View Orientation Question 2

[flash3780]

We often use a section view to create "other than orthogonal" projected views of a part (ex. VIEW A-A). It's handy, especially since you can move the view around on the sheet without confusing anyone too badly.

In a recent drawing, I needed a view of a angled face of a part. The face was fully defined with basic dimensions and located back to datums. The customer's manufacturing engineer came back and asked that we add a basic angle dimension to a section view line.

Of course, we did, since he's the customer, but I was wondering if it's actually necessary. Or if a section view is shown parallel to a feature/face, is it assumed parallel?

I put together a quick example of what I'm talking about: Is the safety wire hole in the attached drawing fully defined?

 

[ewh]

I think adding a basic dimension is overkill; at most I may have added a reference dimension if the orientation was ambiguous, but the example is quite clear in meaning. I'm suprised that he didn't also ask for identification of datum B in the view.;-)

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[flash3780]

Thanks. I thought that I had it covered. Does ASME Y14.5-1994 mention anything about that?

Oh, and before anyone calls me on it, I know that the MMC modifier on the thread perpendicularity shouldn't be there, I left off some diameter symbols from cylindrical tolerance zones, the hex won't fit a standard wrench, and the threaded side-hole has no definition on the threads. This is just something I threw together for an example, but my OCD forced me to fix it.

 

[pmarc]

flash3780,

Regarding adding basic dimension to B-B section line - I think there is no need for it. As ewh said, drawing is quite clear.
Also you will not find anything about dimensioning section lines in ASME Y14.5-1994 as well as in 2009 edition.

One thing I have additionally noticed after very quick look on your example - since position of perpendicular thread is relative to datums A and B, a basic dimension from datum A to the center of the thread is still missing.

 

[vigildesign]

I usually drag the center line from the auxilliary view to connect the views (and cross the section view line) to take advantage of ASME Y14.5M 2.1.1.2, implied 90 degree angle. But I also keep the view in line and do not move it from the aligned state.

 

[Belanger]

Hi -- the view that you are asking about (View B-B) is called a "removed view" and the pertinent standard is ASME Y14.3. View A-A would be a section view.

The standard doesn't come out and say it, but I think it's safe to assume that the removed view is still orthogonal; that is, looking straight on at the flat side of the hex. So no need for a basic angle really.

A couple thoughts -- I think there should be a 6X in front of the basic 60º angle. Plus, I wonder if there might be a need for a tertiary datum. The position tolerance on the .209 hole references A and B, but it's possible to be the correct height from A, and have its axis be in line with B, yet angle slightly to the left or right. Is there a need to control the relationship of that hole to the hex, or vice versa?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[fcsuper]

Ditto to Belanger's comments except I can see why there is no C datum too.

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

http://groups.yahoo.com/group/solidworks & http://twitter.com/fcsuper

 

[flash3780]

Thanks for the help, everybody. It sounds like Y14.3 is where I should be looking and that an implied parallelism is a fair assumption. However, if the view looks at a curved surface, it's probably necessary to give a basic angle. In regard to your other comments:

JP,
As far as the angle goes, I think that it should actually be 2x. The basic width dimension controls the angular relationship of the opposing sides. You're right, I should have called one of the faces a tertiary datum to establish a rotational orientation.

pmarc,
Good call with the basic dimension to the threaded hole. I also think that the thread pitch diameter could (theoretically) move independently of the tapped hole, so it should probably have its own control since it's called out in a separate view.

Well, I suppose that my example's a fully defined part now. Feel free to add a material and surface finish and order as many as you'd like.

 

[dgallup]

Just a few nit-picks since you asked for it.

I would show the hidden lines of the safety wire hole in the top view. I think that would improve rapid comprehension of just what that feature is.

Also, as a matter or personal preference, I detest the use of the same letters for datums, views and sections. The alphabet has lots of underutilized letters looking for a home.

 

[flash3780]

Ok, Ok, I agree. I never reuse letters on anything that we do for the customers. I was just being lazy. I don't like using hidden lines unless I have to because they clutter things up: I just added THRU for clarity.

Also, I figured that a few lead-in chamfers would be good - so I added them.

I know that I've deviated from the original post, but I blame it on the OCD. I think that the consensus is that a "removed view" pointed towards a surface is assumed orthogonal to that surface.

 

[ringman1]

Flash,

My thoughts are that you should re-examine the tolerances for the holes. They appear unnecessarily restrictive. I would also ask why the safety wire hole requires the use of a diametric positional tolerance in addition.

 

[SeasonLee]

Flash5780

1. On the front view, there is hole callout Ø.209±.005, this should be the tapping hole on the section A-A, I’m sure you are trying to tell the 1/4-20 UNC thread hole tapping process ,but this separate callout for the same thing always makes people confused, so I will recommend you to combine these two in a single callout

2. On the 2nd of your post, you mentioned that the MMC modifier shouldn’t be on the perpendicularity callout and you removed it accordingly on section A-A, as for what I know MMC modifier is legal to apply on the perpendicularity callout.

please let me know if I am wrong.

SeasonLee

 

[Belanger]

The thinking was that MMC is not allowed because it's a threaded feature, not because of the perpendicularity symbol.

That is probably a whole other thread itself! GD&T experts have debated that for a long time. Some say that since a tapped hole will have something threaded into it tightly, there can be no such thing as bonus. (Think of bonus as jiggling or slop.)

Others say gee, the threads DO have a tolerance -- not given on a drawing, but perhaps from the Machinery's Handbook-- so there could be a bonus. The thinking is that any possible bonus might still be affecting the position slightly, but it won't be directly visible once the fastener is torqued down in the assembly (i.e., it might hit its designated torque earlier because of an extra position error).

I see valid points on both sides, so it might be too strong to automatically ding a drawing just because of MMC on a thread.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[flash3780]

LoL so much for the original topic.

Yes, I have to give both the tap drill hole and the thread callout to give the minimum thread depth requirement, and the tapped hole depth requirement.

One can see on the example part that if the tap drill were run too deep, it would interfere with the other threaded hole. Also, it isn't possible to run the tap all the way down the blind hole. So, I'm not so much trying to dictate the process, but I need to recognize the likely process and define the allowable limits.

As far as putting them in the same callout? Sure, that might be a bit clearer. But, I think the way it's defined now is perfectly legit.

I don't put MMC modifiers on threaded holes. Yes the pitch diameter does, in fact, have a tolerance. So, as JP mentioned, it may be possible to squeeze some extra tolerance out in that way. But how do you stack it?

In a production environment, they're usually going to check the position with a threaded gage pin inserted into the threads and mated with the a hole representing the virtual condition. If that's how they're going to measure it, you're going to be concerned with the absolute position of the pitch diameter. I'm not sure that a bonus tolerance is going to add value.

 

[SeasonLee]

Thanks for your input, Belanger. I agree with what you said here, please take a look on this link :

http://www.tec-ease.com/tips/june-03.htm

I can’t understand MMC modifier is needed on the threaded feature for a positional callout but not perpendicularity. Why?

SeasonLee

 

[flash3780]

I stand corrected. It looks as though an MMC modifier is, in fact, proper if you wish to use fixed gaging. I'll add it to my drawings from here on out.

However, in practice, I think most shops would inspect both callouts in the same way.

 

[KENAT]

Geez, and you wonder why some others think GD&T/Drafting standards folks can be a bit anal. It was a rough sketch, move on;-).

Anyway, back to the topic of the thread I'd actually be carefull adding an angular dimension. 1.7.5 & 1.7.6 of ASME Y14.3-2003 talkes about rotated views and adding an angle below the view or next to a direction of orientation arrow to indicate rotation of the view. While this isn't quite what you're proposing I'd still be carefull.

Also, what you have could be done as an auxiliary view if I understand correctly (section 2.7) except I suspect your CAD wont let you. As an Auxiliary view would wouldn't need the 'B-B' etc. and could extend projection lines to indicate orientation.

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