Anodising - Effect on M6 x 1.0 internal threads

[peter]

Anodizing - effect on internal threads - we have a sub-assembly machined and anodized which has M20 x 1.0 and M6 x 1.0 internal threads. We find that the mating Parts are a 'tight' fit in the threads and that they will not 'accept' a GO thread gauge. The mating threads (a standard fastener and threaded Sensor) are ok to gauge. Our supplier tells us that 'the thread edges get excess disposition, and this is to be expected'.

Could they use a pre-plate tap as used when Zinc or Chrome plating threads, should they blank the holes prior to Anodizing or is there an alternative solution?

[sonflowerinwales]

Peter
What anodisinng process is it? Is it natural or coloured? Were the threads right before anodising?
Paul

[peter]

Paul,

The units are received Black anodised, so we rely on the manufacturer (in India) to confirm they are ok prior to anodising. (one of the drawbacks of global sourcing)!!

[sonflowerinwales]

Peter
Suplhuric anodise is about 0.01mm per surface, 0.04mm on effective. If the parts are a snug fit prior to anodise, then you may well have a problem.Some thoughts:
1) Ask for un treated samples, check the threads and get them anodised here in the Uk
2) Ask for copies of the calibration certificates for the gauges
3) In my experience, you ususally get less deposit in the threads than on anohter surface.
4) Is there damage on the thread from jigging?
Hope this helps
Paul

[CarolX]

Originally Posted by peter

Our supplier tells us that 'the thread edges get excess disposition, and this is to be expected'.

I believe this is call "capillary action" where your coating thickness is greater at or near edges than on a flat surface. The coating is pulled toward the edges.

Has anyone else heard this term before?

Originally Posted by peter

Could they use a pre-plate tap as used when Zinc or Chrome plating threads, should they blank the holes prior to Anodizing or is there an alternative solution?

Absolutely - this is done all the time. We use threaded hardware in our sheet metal applications. Parts are made of steel and zinc plated and are fabricated to meet the specification after plating.

Good luck!

[Al Rosen]

Originally Posted by CarolX

I believe this is call "capillary action" where your coating thickness is greater at or near edges than on a flat surface. The coating is pulled toward the edges.

Has anyone else heard this term before?

Yes, capillary action is due to surface tension.

[walking eagle]

Have your manufacturing people look into oversize taps in metric taps I beleive the size designation is stated with the letter "D" (ie. D4, D8) the larger the number the larger from nominal the tap will be on the major, minor, and pitch dia. Remeber on a thread you not only have the "per side" build up as a normal inner dia. but you also have the build up of 2 surfaces of the 60 degree "V" of the thread per side. A good tooling salesperson will be helpful with this.