Lathe center marks

[marshell]

When specifying the center mark left on the ends of a lathe built part, should it be fully defined via GD&T, or can a simple note allowing a max diameter and max depth be specified?

Thanks in advance.

 

[greenimi]

My 2 cents:

I would say that is a risk management assessment, when the designer will get away with max diameter and max depth or more robust product definition must be used. (profile for the conical surfaces, etc.). When is good enough?

The same as: how to define radii?
R with ± or with profile.

Where you draw the line? Up to the designer to decide; the complexity/criticality of the feature. Function again.

 

[drawoh]

marshell,

If the lathe centre mark is not functional to me, but otherwise I don't care, I would specify a maximum geometry for it. Don't require the feature. Allow them to do the feature.

--
JHG

 

[mkcski]

Cutting tools used to machine lathe centers are designated as such and have an incldued angle and tip-clearance hole per industry standards for lathe centers - typically 60-deg included angle. So don't bother using GD&T to control the dimensions of the center-hole.

Certified Sr. GD&T Professional

 

[FACS]

It's not a functional feature, and has no fit requirements.

The position is by default, and is concentric with the part.

So specify the maximum depth only, and that should be it. The standard included angle will default the OD by the depth.

 

[CheckerHater]

Agree with mccski:

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[mkcski]

So specify the maximum depth only, and that should be it. The standard included angle will default the OD by the depth.

Considering this comment: you could put a MAX diameter and MAX depth to limit any concerns with structural or other design requirements.

Certified Sr. GD&T Professional

 

[FACS]

With a 60 degree included angle, calling out both diameter and depth is considered a redundant dimension.

 

[CWB1]

Neither is necessary. Call out the location and max center size, not to be confused with center geometry. Also be sure to include a note stating so if centers are optional and not necessary for inspection.