Help with datum

[ms]

Generally i like solidworks, but this is one area in which it really sucks.
I have a drawing of a cylindrical part. I am trying to attach two datums in
an end view of this part (imagine looking into the end of a toilet paper
roll). The part is revolved about the intersection of the top and front
planes. I want to show datum markers attached to the top and front planes.
How can I do this in 2005, sp 4? I've tried attaching to the center mark on
the drawing--no luck. I've tried attaching to the planes in the part--can't
position them to look good in the drawing. Anyone can help?

[That70sTick]

Attaching GD&T datum flags to planes and axes is not realy valid.
Datum flags should be attached to faces and edges.

[IYM]

As "70's" mentioned - a datum 'flag' is really a datum feature symbol that
specifies the FEATURE(s) of a part from which functional relationships are
established. A better question for me to ask, is what kind of geometrical
tolerance are you trying to establish on your roll of TP? Runout?
concentricity?

Scott

Post by That70sTick
Attaching GD&T datum flags to planes and axes is not realy valid.
Datum flags should be attached to faces and edges.

[IYM]

BTW, to answer your question on how to do/fudge it even though it's not
really correct - Is that while a datum feature symbol won't work with a
center mark, it will attach itself to a centerline. So in place of a
centermark, if you create two centerlines, constrain their mid-points to
the origin (or appropriate planes), to look like a centermark and then you
can attach a datum symbol to it.....

Scott

Post by IYM
As "70's" mentioned - a datum 'flag' is really a datum feature symbol that
specifies the FEATURE(s) of a part from which functional relationships are
established. A better question for me to ask, is what kind of geometrical
tolerance are you trying to establish on your roll of TP? Runout?
concentricity?
Scott

Post by That70sTick
Attaching GD&T datum flags to planes and axes is not realy valid.
Datum flags should be attached to faces and edges.

[ms]

I am not terribly familiar with GD&T, so I was copying from the customer's
origninal ACAD drawing. It had -A- and -B- datum marked as the front and top
planes (when looking from the side). The GD&T frame called out the position
and diameter as referenced from the centerline intersection of those two
planes. After reviewing my tech drawing book it looks like this is not a
valid method of applying GD&T. What they probably should have done was mark
the inner diameter as a datum and refer to it when dimensioning/ tolerancing
the outer diameter. I'll have to pick up a book on GD&T and brush up on it.

Post by IYM
BTW, to answer your question on how to do/fudge it even though it's not
really correct - Is that while a datum feature symbol won't work with a
center mark, it will attach itself to a centerline. So in place of a
centermark, if you create two centerlines, constrain their mid-points to
the origin (or appropriate planes), to look like a centermark and then you
can attach a datum symbol to it.....
Scott

Post by IYM
As "70's" mentioned - a datum 'flag' is really a datum feature symbol that
specifies the FEATURE(s) of a part from which functional relationships are
established. A better question for me to ask, is what kind of geometrical
tolerance are you trying to establish on your roll of TP? Runout?
concentricity?
Scott

Post by That70sTick
Attaching GD&T datum flags to planes and axes is not realy valid.
Datum flags should be attached to faces and edges.

[IYM]

Gotcha - erg! Your right - that's a horrible use of GD&T - It's a great
tool when used right, nasty when used wrong - It depends on the final
application on whether the ID or OD is used as the datum, (again depending
on the application....eg: If it's rotating (ie a shaft) runout or
concentricity should be used on the other diameter to control it in regards
to the datum)....Anyway, a great reference GD&T book that I keep around is
the workbook by Al Neumann...If your interested -
http://www.geotol.com/textmaterials.htm

Scott

Post by ms
I am not terribly familiar with GD&T, so I was copying from the customer's
origninal ACAD drawing. It had -A- and -B- datum marked as the front and top
planes (when looking from the side). The GD&T frame called out the position
and diameter as referenced from the centerline intersection of those two
planes. After reviewing my tech drawing book it looks like this is not a
valid method of applying GD&T. What they probably should have done was mark
the inner diameter as a datum and refer to it when dimensioning/ tolerancing
the outer diameter. I'll have to pick up a book on GD&T and brush up on it.

Post by IYM
BTW, to answer your question on how to do/fudge it even though it's not
really correct - Is that while a datum feature symbol won't work with a
center mark, it will attach itself to a centerline. So in place of a
centermark, if you create two centerlines, constrain their mid-points to
the origin (or appropriate planes), to look like a centermark and then you
can attach a datum symbol to it.....
Scott

Post by IYM
As "70's" mentioned - a datum 'flag' is really a datum feature symbol

that

Post by IYM

Post by IYM
specifies the FEATURE(s) of a part from which functional relationships

are

Post by IYM

Post by IYM
established. A better question for me to ask, is what kind of

geometrical

Post by IYM

Post by IYM
tolerance are you trying to establish on your roll of TP? Runout?
concentricity?
Scott

Post by That70sTick
Attaching GD&T datum flags to planes and axes is not realy valid.
Datum flags should be attached to faces and edges.