Dimensioning angled feature

[jplesetz]

My textbook Dimensioning and Tolerancing Handbook, by XXXXXXXX states the following correct and incorrect method for dimensioning a hole on an angled surface relative the datums on the print (see attached image). Is what the book is stating actually true? It seems like a typo but I could not verify in either in the 2009 standard. I don't understand why you would want to dimension a hole, cylinder, etc. from an intersection point of the datums rather than dimensioning straight from the datums to an intersection point on the angled feature.

angled surface question.pdf

[Kelly_Bramble]

Ok, I removed the Author name before I commented on this.

The only typo I see is the use of the words "Implied Datum - a common error" as the datum's are NOT implied.

The basic dimensioning method shown in figure 5-105 would be preferred however the dimensioning method shown in Figure 5-106 still gets the job done.

Figure 5-106 would require the quality inspector as well as the machinist using manual setup methods to perform some math to get usable basic dimensions where the Figure 5-105 method is more direct for manufacturing and quality. Rotating the part using a sine-plate is academic and requires little mathematics for manufacturing and quality.


When using a programmed CNC and CMM the dimensioning methods become less critical.

IMHO, dimensioning and tolerancing should be presented so that manufacturing and quality do not need advanced math skills to get the job done. All engineering drawing creators should work hard to ensure that the engineering drawing is complete, accurate, and focuses on function and manufacture-ability and is easy to read.

[lucien tian]

i checked the drawing. I think both drawings need dimension in the other direction. currently the holes have not been restrained.

[Belanger]

If you mean sideways relative to datum B, nothing is needed because the true position of the holes is exactly in line with datum B. (Datum B is actually the center plane of the width.)

[lucien tian]

see attached image, that shows what I mean. but you are right, what I added has nothing with the hole positions. but I also feel that they at least is, in some degrees, relative to what we are saying.