Measuring Roughness with an SJ-210

If you just purchased a Mitutoyo SJ-210 surface roughness tester, you may want to know how to set it up for measuring roughness.  To achieve maximum usefulness, you will probably need to buy some more parts.  The most important thing is a way to hold the instrument so you can make measurements.  Mitutoyo offers several ways of holding the SJ-210.

The simplest accessories for holding the SJ-210 are the flat surface nosepiece (part # 12AAA217) and the cylindrical surface nosepiece (part # 12AAA218) if you only need to measure these types of surfaces.  Mitutoyo’s support feet (part # 12AAA216) hold the detector at a fixed height above a surface.  This is a good option if you have a lot of similar parts to measure.  More flexible is the magnetic base adapter (part # 12AAA221 for 8 mm diameter rods or 12AAA220 for 9.5 mm (3/8″) rods).  This adapter allows you to easily adjust the height and angle of the SJ-210 if you will be making your measurements on a magnetic surface.  Mitutoyo most convenient adapter uses a height gage to hold the SJ-210 and gives you control over it’s angle.  If you height gage is the American style, with a 1/4″ x 1/2″ probe, order part # 12AAA233l if it accepts 9mm square probes, order part # 12AAA222.  A significant advantage of the height gage adapter is that it allows you to gently lower the detector onto the sample or raise it for sample removal.  Here is a picture of our height gage setup:


Measurement Setup

To attach any of these accessories to the SJ-210, first remove the detector from the underside of the display unit.  (Turn the unit upside-down, push the probe end of the detector in slightly to release it, and then lift the detector up.  Be careful not to touch the probe.)  Second, attach the provided cable to the display unit and the detector.  Finally, attach the detector unit to the chosen accessory.  Now is a good time to turn the instrument on by pressing the Power/Data button.  Here’s a close-up of the detector bolted onto the height gage adapter:

SJ-210 Height Gage Adapter

Height Gage Adapter

With the detector mounted onto its holder, gently lower the probe onto the sample you will be measuring.  The following photo shows the detector on a small plastic lens that is held in place by a piece of modeling clay (plasticine).  It’s cheap and effective, but not does not give reproduceable placement.

SJ-201 Detector on a Lens

SJ-201 Detector on a Lens

If you watch the display as you are lowering the probe, you will note that the red bar across the top changes to blue, assuring you that the probe is in contact with the sample.  This is shown in the following photo.

SJ-210 Settings Screen

SJ-210 Settings Screen

The display also shows my preferred measurement settings.  The first item, λc, is the distance the probe will travel for a single measurement, and the second, λs, is the width of the smallest feature that will be considered.  N is the number of consecutive measurements that will be used for averaging.  Measurement Speed and Range are left at their default values.  To adjust these values, hold the rough parts on the sides of the case near the top middle, and slide the cover away from the display.  Press the Enter/Menu button, then use the down arrow followed by Enter to select Meas. Condition.  Select Setting in the same way.  We prefer ISO1997 for the Standard.  Profile must be set to “R” for roughness, not “P” for profile. Parameter may be left at 3 and filter at Gaussian.  You’ll need to scroll down past λs to set N.  Everything else may be left at the default setting. Finally, press Esc a few times or just press the blue button to return to the home display.

By default, the SJ-210 measures Ra (the average roughness), Rq (the RMS roughness) and Rz (the maximum deviation averaged over the N measurements).  Ra is the standard for mechanical surfaces and Rq is the standard for optical surfaces.  Rz is useful for determining if the Ra or Rq value is being skewed by a single large deviation; it will always be larger than Ra or Rq, but should not be more than about 5X larger.

To make a measurement, press the Start/Stop button and wait until the result is displayed.  Alternatively, Mitutoyo has software that may be downloaded for free from their website.  It requires a computer with Microsoft Excel installed for operation, but is really handy for capturing data and printing out inspection reports.  Communication between the computer and the SJ-210 is via a USB cable exactly like the ones commonly used for cameras.  You probably already own everything you need for this.  Here’s a picture of the SJ-210 with the cover off, showing where to plug in the USB cable (It’s on the right side, near the center):

Mitutoyo SJ-210 showing USB connector

Mitutoyo SJ-210 showing USB connector

When you are finished measurint roughness, you need to turn off the SJ-210 and retract the probe for safe-keeping.  Yes, the order seems backwards, but it’s the only way to do it.  To turn the instrument off, retract the cover and hold down the Esc/Guide button.  (Yes that too is wierd.)  Once the display is off hold down the Power/Data and Start/Stop buttons (at the same time).  The screen will turn back on and display the word “Escaping.”, and the probe will be retracted back most of the way into the detector unit for safety.  When you reinstall the detector into the display unit, the probe is reasonably well protected.