Hi all :bigwave:

I'm new to the Elsmar Cove; this is actually my first post. I realize the title of my thread doesn't really have much to do with MSA perse, but I was unsure which forum fit my question better.

I'm wondering what is meant when a datum (feature) is called a "6 way" or a "4 way" or even a "2 way" for that matter? I know it probably has something to do with restricting the 6 degrees of freedom of an object in 3D, but I'm not sure exactly how. I've read (ok, skimmed :read:) the ASME Y14.5M-1994 book on GD&T, but I don't see any reference there. I have also searched the internet for info, but to no avail. Can someone please provide a link, reference, or explanation to help elucidate my boggled mind? Thank you in advance, and thank God a site like this exists!

Gyro-

Moved thread to more appropriate forum to encourage more response.

I can help you on 4 way locator and 2 way but I have a feeling that they correspond to 6 & 4 degrees of freedom.

If you look at your feature control frame, you will see that the secondary datum (2nd reference datum in on the right side of the feature control frame) and tertiary (3rd or last datum referenced) are holes.

All measurements are take from the secondary and is called the 4 way locator. From this datum hole, one could measure up and down plus sideways. To fixture this datum one would have a cylinder of MMC.

The tertiary datum is only to orient the part. Measurements do not come from this datum. This is call a 2 way locator since it is the "stopper" for the part. To fixture this datum, it would have a oblong cylinder with the larger size the MMC size (or could be virtual condition size). Again, it just stops the part from rotating.

I am hoping the MMC (M with a circle around it) is referenced in both the secondary and tertiary datums in the feature control frame.

Hope this helps.

Hi all :bigwave:

I'm wondering what is meant when a datum (feature) is called a "6 way" or a "4 way" or even a "2 way" for that matter?

Gyro-

Hello Gyro,

Welcome to The Cove!

Where did you find/hear/read this term: "6 way - 4 way - 2 way" datum feature?"

A reference may help us to help you.....:)

Stijloor.

The term 4 way or 2 way locators are not in the ASME Y14.54M-94 standards but it is a term used in stamping and tool shop.

Hello again :bigwave:

Sorry I've not been able to respond till now. Thanks for your input Dave.:) Does your answer mean that all secondary datums (on the feature control frame) are 4-way locators, and all tertiary are 2-way?

Stijloor, the terms 4-way and 2-way, etc. I often see on part prints used at the facility I work in. They usually point to the B and C datums, respectively. As an example, a part we manufacture is fixtured in a gauge with A1, A2, and A3 used as 'nets' (the primary datum), and the B and C datums are used to 'locate' and 'orient' the part correctly. My misunderstanding revolves around how many degrees of freedom a 4-way datum (for example) restricts the movement of the part. My mind wants to say that a 4-way locator restricts movement in 4 degrees of freedom, but as Dave pointed out in his first response, it may actually be restricting 6 degrees of freedom. So therein lies my confusion. And not being able to find any references / links / books, I'm still left somewhat confused... :bonk:

I appreciate the answers so far, but am hoping for any more clarity. Thanks again.

Gyro-

Try tec-ease.com or cmmtalk.com

Yes, if the secondary datum is a hole or pin, it will be a 4 way locator and all dimensions should come from this feature. 4 measure up - down - r side & l side.

The tertiary datum if it is a hole and a 2 way locator or stopper. It controls the movement of the part side to side or r side and also l side.

Yes you certainly could try those areas but I have been training in this subject for 20 years in Canada and sometimes in the USA and am certified as an ASME GD&T Professional - Technologist and Senior.

Gyro,

I am not well versed in sheet metal gauging terms but I know that they have a practice of using terms like “Nets” referring to cross hatched datum target areas, “4-way” locators usually referring to a round pin in a round hole, and “2 way” locators usually referring to a round pin in a slot. If you were trying to relate this jargon to “degrees-of-freedom”, the “nets” or the primary datum feature target areas would typically restrict three degrees-of-freedom (two rotation and one translation), the “4-way” would typically restrict two (two translation), and the “2 way” would typically restrict the one remaining degree of freedom (one rotation).

I got to admit that I haven’t heard of a “6 way” locator before but if you extended what is known about the sheet metal gauging practice, I would have to guess that a “6 way” locator is one that can constrain three degrees of freedom, like a slot or rectangle used as the secondary datum feature restricting two translation and one rotation or a sphere which would restrict three translation and no rotation. I can think of many examples but I cannot imagine what type of locator that restricts three dof's would be common to sheet metal stuff other than the “nets”. It’s not a cylindrical surface because that would an “8 way” locator restricting 4 degrees-of-freedom (two translation and two rotation). I’m stumped!

Paul

Hello again :bigwave:

Sorry I've not been able to respond till now. Thanks for your input Dave.:) Does your answer mean that all secondary datums (on the feature control frame) are 4-way locators, and all tertiary are 2-way?

Stijloor, the terms 4-way and 2-way, etc. I often see on part prints used at the facility I work in.

Hello Gyro,

Could you share a picture of this particular callout with us? A partial drawing scan or so?

Stijloor.

Hello again everyone :bigwave:

Thank you all very much for your input. I appreciate each of the responses I received. They all, in some way or another, helped clarify my misunderstanding (or at least elucidated it to a tolerable level).

I did some "eye-spying" at my facility, and indeed, it seems the "6-way" locator is a sphere, restricting 3 dof (all translation). I could still be incorrect in my understanding but, it seems that in conjunction with several "nets" the part is further restrained in 3 more dof (all rotation). Practically, the feature is a ball-stud, which, when the part is assembled into the vehicle's sheet metal, mates with an hemispherical housing, which is then enclosed by another casing (internally called a "basket"). And with the other "nets", the part is disallowed movement in any fashion, securing it into the vehicle, without over-constraining the part.

As alluded to above, I could still be in err in my explanation, but at least I have come to a much better understanding of how a 4-way and 2-way locator functions, as well as reprogrammed my mind from thinking, "4-way locator restricts 4 dof", which was one of the original stumps I had in my train of thought. So, thank you all for your assistance! :thanks:

A propos, I would also like to extend my gratitude to all the people involved in creating and maintaining the Elsmar Cove website. Keep up the great work!:applause:

Sincerely,

Gyro-