how to align two holes colinear with each other

[Daewoo200]

Hi all,

I currently have an issue where I have a flat long rectangular plate and am trying to callout two press fit holes. The main face of the rectangular plate is datum A, the short right side of the rectangular plate is datum B, and the long bottom side of the plate is datum C. I don't particularly care where the first hole is drilled/reamed. I have it called out as true position of .014 to datum A (primary), datum C (secondary), and datum B (tertiary). This hole is called out as datum E.

However, I really need the second hole nearly colinear (perfectly in line) with this first hole. I don't really care on the plate where the first hole is drilled. Just when the first hole is drilled, I want the second hole colinear with it.

Thus, I was not going to make the holes a pattern and call out true position since that wouldn't guarantee colinearity. Plus the both holes' locations relative to datums B and C isn't important.

My plan was to make the second hole have a dual position control. The first would have a true position of .014 relative to datum A (primary), datum E (secondary which is the first drilled hole), and datum B (tertiary datum). Then, the second position control would be true position of .003 relative to datum A and datum E (in that order). Note that the distance between the two holes is critical. The distance from the holes to the edges of the rectangular plate is not.

Does this sound like a reasonable plan? how else would you guys do it? Could I make the centerline between the holes a datum plane and reference that datum in the holes' feature control frames?

Thanks

 

[pmarc]

Daewoo200,

Two holes will always be in line with each other regardless of their position relative to |A|B|C|(assuming we ignore the 3D effect of the perpendicularity error to A).

So should we assume that apart from spacing between the holes, you want the virtual line connecting the holes be tightly controlled for orientation relative to one of the side faces of the part?

 

[Daewoo200]

yeah I think that is correct. I don't necessarily need the position of the holes to be a tight tolerance to B and C. But I do want the centerline between the 2 holes parallel to within a tight tolerance of datum C. And also hold the distance of the two holes along that centerline relatively tight to each other.

 

[pmarc]

In that case you could consider a composite position tolerance with:
-- the looser tolerance to A|B|C in the upper segment;
-- the tighter tolerance to A|B in the lower segment.

Also, to be able to do that, you would need to make the longer side of the plate B and the shorter C, not vice versa, if functionally acceptable.

The scheme you originally proposed would not control the orientation of the centerline between the two holes to the the same tolerance as the spacing between the holes.

Note: Putting .003 in the lower segment of the composite callout will allow for a larger hole-to-hole spacing tolerance than as if the first hole was assigned as secondary datum feature for the control of the second hole.

Alternatively, you can just control the first hole as you proposed, make it datum feature D and then apply a single position tolerance to the second hole with respect to A|D|B or A|D|C (this isn't a solution I would necessarily prefer, but it has been shown in different GD&T books).

 

[mfgenggear]

Daewoo200

with a drawing it would be easier to make suggestion. there is three methods functionally to make to holes inline.
#1) match drill if possible holes will be exact , drill jig,
#2) hole precise true position of holes true position .0005, more difficult but doable. unfortunately now the datums have to be machined precise so it will
be achievable for all parts.
#3) have a drill jig coordinated to produce the exact hole location. ( coordinate with tool design & mfg eng)
have note on drawing holes must match.

 

[engAlright]

Per Y14.5-2009 you can use the "Continuous Feature" symbol to control both holes together as a single feature. In this case the coaxiality of the two holes is controlled within the limits of size.

 

[greenimi]

Per Y14.5-2009 you can use the "Continuous Feature" symbol to control both holes together as a single feature. In this case the coaxiality of the two holes is controlled within the limits of size.

The problem is: there are TWO features (not a sigle one). And those two features/ holes ARE NOT coaxial.

 

[engAlright]

Ah ha seems I grabbed on to OP's "collinear" description incorrectly. pmarc's covered it in regards to positional tolerances...if the tight requirement between the two holes was strictly to have their axes parallel then a parallelism refinement could be applied on the composite positional tolerance.