Symmetrical Part problem!
Symmetrical Part problem!
(OP)
My part is symmetrical throughout except for two cutouts. I want to use symmetrical dimensions to minimise my time spent and make it look good. So now I just have a note in my drawing which reads "the part is symmetrical about the centre line except for connector cutout" and on the drawing view I have an arrow saying these are the two cutout locations. Is this acceptable? or are there any other options which will be time saving and easy to read?





RE: Symmetrical Part problem!
Do you make use of geometric controls?
What you've done doesn't sound like it is explicitly supported by drawings standards I'm familiar with so it may be misunderstood/misinterpreted.
If nothing else think about this - how symmetric is symmetric? I.E. how far off from symmetry can the features be and relative to what datum?
ASME Y14.5M-1994 does have some suggestions for general notes such as "PERFECT LOCATION OF SYMMETRICAL FEATURES AT MMC REQUIRED FOR RELATED FEATURES." take a look at section 2.7.3 if you work to this standard.
What can seem like a nice drawing short cut doesn't always seem so smart when parts come in wrong
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Symmetrical Part problem!
If you show features that appears to be symmetrical across a centre line, I would assume that they are nominally symmetrical. This is especially true if you dimension one side only from the centre line, or show dimensions across the centre line. I strongly prefer the latter, since the dimensions are measurable.
Use profile tolerances to control the symmetrical faces. I claim that the symmetry is of extremely limited use.
Asymmetrical features are no problem. Just show them.
--
JHG
RE: Symmetrical Part problem!
lightweight, cheap, strong... pick 2
RE: Symmetrical Part problem!
lightweight, cheap, strong... pick 2
RE: Symmetrical Part problem!
This is a separate question. How about starting a new thread?
--
JHG
RE: Symmetrical Part problem!
RE: Symmetrical Part problem!
lightweight, cheap, strong... pick 2
RE: Symmetrical Part problem!
Nowadays, I would dimension the part (not from centerlines) AS IF it were not symmetrical in any way.
Oh. Also, if the few asymmetrical features on your part are not OBVIOUSLY asymmetrical, I would make them so, or add otherwise vestigial features that are fluorescently asymmetrical.
Mike Halloran
Pembroke Pines, FL, USA
RE: Symmetrical Part problem!
Your note tells the reader what the part is NOT. Drawings must define what the part IS.
Consider a dimension that states "This dimension is not 123 mm". Not very useful is it?
Drawings need to be complete, clear and unambiguous.
"Easy to draw" is way down the list of important requirements.
RE: Symmetrical Part problem!
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Symmetrical Part problem!
Your drawing looks fine to me. It conforms to my first suggestion, above. To apply form controls, you must select features that define your centre lines.
--
JHG
RE: Symmetrical Part problem!
The OP is asking if his note is acceptable or if there is a better way. My direct answers are; the note is only acceptable if it’s clear (requires no phone call) and the drawing example I presented is IMO a better way because it’s clear and does not require a note at all.
The problem here is the abuse of overusing the word symmetrical to describe a part who’s features only need to be positioned about a centerplane. The OP does not need to include a note at all.
lightweight, cheap, strong... pick 2
RE: Symmetrical Part problem!
1. According to CASA (atleast that's what I was told) every dimension on the drawing needs to go through FAI (first batch) & Goods receiving inspection everytime we receive (check 10% of parts again all dims). So it's easy to put dim's on the drawings but in reality I can't get my instruments to measure those dims. (we have calipers, micrometer, hole & bore guages for now)
2. Koda94's drawing would be another way but when you need the part toleranced from the centre ordinates are not recommended (plus I do not want overalls as they are don't affect anything so I want give the supplier some freedom). Plus too many features for my part and it will look very messy (both hard for machinist and the inspector).
3. We are currently putting in place various standards and I am setting up design drafting standards. To answer Kenat's question , No we are not following any standards as of now.
4. I only have one boss with fillets not symmetrical in the entire part - currently showing them with an arrow to refer to the notes. (Still going against the standards which I do not wish to do in future when we have established standards to work towards)
Mintjulep gave me a good point to think about.
Cheers,