Orientation & Length

[FlowMonkey]

Morning All

I have a cast part with a defined length and two orientation features, see attached.
The length will be reduced to 189.4 +0.25 -0 how does this affect the two orientation features?

I'm no expert in GD&T!.

Many Thanks

 

[CheckerHater]

Generally, changing length should not affect your orientation requirements, BUT I really would like to see more of your part.
Your GD&T looks suspicious to me.


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

 

[FlowMonkey]

It's just a cast cylinder with flanges. The X datum is the centre line

 

[CheckerHater]

Could you be more specific, how do you specify datum X, what are datum features A and B, and what is the feature you are trying to control?

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

 

[FlowMonkey]

OK bigger drawing attached.

 

[ewh]

Datum X cannot be the centerline. It has to be tied to a feature. Which feature? There are three diameters shown.
As drawn, datum A is the centerplace of the 190.60 dimension, not an end face.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[CheckerHater]

Normally, FCFs applied to dimension line would mean that feature of size 190.60 is being controlled, but in relation to what?

Datum feature A if FOS 190.60 itself and sloppy placement of datum feature symbol B doesn't help either.


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

 

[drawoh]

FlowMonkey,

It is good practice to select datum features that do not get machined off. I am looking at your datums[ ]A and[ ]B. Also, it is good practice to separate your casting drawing from your machining drawing. Let the foundry worry about making moulds and melting metal. Make a separate drawing for machining.

As noted by ewf, your datums must be a feature on your part. You cannot attach datums to centrelines.

--
JHG

 

[Tunalover]

Flowmonkey-
In a way, a datum IS associated with a center line if the datum is established with a diameter. Based on this thread, sounds like you need training and a D&T reference book. I also concur with drawoh that the machined part needs to be shown on a separate drawing with a different part number than the cast part.



Tunalover

 

[CheckerHater]

From what I see on the drawing, datum features A and B ARE machined surfaces. In fact, drawing looks like it actually may be separate machine drawing.

It is unfortunate use of GD&T (or is it GPS?) that's troubles me.


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

 

[ewh]

The OP needs to control the perpendicularity of datum A and/or B relative to datum X (which he has), then control parallism of one to the other.

My point regarding the center line is that the center line cannot be the datum, only the axis of a datum feature (which is not specified in the example). Y14.5M-1994 ¶4.3.2 states "... shall not be applied to center lines, center planes, or axes...". While I could not find this same statement in the current version, the application requirements are still clearly defined in ¶3.3.2 of the '09 standard.

A good review of the standard should help the OP understand where the example is lacking.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[FlowMonkey]

We now have a copy of Y14.5 and I also bought a book on GD&T.

From my understanding and reviewing the examples in the standard how does my latest effort look?

For the curious the drawing IS a machined casting and I do produce a separate casting and machined drawing.

Many Thanks.

 

[FlowMonkey]

Here is the attachment.

I'm interested in my understanding of GD&T on this view.

Many Thanks.

 

[ewh]

You probably want to specify Ø68.10 as a continuous feature (or add a quantity). If a continuous feature, both can define the axis of datum A, otherwise only one will be the datum feature.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[CheckerHater]

I would reserve Continuous feature for features that, well... continue.

This case looks more like Two features One axis (see Fig. 4-24, 4-25 in Y14.5-2009 book)


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

 

[ewh]

This may be true, if the diameter not dimensioned is other than Ø61.10. If the diameters are the same, I see no issue with making them a single continuous feature. Otherwise, the undimensioned diameter will also have to be controlled relative to datum A (or not, depending on function).

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[CheckerHater]

If you look into definition of <CF> in Para. 2.7.5 and 3.3.23 as well as Fig. 2-8 thru 2-10, you will see that it is defined as "interrupted" feature with no material in-between the "sub-features".

One may argue that this definition is open to more than one interpretation - well that's exactly the reason I would avoid it alltogether.


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

 

[Belanger]

And note that imposing a <CF> modifier automatically makes them aligned with one another (per Rule #1).

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