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tardis roundel reference

Started by woodenconsole, May 29, 2006, 07:03 pm

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tony farrell

Jul 29, 2017, 04:36 pm #45 Last Edit: Jul 29, 2017, 05:20 pm by Tony Farrell
Quote from: karsthotep on Jul 29, 2017, 03:44 pm
  Tony,  checking on the measurements of the roundel, in several sections and your 19.6 is the closest. some spots on mine were 19.5, some 19.6 and some a little bit more than that depending on the area,  so not a perfect circle by any means due to warping as well as the thickness of the fiberglass in any one area.  

I laid it on the counter top as I was curious how much further the inner circle protruded down past the outside flange,  Again, taking into consideration warping and its not perfectly flat,  the inner circle sat about 5/8's of an inch further than the flange of the roundel.


Thank you for those measurements Karsten - much appreciated.

I've been doing a bit of research into fibreglass and how much it actually does warp over time for a separate project (recreating the Daleks' Saucer from the second Cushing movie). So as well as research into the Newbery Wooden Tardis Control Room, everyone's comments will very helpful for that too. (I also notice that Matt Sanders has experienced problems with his Met Box build as some fibreglass distorting occurred there as well - but, if I've understood Matt correctly, this is down to heat building up between the inner and outer fibreglass shells of his Box.)

Anyway, back to distortion. I've looked at several fibreglass suppliers websites and - according to them - there are two basic types of fibreglassing 'systems' available: One where the resin is a polyester-based material and the other where the resin is epoxy-based. Again according to all these sites, whilst polyester-based resins are prone to distortion (warping), epoxy resins are not.

All the sites I've looked at state that epoxy resins don't shrink or warp provided you allow them to cure before removing the cast from the mould. The draw-back to epoxy-based resins is that they are not 'UV light-fast' and therefore will not only yellow over time but will also become brittle. They therefore require a protective coating to block UV rays.

If you look at the earliest appearances of the clear roundels in Season 15 of Dr Who, they are virtually colourless and - as the seasons progress - they become progressively more 'straw' coloured. Indeed in Stones of Blood, because of the back-lighting, they have an almost blue tinge to them.

Now clearly we don't know what resins were used by the BBC or, indeed, what resins were used in both Karsten's and Theta Sigma's casts of the roundels. The second problem as I see it is that Theta Sigma's is a partial cast - it is not a full roundel and therefore might be prone to more warping than a full-roundel i.e., it might lack the structural strength afforded by a full roundel and its 'open' edges might therefore distort more than the 'closed' edges of the full roundel which Karsten possesses.

That said, Karsten and Theta Sigma have both stated that the central disc is more deeply recessed than the outer flange. Karsten has measured this difference as 5/8ths of an inch. It would be interesting to know what the difference in depths are for Theta Sigma's partial cast. If the difference on Theta's roundel is more-or-less the same, I think it might be reasonable to suggest that this difference in depths between the flange and central disc was intentional (i.e. part of the original mould) and not due to any warping which might have occurred.

It would also be interesting to ask Karsten if the central disc of his full-roundel is broadly flat i.e., has any obvious distortion or warping occurred? Even if the disc is slightly convex, providing this curve is relatively even, it might be reasonable to conclude that this - again - was a characteristic of the original mould and that the central disc was never flat in the first place.

So Karsten and Theta Sigma, over to you guys to answer those questions!   ;)

And- once again - thank you for your help.

T

karsthotep

 Tony,

   Looking at mine right now, there is a bit of a slope at the beginning of the inner circle. I re-positioned the gauge and made sure everything was lined up and I also checked on several sides of the roundel to make sure it wasn't occurring in one area. if you look at the picture you can see that the roundel center circle starts to drift up towards the center, I can see it with the naked eye all the way around however, it does seem to level out the closer you get toward the center and there are visible waves in the fiberglass

IMG_0202.JPG
I want notes, lists and answers by the time I finish this here Juicy-a-Box! WARNING: I am Thirst-ay! And it is Fruit Punch! And it is Delicious!"

Theta Sigma

Jul 29, 2017, 07:31 pm #47 Last Edit: Jul 29, 2017, 07:46 pm by Theta Sigma
Here are some pics of my partial roundel and mold that I got from an anonymous person who possesses a roundel cast from an original BBC mold.  So this mold is made from a 1st generation roundel.

He made the black partial mold for me, then cast a white partial roundel from that mold.  

When it arrived, the black mold had already badly warped to the point that the casting would no longer fit inside it without being forced.  You can see the stress cracks in the mold and how badly it warped.  

Granted, a full roundel would be less likely to warp, but those stresses are still there and would be distributed throughout the roundel causing warping somewhere.  

I had to clamp it down to this board to get my plaster cast.  I found the center radius line of the casting, which I then cut to get the cross section picture I posted.

IMG_1956.JPGIMG_1957.JPGIMG_1958.JPGIMG_1959.JPG

If you look at my casting, the center is convex, just as Karsten's roundel is.  If you force it flat, the flange is about 12mm above the measuring surface, minus approximately 4mm for the thickness of the casting.  So, lets say that on this particular casting, we have an 8mm difference between the center disc plane and the mounting flange plane.  That would be about 0.314961 inches, or somewhere between 5/16 inch to 21/64 inch.  But take into consideration that I don't know what shape the mold was in when the actual casting was done from a warping perspective.  I would think it was probably less warped than it was when it finished it's trip across the pond.

IMG_1961.JPGIMG_1962.JPGIMG_2003.JPG

On the subject of resin, I am fairly certain that polyester resin was used.
"I just put 1.795372 & 2.204628 together." - 4th Doctor

tony farrell

Jul 29, 2017, 08:19 pm #48 Last Edit: Jul 29, 2017, 08:37 pm by Tony Farrell
Thank you for the replies gentlemen.

I think the interesting thing about the picture where Theta Sigma is holding the central disc flat on his kitchen worktop is that this 'forces' the outer edge of the moulded section back to being almost vertical. I think this would tend to confirm that the central disc was actually intended to be lower than the flange for two reasons:

Firstly, when the casts from the mould were originally made for the Wooden Control Room, they were mounted through holes cut in the wall panels. You wouldn't cut these holes with sloping sides, they'd be cut through the plywood wall-panels at right-angles. So, rather than forcing a sloping-sided roundel through a hole, you'd want to make the roundels edges parallel to the cutting angle so that it slots in easily.

Secondly, if we look at Season 15, video evidence would seem to show that two roundels were fitted to the main Tardis doors - one either side of a disc.

DoorRoundelIntoDoor.jpg

If we take the doors' supporting discs as 20 mm thick, the backs of the roundels central sections would be more-or-less touching one another i.e., the central disc in each roundel is approximately 8 mm deeper than the flange (which exactly matches the 8 mm as stated by Theta Sigma).

T

Theta Sigma

Here is an overlay image of Karsten's contour gage, and my plaster casting.  No amount of resizing or rotating the image makes them match up.  It's amazing the difference warping makes.  To that end, I don't think we will ever truly be able to determine the exact measurements of this complex shape.  Unless someone can ever get their hands on an original mold, and throw one of these contour gages on it.  But then again, every mold was probably different too, as they would be prone to the same warping if they were made from fiberglass too.

overlay_contour gage.jpg
"I just put 1.795372 & 2.204628 together." - 4th Doctor

tony farrell

Jul 29, 2017, 09:19 pm #50 Last Edit: Jul 29, 2017, 10:27 pm by Tony Farrell
If at all possible, can you try doing that overlay with the outer - straight - edge of your mould raised up slightly but still keeping the inner-most curve where it is (i.e., so that your version is tilted/slightly rotated relative to Karsten's picture)?

overlay_contour gage.jpg

With the exception of the middle portion of Theta Sigma's mould which is higher than Karsten's, I think you find that the match is much closer.

A possible explanation of the 'raised' section in Theta Sigma's is warping/shrinkage:

match_this.jpg

T

karsthotep

I will take some additional pictures of the gauge from other locations on the roundel as some areas are softer than others depending on the thickness variations in the fiberglass
I want notes, lists and answers by the time I finish this here Juicy-a-Box! WARNING: I am Thirst-ay! And it is Fruit Punch! And it is Delicious!"

Theta Sigma

Jul 30, 2017, 03:45 pm #52 Last Edit: Jul 30, 2017, 06:55 pm by Theta Sigma
Is this any better Tony?  


overlay_contour gage2.jpg

I have posted the file layered file here if you want to play with it on your own.  It's a paint.net file.

https://drive.google.com/file/d/0B9wuQYOPzaXcT0xIWWYxSUxEak0/view?usp=sharing
"I just put 1.795372 & 2.204628 together." - 4th Doctor

Theta Sigma

Jul 30, 2017, 03:50 pm #53 Last Edit: Jul 30, 2017, 06:56 pm by Theta Sigma
Quote from: karsthotep on Jul 29, 2017, 10:38 pm
I will take some additional pictures of the gauge from other locations on the roundel as some areas are softer than others depending on the thickness variations in the fiberglass


I'm actually quite fond of this "forced upward" center of detailed section.

I would actually argue that the outer flange warping up on the outside edge would correspond to this center of the detailed section warping downwards. 
"I just put 1.795372 & 2.204628 together." - 4th Doctor

Rassilons Rod

I've always thought the middle disc was intentionally slightly domed :)
In the cities in the streets there's a tension you can feel,
The breaking strain is fast approaching, guns and riots.
Politicians gamble and lie to save their skins,
And the press get fed the scapegoats,
Public Enema Number One.

tony farrell

Jul 30, 2017, 06:27 pm #55 Last Edit: Jul 30, 2017, 06:56 pm by Tony Farrell
Quote from: rassilonsrod on Jul 30, 2017, 04:28 pm
I've always thought the middle disc was intentionally slightly domed :)


You could well be correct Marc! This is a close-up of the wall panel from The Masque of Mandragora:

are the roundels curved.png

With the best will in the world, given the time-constraints involved and the fact the set was designed for 625-line transmission, we are unlikely to have roundels with central discs that were perfectly flat or, indeed, perfectly symmetrical.

However, the point I made a couple of posts ago about Theta Sigma holding the central disc of his cast down on the kitchen worktop still stands - holding it flat(ter) does have the effect of straightening the outer edge; having an outer edge which is parallel to the sides of the holes cut into the wall panels would make it much easier to mount the roundels. Why would the set builders make life harder for themselves by casting something whose outer edge tapers inward?

So, I think some distortion of Theta Sigma's cast has occurred and because it is only a partial cast, this distortion is - perhaps - slightly greater than would be the case on a full roundel because, put simply, a full roundel would have greater structural integrity.

Quote from: Theta Sigma on Jul 30, 2017, 03:45 pm
Is this any better Tony?  

No message is associated with this attachment.

I have posted the file layered file here if you want to play with it on your own.  It's a paint.net file.


Thank you Theta Sigma. (I'm not used Paint.net before so I had to have a play.) I think I've worked out how to use the program and have very slightly altered the position of the two 'layers' so that the images of your cast and Karsten's 'pin gauge' are now in alignment:

overlay_contour gage2.jpg

I think your partial cast has distorted more than Karsten's - rather like a dead spider, it has slightly curled in on itself:

overlay_contour gage2.jpg

If you were to press down at the point indicated by the red arrow, the outer edge (yellow arrow) would be forced into a vertical position. If that were to occur, I think both Theta Sigma's and Karsten's  casts would be an almost exact match.

So Theta Sigma, I think all the effort you've put into calculating the diameters of the curves has been well worth while and that these calculations still hold true. The only slight change needed would be because the central section of your cast appears to be slightly higher than it should be purely because your cast has done an 'impersonation of a dead spider' and curled up on itself!  :)

Does that make sense?

T

Theta Sigma

Makes sense to me.  I see what you are saying now.

Have we come to a conclusion regarding the flange and central disc being in the same plane or not?

"I just put 1.795372 & 2.204628 together." - 4th Doctor

tony farrell

As I stated in my earlier post about the roundels being fitted either side of a supporting disc on the main doors, I do think that the central disc and flange should be at different heights - as you said when you measured yours, the difference is approximately 8 mm (which itself, ties in with Karsten's observations of his cast).

T

tony farrell

Aug 04, 2017, 09:19 pm #58 Last Edit: Aug 05, 2017, 12:23 pm by Tony Farrell
Right, as I promised Karsten, a printable drawing.

I've used the same sized circles as determined by Theta Sigma from his partial mould but re-positioned them to match the pin gauge profile provided by Karsten from his full mould. (Obviously - because of the widths of each pin - whilst the pin gauge 'follows' the over all profile of the full roundel's sculptured border, there has been some loss of definition.)

The first diagram shows the revised positions of circles with the diameters drawn to match the dimensions determined by Theta Sigma. The second shows this diagram 'overlaid' onto the picture of the pin gauge profile (see the previous posts for the original picture).

Roundel moulding.png

Lastly, a diagram drawn at precisely twice the size of the actual roundel moulding which - if printed at 50% - should be suitable as for use as a 'former' for reproducing the moulding.

Roundel moulding template twice actual size.png

T

Angelus Lupus

Now that's what I call a successful collaborative effort!
Moulds, casts, reference and measurements from all over the place, shared and compared to produce the result! (Which, now I see it written down, I realise is basically the very ethos of this place)
A mixed-up non-conformist, trying to fit in.