proper datum callout 1

[Dudeman555]

I have a hole that I want to use as Datum B, but I only want the datum to control one direction, not both. I'll have a diamond pin for this hole. Actually there will be two of these holes, one at each end of a long part.

 

[drawoh]

Dudeman555,

Read up on datum targets.

--
JHG

 

[weavedreamer]

See Fig. 5-41 in ASME Y14.5M-1994

 

[Dudeman555]

Well that didn't help much! I have read up, but there's no example showing what I'm trying to do.
I'm using the Y14.5 2009 standard. I have a long plastic part with three holes; One at each end and one hole in the middle. The two end holes, Datum B, will control 'Y' and the middle hole, Datum C, will control 'X'. Being holes, how do I show them as Datums controling one direction only?

 

[weavedreamer]

See Fig. 7-289, 7-29 & 7-34 in ASME Y14.5-2009

Instead of using both DRF's on one hole, apply the applicable direction to the applicable hole individually.

 

[weavedreamer]

Fig. 7-289, should have read Fig. 7-28,

 

[drawoh]

Dudeman555,

If you specify a hole as a datum, you are controlling X[ ]and[ ]Y. If you apply a datum target to one side of the hole, you constrain motion against the datum target. A diamond pin controls X[ ]or[ ]Y, completely. Your fixture should be a much smaller round pin, or a triangular pin that engages the target face.

You call all this up by applying a datum target.

--
JHG

 

[Dudeman555]

How do I place the Datum symbols to achieve what's on the attached picture. Notice the diamond pins in all three holes. I understand Datum B may need to have targets B1 and B2. But I still need to know how best to place the Datum symbols on the dimensions to communicate this type of setup?

 

[drawoh]

Dudeman555,

How about a datum target on each side of each hole, where the diamond pins contact? Note how you need datum targets A1, A2, B1, B2, C1 and C2.

--
JHG

 

[Dudeman555]

I suppose that's one way to do it. I was hoping there was a way similar to how you would do a slot.
Where you would dimension the width of the slot, then put the datum callout off of the dimension
line. Only with a slot it's more obvious which direction you're appling the datum to.

 

[drawoh]

Dudeman555,

I strongly prefer to dimension round things with an arrow pointing at the round thing. I don't have any standards in front of me, but I believe that dimension lines with vertical or horizontal arrows are a valid way to dimension round things. The horizontal or vertical orientation of your dimension communicates no information.

--
JHG

 

[3DDave]

Dudeman555,

The method of indicating the location tolerance applies in one direction is what weavedreamer was indicating by Fig. 5-41 in ASME Y14.5M-1994. I don't have a released copy of '2009, but I presume it's a similar figure that wearvedreamer indicated by Fig. 7-28, 7-29 & 7-34 in ASME Y14.5-2009

In either case, it is applied exactly like it is to a slot.

 

[powerhound]

The way you can do this per the 2009 standard is by overriding datum precedence. It's new to the 2009 standard. I don't have a copy here with me but maybe one of these guys can refer you to the correct section.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ewh]

...dimension lines with vertical or horizontal arrows are a valid way to dimension round things

Locating dimensions, yes. Diameter or radial dimensions with leader, no.
Per ASME Y14.5-2009 ¶1.7.4 "A leader should be an inclined straight line except for a short horizontal portion extending to the mid-height of the first or last letter or digit of the note or dimension."

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[Belanger]

ewh, it is legal to dimension a diameter in the manner described by drawoh. What you quote from the standard is a correct description of a leader, but the standard doesn't say that a leader is the only way to dimension a diameter.

See the second example shown within Fig. 1-36; it's using dimension lines with vertical arrows.

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

 

[drawoh]

ewh,

The ASME Y14.5 standard allows you to dimension a circle with two horizontal or vertical lines, extending from quadrants, with a dimension between them. SolidWorks tries very hard to dimension things that way. I don't like it. I systematically use the leader.

--
JHG

 

[CheckerHater]

Dude,

Does your part have any features that you want to control wrt your A, B, C?

Also, do you imply having A primary, B secondary, C tertiary?

 

[ewh]

I stand corrected. Like drawoh, I habitually use leader dimensions for most holes, but admit to using extension/dimension lines when the situation dictates.
I have recently been fighting vertical and horizontal leader lines used by co-workers, and I had my blinders on.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[jassco]

Hi, Dudeman555:

I think you can achieve it by specifying the following:

| C[x] | B1[y] - B2[y] |

where C is datum for the middle hole, and B1 & B2 are datum for left and right holes.

Best regards,

Alex

 

[SeasonLee]

Dudeman555

The two end holes, Datum B, will control 'Y' and the middle hole, Datum C, will control 'X'.

I am trying to figure out your intent, and hope I understand it correctly.

Datum B is selected as the two end holes, it’s a hole pattern as datum B, the datum planes are set as the average between the two holes, datum axis B is at the theoretical center of the pattern, a second and third datum plane exist from the datum axis. When the part is mounted on the primary datum surface, the pattern holes establishes the second and third datum planes of the datum reference frame, so the tertiary datum reference is not necessary since all 6 degrees of freedom are constrained. Datum Reference Frame can be expressed mathematically as shown:

Primary datum plane A will constrain rotation u and v, and translation z, while the hole pattern datum B will constrain the remaining three degrees of freedom, two translations x and y, and rotation w.
Now, you want to control the translation x by datum C (if I understand your intent correctly), you may move the translation x from the B compartment to C compartment as shown:

This is the customized datum reference frame in Y14.5-2009, you may find out more information from Fig.4-44, 4-45 and 4-46.

Season