×
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

Pattern of features

Pattern of features

Pattern of features

(OP)
Hi all,
i have a tolerancing problem similar to this example:
a. 5 holes on a flat surface, along a line;
b. the distance between each hole should be 10 +/- 2
c. the distance between the fisrt and the last hole should be 40 +/- 5

With dimensional tolerancing only the 2 tolerances don't stack up but I need them to be exactly 2 and 5, not bigger nor smaller.

Ideas?

thansk

RE: Pattern of features

Disregard your tolerances as stated and determine what the mating feature will allow tolerance wise.

RE: Pattern of features

(OP)
That's what the mating feature allows +/-2 for the hole and +/-5 for the overall length. For manufactugin purposes I can't tighten the +/-2 to match the +/-5 overall tolerance

RE: Pattern of features

I would use a "non-cumulative" approach, referencing the distance between holes and using a toleranced hard callout on the overall pattern, such as "(4X 10 =)40±5".
I am interested in learning how others would approach this.

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

RE: Pattern of features

(OP)
Can't then the part be manufactured with the distance between holes outside the +/-2?  

RE: Pattern of features

No, the max between holes would be 1.25 (5/4 spaces).

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

RE: Pattern of features

Heck,

I would just specify match locate at assy and let it go.

RE: Pattern of features

Gubo,

   Apply your four hole to hole dimensions at ±2.  Apply a dimension from the first to the last hole with the ±5 tolerance.  The tolerance provides a requirement, so this is not a reference dimension, even though the dimension value is redundant.

   How do you control your holes moving side to side?

   You should think through your requirements a bit.  I cannot visualize why you would want tolerances like that.  If you explain to us what you are trying to do, I can probably explain why it will not work.

   This may be a job for a composite positional tolerance.  

               JHG

RE: Pattern of features

Wouldn't using positional more or less solve the problem?  Ok it'll effectively restrict the overal length tol tighter than +-5 but that wouldn't conflict with stated requirement.

As Ringster says though, I'd be interested in what function/tol schem on the mating part makes this necessary.

KENAT,

Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Pattern of features

(OP)
Thanks for the suggestions!

The general problem is that for manufactugin purposes i can't tighten any tolerance.

The mating part is similar to a part with 2 pins that mate with each hole 10+/-2 aside. Then i need the mating part to be in an area 40+/-5 in length.

In reality the problem is more complicated, i have 48 spiral features, that's why if i use a reference dimension between each feature the tolerance becomes too tight. Or the other way around, if i tolerance each feature the overall length can vary too much.

thanks
 

RE: Pattern of features

Gubo,

   Your tolerancing scheme does not work.

   Let us arbitrarily select one hole to locate the two parts together.  How about the first hole?

   There is a very limited need to locate accurately the first hole in each part.  You need the second holes to keep the second part rotating on the first.  These holes have to be close enough that your bolt will pass through both pieces.  You could slot them.

   Each and every additional hole must be located accurately in two dimensions.  Probably, you need to enlarge your clearance holes.  Slotting might work, depending on what causes your accuracy problems.  Maybe you only need two fasteners!

   This is the scenario addressed by composite positional tolerances.  The hole pattern must be accurate enough to locate the two parts together.  Possibly, this is not very critical.  The holes within the pattern must be accurate enough to accept your fasteners.

               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