profile on trimmed edge 8

[DGN1975]

does anyone have idea or references how to profile tolerance a complex trimmed edge on say a vac formed part? I don't really see any good examples in the standard to other places. Would it make sense to just point to the trimmed edge with a 'ALL OVER' profile tolerance with a note below that states "trimmed edge". using "all around" wouldn't work to me as it is controlled only in the view its shown in and a trimmed edge would go all around in 3d.

 

[Tarator]

3DDave,

You will still have a datum reference frame with just | A |.

 

[Garland23]

Tarator, I agree. But the terminology can get confusing; in Fig. 7-14 of Y14.5 they label the datum axis, but they also label the intersecting planes as "datum planes." They should have said "datum reference frame" as they did in most other pictures.

 

[3DDave]

You can have a datum reference frame with zero references.

It is short for CMM coordinate system, which a good portion of the standard is designed as a sales tool for.

 

[Tarator]

3DDave,

I am sorry, I am not following your last message.

 

[Tarator]

Garland23,

Datum Reference System = Coordinate System (cartesian), which consists of 3 datum planes, 3 datum axes, and 1 datum point. So a datum plane for instance is just a part of the Datum Reference System.

 

[3DDave]

Tarator,

Per the standard the datum reference frame exists independently of all parts; it is the datum references that tell how to align the part to it.

Also per the standard, it doesn't exist.

Sufficient datum features or designated portions of these features are chosen to position the part in relation to one or more planes of the datum reference frame.

This reference frame exists in theory only and not on the part.

 

[Burunduk]

1. What is the difference between a datum axis and a datum line?
2. For a conical feature (identified as a primary datum feature), would we have 2 datums (1 datum axis, and 1 datum point) or 1 datum (datum axis and datum point counted as 1 datum)?

1. A datum axis is a special case of a datum line. A datum axis is the center of a TGC shape that has rotational symmetry about it. A datum line that is not an axis is a line used as a datum, but doesn't fit the above condition.
2. For a cone, we would have a datum that is a combination of elements. The datum would be an axis and a point (as shown in fig. 7-3) or you could make one step forward to DRF establishment and say it's an axis, a point, and a plane (through the point and normal to the axis).

Tarator, here's an offshoot question to yours: Is a datum axis a single datum, or is it comprised of two intersecting datum planes?

Good question. Unfortunately, the Y14.5 standard is not consistent about this terminology. Sometimes the planes of the DRF are described as datums (and they clearly are in the case of datums derived from planar TGCs), at other times it is indicated that they are not the datums but established based on datums (such as for planes related to a datum axis).

 

[3DDave]

There are no examples of datum lines and no explicit definition of what constitutes a datum line.

It seems like a Winston Smith moment to claim to see them.

 

[Burunduk]

It seems like a Winston Smith moment to claim to see them.

You had such moment too in this thread, suggesting it may be a spine.

 

[3DDave]

Burunduk,

I realize you cannot find your own support for your claim, but don't fabricate one by altering the context for a statement of mine.

 

[Burunduk]

Which my "claim" I can't find support to?

 

[3DDave]

Right - you didn't make a claim, just more parrot nonsense.

 

[Burunduk]

You didn't really make a claim either,
unless your claim is "no example figure in the standard =inapplicable" which is BS.

 

[3DDave]

Only one mention and zero application = BS.

 

[Burunduk]

You brought up an application yourself: "Probably it was meant to reflect the idea from Y14.5.1 of a spine", but that doesn't stop you from complaining.

 

[3DDave]

Again, the context is another failure to make any use of a term, not that there is a use.

You included it as a copy/paste from a list.
I say it's a gross defect.
You White Knight to defend the gross defect = BS.

 

[Burunduk]

I know you only meant to complain again - who cares? You ended up with an example for a use of the term. Which means it is not in the list for no reason.

 

[3DDave]

You ended up with an example for a use of the term

I literally did not as there is no use for the term. What it might have been meant for doesn't matter. It has no use.

There are no examples of datum lines and no explicit definition of what constitutes a datum line.

It seems like a Winston Smith moment to claim to see them.

* line (note the differentiation between line and axis).

What is the differentiation you can link to?

 

[Burunduk]

You can't say "no use" unless you know every single use/application in the world.
The standard did everything it could to unlimit the variety of geometries that can be used as a datum feature.
If from whatever reason a bent tube is labeled and referenced as a datum feature that stops all 6 degrees of freedom, and it is considered that the spine (line) of the true geometric counterpart is the datum, being the foundation for a datum reference frame, it is a valid solution not in conflict with any rule or definition no matter how much you dislike it or think it is a bad idea. Your personal preference or recommendations to do otherwise won't matter.

 

[Tarator]

Burunduk,

1. A datum axis is a special case of a datum line. A datum axis is the center of a TGC shape that has rotational symmetry about it. A datum line that is not an axis is a line used as a datum, but doesn't fit the above condition.

I am having difficulty understanding what a datum line is. Is the term `line` used for curve, like in `median line`? To me, the difference between a datum axis and a datum line would be that the line would have 2 end points (fixed length), where the axis would have an infinite length. That's why it doesn't make sense to me to differentiate axis and line. Would you be able to show an example of a datum line?