This week’s tip: Size matters

Posted in Uncategorized on October 13, 2009 by Peter

Here’s a basic rule:  The larger the tool, the more temperature will affect it.  A thirty-inch mandrel micrometer, for instance, will go much farther out of tolerance at 90 degrees than a one-inch micrometer will. 

But there are tools less susceptible to temperature:  Calipers, for instance, or indicators.  Calipers don’t measure at a fine enough resolution for temperature to be as critical as it is for mics.  Indicators, while they can be found measuring down to 50 millionths’ resolution, are also a little more easygoing with regard to temperature.  That’s because there isn’t nearly as much metal in them to expand or contract.

On the whole, however, always strive to stay in that sweet spot of 68 to 73 degrees in your shop.  The better control you have over temperature, the better control you’ll have over your quality.

Next time:  Setting up a mandrel micrometer

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This week’s tip: Temperature-sensitive tools

Posted in Uncategorized on September 29, 2009 by Peter

Jerry likes to tell the story of a shop boss who brought a newly-calibrated micrometer back to the mobile lab.  The machinist using the mic claimed it was off by several tenths (tenth = .0001″).  That’s a significant error because mics are only allowed a one-tenth deviation, plus or minus.

Jerry let the tool sit for a while so it would be the correct temperature; then he checked it again, and it was right on the money.  A brief inquiry of the machinist followed.  Sure enough, he’d been holding the mic in his bare hands.  That warmed it up to nearly 100 degrees, expanding the frame and yielding undersized readings.

So this week’s tip is simple:  If you must hold a micrometer, hold it with something to insulate it against your body heat.  A rag is fine, for instance.  Many mics are now made with plastic insulators attached (such as the one pictured at the top of this page), so there’s less chance of heat expansion.  However, always be aware of how you’re handling your tools.

Next time:  Size matters; also, other tools’ heat sensitivity

This week’s tip: Control your temperature

Posted in Uncategorized on September 17, 2009 by Peter

Mobile Precision’s ad copy about a “climate-controlled mobile lab” sounds like boasting, but it’s not.  Climate control, especially temperature, is a vital facet of tool calibration.   All national and international standards of measurement are specified under exacting environmental conditions.  For our purposes, we operate in temperatures from 68 to 73 degrees Fahrenheit, and 38 to 58 percent relative humidity.  This keeps us in compliance with NIST, and gives the end-user a benchmark for standards and quality.

We’ll deal with specific tools and conditions next time.  For now, keep in mind that nearly every tool you use to check dimensions has at least some metal components, and that metal responds to temperature changes by expanding or contracting.  These changes can be significant and even critical, and they affect how your tool acts.

Next time:  What tools are most sensitive to temperature?

This week’s tip: Choosing the right brand

Posted in Tool Tips on June 25, 2009 by Peter

The best brand MPTS has found in its nearly forty years of business is Mitutoyo — and they’re not paying us to say that.  They’re reliable and accurate, and have an enormous variety of all tool types, from one-inch micrometers clear up to massive coordinate measuring machines.  But they’re not the only good tool-maker.

Brown & Sharpe, which also makes Etalon brand tools, excels in mechanical calipers and micrometers.  They’re very smooth-working, long-lived, and accurate.  B & S calipers have one drawback:  The rack is difficult to clean.  However, if you follow the tips in this blog, your troubles should be minimal.

You’re going to pay for the quality of Mitutoyo and Brown & Sharpe tools.  Just remember:  It’s worth it, if you want to make good parts.

Next time:  Something completely different.

This week’s tip: Do brands matter?

Posted in Tool Tips on May 19, 2009 by Peter

Yes, brands matter.  They matter a lot, for a simple, two-sided reason:  Accuracy and reliability.  In precision work, very small errors can cause very big problems.  A tool that doesn’t measure correctly all the time is worse than useless; it lets bad parts slip by and can force you to re-do entire runs or even lose a good customer.  Buying the right brands can save you that headache.

This week we have two “Do Not” rules:  First, don’t buy Chinese.   They’re garbage.   Second, don’t buy Fowler (yes, we’re going to name names here).  Fowler makes better tools than the Chinese companies, but they’re still not very good, especially their calipers.  To be fair, Fowler micrometers are passable; but they’re still not the best.

The fundamental “Do Not” rule is this:  Don’t buy a cheap tool.  Quality costs money, period.  If you don’t have the money for a good tool now, save the thirty bucks you were thinking of spending on a piece of Chinese junk, and start a sock fund for something decent.

What’s decent?  Find out next week.

This week’s tip: Cleaning your micrometer

Posted in Tool Tips on April 28, 2009 by Peter

Micrometers are probably the simplest tool you’ll use, but also the most accurate and therefore the most affected by damage or their environment.  The slightest bit of dust on the anvils, or even the oil from a finger, can change a reading. 

So the first thing is:  Make sure the anvils are clean.  The handiest way is with a normal piece of clean paper, or even a business card (as shown), so long as it’s not a glossy finish.  Tighten the mic on the paper so that you feel some resistance as you slide the paper back and forth.  This will remove any dirt or grime without scratching the anvils themselves.  Make it a habit to clean the anvils prior to every use.  You’ll get consistent, accurate readings.

MPTS Mic

If you have a lot of buildup on the anvils, try wiping them down with isopropyl alcohol first; then use the paper.  For the rest of the mic, just use the toothbrush and alcohol as you’ve been doing with your calipers.  However, pay careful attention to the spindle, since that’s how most contaminants are going to get inside the mic.  Keep it clean at all times.

Next week:  Do brands matter?

This week’s tip: Cleaning fluids

Posted in Tool Tips on April 17, 2009 by Peter

The best cleaner is isopropyl alcohol.  It dissolves coolant residue, and it won’t hurt electronics or most plastics.  If you’re cautious and sparing in your use, a squeeze bottle — or even a water pistol — can be used to spray the alcohol on a tool’s moving parts.  Then work the tool back and forth through its range, and wipe it down.

WARNINGS:  1) Don’t use any other kind of alcohol.  2) DO NOT use acetone (nail polish remover); it degrades and weakens plastic.  3) Be careful not to get too much alcohol on your tool’s crystal or readout screen.  It can fog them up.  4) You may get an error reading from an electronic tool after using isopropyl because it hasn’t fully dried off the circuit board.  Let it sit for a few minutes, then try it again.

Lastly, isopropyl alcohol doesn’t work well on adhesive residue.  You can use a solvent (lighter fluid is excellent), but it takes only a little bit.  Solvent leaves its own residue, but luckily it’s soluble in the alcohol, so make that your final cleaning step.

Next week:  Micrometers