GD&T Involing Conical Surface

[filippoGDeT]

Dear All,

I've trouble to setup a proper DRF for the part reported in the picture. The datum concept here is set a DRF in order to use the conical surface as secondary axis in order to control the location of the cylindrical hole respect to it.

Do you think that what is set up is correct?

Looking forward to receive your help.

Regards,

Filippo

 

[jassco]

Hi, Filippo:

It depends on your design intents. Without seeing application where it is used, it is hard to tell your intent.

Do you want your hole (14.38, missing a diameter symbol here) perpendicular to datum A or do you want it to be parallel to axis of the cone? You need to realize that datum axis B is related to datum A. In another word, datum axis B (which is perpendicular to datum A) is different from true axis of the cone.

Best regards,

Alex

 

[mkcski]

jassco:

At a quick glance, can you "avoid" locating the edges of the part from the conical hole and "flip" to locate the conical hole from the edges of the part. I'm having trouble with the simulating the datum for the conical hole.

Certified Sr. GD&T Professional

 

[Belanger]

I think what you have right now is OK. For those who have access to the ASME standard, there is an example of a conical datum on page 50, near the middle of the page. What's unaddressed in your drawing is the form, location, etc. on the semicircular outside surface.

Just remember that the difference between profile and position is that profile controls form (and usually size, location, orientation), whereas position only controls location and orientation.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[mkcski]

J-P:

I was thinking of figures 4-44 and 4-45 when I said I was "having trouble" with simulating the conical hole, especially as a secondary datum and its RAME relative to A (for locating the right edge of the part and the hole).

Certified Sr. GD&T Professional

 

[mkcski]

Filippo: I am curious, does the profile on the edge of the part just for that edges or the entire periphery?

Certified Sr. GD&T Professional

 

[pylfrm]

filippoGDeT,

What you have appears correct to me. In terms of degrees of freedom: datum feature A constrains two rotational and one translational, datum feature B constrains two translational, and datum feature C constrains one rotational.


mkcski,

I'd say using the conical surface as secondary datum feature instead of primary should actually be easier, because three degrees of freedom are already constrained. This eliminates the potential for rocking of the part relative to the simulator due to form error of the cone. Admittedly, it only shifts the issue to the planar feature, but that's a much easier place to deal with it.

The theoretical datum feature simulator is a conical surface that is entirely outside the part material, and has the greatest possible uniform offset from the true profile in the direction corresponding to reduction of material on the part surface.

A simple physical realization of this would have a flat surface to contact datum feature A, and a spring-loaded pin with a conical tip constrained to slide perpendicular to the flat surface. I have used this scheme in the design of fixtures to locate castings for machining, and it works quite well.


pylfrm