I'm designing some small (about 2"x4"x.05") aluminum
cover plates for an instrument. I'm facing the usual
expensive process of having the part fabbed, bare
spots masked for emi shielding, powder coated and then
silkscreened.

I was wondering if the part could be run through a
vibratory tumbler to deburr it and give it a satin
finish. Just deep enough to eliminate the tool marks.
I could then get it alodined and silkscreened. The
alodine process enhances conductivity and would eliminate
the expensive masking and powder coating.

Is this worth a shot? What sort of media would be
best for the application?

On Dec 10, 11:11*am, Jim Stewart wrote:
I'm designing some small (about 2"x4"x.05") aluminum
cover plates for an instrument. *I'm facing the usual
expensive process of having the part fabbed, bare
spots masked for emi shielding, powder coated and then
silkscreened.

I was wondering if the part could be run through a
vibratory tumbler to deburr it and give it a satin
finish. *Just deep enough to eliminate the tool marks.
I could then get it alodined and silkscreened. *The
alodine process enhances conductivity and would eliminate
the expensive masking and powder coating.

Is this worth a shot? *What sort of media would be
best for the application?
See if your FAB plant can use aluminum sheet with a plastic protective
coating. That can be removed later to reveal a nice finish.

Paul

I've found that most commercial/industrial and even military equipment
manufacturers often utilize bare spots (near a fastener) in coatings for
earth grounding.

The bare spots may have been masked during the coating process, or more
commonly, a spot that's been hit with a ginder or sander before or during
the assembly stage of manufacturing.
Sometimes the bare spot(s) may just be the around the corner attachment hole
in a panel or cover. Some variations include a (forget the name) lock washer
that ensures penetration of the oxidation that may be present on an aluminum
panel.

If a panel is secured in place with nuts, kepsnuts (with integral
lockwashers) will make a secure electrical connection (provided that they're
tightened properly after any servicing is performed).

Another common method is adding a headless screw post to a panel for a
ground lead to be attached to. These are the pressed-in studs which are
nearly/almost invisible on the exterior surface.
The grounding posts/studs are generally a chassis feature, but sometimes
used on a cover panel as a secondary earth grounding tie-point.

The bare spots on mating surfaces can be accomplished with a Dynabrade or
Dremel-type tool with a sanding drum.. a fairly effortless step that can be
accomplished in seconds.

Vibratory tumblers can probably provide almost any desired finish by using a
specific abrasive compound.

Don't know about the alodine process, although I may have seen it and not
realized what it was.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Jim Stewart" wrote in message
.. .
I'm designing some small (about 2"x4"x.05") aluminum
cover plates for an instrument. I'm facing the usual
expensive process of having the part fabbed, bare
spots masked for emi shielding, powder coated and then
silkscreened.

I was wondering if the part could be run through a
vibratory tumbler to deburr it and give it a satin
finish. Just deep enough to eliminate the tool marks.
I could then get it alodined and silkscreened. The
alodine process enhances conductivity and would eliminate
the expensive masking and powder coating.

Is this worth a shot? What sort of media would be
best for the application?