×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Datum selection based on manufacturing or upper level assembly

Datum selection based on manufacturing or upper level assembly

Datum selection based on manufacturing or upper level assembly

(OP)
Just wanted an opinion on this one...

This is my thought on the subject.

Plate with a hole in the center.
The center hole is created by holding the bottom surface and 2 sides.
The plate is assembled by placing a bolt to the hole and clamping against the large bottom surface

I would do the following:
Bottom of the plate has primary
The hole as secondary
Possibly one edge has tertiary (if needed)

Some people follow the manufacturing method.
Bottom as primary
Side as secondary
Side as tertiary

Any thoughts on this??

RE: Datum selection based on manufacturing or upper level assembly

If the hole is effectively the critical feature I'd probably use it.  

We have cassettes that are located by a pin through a hole.  On the drawings of the cassettes we use the hole as the secondary datum if I recall correctly.

Function/Inspection of the part is more important in the dimensioning scheme than manufacture.

You could perhaps make the face and sides Datums A, B & C then make the hole datum D and relate other features to it.  Depends on the function/design of the specific part though.

RE: Datum selection based on manufacturing or upper level assembly

(OP)
But....  the datums should be defined by part functionality.
Not in an attempt to mimic the manufacturing method.

RE: Datum selection based on manufacturing or upper level assembly

That was the point I was trying to make and didn't mean to imply otherwise.

Hierarchy in dimensioning is:

Function
Inspection
Manufacture

Of course as there's no point putting a requirement you can't inspect or otherwise verify it almost ranks equal to Function.

RE: Datum selection based on manufacturing or upper level assembly

You are correct by using the hole as a secondary and the mounting face as the primary datum. If the part is assemetrical, then a tertiary is a must and probably another hole should be used rather than a side.

Manufacturing must somehow follow your datum set and not change it.

Dave D.
www.qmsi.ca

RE: Datum selection based on manufacturing or upper level assembly

I use the datums based on how the parts are assembled to each other, not per manufacturing.

Chris
SolidWorks 06 5.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)

RE: Datum selection based on manufacturing or upper level assembly

Datums should always be developed by the function of the part. That is it!!

Dave D.
www.qmsi.ca

RE: Datum selection based on manufacturing or upper level assembly

Of course!
But you need to look at how the part is assembled in relation to a mating part ... not to a machine.
It is all I was trying to say.

Chris
SolidWorks 06 5.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)

RE: Datum selection based on manufacturing or upper level assembly

theedudenator,

What is it that you are looking for thoughts on?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources