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rknair73 (Mechanical)
18 May 10 1:55
Hi,
We have a plastic housing design in which both the halves when assembled together, the max, mismatch( shift) on the mating edges should ne .01 inches. Please help me how to specify this on the part drawings of each parts?
Thanks in advance for your suggestions
Belanger (Automotive)
18 May 10 10:20
The GD&T system is probably best for this.  Use the symbol for either "profile of a line" or "profile of a surface" to call out the appropriate tolerance value.

And profile often references datums -- that is the tricky part on plastics.  Are you merely interested in controlling shape and size, such that they fit together?  Or might the outline of the mating edge need to be tied back to other features?

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

KENAT (Mechanical)
18 May 10 10:59
As Belanger says, this may be a good application for the use of surface profile.  Simplistically if the surfaces that have to align are both given a .010 surface profile this will get what you need.

However, for some plastics processes, especially larger parts, .010 is pretty tight, so are you sure it's possible with your process?

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
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fcsuper (Mechanical)
18 May 10 16:11
There is also a common note "Mismatch not to exceed .XXX." that I've seen used.

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

&

SeasonLee (Mechanical)
19 May 10 11:23
You may get the mismatch information from chapter 3 on ASME Y14.8 Casting, Forging and Molded Parts standard, the attached will help you.

SeasonLee
 
ewh (Aerospace)
19 May 10 11:43
I thought the mismatch note was in regards to (single part) mold components, not matching resultant parts (i.e. two mold halves).
The only way I know of maintaining your requirements is to either use a .010 profile tolerance or a +/-.005 dimensional tolerance.  The profile tolerance would probably be the better choice.

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

KENAT (Mechanical)
19 May 10 11:55
Agree with ewh.

The mismatch is for two halves of a mold as I recal - not for mating parts in an assy.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

fcsuper (Mechanical)
19 May 10 14:03
If between two halves, mismatch can be a specification is clearly stated.  I would agree with others to use profiling as a better approach.

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

&

MechNorth (Mechanical)
2 Jun 10 19:31
Y14.8 makes sense for a moulded article.  Profile tolerances make sense for mating parts ... maybe even unilateral profile tolerances if they are nominally size-on-size.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

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