×
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

No [ - C - ] datum on engine bracket?

No [ - C - ] datum on engine bracket?

No [ - C - ] datum on engine bracket?

(OP)
Every hole or slot is toleranced to [-A-],[-B-]. [-B-] is a slot. [-A-] is a plane perp to the slot. How do I align the part for layout purposes?  The part is 8 times longer then the [-B-] slot.     

RE: No [ - C - ] datum on engine bracket?

Well, you should have a teriary datum. All dimensions should come from the centre of B datum with a tertiary datum included for orientation. In your present situation, you should align the sides of the slot for orientation but there is a BIG chance for error here especially since the part is quite long.

It would be better if the hole was in a positional tolerances in MMC and the slot was also in MMC. Now you could use a checking fixture (functional gauge) where there would be a pin the shape of the datum B slot but in a MMC size and theoretically oriented to the hole. Place the part over the datum B pin and one will see a certain slop. The positional checking pin for will be placed in the hole to confirm its location.

Dave D.
www.qmsi.ca

RE: No [ - C - ] datum on engine bracket?

(OP)
Thanks Dave,

 Appreciate the function gage info. I do have MMC. For capability studies of machined hole positions I plan to set it up on the CMM RFS for the variable readings. Maybe if the [-B-] slot locater had 2 spheres with a spring in between forcing them apart, but I just don't think I'll pass an under 10% R&R with that.

Thanks Again,

Gary  

RE: No [ - C - ] datum on engine bracket?

Love to see how you do capability studies on positional tolerances since I know it can't be done. It is all hocus-pocus and make believe. I hope to have something online from a presentation I make to an ASQ group on why it can't be done properly.

As far as the 10% R & R value on critical characteristis, one must remember it is a percentage of the process and not the tolerance per MSA 3rd edition. The way it is set up on the B slot, I am pretty sure that you will not make it. You probably will be lucky to get under 30% and most likely 30 - 50%.

Good luck on that one!

Dave D.
www.qmsi.ca

RE: No [ - C - ] datum on engine bracket?

JoeBlock:

I finally figured out how to do this. I have enclosed a web site reflecting capability studies on positional tolerances and how it just doesn't work out. This is a part of a presentation that I made to an ASQ group in one of their dinner meetings.

See if it makes any sense to you. I hope that this will help you.

http://www.qmsi.ca/capabilityindex.html

Dave D.
www.qmsi.ca

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