Small gap measurement techniques

Question

Small gap measurement techniques

IKBrunel (Mechanical)

(OP)

8 Jul 09 05:18

Hi,

I have a precision shrink-fit rotor assembly that features a shaft with a stack of heated aluminium hub discs (~150mm dia) that are press-fitted onto a LN2-cooled shaft. We are left with small gaps remaining between the discs (shrink-back) and the measurement of these is critical for our product development.

The gaps are typically between 10 and 150 microns. We can not probe easily because the hub discs are a large diameter and a micro probe would be too long/slender.

We have used both feeler gauges and a shadowgraph to measure the gaps. The latter is obviously preferable but there is a penumbra which reduces the accuracy unacceptably. I am looking at sharpening the shadow but I am curious to know if there are better measurement methods.

Please can you help by suggesting alternative measurement techniques.

Thanks

CoryPad (Materials) · Answer 1 · 2009-07-08 08:38:23

This has to be non-destructive? If so, I would look for a laser solution from Keyence.

IKBrunel (Mechanical) · Answer 2 · 2009-07-08 10:34:31

Thanks, CoryPad, they've a 2D displacement sensor that is a good option. I've asked what the cost is.

It's non-destructive and measurements are taken within a controlled inspection room.

Matt

unclesyd (Materials) · Answer 3 · 2009-08-28 13:41:29

I would take a look at these type devices added to an alignment scope. This isn't the particular device we used but is somewhat similar. I'm looking for information on the device we used as it would easily resolve 0.0005" at 12".

http://www.brunsonkc.com/Products/PN15206.asp

jackdaniels (Nuclear) · Answer 4 · 2009-12-18 05:33:17

IK Brunel,
I have had absolute success using capacitance gauges for the precision and accuracy that you might need. The gauges can be as this as 0.10 mm fixed to measuring equipment or wands. I know capacitec inc have a bore diameter checker - they might be a useful contact.

Cheers,

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Small gap measurement techniques