Symmetry or True Position?

[umctkim]

Hello,
I'm fairly new to this so I'm hoping someone could help me out please. To position these tabs below, I was going to use symmetry GDT. But after googling a bit and asking my boss, I don't think that's a good idea. So what would be the best way to position them via GDT? Thank you in advance.

 

[Johnnymo62]

The picture didn't come through. I think you have to have 5 posts before you can attach anything. This is about eliminating bots, I think.

 

[umctkim]

Ok sorry - I am trying to attach a picture, and I can only attach via a link. How can I just copy and paste, or upload direction from my computer?

 

[Randy]

Ok sorry - I am trying to attach a picture, and I can only attach via a link. How can I just copy and paste, or upload direction from my computer?

Yes you do but not in the way you tried to do it. You need to be a participant, not a potential SPAM artist.

 

[umctkim]

I think years ago I made some posts asking questions about PPAP and GR&R, but after that I haven't been on for a while until today. If any admins are reading, please allow me to post a pic please. Thank you

 

[Miner]

Hello,
I'm fairly new to this so I'm hoping someone could help me out please. To position these tabs below, I was going to use symmetry GDT. But after googling a bit and asking my boss, I don't think that's a good idea. So what would be the best way to position them via GDT? Thank you in advance.

In general, using a position tolerance is better than using symmetry. Symmetry is very difficult to measure, and you cannot use a functional gage to check it, whereas position is easier to measure, and you can use a functional gage. In addition, 2018 ASME Y14.5 removed symmetry as an option.

 

[umctkim]

I'm not sure about how to use position in my case. I am welding tabs to a large ring. The tabs are mirrored from the center (they are the handle/lock attachments for the cover).

 

[joezilla86]

Think of it less as how to define the relationship between the two tabs and more how to define the relationship of each tab individually to a common datum reference. What I mean is, don't try to tolerance the tabs as being symmetric, draw them symmetric nominally, but tolerance them individually such that your worst case tolerance stack is still functional in the design. You have to have some level of acceptable asymmetry, you just need to translate that into a tolerance zone for a single tab.

 

[Miner]

I'm not sure about how to use position in my case. I am welding tabs to a large ring. The tabs are mirrored from the center (they are the handle/lock attachments for the cover).

Would a profile tolerance work?