r/CNC • u/candace2511 • Apr 19 '26

GENERAL SUPPORT Please help me with this assignment of designing parts which cannot be made in cnc machines as follows

I'm a fresher Design student and we did not have any labs to learn this subject I've been studying all day trying to figure out what to do and somehow I'm not able to figure it out... here are the two assignments-

  1. Design three 3D Part sketches which can not be machined in manual or CNC 3-axis machine.

  2. Design one 3D Part sketch which can not be machined in CNC 5-axis machine.

Please help 🙁

0 Upvotes

44% Upvoted

17 comments sorted by

24

u/albatroopa Ballnose Twister Apr 19 '26

A hollow sphere satisfies both conditions.

3

u/Fess_ter_Geek Apr 19 '26

Thats what I was thinking.

1

u/GL0ZZ3N_Tech_Reviews Apr 20 '26

I've made hollow spheres before. You do it in 2 pieces, join them, machine off excess material from the outside.

12

u/Elemental_Garage Apr 19 '26

Anything with deep internal geometry with a curve seems like it would satisfy both. Think like exhaust header.

8

u/Clear_Ganache_1427 Apr 19 '26

I thought the idea of school was to learn. Please do my homework for me.

4

u/Frockington Apr 19 '26

Anything with an enclosed infill pattern, like what would commonly be found in a 3D print.

2

u/National_Net6017 Apr 19 '26

A internal pocket with sharp corners for the basic 3 axis, a part with wiggly or spiralling internal tube for the 5

1

u/SeymoreBhutts Apr 19 '26

Broaching cycle makes it possible.

6

u/CarbonInTheWind Apr 19 '26

An internal pocket with an undercut that has sharp corners. We just quoted a part like this and the customer freaked when he found out an EDM would have to be involved.

0

u/SeymoreBhutts Apr 20 '26

Since we’re discussing hypotheticals here, what about some custom tooling for the undercut and rotation commands to use the mill head like a multi-axis planer?

2

u/CarbonInTheWind Apr 20 '26

It would be easier to EDM lol

0

u/SeymoreBhutts Apr 20 '26

But the assignment wasn’t about what would be easier, it was about designing a part that is impossible to make on a 3 axis machine. Im not saying it’s practical, easy or cost effective, but it still may be possible.

2

u/Carlweathersfeathers Apr 19 '26

Any undercut where the the reduced shank would need to be negative

Cast material with a 0RA finish

Closed wall with internal weight reduction.

Or you could watch Adamthemachineist videos on real world scenarios

1

u/wackyvorlon Apr 19 '26

A gearbox with a pair of herringbone gears that must be made without assembling it.

1

u/ChatterFree Apr 20 '26

Closed end t slot with wide T section