't being snarky. If your going to do this kind of work your going to have to learn trig. In your first post you said "Since we don't have CAD/CAM software anymore" what's the backstory on that? There are so many free cad programs out there, that's no reason for a shop that has a cnc lathe not to have some sort of cad program. One last question. what level of math are you comfortable doing?

#### CarbideBob

##### Diamond
Just use TNR comp.
^^This^^
Makes life so much easier and is faster to get-r-done.
Let the control draw the triangles and do the math work for you.
Added plus is that the G-code matches the part print so mods are easy for anyone.

#### EmanuelGoldstein

##### Diamond
Yuck ! yuck yuck yuck yuck yuck ! Barf ! Gag me with a spoon, pour the puke into your mom's combat boots !

I have an old DOS bobcad, it's really fast for simple drawings and pulling the coordinates of your points. Knowing trig is good, that way you can understand why, but most any simple cad program will give you the correct geometry for center-of-the-tool-radius programming, like it should be done, without that stupid comp fucking everything up

Sent you a PM

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