Position of holes in a triangular pitch pattern on a circle

[L Fultz]

Not sure what datum callouts are needed. I have a thin circular disc with a radially symmetric, triangular pitch hole pattern.

I think if I add another 0.292 basic or the 60° basic to the pattern, and change the vertical and horizontal lines through the part to actual centerlines, the holes are then dimensionally specified. Otherwise, the central hole could be established as Datum B and the remaining hole positions could be relative to A | B. I may impose a material condition on the feature, but it will not be on the datum(s).

I would appreciate guidance on this.

Your brother in engineering
Lonnie

 

[chez311]

L_Fultz,

Is your plan to have this drawing fully compliant to a drawing standard, say for example Y14.5-2009 or 2018? If so - see the end of my post for some of my recommendations on other features on the drawing.*

I think if I add another 0.292 basic or the 60° basic to the pattern, and change the vertical and horizontal lines through the part to actual centerlines, the holes are then dimensionally specified.

Presumably you are talking about the detail view sketched in the top right hand corner of your drawing? This could be included, with either basic or reference dimensions to give some idea of what the pattern looks like in your 2D drawing, however this could also be utilized in conjunction with 3D/math data to fully define your basic dimensions of the pattern with a note. If not, you need to somehow show the repeated relationship between instances of the pattern with basic dimensions, as well as within each instance of the pattern (ie: with the detail view you show). "TYP" notation I think can be removed and instead replaced with a number of instances.

Alternatively, I see a crossed out reference to a "TUBE HOLE LAYOUT". Is this a hole table showing (x,y) coordinates of the holes? This could be unwieldy for a pattern of 147 holes but if it is something that already exists it could certainly be utilized.

Otherwise, the central hole could be established as Datum B and the remaining hole positions could be relative to A | B.

If A in this scenario is still the OD, I would not recommend this. This would be redundant (two coaxial holes**) and not supply any additional constraint. Could you describe how this part is assembled/functions in reference to its features? If none of the shown features able to constrain the additional rotational DOF desired makes sense to establish as a datum feature then all features shown could be held only to |A| and to each other through simultaneous requirements.

I may impose a material condition on the feature, but it will not be on the datum(s).

When referenced in a FCF, all features/datum features have a material condition - RFS/RMB by default.

*Recommendations:
If so, I would recommend standardization of several of the callouts for example - nX notation instead of "PLCS". I am unsure what O.T.L. stands for, perhaps this is a well known abbreviation in your industry but it may not be to everyone - also not sure how it relates to your part, it seems to not quite lie at the full depth of the 4X slots. I'm not sure how others feel about this, but I would personally either change the notation for the 140 full/7 half holes to either fully grouped into a 147X (DIA) pattern or separate into a 140X (DIA) and 7X (DIA) patterns, removing any reference to "full" or "half".

I would also recommend utilization of position with your 4X slots - this requires a basic 9deg dimension. Profile could also be used - requiring fully basic definition.

If the interrupted bottom flat feature is at all critical, a coplanar profile could be implemented similar to Y14.5-2009 Fig 8-15. Otherwise a directly toleranced dimension could be utilized from the OD to the flat (instead of the centerline to the flat - theoretical points/planes/lines should not be references for directly toleranced dimensions) in conjunction with an orientation refinement if desired.

**There are times when this is acceptable/desired (take the case with two coaxial diameters on either end of a long part, especially to control runout). This is not one of those times.

 

[Burunduk]

If you call out datum feature A only, it means your holes should only be parallel to A and located to it. You might want to consider designating one of the flat faces A and make it primary datum to orient the holes perpendicular. The periphery (now A) will be B and take care of the location of the pattern. Just my non-expert two cents.

 

[chez311]

If you call out datum feature A only, it means your holes should only be parallel to A and located to it. You might want to consider designating one of the flat faces A and make it primary datum to orient the holes perpendicula

Agreed, though for such a thin part it may not matter much. Additionally, these flat faces may not even mate to anything which is why I asked OP for some more details on the assembly condition. Taking some guesses from the drawing - from the pattern and crossed out "TUBE HOLE LAYOUT" note, this part may be slid over a series of tubes and placed somewhere along their length as a kind of spacer.

 

[Burunduk]

chez311,
Agreed. I just thought it could be helpful to point out what the current specification leads to (which is not necessarily a bad scheme), and offer a common alternative. The OP should definitely decide according to function.

 

[L Fultz]

Appreciate the comments. This is a baffle for a tube and shell heat exchanger. Tubes will run through the holes.

I think the diameter should be the primary datum. I believe the parts fit and function is better fulfilled in the bottom of the image in this thread. I think the face is not an important feature.

I desire to be compliant to Y14.5. To be honest we are probably more along the lines of Y14.5-1994. We are small enough that we have lean towards the "adequate".

There are separate tube layout drawings, but they do not provide much detail beyond the triangle detail view, so I wish to eliminate them (I have about a dozen of these with about a half a dozen different hole and pitch patterns) and have the relevant information on the actual drawing.

I think I will move the hole diameter and position tolerance to the detail view (name it HOLE PATTERN) and add the third 0.292 basic.

O.T.L is an outer tube line used in some sizing calculations and is a reference number.

 

[3DDave]

The largest flat face should be the primary datum unless you do not care if it goes in the next assembly at up to a 15 degree angle to the tubes.

 

[chez311]

The largest flat face should be the primary datum unless you do not care if it goes in the next assembly at up to a 15 degree angle to the tubes.

It is not shown (indeed there is only an associated reference dimension?) but the thickness or each individual flat face could be controlled relative to the OD.

That being said, I think the practicalities of measuring/inspecting the UAME of the OD of such a large, thin disk would make a case for making the flat face(s) the primary datum feature as suggested.

 

[Hallec]

Not to sound overly picky, but what's the purpose of the "140 FULL HOLES" note? I believe the diameter symbol along with the picorial representation of the part entirely defines those features. You could simply say "147X ֍.252-.256" and remove the portion about the "half-holes" as well.

I'm not a vegetarian because I dislike meat... I'm a vegetarian because I HATE PLANTS!!

 

[Kedu]

In the context provided by the OP and the picture from one of his replies, may I ask if datum feature A used as secondary in the FCF for position of the central hole provide anything to this location control?
(If assuming also no simultaneous requirement concept is to be used, but strictly as a stand-alone position control). What does Datum feature A secondary do?

 

[L Fultz]

Like the O.T.L parameter, the number of full holes and half holes are used by engineering for performance calculations. There are some common parameters that will greatly aid engineering by being on the drawing and will speed up the analysis.

With respect to the face or diameter being the primary datum, it is more important for fit that the part fits within a cylinder with the hole pattern centered on the part. I guess since the part is so thin, the exaggerated shear of the top with the plane as primary and the diameter of secondary is still valid.

 

[Burunduk]

Is there a general tolerance block on the drawing?

 

[pylfrm]

L Fultz,

When referenced as primary datum feature, a cylindrical surface must constrain one rotational and two translational degrees of freedom. Your datum feature A will be unable to provide any practical constraint of rotation because the length/diameter ratio is much too small. This is a problem regardless of which feature seems most functionally relevant to you.

Do you actually want to allow parts that can only be assembled with the sheet thickness at some huge angle away from perpendicular with the tubes? I can't imagine why you would, but there are better ways to do it if you insist.


pylfrm

 

[Burunduk]

pylfrm,
To be precise a primary cylindrical datum feature should constrain two translational and two rotational degrees of freedom (but as you said, in this case it will be unable to).

 

[pylfrm]

Burunduk,

Apparently I can't count. Thank you for the correction.


pylfrm