Profile and parallelism call out on flat surface

# Thread: Profile and parallelism call out on flat surface

1. ## Profile and parallelism call out on flat surface

How do I interpret the following call out for a surface that is parallel to the datum?

parallel to datum A .003 with an additional .002 profile call out.
Datum A is defined by .004 profile call out.

Wouldn't the .002 profile call out negate the .003 parallelism?

Does the tolerance of the datum come into play at all?

I Don't think I have seen a call out this way before, if I have the tolerance has been big enough I haven't had to take notice of it.

Thanks guys

2. Cast Iron
Join Date
Jul 2009
Location
NW Illlinois USA
Posts
417
Post Thanks / Like
Likes (Given)
98
130
Can you post an image of the GDnT? Sounds goofy but can't really say without more detail.

I've seen a LOT of bogus callouts.

They're the one who ultimately determines whether or not your product meets spec.

- Leigh

4. This is the call out for two parallel surfaces.

Sent from my SM-J337V using Tapatalk

5. Cast Iron
Join Date
Jul 2009
Location
NW Illlinois USA
Posts
417
Post Thanks / Like
Likes (Given)
98
130
You are allowed .003 both surfaces simultaneously parallel to A

You are allowed .002 profile both surfaces without reference to any datum. Think of as a flatness spec both surfaces simultaneously.

.004 profile on your datum A likely could simply be considered a flatness spec. .004 magnitude could potentially cause you trouble meeting the other two specs. Rocking datum. Are there A datum targets?

6. Aluminum
Join Date
Dec 2016
Country
UNITED STATES
State/Province
Wisconsin
Posts
89
Post Thanks / Like
Likes (Given)
0
16
Has to be parallel within .003 of datum A, but the irregularity or waves in the surface cannot exceed .002

They are just using the profile tolerance as a refinement of the parallel callout. Its a volume between two surfaces tolerance, with two hypothetical boundaries, can be on an angle of .003 but the peaks and valleys of the surface cannot exceed .002

7. Aluminum
Join Date
Jun 2011
Country
UNITED STATES
State/Province
Pennsylvania
Posts
193
Post Thanks / Like
Likes (Given)
27
68
Originally Posted by yoke
This is the call out for two parallel surfaces.

Sent from my SM-J337V using Tapatalk
Dumb callout. Parallelism is a tolerance of form. So those surfaces could be anywhere within the size tolerance limits. Profile can be used to locate a feature, but not without datums. So the profile is nothing more than a refinement of the parallelism. I would treat it as a flatness.

I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc

8. Stainless
Join Date
Dec 2014
Country
State/Province
British Columbia
Posts
1,275
Post Thanks / Like
Likes (Given)
361
581
Originally Posted by AdamC
I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc
The worst I’ve seen was a fuel cell compression plate, roughly 20” lo g dog bone shaped with 3d surfaced ports. Pretty much the only tolerances on the part were various profile tolerance GDT callouts and nary a dimension to be seen.

9. Originally Posted by AdamC
Dumb callout. Parallelism is a tolerance of form. So those surfaces could be anywhere within the size tolerance limits. Profile can be used to locate a feature, but not without datums. So the profile is nothing more than a refinement of the parallelism. I would treat it as a flatness.

I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc
Yeah, I thought the profile should have a datum call out to mean anything. There is no feature to feature size on the drawings.

This is an experimental-in-nature part so if they get the results they want they will relax the drawing to whatever we are able to make.

Thanks everyone for your feedback.

10. Originally Posted by AdamC
Dumb callout. Parallelism is a tolerance of form. So those surfaces could be anywhere within the size tolerance limits. Profile can be used to locate a feature, but not without datums. So the profile is nothing more than a refinement of the parallelism. I would treat it as a flatness.

I think the prevalence of CNC machines and 3d cad software has given rise to engineers who no longer understand or feel they need to know GD&T or even basic drafting. I think they are also confused about reasonable tolerances, understanding what they really need, flexibility of parts, finish thickness etc etc
Yes and yes!

A few years back I worked with some really smart engineers (no sarcasm intended), but they could not understand why a 1/8" rad in a pocket 2" deep was a bad idea.

11. Plastic
Join Date
Jul 2018
Country
UNITED STATES
State/Province
California
Posts
35
Post Thanks / Like
Likes (Given)
23
8
If it's profile to datum A, that is correct. Simple profile (to itself, basically), no.

12. Aluminum
Join Date
Jun 2011
Country
UNITED STATES
State/Province
Pennsylvania
Posts
193
Post Thanks / Like
Likes (Given)
27
68
Originally Posted by Kai Kendall
If it's profile to datum A, that is correct. Simple profile (to itself, basically), no.
My company thinks profile with no datum means the surface must best fit match the drawing/model within the tolerance specified, but the surface can be anywhere.

We use it where there is no clear or useful datums. We don’t build cars but imagine a surface profile on a car windshield.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•