Perp Callout - relative to 2 datums
Perp Callout - relative to 2 datums
(OP)
On page 182 of ASME Y14.5, 1994, it show a perpendicullarity callout relative to 2 datums. Datum A primary and datum B secondary. If I am setting up a gage to check this do I pick up the whole surface of datum B or can I use two points and use it basically for clocking. (I never knew you could have this secondary datum....) Thanks in advance.





RE: Perp Callout - relative to 2 datums
Use Datum B for clocking. There is no reason to assume that the entire face of datum B is perfectly perpendicular to Datum A.
JHG
RE: Perp Callout - relative to 2 datums
David Strole
Engineering Systems Administrator
GDTP S-0132
RE: Perp Callout - relative to 2 datums
The datum plane B is exactly perpendicular to datum plane A, by definition. The second face of the fabricated part is out of perpendicular by, hopefully, a small amount.
Ideally, the datum A surface locates at three points, and the datum B surfaces locates at two points, and in this case, controls rotation.
JHG
RE: Perp Callout - relative to 2 datums
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Perp Callout - relative to 2 datums
Theoretically, datum A should sit on a plane and not 3 points UNLESS it has a high spot in the centre. Now it would wobble and a measurement cannot be taken. In this situation, I would suggest a 3 point set up but only as a last resort.
Datum B is for clocking as other people have suggested.
Here is how I would measure this requirement.
Place an angle plate on a granite surface that is located in the Tool Room. Now datum A is clamped to the vertical surface of the angle plate so that, in theory, the feature in question should be parallel to the granite plate. Zero up (rotate) datum B so that if one ran a dial indicator on a stand along the feature, it should read zero all the way.
Sweep the feature with the dial indicator and report the TIR or FIM which should not exceed 0.12 mm as per page 182.
Perpendicularity of a plane is a combination of angle and flatness.
Hope this helps.
Dave D.
www.qmsi.ca
RE: Perp Callout - relative to 2 datums
Per the illustration in Figure 6-35 on page 182. The secondary datum feature is shown as a plane. The two-point contact for the secondary datum feature is at 90 degrees to the primary datum feature. The two high points on the part would come into contact with the simulated datum plane (say an angle block at 90 degrees to datum plane A).
If it is desired to have only two fixed points as a secondary datum feature to prevent rotation, they should be noted as datum targets.
David Strole
Engineering Systems Administrator
GDTP S-0132
RE: Perp Callout - relative to 2 datums
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Perp Callout - relative to 2 datums
Dave D.
www.qmsi.ca
RE: Perp Callout - relative to 2 datums
If the entire surface of the secondary datum feature (Fig 6.35 Page 182) is being specified as the datum feature, then the set up would need to be two perpendicular planes (say a surface plate and an angle block) to establish the DRF. The two high points from the part would contact the datum simulator, but the simulator needs to be a plane. That is what Figure 6.35 is showing.
If only two target points or areas at fixed locations are intended to be used, then the secondary datum plane needs to be specified using target points or areas.
David Strole
Engineering Systems Administrator
GDTP S-0132
RE: Perp Callout - relative to 2 datums
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Perp Callout - relative to 2 datums
If I wanted a fixture to pick up two points of the datum B surface, I would specify those points with datum targets. If the surface is not very good, like a sand casting, I might just do this!
If the entire face is datum B, then the datum is picked up by an angle block, or by the granite table as per dingy's email, above.
JHG
RE: Perp Callout - relative to 2 datums
That is what I was saying or trying to say. My applogies if I misread your initial reply and implied differently.
David Strole
Engineering Systems Administrator
GDTP S-0132
RE: Perp Callout - relative to 2 datums
RE: Perp Callout - relative to 2 datums
What you need to do is immobilize your part. You need to clamp to datums A and B and a datum C that prevents side to side movement.
JHG
RE: Perp Callout - relative to 2 datums
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Perp Callout - relative to 2 datums