"Closed" dimensions 1

[evolDiesel]

Guys,

I'm suffering memory loss and need some help and possibly a reference [standard] to verify but I've always known "closed" dimensioning to be wrong.

This is where you have:

|<----- 1 ----->|<--------- 2 --------->|

as opposed to this:

|<-----------------3 ------------------>|
|<----- 1 ----->|

Help me out - is this a will/shall type thing or a best practice and more a result of getting more out of your tolerances? I'm struggling to remember and I browsed through an old engineering drafting textbook and couldn't find anything on it.

Thanks,

Jack Lapham, CSWP
Engr Sys Admin
Dell M6400 Covet (24 Season 8, Ep 22)
Intel Core 2 Duo T9800, 2.93GHz, 1066MHZ 6M L2 Cache
8.0GB, DDR3-1066 SDRAM, 2 DIMM
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W7x64 | sw-01: 55.92
SolidWorks 2011 x64 & EPDM both sp2.0

 

[pmarc]

Do you have access to Y14.5 standard ('94 or '09 edition)? Fig. 2-4 plus para. 2.6 might help you.
Figs. 1-19 & 1-20 in '09 or 1-17 & 1-18 in '94 may be also helpful.

 

[KENAT]

Either is legal and either may be appropriate depending on end function etc.

If the dimensions are basic then the 2 schemes are equivalent.

As pmarc says 14.5 has a little bit on this, but maybe not in the detail you want.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[thebuc1010]

Depends on which dimensions are important and which aren't.
Say you had +-.005 on all the dimensions in your examples.

it could be:

<----1.005--->|<--------2.005------>|
for a total of 3.010 max dimension.

while for the other method
3.005 would be the max dimension.
but this could happen:

<-----------------3.005-------->|
<-----.995---->|
implying:|<-----2.010----->|
Just depends on the type of control you need.

 

[EMorel]

Either are fine to use, no requirement for one to be used over the other. As thebuc1010 stated though, beware the tolerance stack-up when chain dimensioning.

 

[evolDiesel]

Thanks guys - you cleared it up perfectly!

Jack Lapham, CSWP
Engr Sys Admin
Dell M6400 Covet (24 Season 8, Ep 22)
Intel Core 2 Duo T9800, 2.93GHz, 1066MHZ 6M L2 Cache
8.0GB, DDR3-1066 SDRAM, 2 DIMM
1Gb nVIDIA Quadro FX 3700M (8.17.12.5896)
W7x64 | sw-01: 55.92
SolidWorks 2012 sp3 x64 & EPDM sp2