What to do with surface roughness tester

Tom Kitta

Ultra Member
#1
Some time ago, like few years ago I got this bin filled with stuff. In the bin there was this Surftest 211 surface tester. It works fine at least against reference plate. I seen then go for a lot of money online and newer version exists which has cool display and stuff. Basic operation is a stylus goes over surface and when it encounters bumps it records it & that is displayed value.

The question is what is practical application for a machinist? I guess I can compare one of my finishes to another - but reality most of the time I can see the difference.

Is there maybe application in machine rebuilding?
 

PeterT

Ultra Member
Premium Member
#2
I only have a basic understanding but I think they are more common in production shops making parts. So not only does it have to fall within +/- dimensional tolerances , but also certain surfaces must also fall within specific 'roughness' ranges. I don't know much about the meters but suspect they are probably orientated to a certain um ranges depending on the application for example surface grinder vs lapping vs polishing. I think optical is a different animal again. This kind of shows a practical range
https://www.engineeringtoolbox.com/surface-roughness-d_1368.html

And then there is the trusty Visual-O-Matic coupon method
http://www.an-engineering.co.uk/surface-finish-chart/
 

Brent H

Ultra Member
#3
We use a surface roughness tester for honing cylinder liners to make sure the liner has the correct (specified) surface finish for bedding in. The manufacturer changed specs about 15 years ago to reflect using a surface gauge verses honing to just a cross hatch pattern with a specific stone hardness.
I could also see it being used to gauge finishes on sealing surfaces or finish grinds on things like fuel pump barrels and plungers where the fit required is very precise.
I gather you could also use one to check finishes before paint applications or other treatments like chroming to make sure things were going to stick properly.
 

Alexander

Super User
Administrator
#5
I would suggest selling it. I use one at work to check that customer parts conform to the drawing. It wouldn't be necessary for a hobby machinist.