This Week’s Tip: Surface Plates

Surface plates are indispensable in machine work as part of your inspection process.  Because they’re so simple — very, very, flat, and nothing more — they have a great deal of flexibility:  Any part with at least one flat surface of its own can be inspected to one degree or another.

Starrett has an excellent FAQ page on surface plates, covering everything from the different grades (shop, inspection, and lab grades) to correct three-point support to keep plates from warping.   Here’s the link:  What we’ll discuss here is just the basic care of your surface plate.

As with all other tools, cleanliness is priority number one.  And, as with almost all other tools, isopropyl alcohol is our cleaner of choice at Mobile Precision.  Simply spray a little on the plate, and then wipe it down thoroughly with a lint-free cloth.  You shouldn’t use a paper towel, but some companies (Kim-Wipe is one) make lint-free paper wipes or tissues. 

As the alcohol evaporates it will cause some cooling on the plate, and hence some thermal warping.  So if you’re planning on measuring something with extremely close tolerances (less than +/- .0001″) you should let the plate normalize for at least thirty minutes after you’ve cleaned it.

Cleaning should happen at least twice a day:  The beginning and end of your shift.  If you use the surface plate a lot or it’s in a dirty environment, check it frequently for dirt/dust/coolant, and clean it as needed.  You should also look for nicks, pits, or scratches.  They won’t ruin a plate, but they may affect where you place a part for inspection.

Next time:  A few special tools of our own.


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