This Week’s Tip: Surface Plates

Posted in Uncategorized on November 23, 2010 by Peter

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.


Dial Test Indicators

Posted in Uncategorized on August 3, 2010 by Peter

We’ll start this blog with a picture of a standard dial test indicator:

Looks relatively simple.  But now take a look at the same indicator with the side cover removed:There’s an awful lot in there.  And we haven’t even gotten to everything inside the head itself:

Here’s what’s happening:  You move the needle, which moves an arm, which has teeth on the other end, which move a crown gear, which moves a pinion gear, which moves the needle (and sometimes another gear, which moves another needle).  It’s worse than the house that Jack built.  What’s really amazing is that some test indicators are accurate to plus-or-minus fifty millionths of an inch.

So, take good care of your test indicator.  Don’t plunge it into a mill’s work surface, and don’t spin it up in a lathe.  We can fix it, usually.  But it will usually cost a lot.


Posted in Uncategorized on April 24, 2010 by Peter

There are two basic types of indicators:  Dial, and dial test (sometimes called a finger gage).  This time we’ll talk just about dial indicators.  They work essentially like a dial calipers, except that the rack moves across the gears rather than the gears across the rack.

If you remove the back of an indicator, it will probably look something like the first picture below .  You can see where the rack (the vertical steel rod) meets a small pinion gear just right of center, near the bottom of the housing. 

The next four shots, starting from top right, give a clear view of the rack’s teeth; the pinion itself (as well as the larger gear attached to the pinion); the gear to which the needle is attached; and the backlash spring with its gear beneath it.  You’ll have to zoom in pretty close to see some of the gears.  But it’s easy to understand why they all need to be free of chips and dirt, as well as having no broken or missing teeth.

Indicators can be tricky and difficult to work on, so we suggest you give us a call if you have trouble with one.  But hopefully, this posting will help you understand how they work.

Next time:  Dial test indicators.

The depth mic: Another multi-anvil tool

Posted in Uncategorized on February 8, 2010 by Peter

Despite the very different uses for a depth mic as opposed to an outside mandrel mic, the depth mic also needs a specific procedure in order to be set up properly.   The picture at left shows the three main parts of the mic, all of which need to be cleaned.  Pay special attention to the black collar at the top of the thimble (left) and the bottom of the collar on the anvil (or rod) on the right.  They’ll be in full contact with each other, so they have to be totally clean.

The second picture shows how you hold the mic assembly when you’re putting it together.  As you screw the cap down over the rod collar, rotate the rod with your bottom hand.  As the cap tightens, the rod will become more difficult to turn in some spots, but slightly easier in others.  That’s because the two collars aren’t perfectly flat.  What you’re after is to find the last spot in the rotation that tightens up.   Once you do, tighten the cap the rest of the way so the rod won’t rotate any more — but don’t over-tighten it.  Snug, or a little past snug, is just fine.  This procedure will line up the two collars the same way every time.

Finally, check the face of the mic (click the pic).  Make sure it’s clean and free of nicks or burrs, especially on the edges.  Once that’s done, the mic is ready to use.

Next time:  Indicators

Some personal philosophy

Posted in Uncategorized on January 22, 2010 by Peter

While reading through the different posts I’ve done since the start of this blog, I noticed a recurring phrase:  Reliably accurate (or some version of it).  It wasn’t consciously intended as a theme for our Tool Tips, but it’s certainly appropriate.  Everything we do at Mobile Precision Tool Service is motivated by one goal:  To make sure our customers’ tools give them the right readings every time.

Merriam-Webster’s OnLine Dictionary defines precisely what MPTS is after regarding “accurate”: 

1 : free from error especially as the result of care <an accurate diagnosis>
2 : conforming exactly to truth or to a standard : exact <providing accurate color>
3 : able to give an accurate result <an accurate gauge>

Merriam-Webster’s is also dead-on with “reliable”:

1 : suitable or fit to be relied on : dependable
2 : giving the same result on successive trials

Between us, Jerry and I have had “reliably accurate” on our minds for a total of over four decades.  It couldn’t be otherwise, or Mobile Precision Tool Service would not have been in business all these years.  2010 thus begins for us the same way all the previous years have:  Calibrating and repairing our customers’ tools so that they’re reliably accurate.

Next time:  More multi-anvil tools

This week’s tip: Mandrel mics, part two

Posted in Uncategorized on December 8, 2009 by Peter

The best piece of advice we can give about mandrel mics is, don’t mess with the interchangeable anvils.  Simply make sure they’re clean, and that the reading is zero when checked against the standard.  If it’s off, don’t adjust the anvil; adjust the vernier barrel on the spindle end (and of course, when you’re done, put the barrel back where it was). 

If you adjust one of the anvils, you change a lot of variables in how the mic works, particularly the parallelism between the spindle and the anvil.  Sooner or later you’ll end up adjusting all the anvils, and then no one will be sure how accurate the mic is.

When MPTS calibrates mandrel mics, we take all the variables into account and set everything up so you’ll get good, reliable readings.  If you leave them the way we give them to you, you can have much more confidence in them.

Next time:  Some personal philosophy.

This week’s tip: Setting up a mandrel mic

Posted in Uncategorized on November 10, 2009 by Peter

The advantage of a mandrel micrometer is, one tool can do the work of several, saving you money and space.  A typical mandrel mic covers a range of six inches, versus only one inch for a regular mic.

Here’s the issue: Because mandrel mics have multiple anvils, you have to set them up correctly,  which means consistently, which means a procedure.  Check out these two pictures, paying attention to the tube face in the first and the back of the locking ring in the second.

ToolTipsMandrel (2)ToolTipsMandrel

Both of these surfaces have to be extra-clean so that they sit perfectly flat against each other.  If they don’t, the anvil will be at a slight angle and you won’t get reliably accurate readings.

Now look at the next picture.  ToolTipsMandrel (1)You’ll see an arrow etched into the  anvil tube, and numbers on the anvil itself.  With this particular mic, you would always line up the numbers on each anvil with the arrow (each manufacturer accomplishes this a little differently).  That’s what MPTS does when we calibrate mandrel mics.  You’ll get good measurements when you do the same.

Finally, mandrel mics usually come with a set of standards spanning the range of the mic.  After you’ve attached the anvil you’ll be using, always check the mic against the standard.  If it measures right on, you’re good to go.

Next time:  Other mandrel mic issues.