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


Specifying/Inspecting conical surface

Specifying/Inspecting conical surface

Specifying/Inspecting conical surface

We buy machined and hardened 440C blanks that we grind to the finished dimensions.  Inside the blank is a conical surface that becomes a valve seat.  We have to grind this to a very tight roundness and surface finish.  If the blank part has grooves or ridges on the conical seat it causes our grinding wheels to break down and we don't meet the finished part requirements.  

We currently specify an Ra value of 32 microinches on the blank part seat, however, because of the small size of the parts we have to use the shortest (.003") sampling length to measure them.  At this short sampling length the tool marks are filtered out.  However, it is the peaks & valleys of the tool marks that cause us problems with our grinding wheels breaking down.  If the part was bigger and we could use a longer sampling length these parts would fail the surface finish specification.  Reduceing the Ra value is not effective because the measurement is still ignoring the tool marks.

So what I need is some other way to specify the short conical surface in the blank part.  If it was a flat surface I could use flatness or if it was cylindrical I could use  total runout.  What can I use on a conical surface?

RE: Specifying/Inspecting conical surface

Have you thought about changing you measurement parameter?  Since this is a critical surface you may want to look at Rq(RMS) and possibly even ask for a print change that would ask for a tighter tolerance, or a note that would specifically ask that no nicks, sctraches, or ..... be permitted in this area?
Either of these ideas would probably cause the price of the blanks to increase though.


RE: Specifying/Inspecting conical surface

The problem with notes (no nicks, etc.) is that they are totally subjective.  I need a numerical criteria.  Any surface finish parameter Rz, Rmax, etc, is going to suffer from the same high pass filtering due to the short cut off length.  I need something that will not filter out the tool marks.  

I'm thinking that profile of a line is what I want, possibly in conjunction with profile of a surface?

RE: Specifying/Inspecting conical surface

An issue that comes to mind with the profile of a line or surface would be the specialized equipment that you would need to accomplish what you had asked.

From my research on surface finish, I found that on Rq(RMS) IS sensitive to peaks and valleys on a surface and the reading accounts for the extreme peaks or valleys whereas Ra averages them into the reading.


RE: Specifying/Inspecting conical surface

I'll try Rq and see if we get sepparation between the good & bad parts.  We have equipment to do profile so that is not an issue (but our recieving & inspection people may not want to use it).

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! Already a Member? Login


eBook - 10 Reasons to Choose CATIA on the Cloud
To compete in today’s fast-paced and competitive market, smaller and newer firms need a powerful platform that will enable them to compete with bigger players, without the heavy investments needed in computer hardware, software and personnel. Download Now
White Paper - Smart Manufacturing for Electronics
This white paper describes a transformative approach to electronics manufacturing made possible by the addition of Mentor Graphics to the Siemens family. It describes a completely digitalized strategy that supports both printed circuit board (PCB) and mechanical design and manufacturing, uniting the entire product lifecycle – from idea and production to customers and back. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close