Perpendicularity callout with curved datum

[bc23]

I re-created this drawing for illustration purposes. All the flat sides/surfaces are actually not flat (so cannot be used as datums).
The intention is for dia4 hole to be perpendicular to curved surface (R10). But is this FCF correct? (whether by ASME or ISO)
If Datum A was re-defined as a specific line on this curved surface, would it be legal? (But it would be difficult to measure also)

 

[3DDave]

How odd.

3.46 PERPENDICULARITY
perpendicularity: the condition of a line element, surface, tangent plane, feature’s center plane, or feature’s axis at an implied or specified basic 90° perpendicular) angle relative to one or more datum planes or datum axes.

So, no to specific line.

However, if there is perpendicularity to an axis then a plane can be constructed through the axis and where that plane intersects the outer surface, one can create a tangent plane. However, that feature might be anywhere on that plane and need not intersect the axis. If that is acceptable, that feature control frame will do it.

A position geometric characteristic tolerance would act similarly, but restrict the true position to passing through the axis.

 

[drawoh]

bc23,

Is this your drawing, or are you trying to interpret something somebody else has done?

Your hole can be perpendicular to your datum in one axis only. Your curved face defines an axis, at least, geometrically. Have fun figuring out where this axis is in your inspection lab.

If you are fixturing to weird shapes, look into datum targets.

 

[Garland23]

It sounds like the OP wants the axis of the hole to be perp to a theoretical plane that is tangent to the arc.

 

[ghostdigital]

I re-created this drawing for illustration purposes. All the flat sides/surfaces are actually not flat (so cannot be used as datums).
The intention is for dia4 hole to be perpendicular to curved surface (R10). But is this FCF correct? (whether by ASME or ISO)
If Datum A was re-defined as a specific line on this curved surface, would it be legal? (But it would be difficult to measure also)
View attachment 7894

"IF" datum A was a datum target line, with a specified location it would work. Or, if an additional datum (B?) was specified in the FCF which would orient Datum A - that would work.

As is - the orientation relative to Datum A is unspecified.

 

[Burunduk]

"IF" datum A was a datum target line, with a specified location it would work.

I would say that a datum target line alone cannot sufficiently constrain orientation to make a perpendicularity control useful.

 

[greenimi]

I would say that a datum target line alone cannot sufficiently constrain orientation to make a perpendicularity control useful.

Or maybe perpendicularity works, but adding the tangent plane modifier could be something to consider...or maybe not...

 

[Burunduk]

Or maybe perpendicularity works, but adding the tangent plane modifier could be something to consider...or maybe not...

A single straight line as the only auxiliary element for datum establishment cannot fully orient a plane.

 

[greenimi]

A single straight line as the only auxiliary element for datum establishment cannot fully orient a plane.

I am thinkg the other way around. make the hole a datum feature and then orient the curved surface to the hole with the perpendicualrity and T modifier.
I am looking to establish a relationship between the curved surface and the hole hence a slight adjustement to get this relationship is what I am thinking could be a good idea.

 

[mfgenggear]

I mean this could work using a cmm to establishing datum with a CMM.

Think about how this has to be restrained in CNC in a fixture. Even thou the opposite face is not flat , the surface would have to be held consistent for tooling. The fixture would simulate a sine plate . To make datum A to held equal to centerline . Then the hole can be held perpendicular , that would be upto the shop.

This Done often with shafts with holes held to centerline.

Far as inspection I would throw this up on a magnetic sine plate. On a surface plate or pick multiple hits with cmm probe. To establish center line . Then continue to inspect hole perpendicular. .
But is thus allowed with ASME rules?
This may be a good application of profile of surface?
Either way no problem mfg or inspecting.

 

[Amp Dylan]

Yeah defining perpendicularity to a curved surface like that is tricky. If you really want the hole axis normal to the R10 surface, you’d need to define datum A as a tangent plane at the point of intersection but that's a pain to inspect.
Might be cleaner to just define perpendicularity to the center axis of the part if that makes sense functionally. You fixturing off the curve?

 

[pmarc]

Define the plane tangent to the arc at its quadrant as datum target plane A1.

Next, define datum targets B and C on some other features of the part to fully and repeatably immobilize the part for the check of the perpedicularity tolerance.

Then, specify the following, or similar, note (taken from para. 7.24.10 in Y14.5-2018 or para. 4.24.14 in Y14.5-2009):
WHERE ONLY DATUM FEATURE A IS REFERENCED, DATUM FEATURES B AND C ARE INVOKED ONLY TO RELATE THE TARGETS THAT ESTABLISH DATUM A.

Finally, add the missing diameter symbol in front of the perpendicularity tolerance value and keep A as the only datum reference in that callout.

 

[mfgenggear]

Define the plane tangent to the arc at its quadrant as datum target plane A1.

Next, define datum targets B and C on some other features of the part to fully and repeatably immobilize the part for the check of the perpedicularity tolerance.

Then, specify the following, or similar, note (taken from para. 7.24.10 in Y14.5-2018 or para. 4.24.14 in Y14.5-2009):
WHERE ONLY DATUM FEATURE A IS REFERENCED, DATUM FEATURES B AND C ARE INVOKED ONLY TO RELATE THE TARGETS THAT ESTABLISH DATUM A.

Finally, add the missing diameter symbol in front of the perpendicularity tolerance value and keep A as the only datum reference in that callout.

yeppers opposite face and and adjacent face

 

[3DDave]

It's only missing a diameter symbol if there is a fixed plane to be perpendicular to. If the requirement is only to be perpendicular to the axis then there is no need for a diameter symbol.

Yet again a case of wanting a solution to a problem that is not completely stated.

The position geometric characteristic control forces the true position of the hole to be at the point of tangency if there is no offset basic dimension. In that case the diameter symbol would be appropriate.

 

[ghostdigital]

Or maybe perpendicularity works, but adding the tangent plane modifier could be something to consider...or maybe not...

Yes, on second look you're right there still needs to be a orientation control on Datum A.

 

[bc23]

bc23,

Is this your drawing, or are you trying to interpret something somebody else has done?

Your hole can be perpendicular to your datum in one axis only. Your curved face defines an axis, at least, geometrically. Have fun figuring out where this axis is in your inspection lab.

If you are fixturing to weird shapes, look into datum targets.

Someone else created this and I'm trying to improve/correct it.
"Have fun figuring out where this axis is in your inspection lab." - it's because I was having too much 'fun' figuring this that I thought it was abnormal.

 

[bc23]

Yeah defining perpendicularity to a curved surface like that is tricky. If you really want the hole axis normal to the R10 surface, you’d need to define datum A as a tangent plane at the point of intersection but that's a pain to inspect.
Might be cleaner to just define perpendicularity to the center axis of the part if that makes sense functionally. You fixturing off the curve?

Actually yes, this part is fixed from the curved surface, and this surface is allowed some free play, then a bolt goes thru the hole. Hence this perpendicularity relationship.

 

[bc23]

Thanks everyone for the discussion & comments. It looks like there are some "trade-off's" for each solution.
I think these 2 may work
a) Using Position to control the hole, and also controlling R10 to similar datums. (3DDave).
b) and Pmarc's suggestion.

 

[pmarc]

bc23,
Note that my suggestion was more about addressing the datum target setup itself based on the information provided in the initial post. Keeping perpendicularity tolerance for the hole does not guarantee its location close (that is, within a tolerance) to the tangency point. To guarantee that, a position callout relative to A, B and C should be specified.

If the curved surface interacts with a similarly-shaped surface in the mating part, then I wouldn't probably even consider the option with the tangent datum target plane A1.

 

[Burunduk]

If this radius is the actual main mating interface I would set its dimension R10 as basic and control it's form (including radius value) by profile of a surface, then attach the datum feature A symbol to the profile feature control frame. In the feature control frame(s) for the hole, I would reference A with the [BSC] modifier to state clearly that the simulator related to datum A is of the basic radius R10. Then if any features other the hole itslef constrain the part, and by that affecting the hole's location and orientation in the assembly, I would add those datum features as secondary and possibly tertiary. Alternatively the hole could be the next part-constaining interface feature and then it would be used as a secondary datum feature for other controls. For controlling the hole I would use position and only if necessary, an orientation refinement (I would probably choose the more general angularity over perpendicularity).