×
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

GD&T Rule #1 and Free State

GD&T Rule #1 and Free State

GD&T Rule #1 and Free State

(OP)
Does "rule number one/ the envelope rule" apply to injection moled parts as they could be considered a "free state" exception?

RE: GD&T Rule #1 and Free State

That might depend on what material is being injected into the mold. Aluminum has substantially different 'free state' properties, than say, silly string.

RE: GD&T Rule #1 and Free State

JoelDonn,

   Rule #1 applies when your part is contstrained by your datums.  

   ASME Y14.5M-1994, Section 6.8 has a bunch of suggestions for managing free state variation.  How you deal with this depends entirely on your application.  On sheet metal parts, I usually place a note stating that Datum A applies when the part is clamped to a flat surface.

   How flexible are your injection moulded parts?  The whole point of free state is that your parts are deforming due to weight and flexibility.  If your parts are warping permanently when they are demoulded, then there is no free state.  The parts delivered to you must be within your original tolerances, somehow.

                      JHG

RE: GD&T Rule #1 and Free State

The use of injection molding (or any other production process) does not relieve Rule #1 requirements.

If the part is to be treated as non-rigid, the drawing should include a restraint note that describes the exact clamping conditions that the tolerances apply in.  Drawoh's note describing clamping the part to a flat surface is an example of this.  I would go a couple of steps further and describe the clamping locations, forces, and sequence as well.
 

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: GD&T Rule #1 and Free State

Joeldonn,
         If the parts you mold are made from Plastic then no the Envelope Principle doesn't apply, Plastic parts are non rigid, you should add a free state symbol or note stating that parts are to be measured at a free state.

RE: GD&T Rule #1 and Free State

demmagod, may just be your wording but rule one does apply - regardless of material/process, it just may not be appropriate to invoke.

KENAT, probably the least qualified checker you'll ever meet...

RE: GD&T Rule #1 and Free State

KENAT,
     You are correct, I should have clarified myself,
What I meant is that because most plastic parts have some form issues and maybe subject to free state variation in the unrestrained condition that joeldonn should look at adding the Free state symbol or a note that parts should be measured at a free state or restrained, joeldonn could solve this problem by invoking a form tolerance.

RE: GD&T Rule #1 and Free State

I must agree with demmagod's first post. Rule #1 does not apply to "parts subject to free state variation in the unrestrained condition. [2.7.1.3]" You still have to ask yourself if your part is subject to free-state variation. Some (probably most) injection-molded parts are rigid enough that I don't think this exception would apply. The free-state modifier means that the stated tolerance _does_ apply in the free-state comdition, without the modifier, Rule #1 does not apply.

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