DIY anamorphic lens

[Mark Techer]

Thanks for the link

Mark

[Mark Techer]

Here is the latest in the resin prism casting. I am in the process of making a mold that will allow me to cast two prisms at a time - one 6" x 6" and the other 8" x 6".

I will use silicon rubber to make the mold, but in order to make a mold, you must have an "original" to mold from.

My "original" is made from four pieces of 6mm glass that have been cut to size by a local glazier, then formed into the prisms using a combination of hot glue, modeling clay (that came from the resin place), MDF wedges and tape.

The idea is to build (or find) a container large enough to hold the "original" and then pour the rubber and let it set around it. It will use a lot of rubber, but the mold should be good for many casts

I've been advided to make sure that the surfaces are perfectly clean, or the rubber will replicate the fine details including my finger prints!

So here are todays shots



Mark

[KBK]

I would suggest that the mold body be of a nature where the sidewalls basically conform to the dimensions of the desired wedges? This, because the differing masses of the rubber (Thickness of walls) may deform or flex under the load of the resin's mass.

What you may want to do, is think of exactly how the mass of the resin will deform the rubber mold under the filling and curing situation. That's a quite a heavy mass of resin to go into these puppies! I'd VERY much suspect the resin will cause the mold to flex, unless this consideration has taken place during the creation of the mold itself.

ie, varying the thickness of the mold walls appropriately in the given areas to preven the mold flexture. Then design the side walls of the mold box supprt system to accomodate that aspect. Not just sidewall density or thickness, or distance from the resin wedge flats..but the HEIGHT of the mold taken into account as well.

As a quick estimate on the possibilities, you might look up the mold 'pressure loading deflection levels', then compare that to the mass of the resin across one given laterally calculated sectional area. Toward the bottom of the resin mass,and the thicker area, for example, it may cause the mold to flex enough that the surface of the resin cast piece will 'bulge' at that point. Then you'll have to learn to polish it flat.

I very much suspect that you'll have to polish it in the best of cases/results, but it is best to avoid the possible issue of mold flexture, which is why I provided the link for the soft low temp alloys for a posible mold.

One very good potential way to take care of this, is to be sure to mold with the thin edge of the resin cast pointing downward....and the sidewalls of the mold being exactly paralell to one another. This will to the larger part, keep pressures --potentially-- even (I've not thought it fully through, I could be VERY wrong here). The proper way, may be exactly opposite to that.

Ie, thinner mold walls at the bottom, to deal with the pressure increase on the mold walls...meaning the thickest part of the cast resin at the bottom of the mold, where the possibility of the mold to flex has been decreased in a linear fashion as you move down through the density of the molded resin...due to the thinner mold sidewall. Thinnest mold sidewalls at the bottom, of course, least capacity for deflection.

Does that make sense? Definitely, overall, an issue to consider. It's not the most complex calculation in the world by any means, but I feel it needs consideration in this particular application. The only way around this issue IMHO, is to use the low temperature alloy for casting. And even then, I still feel that some polishing will be in order.

If you look at the cost involved around the molding rubbers, it might be nearly as high as the cost of the alloys, if you can find the alloys at a reduced price level. Ie, used, flebay, etc. Do a bit of searching. Find some, er..hehheh....'off casts'! (get it! )

What I am doing, is I'm tossing my two cents in here, living vicariously/experimenting though your efforts....helping when I have an idea..and letting you do all the hard stuff...generally blowing crap up. When the dust settles, I'll reach in, maybe, and make one or two in the method that looks like it will produce the best results. The usual story. I have time to contribute mentally, but not physically.

[Mark Techer]

The usual story. I have time to contribute mentally, but not physically.

And I appreciate the input KBK

I am using glass because of the clean surface, and resistance to scratching when use repeatedly. The pro molds that I have seen had walls of up to 3" think, so they supported themselves on the bench.

I am going back to vertical pours as the reserch I did suggests that a taper or wedge will be easier to remove, even though the rubber does not stick to anything but itself, a tapered shape is suppoed to POP out of the mold.

Since the photos were taken, I have calculated the amount of rubber needed, and as that amount was over 13LTRs, I have decided to "slim" it down a touch to just under 10LTRs. The wall thinkness will still at least 40mm (approx 3.5"), so I am hoping NOT to have mold flex, but I understand exactly where you are coming from. This rubber costs around $50 per LTR (cheaper when bought in bulk), so is not the sort thing I want to waste money on, and a mold that flexes is a huge waste for what I am doing...

Right now I am thinking about a double VEE mold, but might end up making two different size molds...

This project has moved well beyong "your childs allowance"

Mark

[Mark Techer]

As a quick estimate on the possibilities, you might look up the mold 'pressure loading deflection levels', then compare that to the mass of the resin across one given laterally calculated sectional area. Toward the bottom of the resin mass,and the thicker area, for example, it may cause the mold to flex enough that the surface of the resin cast piece will 'bulge' at that point. Then you'll have to learn to polish it flat.

This part scares me a bit KBK, so what if I used the non reflective glass inside the mold with one side only treated with release agent - IE the out side faces of the prism. Laying the glass into the VEE of the mold will not seal the edges, so some resin would creep around the face. But with a release agent applied to that face, the resin should not stick, and should be able to be cut away without incident.

The glass won't flex, and even if the mold did you would still have the perfect flat plain to work back to...

Mark

[Steve Scherrer]

Sorry--not contributing to this thread in any way (sorry--have nothing to contribute!)

But I am waiting with baited breath to hear the results!

Thanks for all the hard work, Mark.

[Mark Techer]

Thanks Steve,

It is a slow process and has taken longer than I had hoped...

Mark

[Mark Techer]

Originally posted by Mark Techer
surf board resin is said to be the best

NOTE - DO NOT USE Surfboard Resin - Pour great, sets fast (almost bubble free ), but it is NOT clear

Mark

[Mark Techer]

The Surfboard resin (whilst not any good for this project) came away from the glass without any problems or any release agent...The faces are smooth, though I am not sure if they could be called "optical" quality. There is some striations, but over all the prism came out well...

So I have made another mold using the recycled glass and will see how clear casting resin goes this time round...

I am still experimenting with the silicon rubber...

Mark

[Mark Techer]

I removed the rubber mold tonight and whilst the silicon rubber is a useful product, I doubt it will be useful here.

Back to the drawing board for mold making...

Mark