Specifying/Inspecting conical surface
Specifying/Inspecting conical surface
(OP)
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?
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
Either of these ideas would probably cause the price of the blanks to increase though.
Mike
RE: Specifying/Inspecting conical surface
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
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.
Mike
RE: Specifying/Inspecting conical surface