Chieftain MK3 Build

[John Clarke]

David, (My opinion)
Agree, always love to see the suspension in action. but
I'm not a fan of missing bits either unless it's period, Tiger's with purposely missing front road wheels for the Russian winter or the perfect example, Stephen White's Cent adapted to historical harsh environment.
Missing bits or heavy battle damage models, I always think they are reserved for the Static Brigade.
Who wants to see a limping model tank traveling around and coming back after that, abused

I haven't fitted my bogies due to the weight, knowing I'd have to move the hull round several times on the bench, it sits on a little wheeled dolly trolley which allows with a little effort a 180 degree spin.

I don't know if the Bogie geometry is correct or not, probably wouldn't understand if it was explained to me either.
Early on, other modelers tried to get more "correct" travel by hollowing out the bogie frame tunnel, I did a couple of simple things including extending the tie rods about 10 mm, that helps prevent the springs from falling out when the bogie is not under tension. (Track removal)
Not sure what the final outcome will be.

On a serious note, I believe some Chieftain builders have experience scrubbing on the inside of the road tyres from the bolt heads on the shirt brackets.
Beware.
Another one for Adrian

[Adrian Harris]

[David Battson]

Compared to the real thing, the front face of the kit suspension housings appear a little tall and the side cut outs too big. To improve the look, the top surface was lowered by cutting it down on a slope at right angles to the hull side until it just met with the outer top corner of the bump stop. The centre sections were then widened by the addition of half crescent shaped inserts on either side and blended in with filler.
To avoid any issues with the wheels running close to the kit bazooka plate support arm brackets and fixings, I decided to replicate the look of the real thing and made six short support arm mounting brackets. The brackets were embedded into the side of the suspension housings and will be blended in with filler to give more of a welded look at at a later date. The rest of the arms will also be made up later, once the mudguards are finally fixed in place.
.

Bovington

suspension unit.jpg (14.66 KiB) Viewed 6071 times

Bovington 1.jpg (90.77 KiB) Viewed 6071 times

Front suspension unit

Bazooka plate support arm bracket

Rear suspension unit

Rear suspension unit

[Charles A Stewart]

Attention to detail, David, brilliant.

Now wishing I could put mine back in the box and start again, say five years later. Obviously that's not going to happen, too far in; Totem program could be a possibility in the future.

Great insight to the build.

Cheers Charles

[David Battson]

More work to finish off the suspension units by adding the central strengthening rib and return roller housing. The roller housing was re-profiled and a 'D' shaped dummy bolting flange added.
The look of the inner face was also improved by grafting on a 5mm thick strip of aluminium sheet to the lower edge. This gave enough material to create the correct bevel profile to the bottom edge and add the dummy swing arm bump stop bolt details. The outer edges of the unit were thinned down locally and weld lines cut to give more of a fabricated appearance.

Strengthening ribs

Suspension unit side

Suspension unit outer face

Suspension unit inner face

[John Clarke]

Awesome work David, at first when I saw the initial pictures of the bogie frame I thought you'd cut too much off top flange, not allowing enough space for the bolt heads, but the later post picture shows the chamfer along the top of the spring housing allowing the flange to "grow" back again. The detail is truly amazing. Changing the idler bearing mount and addressing the support webs for the shirt brackets. If you were to paint the changes there'd be very little left of the original model bogie frame surface.

Not sure how you do it. Would you dial in and make the six same machined cuts, one frame after another?

Or will you make each one independently?

Keep it up, I'll be eagerly waiting for the next installment on this most excellent build.

This sort of work on my model will be left as "Model Warranty Standard" .
Something the next owner could possibly improve on, "To make it his own".
(Car salesman speak, on an unfinished project)

[David Battson]

Hi John,
Many thanks for your comments and interest.
I find that the most time consuming part of machining is more often than not, setting up a cut rather than actually making it. So wherever possible work is done in batches to minimise set ups, rather than make one item start to finish and then move onto the next. I don't have CNC, so things like the rollover curve between the front and upper surface was created by cutting steps at 1.0mm or 0.5mm vertical intervals and then filing the surface smooth.
David

[David Battson]

Next up to be fitted are the suspension swingarms, which are a nice aluminium casting with a brass bearing insert. The bearing insert finished flush with the back face of the arm however, allowing the rear of the swingarm to scrub across the inner face of the suspension housing as it moves. To improve freedom of movement, the back of the swing arms were trimmed down to give space for the addition of a new rear bearing and shims. This mod provided a useful overall clearance of 3mm between the swingarm and the housing, which should help reduce the possibility of grit or sand getting jammed between the surfaces.
Any bearings that seemed a little too loose in the swingarms were bulked up with a light knurling to give a closer fit.
To finish off with some details, the bump stop bracket was re-profiled and hollowed out and an insert detail added to the back of the axel, to reflect the look of the real thing.

Swing arm additional bush and shims

3mm swingarm clearance

Brass bearing

Swingarm rear

bump stop bracket reprofile

Chieftain swingarm

[John Clarke]

Nice detailing Expecially enjoying the pictures, looking forward to see how you deal with the spring units

[David Battson]

Looking at the return rollers, the inside face of the kit parts are concave in long section. Whilst this profile was correct for an early MK1 Chieftain, by the time of MK3 and onward the profile was much more parallel sided and included the distinctive protective lip over the front face of the tyre. To improve the look, the easiest approach was to turn up a new wheel from scratch rather than try and modify the kit piece. A centre insert was added to bring the wheel fixing nut proud from the inside face and the axel shaft adapted to take a closer to scale M5 nut rather than the kit M6.
To address the track horn clearance issue picked up on other builds, I reduced the diameter of the return roller centres to give the required clearance rather than face the task of trimming down the horns on 200 track links.

return roller profile

comparison in progress

insert

m4 shaft

finished comparison

Finished return roller

[John Clarke]

Beautiful workmanship. I might just say "wow" from now on.

But I do worry.

I worry, do you have a big enough box for the discarded items, if not, send them to me

There's another obvious question, but I dare not ask

And the Tracks, no biggy, once you get into it. I think the horns are too tall/wide anyway and there were different shaped horns on the originals too.

[David Battson]

Hi John, thank you for the comments.
I can’t find the measurement I took, but seem to remember that the height of the kit track horn was actually very close to the real thing. From the return roller drawing it is evident that the diameter of the axle shaft on the real thing was quite small. Rather than grind the track horns down or wait for things to wear in over time, I thinned the walls of the return roller sleeves down as much as I dare (to about 0.8mm) to give some clearance to the track horns. Hopefully there’s still enough strength remaining.

Road wheel hubs - Comparing the kit piece against the drawing, there were two areas of the road wheel hub I wanted to improve.

Firstly, the ‘nose’ of the hubcap should be in line with the outer wheel rim, whereas on the kit the hubcap protrudes by about 8mm beyond the wheel rim. To improve the look, I re-profiled the hubcap cone angle to 45degrees and slightly reduced the height and diameter of it’s base. This reduced the effective ‘height’ of the hubcap by 4mm. To complete the job and bring the nose of the hub cap flush with the rim, a 4mm spacer was added to the front face of the wheel mounting flange and blended in with filler. Hopefully the extra thick wheel mountings won’t be too visible from underneath. A corresponding 4mm was taken off the axle shafts to bring the road wheel positions back into their original line,. The oil filler cap was made by trimming down the head of an m3 countersunk hex screw.

The second area for improvement was the back of the wheel hubs which are surprisingly on show with Chieftain, for the front wheels at least. To improve the look, the RS bearing was hidden by the addition of the sealing ring and back plate detail. The overlap between the wheel hub and back plate is kept to an absolute minimum to stop anything from getting caught between the two surfaces.

David

Drawing

Wheel hub.PNG (347.33 KiB) Viewed 5420 times

Hubcap comparison

Original kit piece

original wheel hub 1.JPG (79.41 KiB) Viewed 5420 times

Axle back plate

Completed wheel hub

[Charles A Stewart]

David, all I can say is that I am very impressed by what you are doing and I will pre-empt John:- WOW

Cheers Charles

[John Clarke]

Wow, brilliant workmanship David.

Hey Charles that Kylie's and my saying you've used there.

Now complete, that suspension unit just needs a nice varnished mahogany plinth.

I'll have to agree to disagree on the track horns, the shape and size varies from what I've seen. With the most common being the sharper rounded type. My tracks came with horns that have a flattened top, which were rounded after clipping and shaping.

Scale wise, the model track I have is about 1mm wider than scale, which is a good thing.

Less ground pressure

They'll only be one winner between steel track and alloy idler

Will you be hollowing out the horn roots? I'm tempted to do just the spare track pieces.

SAM_149511.jpg (220.72 KiB) Viewed 5337 times

[David Battson]

Finishing off the suspension build with the two front units. Aluminium bocks were grafted on to make up the shock absorber housings and bump stops. The kit shock absorber arms were reused, tapered down and thinned to offset the fork like the real thing. Whilst not really an issue for the original kit unit, the track links run very close to the top corner of the modified unit and so the track deflector guards are must have items and may need to be remade in steel if they get to see too much action. Still very much work in progress, with more bolt and weld detail to finish off, but enough done for now to move on to the next area for improvement.

Front LH suspension unit

Front LH suspension unit.JPG (100.3 KiB) Viewed 5147 times

front LH suspension unit

Front LH suspension unit

All four swing arm drop link brackets were made up at the same time, cut out from an aluminium disk turned down to the shape of a movie film reel.

Swing arm drop link brackets in production

This picture from a mk1 Chieftain shows what can happen if the track deflectors are omitted from the real thing. Also is that yet another different track link design for your picture gallery John ?

Mk1 Chieftain track link and return roller