New to cnc, general questions.

scorpion411 · Nov 26, 2019

Hello, i am new to CAD design and machining and i have some general questions because i want to prepare a 3d model for the machine shop for CNC.

Lets say that i want to design a hole of 15mm with tolerance +0.00 to +0.10mm and a 15mm shaft with tolenrance -0.00 to -0.10. What dimensions will i have to design in the 3d model? Should both be 15mm and refer the tolerances or should i design for example 14.95mm for the shaft and 15.05mm for the hole?

Or in other words what dimensions the CNC machine "see" from the 3d model as to generate the Gcode? Does it take into account the tolerances or these are only for the machinist?

Thanks!!

mneuro · Nov 26, 2019

The model does not get converted to Gcode. Either the machinist will program the parts at the machine using conversational format, or it will be programmed offline using CAD software.

My experience has been that the model should be generated at nominal dimensions. So in your example, it would be modeled at 14.95mm, but the print should be dimensioned with +0.00 and -.010.

How you dimension a print give a lot of clues as to the intended use, but it is easier to program with everything at nominal.

athack · Nov 28, 2019

In our shop and with all of our customers the print is still king. Yes we do have models for CAM purposes but documentation still seems to rule.

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New to cnc, general questions.

scorpion411

Plastic

mneuro

Cast Iron

athack

Stainless

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