measuring small gaps

dian · May 13, 2020

if i take two beveled straight edges and check them against each other with a fluorescent lamp behind the gap no light is coming through (they are held in a fixture). if i wanted to check how precise they really are, would it make sense to use a violet light? probably not. usually i see violet light coming through from the fluorescent lamp. what else is there to measure a gap that small?

DMF_TomB · May 13, 2020

dian said:
if i take two beveled straight edges and check them against each other with a fluorescent lamp behind the gap no light is coming through (they are held in a fixture). if i wanted to check how precise they really are, would it make sense to use a violet light? probably not. usually i see violet light coming through from the fluorescent lamp. what else is there to measure a gap that small?

.
blue up surfaces and rub one part on the other to indicate contact areas. many parts are lapped or scraped to remove less than .02mm

ChipSplitter · May 13, 2020

Feeler gages???

dian · May 14, 2020

maybe i was not clear, im asking how to measure less than 400 nm (wavelengh of violet light). tom, they are beveled. no surfaces there.

Peter from Holland · May 15, 2020

No real knowledge about wavelenght of light
But real contact is only on small spots (less as 10% I thought I had read somewhere) of the surface
But these contactpoints are randomly spread
And then you have the spots with less as 400Nm also randomly spread Both might block the light The wavyness of the surface too
Reflection might also be a player
It then depends a lott how wide those straight edges are
Sorry I know No help here

Peter

gregormarwick · May 15, 2020

dian said:
maybe i was not clear, im asking how to measure less than 400 nm (wavelengh of violet light). tom, they are beveled. no surfaces there.

I'm not really clear on what you mean.

If they are bevelled, there are surfaces. If they are radiused, then axial parallelism plays a role. If they are knife edged, then parallelism and overlap, and so on. How do you determine contact and gap in the latter two cases? Is your fixture so precise as to somehow guarantee correct alignment of the edges?

thermite · May 15, 2020

dian said:
maybe i was not clear, im asking how to measure less than 400 nm (wavelengh of violet light). tom, they are beveled. no surfaces there.

You might want to consider taking up working in fine woods, like other capable Swiss. Or games with other people's funny-money.

This imaginary "less than 400 nm" bullshit at measuring gaps between two surfaces when there ARE "no surfaces there", is going to make you frustrated, impoverished, both, and/or "more of each than you are, already".

dian · May 15, 2020

knive edged, if you will. and as mentioned i have a fixture. its easy to check them to 400 nm in this way. thats what they are for and how they work. so im curious if there is a way to check them beyond that.

michiganbuck · May 15, 2020

should be able to check to 35 um and even half that with a a jo block or a go no-go gauge.

dian · May 15, 2020

1 µm = 1000 nm.

btw, i tried an usb camera (200x) but that didnt work. a better camera maybe?

dian · May 16, 2020

i have been thinking, maybe i should get a blue laser or a polarizing filter to penetrate the gap? can you polarize a laser beam?

gregormarwick · May 16, 2020

I don't know enough about light sources and their uses in this context to offer an opinion on that, but the mechanics of this are kind of intriguing.

I really don't know how it's possible to manufacture a true knife edge with perpendicular plane straightness better than 1μ. Waviness in the parallel plane would exceed that by any conventional manufacturing process.

Are these straight edges very short? Like a few mm long?

A picture of what you're doing would be interesting.

dian · May 17, 2020

they are 400mm long. while a lot of things are made with a lower tolerance than 1µ, these by far exceed the din 874 00 specs, which is actually common with german gauges. but im intrigued with their precision and thats why i would like to investigate them further. i have been using a fluorescent lamp of the same lenght directly behind the edges.

swarfless · May 17, 2020

Hi, because you are already seeing violet light thro' the gap from white light impinging you can forget photons, a scanning electron microscope is your next 'ruler' if you have one handy that will accept a 400mm long 'specimen'. I suppose if you're a dab hand in thin film techniques you might use mechanical methods, feeler gauges, down to 100-200nm. By that I mean depositing a set of films of something like tungsten onto substrates precoated with a soluble layer to allow you to float your 'feeler gauges' free. You'd need to de-stress them first .. somehow .. to avoid them rolling up into tubes. Or, graphene films ought to do, but you'll only be able to investigate between where you are at 400nm & 100-200nm, hardly significant. AND you may loose your sanity trying. Why not just accept them as they are .. while you're in front.

dian · May 18, 2020

interesting info and ideas. i makes sence that 400nm is the end of optical methods.

i wonder how they check the edges when they make them.

is there a way to have an uv source, say 10nm, and make the waves visible? optical brighteners in washing detergents do just that.

swarfless · May 18, 2020

Are you expecting a long 'lock-down'?

dian · May 18, 2020

yes, i know, i probably need a x-ray apparatus. i just thought maybe there is some kind of "conversion screen" from uv to visible.

CarbideBob · May 18, 2020

I do not even understand what is going on or the why.
You have to be into deep UV which is not seen with a human eye.
A USB scope of any reasonable price will not have optics working in this world. This is the land of big buck lenses so 5 or 10 thousand just for the lens the entry point. Then the sensor.
Talk to the semi making people. Your are in a clean room? You can control dust or airborne to well under your 400 nm on this length?
Wiping it off nice and clean... not good.
Bob

measuring small gaps

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