Armortek

Posted: **Sat Feb 14, 2015 12:21 pm**

Chris,
I had considered that too, but you would expect the masks to be closer together and not parallel. The grinder would twist round, so a fan shaped set of marks would be left. Room for some experiments in the workshop..
cheers, Fabrice

Posted: **Sat Feb 14, 2015 5:40 pm**

Fabrice Le Roux wrote:Chris, Stephen

This whole grinding marks conundrum is of interest. Clearly dozens of small nicks across the top surface does not sit well with the concept of a supervised one-off Quality Assurance type test. It is just too random and too time consuming.

I have suggested the top surface marks could have been cut to add grip, because form follows function, and they are there for a reason. So what else could be achieved from superficial grinding of the other, not horizontal, surfaces? I will run this past grizzled old engineers of my acquaintance too, but here are two thoughts off the top of my head..

a) the plume of sparks would have a specific colour and combustion pattern. This is a classic way of identifying the composition of an unknown piece of metal. Yet the manufacturers knew exactly the composition of the plates (and their hardness) before they entered the production line. This was the 1950's, not 1917, after all.

b) could the application of the grinding wheel to the hardened armour plate have served to "dress" the grinding wheel, and safely test it for concentricity/cracking prior to extended grinding work along the edges as part of the pre-welding preparation? We are assuming that these marks were made *after* the assembly of the 100 Gal tank. They could have been made before, when considerable weld-prep grinding work was taking place.

Is there any record of similar marks being found on other vehicles? Any accounts of this dressing technique being used in other industries, eg ship-building, boiler making or locomotive construction? I will make my own enquiries, but any evidence is would be useful.

Looking at Paul's photos, I am no longer convinced by the "hardness testing" explanation. It does not match the evidence, so there must be a better explanation.

Fortunately, whatever we discover about the reasons for the marks, they are there on the full-size vehicle and should remain faithfully reproduced on the model! Phew!

cheers,
Fabrice

You may have a point about dressing the wheels Fabrice
When the welders at work have done full penetration welds with the stick,they tend to grind about a third of the weld they have put down out to make sure all slag,porosity etc have been removed.This is done as each run is put down.I know from experience it tends to rag the edges of the wheels up so they may well be cleaning the wheel edge back up.
Chris

Posted: **Sun Feb 15, 2015 9:24 pm**

Paul Scott has sent more photos from Australia. The marks would be difficult to see on an unrestored vehicle, with several layers of paint:

Paul has stripped his Cent back to bare metal, primed and re-painted, which explains why the marks are that much more visible:

One telling photo shows that the marks pre-date the stamping of the parts with their part numbers, confirming that they are integral to the manufacturing process:

We strongly believe they are related to armour hardness testing.

Following Chris' lead, I've discounted Brinell (which uses a spherical ball) and Vickers (which uses a diamond shape). Scraping armour to sample its hardness is a technique I came across at the height of the Cold War so we may be on the right lines.

Stephen

Posted: **Sun Feb 15, 2015 9:46 pm**

Made a start on the external fuel tank top cover:

Made spacers and did a trial hanging of the tank on the louvre protection plate (aka hull top rear plate):

Regards

Stephen

Posted: **Mon Feb 16, 2015 1:34 am**

Stephen,
The 100 gal tank sticks out so much, did it impede mobility? Did it dig in like a ground anchor when reversing?

"Scraping armour to sample its hardness is a technique I came across at the height of the Cold War". Such a tease! Please expand with examples.

cheers, Fabrice

Posted: **Mon Feb 16, 2015 9:45 am**

Fabrice

I've not seen any direct evidence that the external tank reduced mobility, although bogging was a common occurrence in South Vietnam:

You'll have to work for an answer to your second question! I recommend these two, particularly the latter which gives a very good flavour from an insider:

http://www.amazon.co.uk/Brixmis-Untold- ... 0006386733

http://www.amazon.co.uk/Live-Let-Spy-BR ... 3EXVTKK3SY

Regards cryptically

Stephen

Posted: **Tue Feb 17, 2015 1:08 am**

Stephen,

Too arcane for my budget, sorry, so feel free to quote. But seems reasonable to have discreetly

scratched the paint on BDRMs, BTRs and T72s etc to see if they were decent steel or aluminium. Hardness files or the like clearly would be quieter than impact testing in a Warpac tank park!

However I can find no record of workshop type angle-grinders been capable of the level of precision required to produce meaningful hardness data. Especially as the cuts in the photos are clearly of different lengths, depths and even crossing over each other.

The only useful information would be from visual analysis of the spark stream. Spark
testing is a well established method, and would explain the clusters of cuts, but it does not explain the very widely spread cuts across the top surface.

Last point, Brindell testing had been in use for decades prior to Centurion, why on earth would Royal Ordinance fall back to such a haphazard method to monitor the QA of a state of the art battle tank?

In the end this will only be illuminated by information from someone who worked in the factories in the 1950's, which may be a tall order. Or perhaps some solid archive source will emerge in due course.

This is certainly a feature I will now look for on other vehicles!

Out.
Fabrice

Posted: **Thu Feb 19, 2015 3:14 pm**

Hi all
Just to add to the armour grinding mystery,I spotted these on a Saladin at Cosford museum today.Im leaning to hardness testing now I have seen the marks up close.
Chris

Posted: **Thu Feb 19, 2015 9:10 pm**

Chris - that's a great find, I was hoping these marks would show up on other British AFV. I'd like to nail this though with a definitive reference.

Progressed with the last of the detailing of the external tank. First the hinge pins were installed with washers and retained with split pins:

The lifting handle was added, together with the retaining bolts for the fixed section, with their fixtures:

I made the mistake of buying some magnifying specs and suckered myself into making functional latches:

They are retained with two fittings on well wall:

That's it. Etch prime and base coat to follow.

Thanks for looking.

Stephen

Posted: **Thu Feb 19, 2015 9:40 pm**

Stephen
That fuel tank is a work of art!

Posted: **Mon Feb 23, 2015 5:42 pm**

Thanks Chris. I've had immeasurable help from Allan Bowers in NZ who did the drawings, Paul Scott in Australia who provided the reference material from his restored Cent, Mike Cecil in the US who has helped with research and knowledge and above all, the gentlemen of the 1st Armoured Regiment in Australia who took the Cent to war. Their interest is what makes me want to get this model right.

Final bits and pieces: the wading fittings and the various fittings on the louvre protection plate. The latter is painted British Army Deep Bronze Green on the inside, making a contrast with the Australian Olive Drab Semi-Lustrless:

Next, paint and mounting the tank:

Now for some markings and then move on.

Regards

Stephen

Posted: **Mon Feb 23, 2015 6:25 pm**

Not a lousy gasoline tank, a real model on its own!

Posted: **Wed Feb 25, 2015 8:31 am**

Hi Stephen

Brilliant job on the fuel tank, whatever angle you look it looks just like the real thing.

I do have one question you have bolted the fuel tank onto the tank with the nuts exposed rather than the bolt head, all of the photographs that I have seen have the bolt head exposed. Is there a reason for this ?

Regards

David

Posted: **Wed Feb 25, 2015 9:45 am**

David

I've wanted to get this build right for the former crews, so you've raised a good question. I've gone back and had a look at the original, for which I've got several contemporary photos.

There's no doubt the mountings on the louvre protection plate were drilled and tapped, so they could take bolts from the outside. Here there are some blanks:

I've used as my detailed reference Paul Scott's amazing restoration. On his tank, there are studs with nuts on the outside, hence my model:

But I've now gone back over the photos of 169064 (the tank I'm replicating) in Vietnam and found one which clearly shows, as you say, bolts let in from the outside. Damn!

Not too difficult to change - I'll ponder and also consult to see which was most common.

All the best and thanks for commenting. It all helps make an accurate model.

Stephen

Posted: **Wed Feb 25, 2015 8:25 pm**

David, you were spot on, I'm very grateful. Mike Cecil has confirmed that the modification kits for the "Armoured Additional Fuel Tank" came with 14 5/8th inch bolts and spring washers but no nuts. The mounting pads were threaded. Mike surmises that it was probably a pain to line up the bolts and that at a major refurbishment, workshops may have replaced the bolts with studs and nuts. That would explain why Paul's tank has the latter. I'll check with the log book to see if it's mentioned. Thanks again for spotting it. I've removed the tank and reversed the bolts:

I also added the fuel outlet union and pipe, which I turned on the lathe in brass. This installation has the pipe running down between the tank and the louvre protection plate, then looping up through the louvres and over the hull rear plate.

This rather crude arrangement was later replaced by a junction let into the louvre protection plate but not on the vehicle I'm modelling.

Full size:

Model:

Regards

Stephen

Armortek

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