×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How do you determine gage hole size using RFS.
3

How do you determine gage hole size using RFS.

How do you determine gage hole size using RFS.

(OP)
I am checking the drawings for some mylar inspection gages that are intended to verify profile and hole locations on flat parts by laying the part on top of the mylar. The engineer specified the holes to be .1285 -.1385 dia and true pos'n w/in .020 RFS. I know that the .020 positional tolerance is added to the hole size, but I'm not sure which hole size to use: smallest, largest, median? I have looked through the ASME standard and can't find anything that addresses this. Any help would be greatly appreciated.

Peace Through Superior Firepower!

RE: How do you determine gage hole size using RFS.

tooldeziner,

   If your positional tolerance is RFS, you must inspect the diameter and position separately.  Regardless of Feature Size means exactly that.

   You can implement a quick and dirty GO gauge using pins.  The pins must be located exactly at nominal position.  Their diameter must be the minimum size minus the positional tolerance.  In your case, the diameter would be .1085".  There is lots of stuff not being inspected, but this might catch your primary functionality.

   I do not know what your holes are required to do.  There is no guarantee that a 4-40UNC screw will pass through your clearance hole into a tapped hole.   

               JHG

RE: How do you determine gage hole size using RFS.

One cannot use GO gauges when the positional tolerances are in RFS - regardless of feature size unless one is willing to make a gauge for every increment in size. The position should be confirmed using a CMM type measuring equipment.

If I had a drawing reflecting RFS, I would go back to the Designer and request MMC. Now you can develop a gauge at its virtual condition size.

Dave D.
www.qmsi.ca

RE: How do you determine gage hole size using RFS.

Quote (dingy2):

One cannot use GO gauges...

   That is why I called it quick and dirty.  

   MMC also is a better description of a lot of design intent.  Presumably, we are trying to clear something.  Ø.020" is a sloppy positional tolerance.

               JHG

RE: How do you determine gage hole size using RFS.

I think Kenat made a good point. To follow up with that, I would ask, what version of ASME is applicable on your drawing?   


 

RE: How do you determine gage hole size using RFS.

(OP)
IMHO, I liked it better when the designer had to specify the M, L OR S. Now an oversight on the engineer's part, accidentally omitting the modifier, may give a result that was not desired or intended. But, that's for another post...
 
 

RE: How do you determine gage hole size using RFS.

On one hand I agree with Dave. Fixed in size pins should not be used for verifying tolerance of position on RFS basis. Dia .1085 pin basically located from datum reference frame would work fine if TOP was applied on MMC basis.

On the other hand, I would not automatically disqualify such TOP with RFS callout on a drawing and go back to a Designer for changing it to MMC without asking him what is the function of analyzed component. There are some cases when TOP with RFS is better than with MMC (centering, symmetry, alignment). Of course the inspection is then almost always more expensive and time consuming but if the function requires such position callout a designer should go for it.  

RE: How do you determine gage hole size using RFS.

pmarc,

   You make an interesting point.  I just assumed that the holes were for clearing screws.  If I provide holes for cable ties or for cable pass-throughs, I would apply sloppy positional tolerances.  Functionally, I would not care where the holes are.

   The gauging I proposed above, looks for a worst case in which the part interfaces with a rigidly located external feature.  The external feature may not be rigidly located, or the intent may be for it to be located by the hole.  

               JHG

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources