×
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

Tolerance requirements on tapped holes forZinc-plated Metric Fasteners

Tolerance requirements on tapped holes forZinc-plated Metric Fasteners

Tolerance requirements on tapped holes forZinc-plated Metric Fasteners

(OP)
Hello,

Background: I have been ordering parts for a machine design prototype used to demonstrate typical industry machine vibration phenomena in an academic environment. The machine is medium-sized (1m x 1m x 0.5m) and is mounted on spring isolators, which are designed so that resonance is induced at certain rotation speeds. It's made of all metal machine parts.

I have spec'd 8.8 Zinc plated hex cap screws for most of the loaded parts and some of the fasteners were only available in class 8.8 but without zinc-plating. I recently read that using zinc coated hex screws with non-zinc nuts or vice-versa results in either unacceptably tight or loose tolerances between the screw and nut, as the zinc-plated nuts are bored slightly oversize. For this reason I am trying to use only zinc screws and nuts together, and non-zinc screws/nuts together. Is this a reasonable general rule?

When the fastener hole is tapped into a blind hole, do I need to call out a larger clearance than standard if the fastener is zinc plated? i.e. 6G instead of 5H

Thanks!

RE: Tolerance requirements on tapped holes forZinc-plated Metric Fasteners

By plating, do you mean electroplated or mechanical plated zinc?  Hot dipped galvanizing?  If you mean plating, then you can use them interchangeably with non-plated parts.  Standard tolerances are 6g for external threads and 6H for internal threads.  For hot dipped galvanized parts, it is common to use 6g for external threads and 6H or oversized 6AZ for internal threads.

RE: Tolerance requirements on tapped holes forZinc-plated Metric Fasteners

(OP)
Corypad, thanks so much for the response.

The fasteners are being purchased from local fastener suppliers according to din/iso spec, specified as either 8.8 or 8.8 zinc plated. I'm assuming that this means that they are zinc electroplated and not hot dipped galvanized. Is it common to find hot dipped galvanized fasteners without specifying  that process separately?  Or are hot dipped more common for structural applications?

RE: Tolerance requirements on tapped holes forZinc-plated Metric Fasteners

It is not common to find any parts with a coating unless it is specified specifically. Hot dipped galvanizing is common for fasteners for structures, not very common for general industrial applications.

 

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