Serrated plate for indexing of fittings

[erik3000]

Trying to gather information on the use of shims/plates with serrations that are used to adjust position of attachment fittings to structure(e.g. hinges, lugs, latch brackets, ...). I.e. the interfacing surface of both a fitting and mating structure are serrated, such that the fitting can be indexed discretely along slotted holes in the plates. Is anyone here familiar with their use, perhaps any standards or specs, standard serrated plate stock, or guidelines for use? I'm able to turn up very little with a general search, perhaps I am missing some key term.

 

[Tmoose]

Do you figure you'll need 90° or 5° adjustment increments ?
Adjust just once at assembly, or before every flight?

 

[rb1957]

we've used them, they are purpose designed for your application. They are intended to be semi-permanent, like infrequent adjustment (maybe as some other part of the system wears/changes).

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

The feature You are describing is machined 'Flat/Parallel Serrations' onto mating surfaces.

I have seen these 'features' used in military aircraft for interchangeable moving assemblies, that are constantly being replaced... such as canopies... for hinges and latches... where fine adjustments need to be made by the mechanic for each installation.

Optimum dimensions are 'typically' based on 60 degree screw threads per FED–STD–H28. These can be UNC, UNF or UNJF profiles

Sometimes/rarely, these serrations are angled to the slotted hole axis for 'special applications'.

Fits.
Typically use -A [external thread profile] for one face and use -B [Internal thread profile] for mating face.
It MAY be possible to gain adequate fits with identical profiles on mating surfaces.
Testing for Your application WILL be required.

CAUTION.
For high quality interchangeability, single milling hobs should be used to machine their respective faces for an entire production run. I have actually witnessed miss-matched serrations on 'supposedly interchangeable parts' that drive the mechanics insane. For this reason these parts [fittings] usually remain together as a matched set on the acft to avoid this problem [remove and install-on the replacement assy. Gaps along serration tips/roots may wick moisture.
For certain alloy-matches, corrosion and/or GALLING may be an issue and will require lubricant or anti-seize, platings [flash chrome, nickel, Cd, etc] or solid film lubricants.

Regards, Wil Taylor

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