Optical flat- whats this worth?

[tarbellb]

Doing a big clean out of the shop and came across some old auction items I didnt know what to do with?

1st- DoAll Optical Flat - 4" diameter, flatness to .000002", used with original case

2nd- Pratt & Whitney Precision Surface Plate- 5" diameter, steel, used with original case

Got these from a guy who was clearly into some high caliber stuff, these were tucked into some drawers. But with anything in the precision world, calibrations, history, and condition play a huge role.

Just looking for some feedback on what I am looking at here

Thanks

 

[PCustoms]

Both looked scratched to hell, I'm sure they need some work (if possible) to get them back to spec.

Probably very little value

Edit: a new 8" one

Do-All Optical Flat: Coated. Dual Sided. 8" – .000002" accuracy – PJ29 – Bullseye Calibration

bullseyecalibration.com

 

[American Locomotive]

You're looking at tools that would probably be used to perform interferometry to determine the flatness of various objects and surfaces. The unfortunate reality is that there's a lot of old high end metrology stuff around, and without a recent valid calibration it loses a tremendous amount of value.

I poked around, and found most used optical flats going anywhere from $30-100. Here's a very similar 3" doall going for $30. https://www.ebay.com/itm/316023591539. One new-in-box with a cal cert went for $650, but yours isn't that.

 

[tarbellb]

Very much along the lines of what I was thinking

Might be better off as the mostest flatest eva beer coasters

 

[e015475]

At one time in my working life I worked on the development of turbine engines.

I remember using optical flats and a monochromatic light to check the flatness of the face that carbon seals ran against in turbine engines and development rigs as part of the assembly process.

IIRC flatness was measured in 'helium light bands" and to be good the face of a seal had to be between 2-3 light bands

One helium light band is about 3 microns - They'd make a very flat coaster. Maybe the most expensive too. A 4" fuzed quartz optical flat sells on MSC for about $1700

 

[neophyte]

Very much along the lines of what I was thinking

Might be better off as the mostest flatest eva beer coasters

You never know when you might need something that flat.
Even if slightly off from original spec, it might still be useful for checking a lower spec straight edge.

 

[American Locomotive]

You never know when you might need something that flat.
Even if slightly off from original spec, it might still be useful for checking a lower spec straight edge.

That's underselling it a bit. At .000002" flatness across its whole surface, it's about 2 orders of magnitude more flat than about any straight edge a mere mortal would have. Even if it were really messed up, it'd still be flatter than just about anything in a hobbyist machine shop.

That thing is so flat, that if you scaled it up be 63 miles in diameter and 7.8 miles thick, the highest hill would only be 2" tall.

 

[tarbellb]

So you're saying my beer won't wobble?

 

[neophyte]

So you're saying my beer won't wobble?

It depends on how well the can forming dies were made.

 

[rlitman]

Both looked scratched to hell.

I think most of what we see on the optical flat is the felt underneath it. At least that's my take from the picture. And as with all flats, scratches are only an issue if there's a raised area around the scratch (not something that happens on glass or stone, which is also why surface plates are less often made of metal).

What I see though is a not-so-special glass optical flat. The really flat stuff gets so flat that the random anisotropy in glass becomes a problem, so you shift to materials like fused quartz.

 

[RoninB4]

So you're saying my beer won't wobble?

-Only when you're holding it.

 

[Rinspeed]

If there are any scratches in the optical flat you might as well throw it in the dumpster.

 

[jar944]

Both looked scratched to hell, I'm sure they need some work (if possible) to get them back to spec.

Probably very little value

Edit: a new 8" one

Do-All Optical Flat: Coated. Dual Sided. 8" – .000002" accuracy – PJ29 – Bullseye Calibration

bullseyecalibration.com

That one is used and chipped.

The one in question doesn't look scratched.

 

[AEAdam]

Guessing at values for stuff like this is tough. The better way is to check completed listings on eBay. If you do that, and I have, you will see a lot of unsold items, and sold items ranging from $30-$300. The difference may be the pictures. My sense is, if you take REALLY good pictures, and have a good description, you will get more money for your flats. For this sort of stuff, condition is literally everything. And we judge condition from the pics you take.