Using multiple arrows for the same tolerance 2

[SVillagrasa]

Hey all,

I am wondering if it is acceptable to use the method shown to indicate the same tolerance to the B datum for multiple beams in my assembly.

Thank you.

 

[KENAT]

Off the top of my head I can't see why not.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[powerhound]

I believe it is okay to use that method to indicate the same tolerance for different features but I have an issue with your statement "the same tolerance to the B datum". If your intent was to call out the B datum parallel to itself then you can't do that. Did you mean "with respect to the B datum."?

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[DeanD3W]

A better look at datum feature B and the feature you're applying the parallelism to is needed in order to tell whether the spec is OK or not. Can you post another view or two, so we can fully understand how capable datum feature B is for serving as a primary datum feature?

Dean

http://www.d3w-engineering.com

 

[SVillagrasa]

powerhound: Yes I meant with respect to the B datum. The B datum is bottom surface of the bar on the right and I want to call out a parallel tolerance with the bar on the left as well as a few of the beams above (not shown) in the structure.

Dean3W: The features that this will be applied to are horizontal beams (5 of them). The datum is referenced off of a bar (on the right) where the bar on the left and a few others above are being related with the parallelism tolerance. Unfortunately I can't really post anymore of the structure.

 

[powerhound]

Parallelism only controls the orientation of the other bars so there could be a 1/4" between datum B and another bar, as long as they are parallel within .005, the part will pass inspection. Is your intent to keep all the bars on the same plane? If so, profile of a surface is the way to go. See fig 6-20 in the 94 standard or fig. 8-14 in the 2009 standard. They are different so be sure you know which standard you are working to.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[SVillagrasa]

I've got the 2009 version, I'll take a look at it. Thank you very much for your help!

 

[pmarc]

SVillagrasa,

The method of showing parallelism FCF with multiple leaders is absolutely legal. You can take a look at figs. 9-4 and 9-6 in Y14.5-2009 standard to see how this is done with runout FCF's as an example.

The other question (already mentioned by Dean) is how capable datum feature B is to serve as a primary datum feature for parallelism callout.

And the second thing is, whether the parallelism is the tolerance you would really like to use. I do not want to go too far beyond the scope of your original question, but you have to keep in mind that parallelism does not locate, so this means that on your print there is no control of a distance between datum feature B and the other bars - unless we can't see it. If that is fine for you, then just forget about what I have just written, but if it is not, then profile of a surface would seem to be a way to go.

 

[SVillagrasa]

pmarc,

Okay it's good to see another person supporting this and I actually found some other figures with multiple arrows the other day when I was looking through the standards.

I read about the profile tolerance and I changed the bottom beam (left) to a profile tolerance since it seems like a much better way to tolerance the piece. I have left the rest of the beams with a parallelism tolerance, but I have dimensions on those.