digital micrometer

[RandyR]

I'd like to get a digital micrometer, metric, accurate to .001mm, for measuring valve shims.

 

Can anyone recommend one in the under $50 price range, or warn me about cheap ones to stay away from.

 

Or have one to sell?

[V7Goose]

Well, valve shims are not critical for measurement, and .001 accuracy is not hard to reach - just about any cheap tool will do that. For just your specific purpose, even cheap calipers will do fine. Check out Harbor Freight - they regularly have some digital calipers on sale for under $20. In fact, they recently had one for under $10 that was such a steal that I just had to buy it even though I do have a full set of VERY high quality micrometers and a high quality dial caliper!

Goose

[dingy]

Randy,

 

I have both digital and dial calipers and I prefer the dial set myself.

 

Digital calipers are nice since you can convert from metric to imperial units, but other than that I like the dial units.

 

With digital calipers, you need to be very consistent with the pressure you apply when taking a reading or they will vary a thousand of an inch or more.

 

I would suggest that you get at least an 8" set. The longer length does come in useful occasionally.

 

Gary

[V7Goose]

The type of indicator on the tool makes absolutely NO difference in how accurate it is or how consistently it reproduces the same result. But both the quality of the tool and understanding the proper usage certainly do affect those things.

 

All measuring instruments need a light touch, not only for proper accuracy, but also to prevent long term damage. The tighter you adjust any tool, the smaller the reading. For example, a high quality micrometer will have a little knob on the end that clicks as you turn it. When you take a measurement with the tool, you never turn the mandrel down to the point of contact with the large shaft. This final adjustment is made with the small knob and you only turn it long enough to click three times. This type of consistent repetition of the same light pressure is the only way you can get consistent readings.

 

A tool of lower quality will naturally have a bit more play in the mechanism, which leads to a lower accuracy standard. But a uniform light touch from the operator is still just as important.

 

Finally, a tool that is only accurate to 1,000 of an inch will LOOK more touchy to the pressure used than one that is accurate to 10,000 of an inch, even if the tool is made to the same quality but simply has a cheaper display mechanism. This is because you cannot see the reading change until it suddenly jumps from something like .111 to .110, which can happen anywhere between those two measurements, where a more accurate tool must properly display every singe change of 1/10,000.

 

The point here is that even the finest tool is of no value to an uneducated person with a ham-fist. You need to understand how it works and practice with it on something of known size until you develop the proper feel for consistent results within the accuracy range for which the tool is rated. When you buy the tool, I'd suggest taking a valve shim with you to the store and carefully note it's exact measurement with a micrometer of high quality, the use that shim to compare the readings with other tools of lower price. And even if you do not have something of KNOWN exact size to practice on, you can still verify if the tool you bought has the capability of consistent readings. Using any valve shim, just repeat the same measurement many times being careful to use the same light touch. The shim is not going to be changing size, so if you cannot get the same reading each time with the tool, take it back and buy a better one.

Goose

Edited November 21, 2010 by V7Goose

[Mel]

Another option to check accuracy/your touch when using a precision measuring instrument would be a set of feeler gages. You know, the kind we used to use to set tappets on the OLD car engines or the rocker clearance on some single overhead cam engines. Varying thicknesses to let you get a feel for the differences and to check the instrument's accuracy on different dimensions.

 

I have high end (Mitutoyo) digital 8" caliper and 1" mic, also 1", 2", 3", 4" mechanical mics, all are Starret, and a mechanical 8" dial caliper. I prefer using the mechanical instruments because the digital ones have to be zeroed every time you use them.

 

If you don't know how to read the mechanical mics, it's not hard to learn. Been doing it so long that I forgot that some may not have that skill yet.

 

My two pennies.

[V7Goose]

Another option to check accuracy/your touch when using a precision measuring instrument would be a set of feeler gages.

Excellent idea on the feeler gauges - I was trying to come up with something that most mechanics would have available, but those escaped me.

Goose

[a1bummer]

You might want to stay away from the ones at Menards. I bought one only to have the display start blinking all the time as though the battery was going dead. This happened even with a new battery. Other times it wouldn't come on unless I took the battery out and then put it back in. Now the blinking stopped and it comes on like it should, but now every time I use it I have to take the battery out when I'm done or it will kill the battery even though it is turned off.

 

I haven't tried any of the HF calipers yet.

 

Bill

[cb1313]

Lowes and home depot sell units like harbor frieght. I have a H/F and works ok.

 

Cb

[KiteSquid]

I have three digital calipers and one dial caliper.

 

The advantage the dial has over the digital is there are no batteries to go dead....... for the occasional user, I recommend the diall type.

[RandyR]

I ordered a $10 metric dial micrometer from a chinese ebay seller.

 

Its incremented in .01mm which is exactly what I need. I'll test it on a couple pieces of feeler gauge to confirm the accuracy.

 

I was thinking I'd like a LCD readout which would be easier on my not-as-good-as-they-used-to-be eyes. But they are more expensive, in the $50 range.

 

One thing I found peculiar, is that for many of the lower end micrometers, they had a readout with more digits than the accuracy. I would expect that the accuracy would exceed the readout, such that you could 'trust' the readout (within the accuracy).

 

btw, my local Home Depot did not have micrometers, just calipers which are not accurate enough, I already have one of those.

[Snarley Bill]

mitutoyo is the best mike made bar none mechanical or digital. i like starret mechanical mikes also. i use both daily. most all digital mikes read out to 1-100,000 ths or 5 places. fowler makes a lower price range digital mike that is pretty good for home use. we do alot of metric work but use mikes that read in decmals. to convert metric to decimal just divide the decmal by 25.4. example, .05 mm divided by 25.4 = .00197 thousandths of an inch. you will never use the fifth place on a digital mike unless you are working on very close tolerances. digital or mechanical dial calipers are okay for rough measurements. but i would never use them on anything precision. i use them all the time just to see if i'm getting close. when the finishcut comes up out comes the mitutoyo. you can also get mecanical digital mikes. i would'nt waste the money on them. also if you don't have the feel for a mike get a friction spindle and don't slam it. rachet spindles are ok but awkward.