On 28 Jul 2020 03:27:51 GMT, "DoN. Nichols"
wrote:

On 2020-07-09, Charlie+ wrote:
On Wed, 8 Jul 2020 09:55:15 -0700 (PDT), wrote
as underneath :

On Friday, November 14, 2003 at 10:03:37 PM UTC+5, surftom wrote:
How do I *accurately* (n.nnnn) measure very small hole diameters?

I can poke them with a numbered drill but that would only get me close by
"feel" and only if the hole was a standard size. e.g. measureing a .0431
hole is kind of hard with a vernier or mic

No real reason - enquiring minds just want to know

Tom

Hi Tom,
you can easily measure min 0.1 from vernier caliper and +/- 0.001 mm to +/- 0.02 mm with micro meter.
Source: a href="https://ahmedtrader.com/kendo-tapes-kobe-spray/"ahmedtrader.com/a

Short of accurate plug gauge, optical projectors used to be the way in
instrument engineering, you could do it as a bodge with a macro lens
photo and calibrating from your nearest fit drill at identical distance
+ simple maths etc. But there will always be an error envelope down at
1/10,000.

Beware that the shank of a drill bit is typically a little
smaller than the hole size which it drills -- at least until it gets
burred by slipping in the chuck. :-)

For measuring in a fairly narrow range, and assuming that the
hole does not have a beveled edge, there are devices for the purpose.
They push a cone into the hole, and measure how far in it goes.

The one which I have is a "Hole Check" by SPI. It comes with a
steel plate with three holes, each marked in both Imperial and metric
units. Only one of the three holes matches the tool which I have. It
is marked 0.070" and 1.78mm. It has a dial indicator with a custom
scale on it to match the point. The range is from 0.030" up to 0.127".

The other two holes a

0.175" 4.44mm
0.300" 7.62mm

If you don't have one of these, a set of wire gauges for the
smaller sizes, or pin gauges for those a bit larger. They come in
0.001" steps in size, and they are not bothered by a beveled edge hole,
while the tapered pin and dial gauge is.

If it is a through hole, you could perhaps measure it by how
much air can flow through it at a given pressure.

For fairly small holes (say down to about 0.100" or so), the
split "small hole gauges" slip in, you turn a knob at the top until they
drag slightly, pull it out, and measure the size with a micrometer.
The big end of a typical set is around 0.500" max, IIRC. Starrett makes
them, Lufkin used to, and likely a bunch of other names by now. But you
need to develop a feel for this the drag on the ID of the hole vs the
drag on the anvils of the micrometer.

Enjoy,
DoN.

Gage pins are what everyone in industry uses, that and a optical
comparator if you can put it on the table....if.

https://vermontgage.com/gaging-produ...gages-and-sets

Example only.

Gunner
Home again for a week or so.
__

"Journalists are extremely rare and shouldn’t be harmed, but propagandists are everywhere and should be hunted for sport"

Yeah..with no bag limit.




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