Dimensioning a Ruler

[TopPocket]

Hi,

So I've found one of those "sounds simple at first" problems.

I have a part with a laser marked scale, imagine a glorified ruler.

I need to specify the tolerance of the laser marks, specifically three things:
- Absolute position of each mark from end face
- Line Spacing between adjacent marks
- Thickness of each mark

Now the standard method would obviously result in an absolute mess, as the scale is 140 mm long (1 mm increments).

Is there a better way?

I've considered using position and TEDs but I think it is unclear. The most important thing is the absolute position of each line from the end face, so this is what I wish to be inspected, not a bunch of 1 mm increments.

There's ordinate dimensioning but I don't know how that works (oh I'm ISO btw, spice it up a bit).

I feel like there should be a way to start speccing them from the end face and do a kind of "..." ?

Any help would be appriciated.

Here's a pic for reference:

 

[TopPocket]

Burunduk - thanks for confirming that. I wish there was someone who knew more about GD&T here.

The spacing spec seems like over constraining but it is needed.

For example, if it wasn't included the spacing could be as bad as 1 ±0.6 mm, with absolute position of one line at USL and the next at LSL. This isn't acceptable. So you need both. Also different requirements drive each.

 

[3DDave]

A typical tolerance for markings is to keep unwanted variation less than 1%, so these variations need to be 0.01mm MAXIUMUM. Any more than that will look like garbage. People suck at evaluating individual measurements, but they are very good about making comparisons.

 

[TopPocket]

0.01mm would be lovely but unfortunately we're nowhere near achieving that. I've gone through an assessment and found ±0.15 mm is just about acceptable.

 

[Burunduk]

The spacing spec seems like over constraining but it is needed.

For example, if it wasn't included the spacing could be as bad as 1 ±0.6 mm, with absolute position of one line at USL and the next at LSL. This isn't acceptable. So you need both. Also different requirements drive each.

It is better to define this by the ISO GPS way of doing what is known in the ASME world as a composite tolerance. The callout would include two tolerance indicators (feature control frames), one on top of the other. The top one would be just as you did: 0.6 relative to the A,B datum system. The one below it would be 0.3 with a CZ (common zone) modifier relative to only datum A, which would be modified by the symbol "><" to reflect that datum A only constrains rotation and not translation. Since you would not reference datum B, that would mean that the tolerance zone can float along the shaft back and forth, and the marks would be good as long as they conform to the upper tolerance indicator (0.6 mm), but the spacing between lines and their orientation to the axis would be allowed to vary only within the zones of 0.3.

 

[greenimi]

....The one below it would be 0.3 with a CZ (common zone).....

CZ= combined zone
The CZ symbol was called “common zone” in the former version of this document.(ISO1101:2017)

 

[Burunduk]

Thanks for the correction, greenimi.

 

[pmarc]

CZ= combined zone
The CZ symbol was called “common zone” in the former version of this document.(ISO1101:2017)

Speaking of corrections, the previous version of ISO 1101 was from 2012, not from 2017. The 2017 version is the most current one ;-)

 

[3DDave]

What does the test part look like?

 

[greenimi]

Speaking of corrections, the previous version of ISO 1101 was from 2012, not from 2017. The 2017 version is the most current one winky smile

pmarc,

Well...that is true, but was not my intent because the sentance you are referencing to IS from ISO1101:2017

So ISO1101:2017 is added by me to clarify where the sentance was copied from ( I mean this sentance "The CZ symbol was called “common zone” in the former version of this document")--see Table 3 last sentance from ISO1101:2017
Looks like my intended clarification just created more confusion.....This is how the words are failing us

By the way, could you PLEASE (pmarc) answer my question about differences between ASME and ISO GPS regarding the datum targets. PLEASE. and Thank you very much

 

[pmarc]

greenimi,
You did not use quotation marks in your previous reply, therefore I did not know you were quoting the 2017 standard. Anyway, I'll try to reply to your question about datum targets in the other parallel thread.

 

[greenimi]

You did not use quotation marks in your previous reply, therefore I did not know you were quoting the 2017 standard.

My bad. Sorry about that. Looks like I made one more mistake for today I keep counting....

 

[Burunduk]

2012, then 2017. How come there is no new one out yet? I bet even training providers barely keep track. Is it the industry needs drive this, or is it the urgency to change terms from common zones to combined zones? Is there a point to having a standard for the communication of engineering information if it constantly changes?

 

[3DDave]

Yes - changes drive sales. New standards, new training, new bullet points for resumes, new compliance requirements to upgrade software, and most of all - frequent flier miles to go to meetings to discuss those changes.

 

[Burunduk]

Ok, it must be agreed upon by everyone except the ISO committee members that GPS is a horrible system. An exaggerated amount of symbols and fancy terminology, both updated way too often and scattered across a multitude of documents, make it very user-unfriendly. No wonder why the majority of engineers that work in companies that "follow" ISO don't even bother to start learning it. As the OP stated, "I wish there was someone who knew more about GD&T here." Give each of them a copy of good ol' Y14.5, and they at least might open it from time to time.