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How to make a Parabolic Array

Started by Other Dave, Jul 04, 2016, 12:02 pm

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Other Dave

Here's how to make a reasonable facsimile of a TARDIS Type 40 Parabolic Array.

parabolic_array2.jpg

First, you will need to purchase a plastic colander that is about the correct dimensions.

The bowl should be about 9 1/4"  to 9 1/2" in diameter on the inside.
The bottom should be about 4 1/4" diameter.
The height, minus the rim and legs, should be about 4 1/2"

Here are Tony Farrell's dimensions. 

sideview.png

If you live in the US, head over to WalMart and purchase the Red and White "Bowl & Colander Set" for $4.47!
( Red & White - MS15-041-992-57 SKU 070652186681)
http://www.walmart.com/ip/Mainstays-6qt-Bowl-and-4qt-Colander-Set/44728135

colander_1.jpg

label.jpg

If you live outside the US, the same colander, but without the red bowl is available online at Amazon here:
https://www.amazon.com/dp/B000HM83OQ/ref=psdc_289761_t1_B0021Y9O1O

I'm writing this in July 2016. There's no telling how long either of these colanders will remain in their respective inventories.
But hopefully you can find one that  matches the right dimensions.

The number of pre-cut holes around the circumference of this colander is 72.  Which is terrific, because it needs to be a multiple of 12 as we will be cutting out segments to get to 24 and 12 sections.  Some colanders I found were a good size and shape, but the number of holes were 30 or some other multiple that would just not work.

Hopefully, you have a tool like a Dremel to make the cuts.  It can still be done, but it will take longer. 

You will need to keep every third segment line and remove the ones in-between.  The green lines I drew here are what we want to keep.

cuts_1.jpg

Here I have cut out the unwanted lines and rows to make a sample of what we want for the whole bowl.

cuts_2a.jpg

Here's what it looks like from the inside.

cuts_2.jpg

Okay, start cutting away.  I recommend waiting to cut the 12 larger holes that are at the bottom of the bowl until all the other ones are cut out. I cut three out, but decided since the lines looked so thin and fragile, that I should do all the others first. Especially the row of 24 new holes at the upper part of the bowl.

cuts_3.jpg

Here I have marked with a Sharpie where I want to be cutting the new holes.  Notice I have already cut off the two handles at the top of the bowl - they were in the way.

cuts_4.jpg

Use whatever you can to get those holes cut out. The Dremel is awesome, but be careful it doesn't cut more than you want. 
If you cut through a line or row mistakenly, I don't know how to patch up polypropylene.  Bondo?  Just be careful.  Use an Xacto knife for corners.

Once all the holes are cut, now you need to file and sand to get them as smooth as possible.  The polypropylene plastic is very sturdy and slightly rubbery.

primer.jpg

We will be removing the existing rim and replacing it with a better one.  I tried to find a place locally that will cut one out in acrylic, but no luck. 
So I decided to just buy a 24" x 24" piece of 1/4" MDF at Home Depot.   I carefully marked out the size per Tony Farrell's measurements.
(11.25" outside diameter, about 9.8" inside diameter, three curved bump-outs spaced along the outer edge measuring a little less then 1" in diameter.)

router_1.jpg

I cut out the ring with a small router - RIGID model R2401.  I didn't have a way to make a round cut, but the router came with an attachment for making trims or something. 
I hit on the idea, that with a piece a small block of 2x4 wood, I could make a decent compass cutter out of it. 
I attached the wood to the trim adapter with a couple of screws and put another screw on the bottom edge and then cut off the screw head to make a sort of pin. 
I then inserted that "pin" into a small hole in the center of my work. 

router_2.jpg

Place your MDF board on a sheet of thick Styrofoam to make the cuts.   Hold down the block with one hand and then slowly swing the router around with the other hand.

For the three little domes, I was planning to find some wooden or plastic beads to cut in half, but couldn't figure out how to cut something that small without also cutting all my fingers off too!

sculpy_1.jpg

As luck would have it, my wife has a nice set of measuring spoons that are round. 
The quarter teaspoon measure is just the right size, so I pushed some Super Sculpy into it like a mold. 
I pressed the end of a lump of Super Sculpy clay and then scored the edges a little. They gave me a way to pull it back out of the spoon. Then I trimmed it along the score lines.

sculpy_2.jpg

Do this for all three, place them on a glass pie plate and bake them in a 250 degree oven for 15 minutes.
Glue the domes to the new rim.  I used E6000 glue.  (available at Hobby Lobby) 
Cut the old rim off the bowl.  Leave a little in order to glue it to the new rim.

rim_cut.jpg

Glue the new rim on.  Paint with silver spray paint.

parabolic_array1.jpg

I decided to leave the legs on the bottom for added stability.  You may want to cut them off.
I also left all the remaining holes at the bottom of the bowl as is. 
You may want to try to fill them with something, or just cut out a 4" diameter disk out of plastic and cover them up.

- David


tony farrell

What a wonderful little 'build diary' - elegant in its simplicity, beautifully described and brilliantly illustrated with photos demonstrating your step-by-step instructions.

Thanks for sharing David.

Just one question: When are you going to build the rest of the Console?  :)

T

handofomega


galacticprobe

Jul 05, 2016, 06:56 am #3 Last Edit: Jul 05, 2016, 07:01 am by galacticprobe
Wow! I don't know what category this one falls into:

It's a magnificent "Build Diary" as Tony mentioned since it details building a key part of a console prop;
It's also a great Console Workshop piece because - well - just look at it! Brilliant! (Quoting Don this time.);
It's also a Console Tutorial as it details the step by step instructions on how to build this great piece!

Amazingly done, David! (Or should this be another case of "Other David" since we have "Proper David" who was here first? - Again, "Silence in the Library"! ;D)

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

Other Dave

Thanks for the nice comments!  I forgot to add this graphic of the new rim.

parabolicArrayDrawing.jpg


- Other Dave


markofrani


Angelus Lupus

Jul 14, 2016, 11:14 pm #6 Last Edit: Jul 14, 2016, 11:16 pm by Angelus Lupus
Buy it, buy it quick! Those look like an excellent base to modify into a parabolic array.

Edit: small print says "31 inches tall, each basket 12 inches wide." so, pretty spot on for size?
A mixed-up non-conformist, trying to fit in.

galacticprobe

Jul 15, 2016, 06:24 am #7 Last Edit: Jul 15, 2016, 06:34 am by galacticprobe
Quote from: Angelus Lupus on Jul 14, 2016, 11:14 pm
Edit: small print says... each basket 12 inches wide." so, pretty spot on for size?


According to Tony's calculations based on known sizes of other components, he puts the "Parabolic Array" at 11.125 inches (11 1/8th inches) in diameter. That extra 7/8ths of an inch, all round, only adds up to less than half an inch on the edge (.4375 inch to be precise). And that "12 inches" could include the three bulges for the domes. So I would call that pretty well spot on!

So as Angelus says, Jonathan...
Quote from: Angelus Lupus on Jul 14, 2016, 11:14 pm
Buy it, buy it quick! Those look like an excellent base to modify into a parabolic array.

There's no telling when another listing for four baskets will pop up! (Okay, so there will only be three domes, but those can have silicone moulds made, and then replicas of the originals cast, keeping the original domes safe in case new moulds need to be made.)

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

Dalex

Just FYI, these baskets are not a perfect match for the original.  There are 10 "windows" between each of the three posts, whereas the original had only 8.

Nevertheless, it's definitely extremely close!  :)
Dalex

galacticprobe

Jul 16, 2016, 06:29 am #9 Last Edit: Jul 16, 2016, 06:29 am by galacticprobe
Thanks for noticing that, Dalex. I thought it looked like there were more "windows" in these, but also thought it was just me or the way the photo was taken. Still, as infrequent as these pop up, I would definitely call them "close enoughs" for now. They'll work just fine until our Brachacki console builders can find the exact baskets... which may take a while.

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

Angelus Lupus

Short of building a working Tardis, popping back to the set-building days of the original, asking where they got the basket, than nipping out and buying some...
Although that might explain why there aren't any around nowdays...
A mixed-up non-conformist, trying to fit in.

tony farrell

Jul 16, 2016, 12:44 pm #11 Last Edit: Jul 16, 2016, 12:48 pm by Tony Farrell
There's a nice picture somewhere showing an identical 'basket' being used in Gerry Anderson's "Super Car".

We know the BBC was fond of buying props from Anderson and re-using them in Dr Who (think Shado's moonbase controls re-appearing as part of B.O.S.S. in "The Green Death" or - again - as part of Linx's controls in "The Time Monster". Indeed, one of the "Captain Scarlet" Angels' fighter-planes appeared as the Master's Tardis in "Colony in Space").

Perhaps the original 'parabolic array' came from Gerry Anderson too!

T

galacticprobe

Jul 17, 2016, 06:26 am #12 Last Edit: Jul 17, 2016, 06:26 am by galacticprobe
Quote from: Tony Farrell on Jul 16, 2016, 12:44 pm
There's a nice picture somewhere showing an identical 'basket' being used in Gerry Anderson's "Super Car".

Perhaps the original 'parabolic array' came from Gerry Anderson too!


There was also one of those baskets, used upside-down and with its legs still on, in an episode of 'Fireball XL-5'. I can't remember which episode, but it was one of the early ones. I know that much because I started watching those episodes on HuluPlus, and only had gotten as far as, maybe, episode 13 before HuluPlus pulled it. (They're getting to be as bad as Netflix with pulling shows from their line-up!)

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"