Micrometer for measuring true tool diameter

I really needed a way to measure the true diameter of the tools I am using, Just a few thousandths off can mess up the accuracy of the cut. My digital caliper is just not designed to measure tool diameter so I found a new inexpensive digital micrometer on Amazon ($40).

So far I am very happy with it. Almost every tool I have was slightly off from the published diameter. Probably because I usually buy the inexpensive Chinese tools.

https://www.amazon.com/iGaging-Digital-Electronic-Micrometer-Display/dp/B0087TMUQ8/ref=pd_sim_sbs_328_1?ie=UTF8&dpID=41jBVFlnbaL&dpSrc=sims&preST=AC_UL160_SR160%2C160&refRID=WKRZTS7XZJ3XNS0G2TP2

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Nice! I have their calipers, and have been really pleased with them so far. Seems like they make some pretty good products.

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For the price they seem hard to beat.

I am not really sure what to with the round ball attachment that comes with it. I assume it is good for making measurements of things that are not perfectly flat. Maybe a machinist can chime in with the real reason to use the ball attachment on the fixed side.

Here is a nice video review of the micrometer

As Amazon isn’t a viable option in Australia (too many items listed with a ‘does not ship to ..’ or with uneconomical shipping charges), I usually give Aliexpress or Banggood a quick search.
For my metal working stuff, I’ve bought non-digital micrometers from Shahe.Prices are good and shipping is fairly quick. Quality of the product is excellent.

What is wrong with the ultra cheap ones like this one: http://m.ebay.com/itm/12-7mm-0-5-Carbon-Fiber-Composites-Digital-Thickness-Caliper-Micrometer-Guage-/201403383294?nav=SEARCH

I got an igaging caliper, really good tool, but the cheap micrometer is perfect too.

Biggest thing I can see is that the resolution on that one is much lower. the ebay one has a resolution of five ten thousandths of an inch. The iGaging one posted above has a resolution of five hundred thousandths of an inch.

Also, the iGaging has an accuracy tolerance of +/- 0.00016" where the ebay option is only +/- 0.004"

Are you seeing this tool as being consistent with your machine? Meaning if you did a fill cut with %100 step over is everything cut?

I think I paid $30-40 for mine but I’ve found for bits I have to consistently input smaller dimensions than what I measure with the calipers, but I wonder if this is because it’s difficult to measure something round, especially if it is a spiral bit, or because the machine isn’t perfectly accurate.

I have not tried doing a 100% step over.

The main place I would see errors is when making inlays. I also had some issues with material being left behind when I would do a roughing toolpath and then a detail toolpath. Where I would tell Vcarve to leave a .02" allowance on the roughing pass.

I tried measuring the tools with digital calipers and was never able to get a repeatable measurement due to the geometry of the tool. The larger pads of the micrometer make measuring the tool diameter very repeatable.

in regards to your question about the ball attachment = Measure dimensions from inside of holes to outside edges. The spherical anvil or spindle contacts the inside curved surface at a single point, permitting accurate gaging of wall thickness to .0001" or .001mm.

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