Micrometers

[Rhyolith]

I am looking into measuring tools for machining. I need stuff reliable to better than one thou (1/1000th of an inch). I am expecting triple figure prices for stuff of sufficent quality new.

Any suggestions for what to look for on the secondhand market?

 

[Rorschach]

What are you measuring? The choice of tool depends on the job at hand.

 

[AndyT]

If you are looking for imperial, old mechanical micrometers are cheap and plentiful. Most will measure to a thou and you could estimate fractions of a thou. 0 to 1" are probably the commonest. Look for Moore and Wright or Starrett.

 

[deema]

You are looking for a measuring device that can measure roughly at least 10 times higher accuracy than the measurement you want to make, and that does not consider type 1 and 2 R&R study issues. So to measure 25 microns (metric) you need an instrument that can measure to 2.5 microns accuracy.

You need a temperature and humidity controlled room first off.

 

[Rhyolith]

I am not bothered imperial or metric.

Mainly want to know what to put into ebay such to find good stuff, just putting “micrometer” produces too many results and tatt.

 

[Rorschach]

Buying second hand is tricky, while the tool may be a good brand, you have no way of knowing how well it was cared for.
Also you still didn't answer the original question, what are you measuring and why do you need such a high level of accuracy?

 

[CHJ]

I need stuff reliable to better than one thou (1/1000th of an inch). .

Some folks may see the following comments as being pedantic, but as deema intimated not something the average individual can achieve with a micrometre or readily available home workshop tools.

"Measure" that is, all home workshop 'measuring' tools are only comparators that need to be calibrated against a standard. **
Use a micrometre as a comparator against a known standard, be it a precision 'standard' or an existing component that you wish to copy, then yes with caution and the right feel you can get within tenths of a thou.

** perfectly fine for most workshop work, but it needs to be appreciated that they are not accurate 'measuring' instruments just comparators.

When talking close tolerances the home workshop relies on feel and fit for close tolerance matching of components with shop temperature and machining heat induced changes affecting the fit.

 

[MusicMan]

Down to a thou/25 microns even cheap and secondhand micrometers will do fine. Worst case is usually a zero error, which is easily adjusted. Below that you need to get fussy. A small set of slip gauges with a calibration certificate is pretty cheap and gives you reassurance.

 

[julianf]

Walk into any commercial engineers, and look for the first set of digital calipers that you see, and it will be a set of mitutoyo.

The small 150mm ones are not massive money. 300mm and it's a much more considered choice.

Most digital calipers are probably similar, but the mitutoyo won't require you to change the batteries every weekend.

 

[Gerry]

Have a look at Moore and Wright digital micrometers.
they have a resolution of 1 micron with good repeatability. I have a full set I use in my calibration laboratory ranging from 0-25mm to 275-300mm. These are reliable, repeatable and accurate instruments and are really good value.
A 0-25mm from cromwells is £97 so you could probably buy it cheaper elsewhere.
https://www.cromwell.co.uk/shop/measuri ... &W3403201A

M&W also do a cheaper range which if your not working in a production environment will be just as good with the same accuracy costing £75
https://www.cromwell.co.uk/shop/measuri ... &W3403181A

Gerry

 

[Rhyolith]

Its for machining components, but that does not matter as I know ‘normal’ size micrometres and verniers (etc) are fine (been stealing others).

The engineers I know do indeed have mitutoyo stuff, their verniers cost £160 each! Which is why I don’t simply get those. Is there any reason they are so dominant?

On a side note, anyone heard of ‘Bensons’ measuring tools? (old stuff)

 

[Gerry]

Mitutoyo were originally a budget brand. Yes they make some really good instruments but they are no better than most other stuff available.
If your machining you need micrometers. Verniers are fine for quick and dirty checks but they rely on the operators feel and will have poor repeatability. They usually have a resolution of >10 microns and are calibrated to +/-20. If your after any sort of engineering fit it will be pot luck.
Having said that I have a Sylvac micron pro which is a 1 micron vernier with a repeatability of 3 microns but it is an expensive premium instrument.
At least with a micrometer you have a constant pressure applied by using the ratchet a set amount of clicks for each measurement.
We always tell the great unwashed on the shop floor to turn them until they hear 3 clicks.

Gerry

 

[galleywood]

What machining processes are you performimg - milling, turning, grinding?

 

[DTR]

I'll confess to slumming it. When I was an apprentice I bought a set from Oxford (Cromwell) containing a vernier caliper and two micrometers. The vernier is still in frequent use (for quick and dirty measurements only!), but I now use three Moore & Wright mics that I picked up from bootsales. The 0-1" and 0-25mm mics can be checked by zeroing, and my 1-2" mic luckily came with a 1" gauge block.

I am a bit sceptical of digital calipers, even Mitutoyo. I have seen too many threads on engineering forums complaining about digital calipers losing their position, or eating batteries.

 

[Gerry]

A digital caliper will give you a resolution of 0.001mm whereas a manual caliper with a vernier scale will only give a resolution of 0.01.
Locking the spindle after use will prevent a caliper or Mic switching on in storage and flattening the battery.
Leave a small gap between the anvils in storage to prevent moisture wicking in between them and causing corrosion.
I have never had a Mic or vernier loose it's position unless it was an ancient model and the transit speed of the instrument was faster than the encoder could calculate. It doesn't happen with modern instruments, at least since the mid ninety's

Gerry

 

[Cheshirechappie]

Its for machining components, but that does not matter as I know ‘normal’ size micrometres and verniers (etc) are fine (been stealing others).

The engineers I know do indeed have mitutoyo stuff, their verniers cost £160 each! Which is why I don’t simply get those. Is there any reason they are so dominant?

On a side note, anyone heard of ‘Bensons’ measuring tools? (old stuff)

Benson Verniers were a Bradford company, started 1946, and acquired by James Neill in 1972. As Neill's also owned Moore and Wright, I suspect they may have been buying out a competitor; I don't know when Benson Verniers ceased production, though. They made very good quality instruments, a couple of examples of which I've used. Their one disadvantage is that the scales, though nicely engraved, are not as easy to read as many decent quality modern ones, and especially so in less than perfect light or when measuring at odd angles - one up to the digitals, here, in my experience. Use with a magnifying glass and they're fine, though.

Second hand micrometers are something of a lucky dip, I'm afraid. If you come across ones with the manufacturer's grease and protection for the anvils and spindles still intact, snap 'em up, but pass on anything unboxed. Buy a new micrometer setting standard for each instrument (they're not that expensive, considering their precision nature), and check the instrument regularly. It's not as good as a 'proper' calibration check, but at least it'll let you know if any gross errors arise.

If you're just using the mic or vernier as a comparator (eg, want a bush 2 thou bigger than a hole for a press fit) then almost anything will do, but for work to specified absolute measurements you need to be a lot more choosy.

Useful instruments depend entirely on what you're making. Some vintage machinery will be quite happy with plus-or-minus a clog tip tolerances, but something like machine tool parts or internal combustion engine parts will demand split-thou accuracy, and far more expensive metrology gear. Hence the question earlier in the thread about what you're measuring.

 

[Inspector]

You haven't said whether you want these micrometers for a home shop or for work. I spent 29 years as an inspector in an aerospace machining factory and used mics every day. I liked Mitutoyo the most and that's what the company usually bought. Brands like Moore and Wright or Tesa were used now and then but not enough for me to develop a preference for them. Well I liked the Tesa but the ham fisted machine operators ruined them in short order. The Starrett manuals were fine but I disliked every electronic tool they made. Clunky and ate those coin batteries like candy. For my home shop I bought a manual set of Chinese micrometers. They measure to 0.0001" and with them I can measure to 6". The fit and finish is good, smooth, consistent and accurate when checked against the gauge blocks we had at work. They are comparable to any of the manual micrometers from the big companies and for under hundred dollars for the set were a bargain. That is what I recommend for a home shop over a used set you can't personally touch. If you are after electronic then go to direct to Mitutoyo. Mine are are like the ones linked below with the frame holes.

https://www.chronos.ltd.uk/cgi-bin/sh00 ... #a41120205

Pete

 

[Rhyolith]

To answer the numerous questions about what I am going to use it for. Its machining on lathes, mills, etc in a workshop making parts for steam locos.

 

[Cheshirechappie]

To answer the numerous questions about what I am going to use it for. Its machining on lathes, mills, etc in a workshop making parts for steam locos.

In that case, just ordinary 'thou' mikes will do fine. You won't need to measure to tenths, and in a steam workshop trying to will be hit-and-miss anyway. Useful sizes would be up to about 6" - larger ones are needed from time to time, but not so often as to make buying them essential. An inside mike is very handy too, say 1" to 8", but they're fiddly to use. You need to develop a 'feel' for them. Depth mike less so.

Don't disregard the old fashioned internal and external calipers, too - two or three sizes of each. Set to a six-inch rule, they can be handy when roughing parts out to know how close you are to finished size. Then finesse with the mike if need be - though with a light touch and a bit of practice, you can easily detect a thou difference with calipers.

By the way - a decent thread pitch gauge is very handy, and a set of radius gauges can be useful too.

 

[Rhyolith]

Thanks, lots of things to have fun looking for on eBay! They seem cheap enough secondhand that i can afford getting a few until I find stuff thats accurate and precise.

Here my benson callipers. Don't suppose anyone knows how old they might be? Ches's information brings it to 1946+ (maybe to 1972?). I could tell soon as I saw them at the car boot years ago that they were well made, defo worth more than £5 I paid for them.

Bensons Vernier Callipers by Rhyolith, on Flickr
Bensons Vernier Callipers by Rhyolith, on Flickr
Bensons Vernier Callipers by Rhyolith, on Flickr