Ebay mics...

[boostin53]

I stumble upon many vintage mics and other machinist tools on ebay often. Recently I've been contemplating on taking a risk and purchasing some more mics to add to my collection. But I'm worried that I may get something that's way out of calibration.

The description of pretty much every mic I look at doesn't give much detail. Just about cosmetic dings and what not. Nothing about comparing them to gage blocks or anything. What are some things to look for when looking at used mics on ebay? I feel as if it's almost worth it to take a gamble on good ol tools compared to buying Chinese stuff. What does the hive have to say about this? Help me spend some money!!!

 

[Bob Korves]

You can calibrate a mic yourself if you have a good reference like quality gage blocks. Good enough for any hobby machinist, even if not good enough for NASA.

 

[Terrywerm]

Ditto on what Bob said, we as hobbyists certainly don't need the type of accuracy that is required in the aerospace industry. If you do not yet have a set of gage blocks, you might want to consider purchasing a set. They have many uses, and are especially handy when used with a sine bar for setting very accurate angles.

 

[mikey]

In my opinion, the best mics are all Swiss-made - Etalon, Tesa and some Brown and Sharpe. The German-made Helios mics are also very good, as are some of the Mitutoyos. Personally, I avoid electronic mics because if they break then they're either expensive or impossible to fix. If I could only have one brand of micrometer, it would be Etalon. Smooth as silk and accurate as they come, and they stay that way.

I look first for where it is made, with preference as above. Then I look for condition. A good mic is treated like the precision instrument it is and the condition will show it. If it is all dinged up and oily then the guy who owned it didn't respect it and he can keep it. Once I zero in on a good candidate, I always send the seller an email via the ebay system to make sure it is perfectly functional and zeros properly. If there is a problem on arrival, you have an email trail that ebay can use to back you up when you return it at the seller's expense for a full refund. You run very little risk on your end other than time.

I agree that you need some way to assess accuracy and that standard are gauge blocks. The typical micrometer standards that look like rods with a plastic center are okay for ball park checks but if you want to actually calibrate the mic then you would do better with gauge blocks. Mitutoyo sells a set from 5/8" to 2" that is just right for this sort of thing, and they come up on ebay fairly often.

Chinese mics are fine if you only dabble. My thinking is that for just a little more than I would pay for a Chinese mic, I would rather have an Etalon from ebay.

 

[bfd]

a lot of the older mics do not have a satin chrome finish and will rust easily. this is what I would look for also no carbide tips which will aid on faces wearing out bill

 

[boostin53]

Thanks for all the info guys. I now have a better idea of what to look for in a used mic. Now the hunt begins!

 

[boostin53]

Also, can a set of 1-2-3 blocks be used to check mics? Given that the blocks are in great shape, as in lightly used with no visible marks on them. While I have no way to guarantee they were true from face to face, they claim to be held to tight tolerances. I wouldn't think of them as gospel, but just something to get reasonable, repeatable measurments on the mics. Until I get real gage blocks that is

 

[Charles Spencer]

You can calibrate a mic yourself if you have a good reference like quality gage blocks.

Before I retired I only had a Japanese 0-1" micrometer that I bought new back in the 1970s. Since then I've bought used micrometers from ebay to get a complete range and more spares than I need, basically doing what Bob said. A couple of observations:

1. You'll need a wrench or spanner to adjust the micrometer.

2. Shadon on Youtube has a video on the accuracy of some Chinese blocks:

3. A 36 piece set of B grade import gauge blocks can be bought rather inexpensively. Once you have them you'll find a hundred uses for them such as setting gaps, measuring and marking heights, etc. Here is an inexpensive set from ebay:

http://www.ebay.com/itm/HFS-R-36-PC...-SET-NIST-TRACEABLE-CERTIFICATE-/291683848888

4. Some if not most of the ebay micrometers may require cleaning.


If it's something you need, you can save some serious money buying good quality used from ebay.

 

[mikey]

Most gauge blocks are accurate to a 50 millionths of an inch (0.000050") or less. Good ones are around 0.000020". Rule of thumb: the block should be about 4 x the resolution of the mic.

 

[wawoodman]

I'm happiest with the Starrett mechanical digital type. These old eyes love 'em.