My Beaut Aussie Cent

[Stephen White]

Just a couple of bits of detail today. First the protective ring around the hatch locking bolt:



Then the chamfer on the undersurface of the episcope mountings. The hatches don't have any parallel or regular edges and work holding is a challenge. I tried a four jaw chuck and the face plate on the lathe without success. The rotary table on the mill only has a three jaw chuck, so no good for irregular shapes. I ended up mounting the part to the lathe face plate using a mandrel to centre it and then mounting the face plate on the rotary table. It had to be the longest set up for the shortest milling cut for a long time. Heath Robinson but it worked, just:







Regards

Stephen

[simon_manning]

very nice indeed, i am coming around to your way of thinking, buy some more tools! regards simon.

[Stephen White]

Simon, I could make do with a Proxxon drill, some milling bits, files and scrapers but somehow having the right kit for the job becomes addictive. It's all because I did woodwork instead of metalwork at school. Scarred for life.

I thought I'd tackle the driver's periscope hoods next so that they will give me the size for the periscope housings. So first a card pattern then cutting out the brass:



Soldering up the basic hood:







Adding the extensions on the sides (and I've no idea why they were fitted):








One more to go and then the periscope housings (Periscopes AFV No 15 Mk 1 in Army speak).

Regards

Stephen

[Adrian Harris]

That's a neat bit of soldering - was that done with the resistive dooberry ?

I've also found that solder definitely only wants to go where the flux has been, so you can be really sparing with it - I started applying it with a small paintbrush, and ended up applying it with the pointy end of a cocktail stick.

Adrian.

[Stephen White]

Indeed so Adrian, the very same. Good point about flux.

The resistance soldering kit is so easy to use but I still find holding the parts together the most difficult thing. Until, that is, I read about rare earth magnets. The guys who assemble brass photo etch kits use this technique and it's foolproof. I use a thin piece of steel as a base and a steel milling angle for pieces which stand up vertically and stick the brass pieces in the right place using the rare earth magnets which are so powerful yet small that nothing moves while soldering. The resistance soldering kit is operated by foot so two hands free for soldering - great.









Regards

Stephen

[Adrian Harris]

What a neat solution.

Just mind your fingers between the magnets !

Adrian.

[simon_manning]

like it, never thought of that, a simple way to free up your hands, great tip, keep the info coming, regards simon.

[Paul Morris]

Hi Stephen.

This is all such great stuff your posts are what this forum and hobby is all about mate, looking forward to a chat in two weeks see you then.
Cheers Paul.

[Kevin Hunter]

Have you thought of writing a text book for these kits Stephen? Your posts lately are excellent in showing us laymen how to achieve your amazing results. I guess you must also have an artistic flair of sorts - I've never really been a creative type.
Regarding your RSU - presume you use what I would call "ordinary" soft solder, with a lowish melting point? What sort of power output is the unit generating? I remember W=VI from school, from the pics you are stepping down to a max of 4.5v, and at best it probably has a 13amp fuse? Does it work based on that 58 watts or so or does the "resistance" in your brass sheet create more heat?
Thanks - and see you at the show.
Kevin

[Stephen White]

Two weeks to the Open Day - looking forward to it.

Kevin - the output is 40A. I'm no physicist but I can say from experience that you do need to select an appropriate voltage, or holes start appearing where they didn't ought to be.

The finished periscope hoods:







Turning to the periscopes, I discovered the Cent had:

Periscopes No 15 Mk 1 three off (driver and operator)
Episcopes No 7 Mk 1 seven off and Episcope No 8 Mk 1 one off (comd’s cupola)
Periscope binoculars no 2 Mk 1/1 (Comd sight)
Periscope sight No 30 Mk 1 (gunner’s day sight).
Plus some IR night stuff







Mike Stannard's episcopes are a good starting point and I've ordered a set for the episcopes. (Thanks for the sizing Mike):



The driver and operator had Periscopes AFV No 15 Mk 1, a very complicated bit of kit which could rotate and elevate. Paul Scott in Australia has sent me some marvellous photos so that I can attempt to replicate it for the driver's hatches, where they'll be seen with the hatches open:











Mike Stannard's Tiger Driver/operator periscope is a good starting point:



The research is half the entertainment. Hope it's of interest.

Stephen

[Kevin Hunter]

Finished scope covers look really good Stephen.
I'll get one of the electrical types to explain the RSU to me hopefully, Adrian perhaps.
Regards
Kevin

[Adrian Harris]

<- my ears burning...

I've not met one of these RSUs yet - I've only done silver soldering with a gas torch so far, but it does look much more controlled as far as where the heat is placed.

My understanding is that it's effectively a controlled short circuit, where the power passing through the resistance of the soldering head causes it to heat up, and hence it heats the metal around where it is touching.

With the power off, you can position the tip exactly where you want it, which you can't do with a normal soldering iron as the tip is either already at 300 degC, and hence heating everything up as you're trying to place it, or you apply it cold and wait 60 seconds for the element to warm up, during which time things can slip out of position.

Adrian.

[Adrian Harris]

Stephen - are you still using your dremel + wire wheel to generate the metal surface texture ?

Adrian.

[Bob Gould]

Brilliant soldering solution

[Stephen White]

Adrian - yes, I use three techniques for texture, Upol High build primer, the wire brush and a Proxxon ball milling cutter. I run it at very low rpm and bounce it across the surface. I like the look of Bob's mystery gel (Windsor and Newton Galeria Gel Medium?)

Now for the periscope housings. First three blanks turned to size (two for the driver and one for the operator):



Next to cut the angles which I measured from Paul Scott's photos. The electronic angle gauge is one of the most useful bits of kit:







Then to mill out the centre using end mills for the top section and then slot drills to cut the centre out all the way through. I finished squaring the corners with a hand file:







Enlarged the cut out underneath to allow the periscope to move in elevation:



Finally with texture:



Mounting to the hatches presents a problem. The housing has to rotate so the original has a flange and sits on a rebate in the hatch. It is retained by a very thin locking plate. My attempts to cut the latter failed miserably. I decided on a bit of lateral thinking and reversed the setup by cutting a rebate in the periscope housing and making the locking ring thicker. In order to get it around the mounting, it had to be cut in two but the two halves are held together by the hatch seating. There isn't much meat either way and I had visions of overdoing it and seeing the mountings fly into two parts but all worked OK:











Finally

I'll now make the elevating outer casing for the periscope prisms ready to fit Mike Stannard's Tiger prisms and holders which are on their way from Las Vegas.

Regards

Stephen