My Beaut Aussie Cent

[Stephen White]

Dave, all I can say is that I've enjoyed every step of the way, learnt a lot by trial and error, stolen a lot of good ideas from more capable craftsmen than I, not all from this part of the hobby either, and have been helped enormously by the members of this great community. I suppose the best attitude is - give it a try.

One little detail which is so curiously British - the engine deck padlock hasps. It was apparently thought necessary to provide a means of padlocking the transmission decks, not that I suspect it was ever used:





The rail mountings for the hull were installed and painted:



I then set about making the resilient rails themselves. The master is in aluminium and I've used a medium hardness two part rubber compound:







There are fifteen separate sections, so I chose the make the master to the size of the largest sections and I'll cut the others to size. Slow process with a one hour de-mold time.

Meanwhile, I machined the blocks on which the front sections were mounted. On the original Cent, these are mounted on a one inch thick wooden spacer, to raise them:



I chose to machine the eight fixing studs and then used a rotary cutting tool to create the simulated wood grain:







Just waiting now for some 10 BA countersunk set screws for the mounting studs.

Thanks for looking.

Stephen

[Kevin Hunter]

I'm running out of superlatives Stephen. Your eye for "useful" detail and the apparent ease with you replicate same just amazes me.
Great work, as always, and looking forward to next instalments.
Season's greetings
Kevin

[Stephen White]

Thanks Kevin, I always appreciate your interest.

Continuing with the resilient rails, I've completed moulding the smaller sections:



I used a small slitting saw in the Proxxon drill to cut the modified sections which were applied when the Type B barrels replaced the Type A. A section was removed to accommodate the fume extractor. Later, the rails were supplied with the modification but 064 was early enough for the mod to be applied in service, resulting in some rather crude cutting marks which I've tried to replicate.

It was then that I noticed my less than deliberate error - the padlock hasps for the transmission decks are on the wrong side. So, remove them, insert a blanking plate, swear a lot, re-do on the correct side:







Next to make the master for the front sections. I've used a wire disk to create the texture:



Moulds making next.

Regards

Stephen

[Stephen White]

Error number two - the front rails were fitted to a one inch thick wooden spacer, which was then bolted with countersunk head set screws to (in the case of 064) eight bosses welded to the hull sides. The rails came in two sections. I mistakenly cut the wooden spacer in two and shaped it to the rail fittings. Oh well, out with the CX5 sculpting clay to fill the gap:






Resilient rails complete. They're a bit starkly black and could probably do with a coat of dark grey to tone them down a bit.









Best regards

Stephen

[Stephen White]

Seasons greetings one and all. Christmas came early here with a set of superb engineering drawings of the External 100 Gallon Fuel Tank by Allan Bowers. Paul Scott and Mike Cecil have helped with measurements and photos, so it's been an international collaborative effort, spanning three continents:





Seeing the digital 3D model rendered is really inspiring:









A couple of interesting features have emerged in preparing the drawings. According to Paul, these marks appear all over his restored tank. They are apparently left when the steel was tested for hardness during manufacture:



We had some good discussions about whether the well in which the fuel filler and gauge sits slopes down towards the front. Paul measured it and it does. I suppose this was designed to allow spillage to drain away:





One most surviving Australian Cents, the infantry/tank telephone is mounted horizontally on the fuel tank:



On 064, in service in South Vietnam, it was definitely mounted vertically:



The change in mounting is undated and the log book for 064 doesn't reveal when it was changed but it involved manufacturing two mounting plates and modifying the conduit which protects the cable between the hull and the telephone box. I'll be making the vertical mount as in service in SVN. The device was useless anyway - rain got in and interfered with the tank intercom. In my experience, the infantry were very wary of it owing to the danger of the tank going into high reverse if shot at. I've known them prefer to fire a rifle round at the turret to attract a commander's attention, which was bad news for any sleeping bags stowed in the bins or basket:



I'm starting with a maquette in plastikard to prove the design:



Happy Christmas

Stephen

[Stephen White]

I thought the definition of futile was attempting to braze or solder aluminium. From time to time, I've had a go, with zero success. Until today.

Some time ago, at the SW Model and Hobby Show, I bought a pack of aluminium brazing rods. They go under the trade name of Lumiweld but I believe there are at least two similar products, Durafix and Alutight.

The instructions require the joined surfaces to be prepared by thorough cleaning with a stainless steel brush to remove oxides. The surfaces are then heated to about 350 deg C and a rod is applied to the hot surface. Once the join is tinned, a steel abrading rod is applied to break the underlying surface tension and the molten alloy then flows smoothly and the join can be made. More alloy can be applied to build a fillet if necessary.

My first attempt succeeded but using a small Proxxon torch took about twenty minutes to heat to the required temps:



Today I went nuclear and bought a canister of Map Pro gas and a torch which can heat to 1600 deg C if necessary. I prepared the butt join with a chamfer and cleaned it as instructed. The new torch worked in a couple of minutes, the alloy flowed perfectly and I was able to turn the piece and braze the other side. Once cooled naturally (no quenching), the join could be ground flush. It's strong and neat. Result:







It remains to be seen whether I can assemble the external tank this way without subsequent joints undoing the previous ones. If it were brass, resistance soldering would overcome that problem. Although aluminium is such a good conductor of heat, I'm banking on being able to localise the heating to preserve the existing joints sufficiently for the assembly to stay together, maybe with some judicious use of heat sinks.

I'm sorry if this is old hat to the more experienced engineers - I'm still having a kid in a toy shop moment. Well, it's Christmas after all.

Season's greetings to all.

Stephen

[Chris glover]

Hi Stephen
Wouldn't it be easier to weld it?
Chris

[Stephen White]

Completed the basic maquette to prove the design. It isn't a true copy of the final thing as the styrene isn't the correct thickness but it's close enough. I decided to add a couple of full depth internal webs to support the front and back and form the sides of the refuelling well but I may not bother on the final tank:





Trial fitting:









Styrene is such a pleasure to work with and so quick, that I could be tempted to use the maquette on the tank but it's not accurate enough for my purposes, so it will sit on the shelf gathering dust.

Happy New Year to all.

Stephen

[simon_manning]

lovely coat of paint, weathering, stick it on!, its all in the mind, regards simon.

[Derek Attree]

Hi Stephen
That is a fine bit of work as Simon said its all in the mind .
Thats going to be fun to build in alloy plate. I woud have gone with brass
sheet and silver solder of different tempratures so it doesnt all fall to bits
when you get to the last bits.

Not that its ever happend to me well maybe once or twice

Happy new year building.

Regards

Derek

[Stephen White]

Derek, Simon, thanks. Derek, I actually ordered some mild steel blanks but failed to calculate the weight, which turned out to be prohibitive and brass would have been the same. I'm concerned about the effect on the rear hull plate to hang a heavy fuel tank from it. I chose to go with aluminium to save weight and minimise the effect on the tank's CG.

I suppose there is a shade of "fools rush in" about what follows. Having trialled the Lumiweld alloy brazing rods successfully with a flame thrower of a torch, I thought I'd give it a go. Progress so far:












Observations:

- the technique is as simple as the manufacturers claim, as long as you follow all the steps, ie thorough cleaning with a stainless steel brush, heating the parts evenly but not applying direct heat to the brazing rod, at melting temp applying a fillet of alloy then making sure to abrade the fillet to remove the oxide layer and set the final joint. Allow the joint to cool naturally, don't quench.

- the joint is stronger than the pieces being joined. I've used a mole grip as a heat shunt to protect earlier joints and haven't had anything come unstuck yet.

- the 2.5mm ally plate has not distorted so far but it does become pliable. Any slight irregularities can be corrected before cooling.

- Firm work holding with wire is essential to eliminate movement when heating.

So far, so good.

Stephen

[simon_manning]

a good new year to you stephen, between you and per the build level is now at another level, manufacturing your own parts to suite, it always amazes me the speed and ability to learn that some builders have, keep it going ,regards simon.

[Iacopo Di Giampietro]

I would first like to wish you a happy New Year to all, Stephen, you and all your loved ones.
I wish to congratulate you both for your selection Bureau of detail but especially for your "versatility"! There is now no material with which you have not become master: My compliments!
Good luck and happy 2015 to everyone!

[Fabrice Le Roux]

Hi Stephen,
Happy New Year. So relieved to see you have sourced a "proper" drawing for this part at long last.
Caterpillar welds rather than continuous welds might be just as strong and less prone to creep. But then you may be planning to fill it with scale fuel, or at least VBs.
Trying to measure the temperature of sheet metal reminded me that I read somewhere that red Sharpie Pen ink (only the red ones!) goes black or oxidises at the right temp for annealing Aluminium. This was from some dentist chap in America who was building 1/24th? WWII fighter aircraft entirely from sheet metal.
Mapp gas burns hotter than regular butane, so it might be worth investing in a hand-held non-contact thermometer (now cheap as chips) to keep tabs on where all that energy is spreading. Very useful round the house too.
Keep up the good work.
Kind regards
Fabrice

[Stephen White]

Happy New Year Iacopo, thanks to you and Simon for your encouragement. Fabrice, great to hear from you and thanks for the insight as ever. I'll follow up on your suggestions. Allan's drawings have been a godsend.

I'm pleased with today's progress with the aluminium alloy brazing. I'd wondered whether there was a high risk of disassembling previous joints given the high temps needed but I shouldn't have worried. I found that if you allow each joint to cool and harden, it is unlikely to come apart when heat is re-applied. I put together the well for the filler and gauge, which involves a lot of close joints, including a 4mm base plate and there was no sign of anything coming undone, although I did use a heat shunt where I could.

The need to abrade each joint thoroughly was obvious where a couple of joints hadn't fully taken first time around. With a quick inspection and re-heating, easily fixed. I'm now confident about the major plate assemblies but it remains to be seen if small details can be brazed, where heat needs to be applied very locally.















Regards

Stephen