I'm again tinkering

[moribundman]

Now I have to start all over and make three more originals, with the design the wrong way round. Then I have to make molds of those originals, then cast them. I'll probably need a couple weeks, which means you guys have plenty time to solve the mystery.

 

[tom slick]

Binocular parts?

 

[moribundman]

I shall call you Hawkeye from now on, Hawkeye. I did make it easy though by giving very particular information away in my previous post, so maybe I ought to call you Holmes.

These parts are custom dust shields, which will be installed around the objective lenses and between the prisms and the eyepieces of old compact binoculars that unfortunately aren't sealed well. More pictures will follow, but I won't get around to finishing this project for a few weeks.

 

[moribundman]

Stripped down binocs: the outer covers, lenses, prisms and eyepieces have been removed. Since the outer covers (not shown -- I will show them later) are not sealing tight, the internals get easily dusty. Custom made dust shields are the only feasible solution.

Front dust shield in place:

Rear dust shields (two pieces) in place:

As I said, these are only test casts. This resin is not suitable for the final casts. The fit is very good. The shields snap in place and stay put. Besides a tight fit, making the shields thin enough to not interfere with the outer casing (not shown) of the binocs was tricky and required some patience.

 

[moribundman]

The binoc's external clam shell covers have baffles, which butt up against the dust shields. Left front dust shield and left upper and lower clam shell covers shown:

The upper, left clam shell cover installed, hugging the left front dust shield:

Small vents (holes to be drilled -- not sure about location yet) with dust filters will be installed in the front and rear dust shields. Since this binocular is not airtight, moisture from condensation due to rapid temperature changes must be allowed to escape.

 

[moribundman]

One of the dust shields, cast in the proper resin. The blotchy surface is residue from the mold release. This resin does not gas out once cured. It also cures with, like the other resin that I used for the test casts, with minimal shrinkage and is extremely durable.

 

[tom slick]

what material did you use to make the initial positive? what is the final resin?

 

[moribundman]

As stated in my original post, the original parts (the "masters") were made with epoxy resin, polystyrene, styrene solvent (glue), talcum powder, Bondo, and Scotch tape. A time consuming multistep process was used. I started out with thin plastic templates. Another approach would have involved carving the masters out of a block of baked poly clay and modifying the part with clay as needed.

The final cast resin is an industrial, low viscosity two-part polyurethane resin that is commonly used for movie prop casting and, for example, for casting underwater housings for cameras and sonar buoys etc. If you want to know the resin brand and the exact resin type, send me a PM.

 

[tom slick]

are the finished parts flexible? I don't care about the specifics on the resin, just curious about the materials and processes. how is the PS used?

 

[moribundman]

This resin is rigid yet flexible. You can bend thin parts at least 90° without the part breaking. The material also has very good memory. Alas, that resin is so toxic that it comes with a 3" skull and crossed bones logo on the containers. You have to use a respirator. That resin is also wicked expensive and available only in, uh, gallon size.

The styrene (Evergreen brand from hobby shop) is used in the form of more or less thin layers (0.1 mm to 2 mm), and as a paste (dissolved styrene -- I use citrus based non-toxic solvent glue).

 

[moribundman]

I should have said I used styrene sheets in layers. File, sand, carve, and fill with epoxy resin (filled with talcum) and Bondo as needed.

 

[tom slick]

interesting process. you are certainly crafty.

 

[moribundman]

I'm also sneaky, Hawkeye!

 

[tom slick]

I'd even toss adroit and potentially furtive at you.

 

[moribundman]

Flatterer!

 

[IndyIan]

Wow, that is impressive, where did you learn how to do this? Any links on-line?
I've got 2 identical snowmobiles but the one has a broken fan shroud which are plastic castings. I was thinking of making a cast of the good one and making a copy out of fibreglass but I don't really know where to start.
Ian

 

[moribundman]

You learn this sort of thing really only by doing. There are some good books on the topic out there. If the basics, which are very simple, are unclear, you could take a model making, a mold making, and a casting class, I suppose. Or maybe you could apprentice with a propmaker or artist (especially a sculptor). You could also study industrial design.

The snowmobile part is almost certainly injection-molded. You can't replicate that process in your garage (unless on a very small scale).

 

[IndyIan]

Yep, I'll have to do some reading and give it a shot, just have to make sure I don't wreck my good fan shroud.
Are your binoculars of some special significance or you just wanted to fix them instead of buying new ones?
Ian

 

[moribundman]

I'm not fixing those binoculars. I am modifying them. I do it for someone who wants this done. Incidentally I have the exact same binoculars, so I'm getting the modification for my own binocs at zero cost.

PS: I have more binocs than you can shake a stick at!

 

[IndyIan]

Well that's cool, what's the modification?
We were ice fishing this weekend on Lake Simcoe and I wish I brought our binocs, to see if anyone is catching anything, or maybe what lure they were using... maybe with something very high powered.
Also there were cars all over the ice, some guy trying to set a land speed record in an old tracker and someone had a turbo something tearing around but they were a few km upwind so I could only hear him. I was amazed the guy in the tracker didn't find a pressure crack as he went for a few km at a time WO. It would've been good to watch.
Ian