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The thinner the aluminum the cheaper - you just don't want something that will be super flimsy and unwieldy. The situation with aluminum is that it's highly reflective compared to other metals, insofar as the percentage of the spectrum that it reflects. It is only out-shined by silver, so maybe silver-plating an aluminum hologram would be a good way to really shine it up. In my experience just polishing up the face of a freshly cut hologram with a rag and some polishing compound can just about double the brightness of the hologram's groove optics and thus the hologram itself.

Aluminum is also pretty soft compared to other metals and lends itself well to having the optics scored into it just by dragging a hard implement over its surface like carbide/diamond. I'm sure other metals will work to some extent, but will be harder to cut and also not as brightly reflective as the grooves will not form as easily, depending on how hard the metal is, and may come out with a rough finish that doesn't reflect light as a nice little glint from one spot.

I have not yet used any plastics but I know that holograms can be made which instead of reflecting light off the face of the hologram they instead refract it from the backside of the hologram. Not sure Holocraft is yet up to the task without spending a day of adding some modifications to code - but it's worth experimenting and looking into.

Plastics may require some finesse, however. I'm sure that reflective specular holograms can be made from dark glossy plastics but I have no experience with making holograms from plastic that yields acceptable results. Maybe coating the plastic afterwards. There's not really an easy way to polish up the plastic without marring it's gloss - not like with aluminum where you can just buff it up with a rag and have all the groove optics become much shiner. Maybe fume polishing?

Also, there's another aluminum supplier that always has 15% off sales (or thereabouts) just sign up for their mailing list. Their prices are competitive with McMaster-Carr: www.onlinemetals.com - 0.025" 5052-H32 Aluminum Sheet  I usually go with 1100 or 3003 alloys because they're more pure, and thus softer/shiner but 5052 is pretty cheap right now and is equally as soft and only slightly less pure. Having followed aluminum prices over the last few years: less than $3.50 for a 12"x12" sheet is a really good deal! I wouldn't pass it up if I were actively making holograms.

Thanks for the questions!

Charlie

That sounds great! Do you also have any suggestions for (or a link to) a specific diamond or carbide drag bit that you have used that works well?

And if so, do you have recommended feed and speed values, or is that controlled by / built into the software itself?

Thanks!
Robert

Speed should be zero: no spindle needed. Feed should be as fast as you can go without inducing wobbles into your grooves - this was the problem I had to fight with my machine because it just has too much flex. If you try to mitigate it by using a slow feed rate the hologram not only takes forever to make but also the grooves don't come out as smooth and shiny. There's something about pushing aluminum out of the way quickly that results in much more reflective grooves.

I fashioned hologram bits from pyramidal carbide engraving bits, by carefully rounding the point into a tiny hemisphere that I can only barely make out with a loupe. I haven't used a diamond-drag bit but I imagine it would work if it's not a super fine point and/or if you minimize the pressure/depth.

Actually getting good groove optics to form is a bit of a trial-error process that may take a few tries to figure out. Holocraft assumes a round tool and takes in a diameter to generate an optimal depth below the surface of the hologram to press into it. The actual value doesn't have to be exact, just experiment and find what works. Holocraft also varies the depth based on the assumed light altitude angle, to maximize the reflectivity of the  groove for a spherical cutter. I think I might replace all this behavior with just a user-entered "cut depth" value instead.

Charlie

Awesome, thank you for the info and tips!