Dimensional Interpretation on Raw Casting Drawings with No Draft Shown

[tz101]

I have been in mechanical design for a lot of years and had not heard the following theory until recently:

This is a drawing of an iron casting that has been generated from a CAD model with no draft. The theory I have been presented with is that dimensions I have circled in red on this print are to be held to the part face shown in the respective orthographic drawing view in which said dimensions are shown, and any cast draft is to be added or subtracted moving away from that face. That said, these presenting this theory would reason that the Ø3.000 basic dimension shown at the top of the far lefthand drawing view would be checked at the "bottom" part face shown in that view and any cast draft would add or subtract material as the part thickens toward the opposite face, regardless of standard pattern making practice normally used. Likewise, their interpretation would be that the .500 basic dimension shown in section A-A would be measured at the "top" edges of that feature (flange in this case) where the dimension's witness lines come away from, and any cast draft would be added/subtracted moving away from that face.

This, to me, is a misguided interpretation of the design intent on this print, reading far more into dimensional placement on respective orthographic views than should be done. Since this is a drawing generated from a CAD model that does not include any draft on vertical faces, my interpretation is that the print dimensions are to be interpreted as applying to that entire feature face across the entire part thickness. On the pattern making side, any necessary draft will be added/subtracted as needed while holding those print dimensions in such a manner as to be material safe on the final as-cast parts.

Any thoughts?

 

[KENAT]

I don't have it to hand but ASME Y14.8 may be of use.

From recollection if draft isn't shown then it should be accommodated by the size tolerances for the features - which meshes with the fundamental principles in Y14.5.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[3DDave]

Seems like a drawing made by someone who never made a sand casting. It could be made just like shown, but with a very complicated set of patterns and much work, but the interpretation is imaginative, and not in a good way.

At least note 'plus draft' or 'minus draft' or just make the model with the desired draft and indicate a parting line.

Better, go to a foundry and show them how patterns work.

 

[MadMango]

Looks like post machining ops are required for the ID and flat mounting surface. At least that would be my interpretation$.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[SwinnyGG]

From that drawing, I would assume (as mango did) that post-machining is required since so many dimensions are basic.

With that said, I would be very reluctant to release a part and just let someone else decide what and where the draft angles should be.

 

[3DDave]

Basic dimensions are applicable to castings. The lack of tolerances for most of the features of the part is more concerning.

 

[SwinnyGG]

I understand that basic dimensions are applicable to castings- but using them on the unforced side of a casting is not a practice I used when I used to design a lot of them. We typically would use a -0/+xxx dimension for casting thickness (locating the unforced side)