Help! How to read/measure length and depth of tears with SJ-210 Profileometer

Hi guys,

In shop I'm a little in over my head, and my mentor/teacher recently passed away. I'm trying to keep operations running smoothly, HOWEVER...

We have parts that require a certain surface finish, and have prints for grind tears that are no longer than (.04), no wider than (.002), and no deeper than (.0002). We're getting a few rejections, and nobody's every bothered to figure out how to use our SJ-210 series profilometer. My question is, can I set my profileomter up to read the depth and width of a grind tear, and how would I read it on the screen?

Really appreciate any input-- Like I said, I'm a little over my head and without much formal training. Any sort of input would be greatly appreciated!

-Sarah

For starters your gauge will not measure length, width and depth.
It is a 2D line scan tool not a 3D tool.
Width and depth is not hard, Get familiar with your manual and read this info directly from the raw (unfiltered) data graphs on the display or better yet printed.
The other axis where you have more room needs something like a toolmakers scope. These won't measure depth.
Processed info like Ra and such tosses a filter into the data so does not give actual measurements.

These things work like dragging a phono needle across your part. The output is a graph of how high the bumps are in the up/down and distance traveled on the side to side. They have no idea how long anything is side to side unless you do a bunch of controlled sideways moves or rotations, track the numbers, do a whole bunch of samples and math.

Watch that stylus scan as the gage runs and think about what you need to know.

Now just what are your rejects for? Has the customer given what they do not like?
(and are these numbers inch or metric, flat surface or round part)
Somehow your shop must have controlled this previously. Why has this gone away?
Bob

Hi Bob,

I really, really appreciate your reply! Our rejects are for very minute grind tears, which show prominently after being chrome plated. Most of the tears we get are on flat surfaces, although sometimes they are also on a round shaft (widths vary, but on average the shafts are 1.3998-1.3996 in diameter, and the flange face width (.151-.1475). In the past, the shop has had a lot of rejects for grind tears. In order to control this, for both customer and shop, the engineers implemented a new policy, allowing for certain grind tear specs, in inches (specs in previous post). I think a lot of our problems stem from a lack of understanding (myself included). For example, while our parts should be "free of scratches, nicks, and dings," they also have their own grind tear tolerance. They're sometimes rejected as scratches, and the part labelled "damaged." However, if I can prove that they still fit, form, and function, and that they meet their grind tear spec, then I know I can get less of these parts rejected. I have to understand my profilometer.

Since scratching my head over this all day, I think it's as you say, and I need to understand the manual and the concept of surface finish in general. We don't have the manual anymore, but what I found online seems to help a little. I think the Rv will give me a reading of the depth of the tear. Rv, as I understand it, is the max of the valley depth. Unfortunately, I have been unable to find out how to read Rv on my profilometer. I watch the stylus scan, as you say, and watch it dip when I run it directly across a tear, but I have been unable to interpret the graph dip into depth.

Thanks again for the insight, Bob. I'll definitely have to keep working on this one!

I would post a question specific to how to gain the inspection data here; http://www.practicalmachinist.com/vb/metrology/ It is our Metrology sub-forum. Sorry I think your question is over my head, I can't help.

If you have the budget, they make some awesome optical equipment that will measure that quite nicely. About 15,000 for a nice manual unit. We also have an SJ-210 and its limitations are forcing us into other options.
I may be wrong, but I understand Rz is the depth from top to bottom. Rq is an average obtained using an algorithm. SJ-210 does not measure Rv.