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Flux Capacitor Solenoids

The Round Base

Three of the major components inside the flux capacitor are the round metal disk shaped elements. It turns out that they are electrical vacuum solenoids used to switch heavy currents in industrial equipment. They have a glass tube running through the middle and exiting at a right angle.

By angling the three glass tubes towards the middle of the box, they form the "Y" of the flux capacitor. They come up on ebay every once in a while but unless you want to drop a few hundred dollars each, you'll need to come up with a substitute. I found the dimensions for the actual solenoids on the web in a BTTF forum. There are also plenty of pictures of these solenoids from all angles, so crafting a replica should be doable.

It so happens that I have a large stash of electrical components and I found a few dc motors with metal gear boxes that have the same dimensions as the metal base of the vacuum solenoids. My plan is to transform one of these into a replica of the actual base. Then make a silicone mold of it and crank out several copies.

I have plans on using clear acrylic rod for the glass tube. I used the acrylic rod for a few parts inside my Lost in Space Robot, so I know how versatile it is.

I took apart the motor and placed the metal ring on a scrap piece of plastic. I then put clay around the base to seal it and I filled the center with plastic resin from Smooth-On. This will allow me to fashion it into a replica of the solenoid.

My replica base is starting to come together. Next I drilled a 9/16 inch hole completely through the middle. I then painted it with primer. After applying the primer, I noticed a few pinholes in the resin. A little automotive Bondo putty filled the holes and I then wet sanded it with 400 grit sandpaper.

Here, I've drilled two holes for the soldering posts and a small slot where the electrical wires exit from the solenoid case.; The base is about ready to be used as my mold master. That is when the fun begins.

I've set in place the soldering posts and added two wires. The wires have one end stripped and wrapped around the top of the posts while the other ends go into the body of the solenoid through the small slot I made. In it's final configuration, the bare wires will be soldered to the posts.

Having finished the replica base I could now make a mold of it. I prepared the base by mounting it to a clean flat piece of PVC. I used my tried-and-true Lego method for building a box around the base and mixed up some silicone rubber. I've documents my molding methods in my Silicone Mold Making Guide. After degassing the silicone, I poured it over the base and vibrated any remaining bubbles to the surface where they could pop. I have to wait patiently overnight for it to cure

I was tempted to crack it open in the morning to peek but didn't as letting it sit another 9 hours would probably be good for it and I could wait until I got home from work. To see how I molded the duplicate solenoid bases, check out my Plastic Resin Casting Guide here..

Painting the Solenoid Base

painting the solenoid bases Brass Paint I finally found time to put some paint on one of the replica solenoid bases.

I found a airbrush paint at a local hobby store made by Model Masters (Testors) that is called "Brass - Non-Buffing Metalizer". I gave it a shot and I'm not sure I like the outcome. I've used Chrome air-brush paint in the past and it works quite well. With the chrome, after your primer layer you put on a glass black base.

Then the chrome is sprayed on and the gloss black is allowed to show through slightly, giving the chrome a deeper look. The brass paint has no base paint so you are painting over your (gray) primer. You have to completely paint your item. I'll reserve my final opinion until I apply the label and add the tubes. I plan on looking at what other air-brush paint companies offer.

Solenoids Solder Posts

relay posts zoom-inTwo tiny black posts protrude from the surface of the vacuum solenoid. Connected to each is a single black wire. These are posts for soldering the wires that will power the solenoid. The black wires are connected to the coil inside the round metal case. The posts look simple enough but finding something now that matches these would be a trick.

test probe socketsFortunately they resemble some other electrical components. I have a hand full of test probe sockets (also called Tip Jacks) that look an awful like what we need. And they are exactly the right size.

posts inplace on solenoid

Here's the soldering posts placed on my solenoid replica. I added the wires that are wrapped around the top of the posts and go into a hole in the base.

Those Fluxing Tubes!

testing light barOne of the trickier parts to replicate will be the glass tube which contains the relay elements. I order from McMaster-Carr several 6 foot acrylic rods. I used 1/2 inch acrylic rods on my B9 Robot Replica and they are great to work with. I have ordered the follow different types.

1/4 in. outer dia. Solid Acrylic Rod

1/2 in. outer dia. Solid Acrylic Rod

1/2 in. outer dia. - 1/4 in. internal dia. Acrylic Tube

1/4 in. outer dia. - 1/8 in. internal dia. Acrylic Tube

3/4 in. Acrylic Balls

Additionally, at my local hobby shop I purchased some other materials from their K&S Engineering display.

1/8 in. outer dia. Copper Tube (Stock #120)

3/32 dia. "Music Wire (Stock #506)

To create the round end I first round the end of each tube on the bench sander. Then I gently sand the rounded end with a 1000 grit wet sand paper. Next I use Novus #2 "Fine Scratch Remover" and then finish it off with Novus #1 "Plastic Clean & Shine".

I started by sanding a flat spot on one side of a 3/4 in. acrylic ball. This allowed me to drill a small 1/8 in. hole part way through. Next I placed the drill bit into the hole. This allowed me to hold the ball against my table sander and sand two more flat spots at right angles to the original and at opposite ends of each other. These flat spots should be exactly 1/2 in dia. I then drilled a 1/8 in. hole completely through from one flat side to the other.

I glued sections of the 1/2 OD, 1/4 ID acrylic tubes on the flat spots. The lower right side, which is placed into the solenoid base can be cut flush to the same length as the depth of the hole. This will allow it to sit flush in the hole. I'm still playing with the lengths of the different tubes to get the right look.

Here I've put it into the hole and set the two soldering posts in place. I added small copper rods for now, but need to get some other steel ones.

Here are all the pieces and parts to the Fluxing Tubes. I decided to add a taper to the upper tube and I added a 1/4 inch acrylic rod in the center to snap the spark plug wire on to. As you can see i also changed the rod to solid steel and added a short copper tube. I also eliminated the vertical rod since the spark plug boot will hide most of the upright tube.

This picture shows you the final dinemsions of the various parts after assembly. This first prototype got beat up a little so I made three more from scratch.

Solenoid Mounting Brackets

I need to fabricate a replica metal bracket that hangs off the back side of the Solenoid Base. It's a simple, bent metal bracket. I have not seen how it mounts but it may be tack welded directly to the round base.

First I made a mock up out of cardboard (sorry, no picture) to get the right look. Then I stretched it out to get the proper length to start with and transferred the bends to a piece of 3/4 inch wide x 1/16 inch thick aluminum strip (purchased at Lowes).

Solenoid Mounting Bracket

I used the end of a old style can opener to get the proper curve and to center the hole on each end. I placed the end of the strip against my belt sander and sanded the proper radius.

After the legs were bent in my vice, I placed it on top of the vice and I put one of my spare molded solenoid bases on top. Gently, but with some force, i pounded the top of the solenoid base with a hammer until I got the proper curve in the bracket. I had to straighten out the legs when I was done pounding, but it came out great.

Solinoid Mounting Brackets

I drilled a hole dead center in the base and used a screw to hold it in place.

bracket mounted to solenoid base

After making two more replicas, they went into the paint booth for a coat or two of the brass metalized paint.

painting the mounting brackets

Besides the above mounting brackets, there are a few other parts on the solenoid bases. The first I'll call the "cradle". If you look closely on both sides of the long tube, there are little wings on both sides which cradle the tube. Additionally, there is a formed wire that holds down the tube.

So a grabbed some cardboard and cut out some a few sample parts. I folded them and trimmed them to the correct size. next i traced the pattern onto some thin sheet styrene plastic and cut those out.

tube cradle prototype

I decided I didn't need the extra little hole that was present on the original. That part turned out to be a pain to duplicate. it just didn't look right, so I skipped it.

I used a small hobby butane torch to gently heat up the styrene and bend the wings up, to form the cradle. Here they are being primed.

All bent up

Next I sprayed them the same metallic bronze color as the base.

Final Assembly - Solenoids

With the bases painted and the fluxing tubes assembled, I was able to complete the Vacuum Solenoid replicas. While not exact, they're pretty darn close.

Completed Flux capacitor Solenoids