Has anyone hung 2x8 #2 common lumber from the ceiling with 1/8" aircraft cable to where you can't see anything but the cable?
I need to find some kind of hardware that I can use to hang these slats, be able to adjust them to level and have them hidden both in the ceiling and on top of the slats.

Gonna need a sketch to help that description. Is the 2x8 hung vertically, or like a suspended ceiling? Also don't understand the "can't see anything but the cable"?

What is going to keep the 2 x 8 from swaying left to right?
How long is the 2 x 8?
You could run the cables all the way through the 2 x 8 and then use a washer and nut but you would need to plug it. I would worry about an insert installed from the top, nothing to keep it from coming loose if the wood shrinks or there is a quake an it shears loose.

You could put a metal tube at a 90 degree angle and brace the tube with x brace metal.

The ones in the picture are about 21' long and are 2 x 6 and connected to a metal structure. Some things aren't meant to float in midair

This is a problem for a licensed engineer to solve.

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The slats are 17' long. They will hang in two different locations. One set will hang below a drop ceiling which poses its own set of problems as far as running the cable through the tiles and up into the actual ceiling. The other set will hang directly from a sheetrock finished ceiling. The architect wants these slats to suspend from both ceilings where all you see is wire, no mechanical fasteners or adjusters. The pic is an accurate look as far as how they will be suspended. My question is, how do you adjust these long slats to level and still achieve the wire only look? One set will be approximately 16' in the air and the other set about 8'.

My guess is your going to be in the sign or cable railing fastener world but the leveling/alignment issues may be the achilles heel. I would press the architect to engineer/offer the solution for anything overhead that is not a system designed specifically for it unless your willing to assume all future liability.

There are tons of shop solutions that still dont allow for very fine leveling if needed. Threaded inserts in the 2x's and similar in the ceiling with cables and swaged on threaded ends. Resaw the 2x's, install t nuts, glue back together (seems horrible option). Install T nuts in 2xs and veneer the entire face and same male ends swaged on the cables.

The cable railing fasteners would likely be the most slick but likely not completely invisible on both ends as you usually need some form of tensioning which would allow for leveling in your case.

Most of the the small cable systems are for artwork or floor to ceiling mount cables.
3Form had their System, B&N has their system, Arkawana (sp) has their system.

Almost all of them edge grip through a hole and have a 2 point mounting system with a tensioner to hold it in place so there is minimal movement.

I had a design a year or so ago the was perforated metal shelving (1/6") thick 4' deep, 18' long suspended with cables every 6'.
The really wanted that floating look, they were going to stack 600 lbs of samples per lineal foot. The drawing looked like a piece of paper floating in the air with boxes of samples on the shelves.

Some things need to be redesigned to work.
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Thanks for all the advice. As usual some architect has dreamed up something on a piece of paper without taking into account all the little details.

Just the air movement from the HVAC system will cause those things to move around without some way of stabilizing them.

Here in California we would never to that because of earthquakes.

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The real answer in these situations unfortunately is the liability. If the architect or designer wants something its not just a matter of tossing it on a shop to make it unless its a massive enough project to cover the cost of engineering a one-of solution so usually you look to an off the shelf option.

2 runs of 1/16" stainless cable are capable of holding miles and miles more than a single 2x8 but the liability to stand behind the connection design, engineering of it all, bleh... no dice for even a million dollar shop unless they are risk tollerant.

We just finished a project that had a huge back and forth with regards to who was going to design, and assume the liability, for a back side vertical support structure. It wasnt going to be us. Thankfully someone picked it up and the project went on.

The leveling needs to be done above the sheetrock. A frame needs to be built that is hung from the ceiling framing. Once that is level you can use the same length wire or rod to hang from the frame. No adjustments on each piece of timber. The frame would probably be built out of lightish pre drilled steel C/L sections and bolted with adjustable all thread.

You need to tell the Architect that if he draws something that he needs to provide details of how it is to be done. You are a fabricator not a designer/engineer. I got stuck with "wood Clouds" hanging from a ceiling on a job a few years back. I did my shop drawings and specifically told the architect that I had no idea what so ever he wanted at these locations and gave them a budget number that could change when further information was availible. They never would provide any information of what they wanted and the job needed to be finished so I just came up with an idea of what he may have wanted ran that by everyone and that is what they got. i was not happy about it, I made plenty of good money off those "clouds" but I should have got what the architect also charged to "design" them. I am still upset about this today, just don't draw something pretty and expect us to put it together for you, have some idea of how to put it together and express that to us that have to do it!

Rich you most likely are going to need to use a unistrut https://www.unistrut.us and/or Hilti https://www.hilti.ca system to make this work.

Obviously you cannot just hang that much wood in the air with out using a threaded rod that is attached to the ceiling, Hilti has easy to use concrete anchors designed for this they also have their own version of the unistruts used to hang wood beams to the threaded Rod.
We use the unistruts and use the Hilti anchors to secure the threaded rod to the ceiling. You will also need to deal with Seismic issues, for this you will need to get an engineer stamp on your proposed CAD drawings and installation method.

I don’t know the building codes in your area, but here Vancouver Canada, if the beams are hanging more than 12” from the ceiling you will need to also use wire ties to stop its from swinging too much. Your engineer will have to tell you where/how and how much is needed.

The architect wants these slats to suspend from both ceilings where all you see is wire, no mechanical fasteners or adjusters.