I'm looking for something like a digital caliper, but with micrometer, or better, accuracy. All of the calipers I've checked out (on the RS web site) have a quoted accuracy of 0.02 to 0.03mm, which isn't much good when the display resolves to 0.01mm.
A normal micrometer isn't much use - I need the external and internal prong thingies that calipers have, along with the step and depth measures. I'm measuring very small components to check whether they're in tolerance, sizes range from a few mm, down to 0.01 or so.
To improve much on a digital vernier (a quality one, not the 9.99 ones) for such small components you probably need specialised measuring equipment. We'd usually use a shadowgraph at work for measuring things like this. It enlarges an image of the part by a factor of 10 and the slides have a digital readout calibrated to
0.001mm. But this is expensive kit -about £10k new with readout, but they crop up on ebay now and then.
A cheaper alternative would be a comparitor (not sure if I've spelt that right) which is basically a stand fitted with a DTI. Can be verry accurate, but you need something to compare the item to (slip gauges usually) and setting the item up can be tricky -sometimes making jigs, etc.
A co-ordinate measurinment machine (CMM) might be useful, but again expensive (£12-20k). Personally for small items I prefer to use the shadowgraph rather than the CMM -it can be dificult to see exactly what you are probing when the item is that small.
If there are large batches of items it may be possible to get gauges made to check them with, but obviously only practical if you have a lot of the same item to check due to the cost of having them made.
There are many companies that have the capability to measure accurately such items, and offer the service on a sub-contract basis, it may be more cost effective to sub-contract the work instead of kitting up to do it yourself, plus the bonus of indipendant verification. Couldn't you get the supplier to issue the parts with a certificate of conformity? -shifts the burded from you to them.
Going to stick my neck out here and say... these digi calipers are not capable of being as accurate as a mic because of the very nature of there design makes it possible for the user to make errors . ie the jaws are so narrow that you can take misreadings just by having it leaning no matter how slight.. have a look around this site ..he sells good stuff.
It's mostly one and two-offs. Multiple-K prices aren't in the picture - £2-300 tops, I think. (Currently using a Mitutoyo digi caliper that cost about £100.) Life would also be much easier if it was a portable hand tool.
Not likely to happen - we're having test jigs made for mass-produced parts which have less than satisfactory tolerances. It got to the point last week where I started to wonder how accurately the jig was made, compared to how close to tolerance the sample parts were. When I read the accuracy spec on the calipers, I was left with something of a question mark about the whole thing - wondered if I had been racking my brains over a set of crap numbers. About the only bit that gives me some confidence is that the jig generally measures well compared to the drawings - but the jig could be out by whatever the caliper is out by. :-)
Since my earlier post, I've found that the accuracy figure would seem to be over 100mm - if 0.02/100 scales down to the sizes I'm dealing with, then that's certainly good enough, but I'm not sure at present if it does scale.
Unless he's cleared out his stock of old machines, Rotagrip have a few used shadowgraph machines lurking at their premises in Birmingham. Worth giving them a call - ask for Ian. 0121 551 1566
Given the budget I don't think you'll do any better than the digital caliper (if your paying more than fifty quid for a mitutoyo digital caliper these days you were robbed!). With careful use these should be good to 0.01mm over the range you are looking at. How you use them is important, as has been mentioned they are not as robust as micrometers -they require a slightly gentle touch.
mmmmm the first person who starts making one that's about 7 or 8mm thick is onto a winner. you would then have the accuracy of a mic plus internal,external,depth and measure six inches as well. you could have the thick one to supplement the thin ones. does this sound like a good idea. all the best.mark
Sorry but no. You can do a couple of tenths on a mike because of the amazing sensitivity of fingertips. Otherwise, it's use a CMM with Renishaw type touch probe which gives you a micron or two over amazing distances, or shadowgraph, if the geometry is favourable, which can do a couple of microns, or manual vernier calipers, maybe a thou or twenty five microns. For some geometries the optical scanning probes (Keyence and others?) are pretty good, they are used to monitor wire drawing on line. Some time ago they were a grand or two but I expect they are cheaper now. Sort of like a
25 mm mike and giving you a micron or two on diameter measurements, and fast.
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