Aluminum for Diamond turning op.
Aluminum for Diamond turning op.
(OP)
I have an aluminum mirror that has very high surface irregularity and roughness requirements which is being diamond turned. We are trying to determine if there is an aluminum available in an 11" or 12" stock diameter that could be substituded for 6061 T6 (our current mat'l of choice) to improve our D.T. machined results ... any suggestions?? Stability is of greater concern than strength.
thank you, Max
thank you, Max





RE: Aluminum for Diamond turning op.
RE: Aluminum for Diamond turning op.
http://www.alumiplate.com/
RE: Aluminum for Diamond turning op.
Are you using single point tool?
I would give TCI a call with your problem. They should be able to help with both the material and the machining.
http://www.tciprecision.com/affiliations.php
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Here is a little more help from two perspectives, finishing and machining.
http://i
http://www.techbriefs.com/content/view/479/32/
You also might be interested in this product
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RE: Aluminum for Diamond turning op.
- more info - Yes we use a single point for D.T. Unclesyd, you bring up another aspect there, may be machining techniques to improve the surface quality?
We found no trouble turning a 4" mirror. I believe the stock for the small mirror is cold rolled and the 12"dia stock is extruded. Does anyone know if it is possible to get 12" dia cold rolled stock?
RE: Aluminum for Diamond turning op.
RE: Aluminum for Diamond turning op.
RE: Aluminum for Diamond turning op.
If you look at the Goddard page you can see that you can license the process. I would check this out to see if you can get a nonexclusive license for their process. At one time this was not a very expensive proposition.
http://ipp.gsfc.nasa.gov/lic-partnerships.html
The plate carried by TCI is the Alcoa tooling plate material which is 6061 T651. It has been my experience that this material is inherently stable due to the mill processing. I believe that you can use the stability treatment from the Tech Brief article to further enhance material during preliminary machining.
A barb from the blue or off the wall.
I've never used SP diamond tools on Al only tool steel and SS so I can't say this will work or not.
We had to finish turn 30" disks of 356 Al to the smoothest possible finish. We used a very fine single point tool bit. To make a long story short we tried every thing to improve the finish. From a local machine shop I picked up on a lubricant they used to machining AL. The lubricant was equal volumes of Lard (cooking) and kerosene. Using this mixture made an immediate quantum improvement in the surface finish. It is still being used today.
RE: Aluminum for Diamond turning op.
The Alcoa "tooling plate" is that not a cast aluminum? I am checking into 12"x12"x2"thk. piece of cold drawn 6061 T651 to see how much different it is from the current 6061 round stock that is extruded. I'm thinking the machining process might be a contributor than the material... your thoughts?
regards, Max
RE: Aluminum for Diamond turning op.
RE: Aluminum for Diamond turning op.
RE: Aluminum for Diamond turning op.
I think the tooling plate is worth a try. I would try to get a couple of smaller pieces to establish a method as a 6" would have the same physical properties as a 12".
TCI at one time had circular drops at very good prices.
If you saw an improvement by using a cut tapping oil with your SP tooling I think using the Lard/kerosene would be beneficial. The smoke would be no worst than eating a biscuit by a kerosene lamp after a hurricane. As I posted this combination worked exceeding well with our SP tool.
Our tooling is essentially a pointed 1mm dia needle with a half diameter flat at the point.
You will notice that I like the lard/kerosene lubricant for Al.
RE: Aluminum for Diamond turning op.
Wavefront error is usually defined as the localized RMS error relative to the ideal surface and usually measures roughness.
In some cases, the measurements can get quite contorted. We had, once, a diamond turned mirror that resulted in "ruts" that each focused to a different point in space. No matter how you wanted to quantify it, it was BAD...
TTFN
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RE: Aluminum for Diamond turning op.
IRstuff - Sorry, I am not familiar with the "surface figure" terminology, thank you for providing the definition! Our results aren't nearly like your example (thankfully), we're getting a "hazing" when we image.
RE: Aluminum for Diamond turning op.
Do you think you can polish out the haze producer?
You might want to contact someone like these people to get a perspective on an electropolish since you state that the 30-80 finish would work.
http://www.ep-systems.com/aboutme1.htm
Thinking again.
Here is a very good Al polish, Simichrome. I have always wanted to add something like a .5 micron friable diamond grit to this polish.
http://www
RE: Aluminum for Diamond turning op.
If the former, then hand post-polish would be the way to go. There are supposedly diamond turners that can give you hand-polizhed surface quality, but I've not personally seen any. The ones I have seen required hand polishing.
A surface profilometer can give you a measure of the surface roughness directly, so it might be worthwhile getting that measurement done.
TTFN
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RE: Aluminum for Diamond turning op.
thanks for your insight ... Max
RE: Aluminum for Diamond turning op.
Here is another perspective on achieving a smooth surface on Al mirrors. The company mention in the paper doesn't have website yet.
http://www.techbriefs.com/content/view/2021/34/
http
You state that the smaller mirror is okay while your larger one is giving problems in machining. This is kinda redundant but have you checked the rigidity of the you machine, tool holder, and chucking device. One thing we encountered quite a bit was that certain weights and speeds caused some vibration problems, small but troublesome still. This would be corrected by slight change in speed.
RE: Aluminum for Diamond turning op.
Max
RE: Aluminum for Diamond turning op.
One thing I forgot to mention was the tool stick-out changed when changing sizes of mirrors?
Does the problem with haze over the entire surface?
I've seen this cause problems with very small changes in stick-out.
RE: Aluminum for Diamond turning op.
RE: Aluminum for Diamond turning op.
How are you addressing the speed as you traverse the larger disk?
RE: Aluminum for Diamond turning op.
RE: Aluminum for Diamond turning op.
The record groove depth I don't know. My understanding is that the machines are capable of speed and feed compensation for large diameters ... whether this is being used properly (or at all) is something else to be investigated. Do either of you have experience with that machine function? I understand the theory but haven't had experience with it and practise doesn't always equal theory!
thanks, Max