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Taper/fillet calculations

CNC1970

Plastic
Joined
Mar 3, 2022
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:

3.jpg


And actual dimensions (in mm):

2.jpg


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?
 

Booze Daily

Titanium
Joined
Sep 18, 2015
Location
Ohio
Yep. You’re going to have to draw a bunch of triangles and use trig to solve for the endpoints you need.
 

CNC1970

Plastic
Joined
Mar 3, 2022
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
Joined
Nov 30, 2018
Location
Michigan, USA
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.
 

SIP6A

Titanium
Joined
May 29, 2003
Location
Temperance
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?
 
Joined
Apr 14, 2018
Location
Airstrip One, Oceania
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 :D
 








 
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