What's Eveyone's Opnion on Dimension About a Centreline 1

[Zibraz]

I am a relatively new Engineer (working on drawings for a year) and I was wondering what is everyone's opinion on dimensioning about the Centre line when features are symmetrical (Example image attached).

I like doing it, it's tidier. Dimensioning about Centrelines allows me to reduce the total number of dimension lines on the drawing.

 

[MintJulep]

How do you inspect it?

Is it the BASIC center line, or the centerline of the actual part that your are measuring?

If your actual part is not perfectly square, then what?

 

[Zibraz]

It's the Centreline of the part. I only use this method of dimensioning when the features dimensioned are equal distance apart from the Centreline and to the edge.

When the features aren't symmetrical or equal I just dimension to the edge.

 

[TheTick]

It's the Centreline of the part.

No such animal. You MUST be more specific--e.g. center of two surfaces or center of a specific cylindrical surface.

 

[jassco]

Hi, Zibraz:

Centerlines are ambiguous as quite frequently there are more than ones. It is better to use GD&T to locate features to datum which can be a center plane (Derived medium plane in this case per ASME Y14.5).

Best regards,

Alex

 

[drawoh]

Zibraz,

The centre[‑]line symbol is no longer recognised by ASME standards. Just show the centre[‑]line.

I do dimensions across centre[‑]lines when they reflect my design intent. I systematically apply GD&T to my drawings, and I specify a datum feature that defines the centre. A Feature Of Size (FOS) datum really ought to be something accurate, probably not the outline of the part. Very much more often than not, I call up a hole pattern as the secondary datum, and I apply a sloppy profile tolerance to the outline.

--
JHG

 

[jassco]

Hi, Zibraz:

I see 8 different centerlines (or planes) in your drawing. When you refer to a center line, you need to uniquely identify it. The best way to achieve this is to use datum. As JHG mentioned, you may want to use pattern(s) of holes as datums.

Best regards,

Alex

 

[ctopher]

I have never seen the = = before. If it's not in the ASME/ISO/MIL specs, don't do it. It will only cause confusion.

ctopher, CSWP
SolidWorks '17
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[Zibraz]

I have copied my method of dimension off the engineers in my work place. It seems that this method of dimensioning is not ideal. I had a suspicion that this method of dimensioning wasn't standard (Hence why I asked), but it always looks neater this way.

I will avoid doing this from now on.

The centre‑line symbol is no longer recognised by ASME standards. Just show the centre‑line.

Ok thanks for specifying that. I will dimension my features to hard edges.

When you refer to a center line, you need to uniquely identify it.

The specific centreline has been identified. There is a note on our drawing template starting that dimensions suffixed with "= =" are equal about the ℄ (Thats the centreline with the ℄ symbol). Even though this is common practise in my workplace, this might not be standard practise to engineering in general.

I have never seen the = = before. If it's not in the ASME/ISO/MIL specs, don't do it. It will only cause confusion.

There is a note on our drawing template stating that "= =" means that the features dimensioned are equal across the ℄. If it isn't specified in specs I will avoid it.

 

[ewh]

As long as it is defined, either on the drawing or in a company standard referenced on the drawing, you can use it. It just isn't common any more, or per ASME Y14.5.


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

 

[drawoh]

ewh,

In ASME[ ]Y14.5[‑]2018, see Figure[ ]4[‑]47. Dimensioning across centre[‑]lines is fine as per ASME[ ]Y14.5. Everything needs to be clear and inspectable.

--
JHG

 

[jassco]

Hi, Zibraz:

No, you have not identified your center lines yet. There are four center lines at each location. They are on top of each other.

Best regards,

Alex

 

[ewh]

I was only referring to the use of the CL and symmetric symbols. Their use is acceptable if sufficient definition is given.

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