Orientation of hole pattern relative to a slot

[ringman]

Ringman,

How is orientation of a pattern accomplished when you have plane say A, a cylinder say B, and a slot,say C running the length or a portion of the length. C being the tertiary and used for orientation, FCF [A B C] I have aome problems, anyone else?

I used to think that orientation was to a point.

Thanks

 

[powerhound]

Orientation can be accomplished by a plane or an axis as the tertiary datum in the case you are talking about. What are the problems you are having. What you have described sounds simple enough.


Powerhound, GDTP T-0419
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[TheTick]

Use the width of the slot as you 3rd datum. Part face on "A", clocks around "B" until slot width "C" is in position.

Used all the time in auto console hinges and brackets.

Honesty may be the best policy, but insanity is a better defense.

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-SolidWorks API VB programming help

 

[dingy2]

Yup - I agree with TheTick on this one.

Both secondary and tertiary datums could either be at MMC or RFS. If the positional tolerances are at RFS, then your secondary and tertiary datums should also be at RFS otherwise one cannot check it.

Dave D.

http://www.qmsi.ca

 

[TheTick]

If you use MMC on 2nd and 3rd datums, then check fixtures are simpler, requiring only fixed pins.

 

[ringman]

Tic,

A problem that I have with your explanation is that the pin you refer to for datum simulator C, would have an axis as the 'true geometric counterpart'. A plane or line cannot in my opinion be oriented to an axis or line in theory.

Furthermore, if the slot is expressed as the datum feature, the datum would be the centerplane of the slot, and not an axis.

 

[121560]

PLEASE SEE ATTACHED. Datum C feature of size is the slot width ( tertiary, midpt of slot width ) therefore datum B & C establish 'X' center plane true geometric counter part ( 'Y' value equals 0 any where along 'X' plane ) and 'Y' plane ( 90 deg ) thru datum B centroid. Datum B & C mate to press fit dowels next assy. We could have designed part with 2 alignment holes in lieu of slot, next assy dowel pin diamond pin.

Ray Doyle
SolidWorks 99-07

 

[powerhound]

In regards to your datum reference frame, I think what you have works fine.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
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[ringman]

123560,

Your explanation illustrates my concern. You are using the midpoint of the slot as the datum rather than the mid plane as would be the case if the width is expressed as the datum feature.

Is there a way that your sample can be scaled up? I am unable to make out some of the details on the dwg.

 

[powerhound]

ringman,
His drawing is clearly indicating the centerplane of the slot as the tertiary datum. The width of the slot has a FCF that positions it WRT A and B and there is a datum feature indicator attached to the FCF which makes it datum C. This makes the centerplane datum C.

Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II