Basic GD&T question
Basic GD&T question
(OP)
Anyone,
I'll do my best to describe my question. Is the primary reference in my "position" symbol GD&T box the plane on which the feature, "say, a hole", resides? Or is this place for the first reference of lateral or vertical position? When is the residing plane included in the GD&T box? I have a book on GD&T and I'm trying to learn but I see both as examples.
Thanks
I'll do my best to describe my question. Is the primary reference in my "position" symbol GD&T box the plane on which the feature, "say, a hole", resides? Or is this place for the first reference of lateral or vertical position? When is the residing plane included in the GD&T box? I have a book on GD&T and I'm trying to learn but I see both as examples.
Thanks





RE: Basic GD&T question
This gives you A B C for your callout.
"Wildfires are dangerous, hard to control, and economically catastrophic."
"Fixed in the next release" should replace "Product First" as the PTC slogan.
Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand
RE: Basic GD&T question
Phil
RE: Basic GD&T question
Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP3.1 / PDMWorks 05
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716
RE: Basic GD&T question
What is important is order of engagement, regardless of geometry. You can have a hole as a primary and plane as secondary if the part is firsty constrained on the hole and then touches off on the surface.
RE: Basic GD&T question
I haven't found a way to attach a picture...so I'm relying on my verbal skills.
RE: Basic GD&T question
RE: Basic GD&T question
RE: Basic GD&T question
May I suggest you look into a GD&T class? The ability to use GD&T fluently in your designs can prevent costly mistakes and some embarrassment at staff meetings. I know some community colleges offer classes in the design programs.
RE: Basic GD&T question
Using the cube example you gave, and assuming that you want to fully fix this part in space, you will need 3 datums.
The primary datum will correspond to a feature which mates with another component and most greatly controls the location and orientation. If the cube is in its operating condition as described, then it will rest in use on the bottom face. That makes the bottom face your primary datum feature; call it Datum K. Affixing the workpiece to Datum K (simulated by the inspection plate) locks three degrees of motion; up/down (along z-axis), and rotationally about two axis (X and Y). Oh yeah, 3 point minimum contact for a primary planar datum.
The next datum feature will further constrain two degrees of motion. Let's make the left face of the cube Datum Feature G. Now two points (minimum) on the left face of the cube will abutt an angle plate mounted perpendicularly on the inspection plate. That eliminates motion in the X-direction and rotation about the Z-axis. Datum G is your secondary datum.
The final datum needs to eliminate the 6th degree of motion; motion in the Y direction. So for your cube, it will be the back face (opposite the drill face); Datum A. You would then push the workpiece into (min 1 pt) contact with another angle plate that is mutually perpendicular to the inspection plate and the other angle plate. This keeps it from moving along the Y-direction.
Your workpiece is now fully constrained with the K/G/A datum reference frame.
I am not in complete agreement with Looslib because of the reference to contacting two locating pins on the secondary datum feature and a locating pin on the third datum face. This indicates either line or point contact at a predetermined location, which means datum targets rather than full datum features. When you're starting out, keep it as simple as possible.
Follow Heckler's suggestion, and get some professional help (training that is). Be careful though, there's a lot of bad training out there, and some outstanding as well. Get references before you sign up.
Jim Sykes, P.Eng, GDTP-S
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