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Mixing Ordinate & "Standard Dimensions

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dmech

Mechanical
Dec 8, 2002
28
Hello,

I have question regarding the practice of mixing ordinate dimensions with standard linear dimensions.

Geometric Background:
I have a rectangular plate with a short edge slot defining the center-line of the plate in long direction. Also the plate has four shallow and narrow pockets running parallel to the slot, symmetrically positioned about the centerline.

DATUM A (PRIMARY) - Large Flat Surface of Plate
DATUM B (SECONDARY) - Edge Slot Width Centerline
Datum C (TRESHERY) - Top Edge of plate

So, I would like to the control the position of one edge of the shallow slots relative to DATUM B as well as the slot width. This is for accurate mounting of four linear slides.

Question: Is it okay to use ordinate dimensions to locate the slot edges and standard dimensions to specify the shallow pocket width?

More generally, is it okay to mix ordinate and standard dimension on the same view and sheet?

Thanks,
Dion
 
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It looks to me like you want to control all of those slotted features to Datum B in the x direction. So a fixture that engages that small radius in the center of your part will be used to located Datum B.

Is that right?
 
ModulusCT, the short answer is; yes. The inspection would be performed as follows:

1. Place Datum A of plate onto granite table.
2. Locate Datum B of plate onto pin protruding from granite
3. Eliminate rotation by pushing plate against Datum C of plate, while engaging pin.

The left side of each slot engages the reference side of each linear slide. This will control the yaw-parallelism between each slide. Pitch & Roll are controlled by the bottom surface of the slot and Datum A. Location of the slide block relative to Datum C is controlled by an adjustable screw.
 
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