My Beaut Aussie Cent

[Stephen White]

Another view of the original MG housing before the addition of the .50 RG:



This one on the "cut in half" Cent Mk 5 at The Tank Museum, Bovington.

I should correct an earlier slip above suggesting that 064 has a 20 pdr Type B barrel. It acquired a 105mm barrel during its time in civilian hands, as the last entry in the AB417 indicates that it left service minus a barrel. The two are interchangeable, opening the possibility that at some time in the future, the correct 20 pdr could be re-fitted.

On the the pneumatics for recoil.

Regards.

Stephen

[Stephen White]

While I'm looking at the recoil again, I decided to re-visit the elevation mechanism. Using a rotary servo has the advantage of responsiveness but the rotary linkage is still not stiff enough prevent the barrel bouncing when moved.



I've now fitted one of the new Firgelli P16 linear servos. I'm using the P-16P 50 mm stroke, 22:1 gearing with a Linear Actuator Control Board, which provides adjustment of throw, speed and accuracy:



Physical installation is simple. I used one of the redundant Cent exhaust boxes with a machined pivot yoke. It needed a bit of care to avoid fouling the traverse motor and I'll need to relocate two of the Motion Pack boxes flat on the hull floor, which is easy enough.

The tricky bit is locating the two pivot points but you can get close on a scale plan and the Control Board provides the fine adjustment to preserve the -10/+18 deg elevation range of the real Cent:









This solution is much more precise and stable than the rotary servo and more responsive than the original leadscrew, so I'll stick with it.

Regards.

Stephen

[Adrian Harris]

Up at the van again Stephen

The addition of a bell crank might mean you could have the actuator flat in the base of the turret. I don't know how that would affect the bounciness of the barrel during manoeuvrers but it would mean you could place the turret flat on the ground rather than needing some kind of stand, especially with the number of turret bins on the Cent.

Adrian

[Fabrice Le Roux]

Stephen,

Very nice. Looks like a much less sloppy arrangement.

Looking ahead, will the responsiveness/latency of the new set up help with your experiments with the Gun Stab system?

Given the robustness of the new support brackets, would relocating the barrel-bounce damper parallel to the P16P simplify the gun-mount hardware?

Kind regards
Fabrice

[Stephen White]

Completing some more mantlet detail while waiting for some bits for recoil and elevation.

Turning the .50 cal Browning Ranging Gun barrel:



I'm using 2mm fibre optic for the flash, so the 12.7mm bore, scaled to 2.1mm, is fine.

For the .30 cal Browning coax MG, the scale bore is 1.26 mm, so I've had to drill out the barrel to 2mm but leave a small length at the muzzle at scale diameter. Drilling the cooling sleeve and assembling the parts:





Paul Scott's restored ARN 169064 and her original condition in Vietnam:





Painted and mounted:




Then added the triangular deflection strip at the bottom of the mantlet (which minimises the shot trap effect when the gun is in depression, as in a hull down firing position) and the mantlet cover retaining lugs around the main armament:



Regards

Stephen

[Stephen White]

A sequence showing one way of applying base coats of paint and texture to replicate cast steel armour.

1. Thorough cleaning of components with a degreaser such as UPOL System 20 Degreaser:



If necessary, a light sanding and/or use of a steel wire brush in a rotary tool is used to remove unwanted material.

2: Priming: etch primer such as UPOL Acid 8. Apply as thin a coat as possible to all surfaces and then assemble components, fill any gaps and cover any visible fasteners with a filler such as Milliput. Apply weld detail using Milliput (although I also use a fabric paint for much finer detail).

3. Texturing: two stages, first is to apply a random pattern using a round burr in a rotary tool. Run the drill at low speed and bounce the burr over the surface in a random pattern. This chips the surface lightly:









I then sometimes re-apply prime to cover fillets etc and check the surface:



Having produced the "troughs" I then use a high build primer to create the "peaks". I spray a small area, lightly, then stipple with a short haired brush:



Before:



and after:



A light sanding will remove any unwanted high points.

4. Basecoat and sealing: I then apply the basecoat. There is a plastic modelling school which believes in all sorts of pre and post-shading, in colour modulation and a hundred other gimmicks. I prefer to apply a basecoat of authentic colour, matched as closely as possible to the original. Weathering can come later. If available, model acrylics are fine and go a long way with an airbrush, although for the Cent, I had the paint prepared by a car restorer who matched original paint chips to get the Australian Olive Drab Lustreless of the original:



I then seal the acrylic basecoat with an acrylic varnish such as Citadel Purity Seal and allow to harden off over at least 48 hours. If you use acrylic as a base, it makes it much easier to weather with enamel based products and especially oils as they can be removed or adjusted without damaging the underlying basecoat.

Finally, here's a puzzle. Why does this cast Centurion component have a regular pattern of circular marks?



Hope this is of interest, in view of a couple of recent posts.

Regards

Stephen

[davidwilkins]

Hi Stephen,

Brilliant work on the texture of the mantlet very inspiring. Thanks for such a detailed instalment on this subject, I will probably go for this system of the base coat in acrylic and then seal it on my next model. As you have pointed out you can play around afterwards without damaging the base work.

Regards

David

[Adrian Harris]

Many thanks for taking the time to document your methods for texturing, I know how much time this adds to a simple task.

It looks like I'll have some free time next week so I should be able to get your recoil timing changes sorted out.

Adrian.

[Fabrice Le Roux]

Hi Stephen,

Re circular marks on Paul's Cent mantlet.

Very mysterious. And we do love a mystery! Looking back at all the photos of ARN 169064's mantlet, it seems a bit of an oddity. I have pored over all the photos I can find (mostly your reference shots!)and compared them with other examples.

Some features appear on most mantlets: the principal parting line/seam usually can be seen horizontally bisecting the mantlet centered on the main gun aperture. The seam therefore typically runs across the lower third of the Coax MG/RMG boss. In some examples casting numbers are seen on the top or bottom surface of the boss. Some castings have both. Paul's mantlet has none on the boss, but in some photos there seems to be indistinct or damaged casting numbers on the left hand (looking forward) front surface of the mantlet. Interestingly the repaired penetration is on the same side of the turret.

The circular marks are not limited to the MG boss, but are found on the cheeks of this particular mantlet.

ARN 169064 Mantlet LH CU

Again no other similar example has come to light.

First explanation. Moulds will often have gates and vents cut to permit the even flow of the molten steel and to allow the escape of gases which might otherwise become trapped and create voids and weak spots. However the circular marks are evenly spaced and too numerous in this case.

Second explanation. The circular marks are cut-off supporting pins that held frangible cores in place to create voids within the mantlet casting. But each mark appears to be about 1" to 1.5" across, evenly spaced even where there are no voids, and with a clear circular lip or groove and often a slight central depression. They do not look like they have been cut off, nor ground back.

Which leaves two entirely speculative explanations to consider. First that the mantlet has been reworked and the marks were made after casting by a rotary machine tool of some type. Or secondly that the sand mould was tamped (packed firm) with a wooden tool that had slightly protruding dowel at its centre which left indentations in the sand and hence the raised marks in the casting. Given no other examples have this feature, it seems unlikely that the master pattern was itself the source of the flaw.

Fortunately, unless you are modelling ARN 169064, omitting this artefact is wholly acceptable!

cheers
Fabrice

[Stephen White]

Perfecting the sound, elevation and recoil has been a long haul but they're finally sorted.

Thanks to Adrian for his MG Splitter Box and for writing some code to synchronise the 3-round Ranging Gun burst sound with the LED on the .50 flashing the three rounds. Thanks too to Mark and Dennis for good advice when it was sorely needed.

This video shows the external view, I'll post the "workings" inside the turret next. Now back to bashing metal.



Best regards

Stephen

[Stephen White]

This is the elevation and recoil system from the inside:



Regards

Stephen

[Frank Breitenbach]

Hello Stephen
A realy perfect sound!
Regards
Frank

[davidwilkins]

Stephen,

I have really missed your updates over the past few weeks but the wait was worth it absolutely brilliant job on the recoil and sound effects, I am so jealous.

Regards

David

[Graham Hough]

Fantastic model and great sound effects. I really like the details on the mantel texture, excellet. Can we get our German friends to make a sound track of radio messages too, Sam?

[Stephen White]

Thanks for the kind comments.

I was admiring James Tzeliki's early Tiger, one of the outstanding models at TankFest and, in discussion about the place of rust on our models, he told me about a product called Scenic Rust. I've been known to sound off about how inappropriate rust is in most cases on operational armoured vehicles, especially on tracks, but the Cent does have very particular rust and scorch patterns on the exhaust manifolds. It's a very distinctive vehicle characteristic. James was kind enough to send me a kit and I'm sold on it.



I'd started the pattern using acrylics and pigments but the exhausts were still not convincing and lacked texture:





Scenic Rust is easy to use. Mix a paste of powder and binder, apply, leave to dry, apply developer and wait for eight hours. Results:









And the steel locally manufactured Vietnam track guards:



and bins:



Thanks James.

Stephen