Centerline Use
Centerline Use
(OP)
In 2d drawings, does a centerline always require symmetry in rectangular parts? Can you use centerlines in quasi-symmetric parts (see picture below)?
Example View:

Centerline labels so you can reference them:
Example View:

Centerline labels so you can reference them:
-Jason Nicholson





RE: Centerline Use
What drawings standards are you working to, and what do you think center lines mean/get you from a dimensioning & tolerancing point of view?
Depending on the 3D geometry all of your centerlines could be correct.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Centerline Use
In my head, centerlines imply symmetry. This may be wrong I know. I don't know where I got this notion and I can't find anything about it easily from the searches I have done (1 hr of searching and reading).
-Jason Nicholson
RE: Centerline Use
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Centerline Use
It's the dimensioning and tolerance scheme that have to explicitly define symmetry or the equivalent (Note I say equivalent because to US standards the application of symmetry GD&T is a bit limited but the same effect can be achieved in other ways.)
Per ASME Y14.5M-1994 2.7.3 "Features shown ... symmetrical to each other must be controlled for location or orientation to avoid incomplete drawing requirements."
Do you have a copy of 14.5?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Centerline Use
Also, the CL could mean the centerline of a feature or centerline of a part. Could be confusing for a machinist.
Chris
SolidWorks 10 SP4.0
ctopher's home
SolidWorks Legion
RE: Centerline Use
Yes I have a copy of Y14.5 2009 and Y14.5M 1994. I am just starting to read them.
-Jason Nicholson
RE: Centerline Use
This not a manufacturing drawing. Most of our drawings are inspection drawings. We only dimension critical features because most of our parts have lots of drafts and lofts which make a drawing very hard to understand. Therefore our manufacturing is controlled by the Solid Models.
-Jason Nicholson
RE: Centerline Use
In that case you may want to take a look at ASME Y14.41 - though it doesn't have too much of use.
Also there have been various threads about partially dimensioned drawings, Model Based Definition and the like. I suggest you try and find them.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Centerline Use
RE: Centerline Use
Sort of a tangent, but the OP's company (or department at least) really need to adopt a standard and work to it, otherwise what each person interprets will be different regardless of how well one person does the work.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Centerline Use
Consider a slot: Often a centermark (as a horizontal and vertical centerline) are put at the center of each arc. If the centerline required symmetry, the centerlines perpendicular to the slot would be incorrect.
However, maybe my interpretation of centermarks versus centerlines is altoghter wrong as well...
-- MechEng2005
RE: Centerline Use
All your centerlines are correct. CL 1 & 2 reference the entire part, CL 3, 4 & 5 reference the center of each flange. Since there is no dimension given for the outter flanges left and right it is assumed that the (circular) objects are centered on the overall centerline of the piece. It is also assumed that the bottom flange is centered on the centerline of the overall object. If they are not they should otherwise be controled by dimension from the center of the overall object or other controlled point.
Like I said I'm not an ME but rather a CE by trade. I am, however, quite meticulous about drafting standards of myself and my team.
RE: Centerline Use
There may be a significant disparity in the drawings generated by a CE and those generated by an ME. In this case, there is no "overall centerline" of this part. I followed this thread when it was originally posted but I did not memorize it or re-read it so I may be saying something that has already been said.
Its hard to tell whether the inner contour is a pocket or a protruding feature because there is no other view but let's assume it's a pocket. The centerlines that cross the center of this part either represent the outside of the part or the inside of the pocket, or one of each...but not all of them together, so CL 1 and 2 do not represent the entire part. CL 1 could even represent the center of the outer flanges only. CL 3, 4, and 5 are solid so you are correct about those. Regarding the outer flanges--one can assume that they are centered on either the OD of the part, the ID of the pocket, OR they may collectively establish a center plane and the rest of the part may be relative to them. Either way, something that cannot be assumed is the tolerance. In reality, they will not be perfectly centered so the amount that they can deviate, and still work, must be stated.
Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X4
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II