Scratch build SDK.FZ 251 / 23 Ausf D Recce vehicle in 1:11 s

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Postby Sub » Mon Oct 04, 2021 4:32 pm

Hi.
Re the above,
Now that i have only 1 scratch build on the go i have started the above vehicle, its an up armoured SDK.FZ 251 Ausf D halftrack which was fitted with a Puma 234/1 turret for reconnaissance purposes housing a KWK 38, 20mm Flak cannon and a MG42 Machine gun.
It was approved for manufacture and deployment late in the war and not many actually made it to the troops due to the fall of Germany, so its quite a rare thing.
It will be built from what i have available plus materials, plastic card, brass etc.
It will be at 1/11 scale, a good size to use off road but not tooo big...and i can make it very robust etc.

Would there be any interest on the forum at all ?.
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Postby 43rdRecceReg » Mon Oct 04, 2021 7:30 pm

Do continue :thumbup: Personally, I always approve of folk who can magic things up from flatpacks, offcuts, hobby detritus, and things that just 'come to hand'. The improvisation (necessarily) involved; the acquired expertise; and lateral thinking can all serve as an inspiration to builders here on the Forum. :) At the same time, a 1:11 scale model is likely to be unique here. :D
Going by your success with earlier challenges, this will be worth following.
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Postby Sub » Mon Oct 04, 2021 8:43 pm

Hi Mr 43rdRecceReg.
Thank you for your reply, at least i now know my PC is working. :haha: .
As there appears to be little interest, i wont bother with a build log, i will just post a few pics for your personal delight and delectation along the way.
Here's a pic of the scratch built turned brass PWK 38 2cm barrell.
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Postby Sub » Tue Oct 05, 2021 3:48 pm

More KWK 38.
Some with and without the removable magazine and one in the mounting of the Hangelafette turret with mount and optic and manual sights.
Still a work in progress.
The vehicles full title is a Hangelafette 38 Auf Mittlere Schutzenpanzerwagon for those intetested.
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Postby Estnische » Thu Oct 07, 2021 2:18 am

Love your work with brass tube Sub. Sometimes forum members don't reply, but that doesn't mean they aren't watching with interest.

Please keep posting build photos - as Roy said, sometime, somewhere it will motivate others to modify or build something different.
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Postby HERMAN BIX » Thu Oct 07, 2021 7:22 am

Hell, I'm watching for sure !!
Way I see it is that anything done in any larger scale could be done in a smaller scale too.
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Postby Herr Dr. Professor » Thu Oct 07, 2021 4:18 pm

Gee, miracle worker: I am watching. You're w-a-a-y beyond my skill level, but I sure do enjoy seeing your photos and explanations.
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Postby midlife306 » Thu Oct 07, 2021 6:37 pm

I’m watching


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Postby Sub » Fri Oct 08, 2021 2:07 pm

Hi chaps,
Many thx for your intetest and comments, they are very much appreciated.
Onto the front axle.
After studying various photos and models of the original axle i decided that at scale this would be a weak point for a model that will be used primarily outdoors in the rough so i decided to deviate from the original design and make my own version of it, much, much more rigid and stronger.

The original is a single solid beam axle with a large inverted leaf spring mounted to an upper pivot point for articulation, i decided this was the weak point as a lot of leverage will be place on this point as the axle tries to move for and aft on the model so i moved the pivot point lower to allieviate some of the leverage, i also did away with the leaf spring and opted for dual coil springs mounted onto the upper beam of the axle and fixed to a full vehicle width mounting beam bolted to the chassis, this would make it very secure.

This axle will be a solid beam articulating axle but with an upper and lower beam for strength.

I prepared a scale drawing of the axle that i had in my head and it looked like it would work so i decided to make it from some rectangular section brass stock thay i had in my metal store.
Sorry for all the above splather but thought it neccesary to explain why i deviated from true scale and a picture paints a thousand words so here goes.

First pic of the brass i was using plus one beam already made and a pic of the drawing.

Second pic shows the steering knuckles made from brass and 4mm steel wheel stub axles

Third pic both upper and lower beams bolted togethet with steering knuckles attached and lower pivot point on upper beam, also steering arms fitted to the steering knuckles with individual adjustment for each knuckle ( more on that later )

Also lower coil spring mounts can be seen on the upper beam.
Just for informaripn, after each beam was cut and bent and soldered in place one end was blocked up and each beam was filled with resin to make it a solid structure and to stop the section from crushing when the bolts were tightened or some of the joints opening up.

Phew!!! Thats enough for now.
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Postby Sub » Fri Oct 08, 2021 5:12 pm

A few more pics.
First pic ,
the complete axle with the upper chassis mount and springs in place, note that with the springs fully extended the pivot mount will not engage, this is by design as when the pivot mount is engaged the coil springs are already under slight compression, this is to stop them popping out from the upper or lower mounts when the axle is fully deflected either up or down.

Second pic,
axle engaged in the pivot, the spring upper and lower mounts have been turned down in the lathe so that they fit approx 3mm inside the spring, again to make sure they are securley located on their mounts and cannot move when in use.

Third pic ,
a better view of the spring mountings.

Forth pic,
close up of spring locating
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Postby midlife306 » Fri Oct 08, 2021 7:03 pm

Blimey, I love the subtle re-engineering


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Postby Herr Dr. Professor » Fri Oct 08, 2021 8:32 pm

"[W}hen the pivot mount is engaged the coil springs are already under slight compression; this is to stop them popping out." If I have any sense of mechanics, the slightly compressed the coil springs will also stabilize the vehicle as it moves.
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Postby 43rdRecceReg » Fri Oct 08, 2021 8:40 pm

:clap: Small scale engineering at its enviable :thumbup: best
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Postby Sub » Fri Oct 08, 2021 10:52 pm

Hi,
Thx,
Mr Midlife and Mr RecceReg.

Herr Dr, you are most correct in your thinking, adds pre load.
Thx for looking in, appreciated chaps.
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Postby Sub » Sun Oct 10, 2021 4:36 pm

Hi.
The front axle now just needs the upper chassis mounting beam cut to fit the tapering front of the model and the 2 long steering knuckle pivot bolts shortening and it is finished.

Moving on to the wheel hubs.

As mentioned earlier i am making this model from various items i have left around from previous build or items not used and in the parts bin.
The wheels i have chosen for the front wheels of this model are left over from a UN 6 wheel drive APC i made a while ago, 6 wheels were changed for WPL units and the original ones kept for further use.
The Tyre pattern on these is identicle to a real SDK.FZ 251 so off i went, although the wheel is slightly wider but the correct diameter for my model.
The issue with the wheels is that they did not have a through axle and were only pushed onto a stub axle to hold them on, this would not be good enough for this model so i hollowed out the wheels in order to fit some brass wheel hubs with phospher bronze bearings that i made that would be glued into the wheel giving it a through axle mounting and secured onto the stub axle via a 4mm Nyloc nut.
These wheel hubs will be recessed into the wheel itself so that the nut and axle do not protrude beyond the face of the wheel.
I then turned up some aluminium wheel centers that matched the full size vehicle, these are hollow in the inner center to fit over the nyloc nut and locate into the recessed brass wheel hubs and can be prised out to remove the nut and wheel.
Pics should make this clear.
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Postby Sub » Sun Oct 10, 2021 4:37 pm

One more pic.
Just need to alter the studs from 12 bolts to 8 (maybe)
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Postby Sub » Thu Oct 28, 2021 4:57 pm

Hi Folks
More insane ramblings.
The scale of this model is 1:11 scale, quite an odd one i admit but there was method behind my madness, in 1/16 scale to me personally it would be too small and fragile and the main reason was that it would be built from what was available to me.
I was looking around for a suitable doner for the wheel arrangement, that being overlapping wheels and a suitable spacing between them, the only thing i could see that would be any where near was a Tiger 1 hull, i measured every thing up and the axle spacings and wheel diameters and the hull tub width were spot on for 1:11 scale, so thats how it ended up at 1:11.
The hull was too long, the gearboxes were wrong and in the wrong place, the wheel configiration was wrong, it had too many axles and the wheel width spacing was wrong...all of which i thought i could overcome with some lateral thinking and jiggery pokery.
A very good friend of mine had an old Tiger hull surplus to requirements so he graciously donated it to science (Cheers Si).
I removed the wheels, axles,suspension, gearboxes and all the internal mouldings, battery tray etc,etc,.
I cut 2 inches off the front of the hull and 1/4 inch of the rear of the hull and removed the idler wheels.
All i had now was a plastic tub.
As we all know the Tiger hull slopes from front to rear, this was no good for my purpose as the Hanomags hull is level from the rear up until it reaches the drive sprocket, it then goes up at a slight angle as it goes over the sprocket.
I cut off both sponsons from the tub and levelled off the hull from the rear up until the point where i decided the gearboxes and sprockets would be placed and angled this part upwards,
I had decided right from the start that the entire body of the vehicle would be removable in one complete piece, only leaving the hull tub and front axle together for easy maintenance etc.

The Tiger tracks were of no use due to their width and niether were the gearboxes so these were returned to my friend.

I calculated the Hanomags outer hull dimensions which gave me the amount of room that i would have to fit a set of tracks into that would look right from the side and not stick out past the hull line nor rub up against the inner hull wall.

I searched my spares pile and located a brand new set of Panther tracks, these looked promising so i measured them up and they were spot on, i also had the sprockets too.
The Tiger has short shaft gearboxes but the Panther needed long shaft gearboxes and i just had a pair that needed a little TLC so these were rectified ( drilling a loose gear and pinning it to the shaft ).
New holes were cut into the side of the hull for the output shafts after measuring all the axles and wheel diameters etc.
I fitted the sprockets to the gearboxes and measured where they needed to be placed inside the hull to give correct wheel allignment and made a 1/8 inch Aluminium plate that both gearboxes were bolted to, this was in turn bolted to the hull floor when i was satisfied with its position.

I removed the front 2 axles and suspension parts from the hull tub and replaced the rest, now i had 6 each side.
The adjustable idler wheel on the Hanomag is the same diameter as the rest of the road wheels so i worked out where that needed to be and also its axle is slightly higher that the other road wheels so this was catered for at the same time.
I decided to fit a 4mm dia solid axle into the hull running full hull width for the idlers and would build some form of tensioner system onto it when i had got all the wheels in their correct places and spaced right.

The Tiger wheels were turned in the lathe to get rid of the Tiger details.
The Hanomags wheels had holes in them, the outer sets have 8 equally spaced holes on a pitch circle diameter and the inner ones had a 6 hole PCD, i calculated these and set about drilling the inner and outer wheels accordingly, these looked ok when done, now all i had to do was to get the correct wheel orientation and wheel widths to fit the tracks,sprockets and idlers that would allow the track to rotate without any binding or fowling, after much experimention and the addition of spacers and cutting axles down to suit it was all fitted and rotated without any problems.

Now to make the idler wheel tensioner system.

Sorry for the long boring, explanation but thought it necessary as it would make the coming photos more understandable

Photos to follow...
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Postby Sub » Fri Oct 29, 2021 10:35 am

Hi,
A couple of pics showing the tracked section that i came up with, hopefully all the previous splather i was on about now makes sense.
In order to disquise the panther sprockets and make it look more scale true to the originals fluted sprocket i looked at the original Tigers idler wheels, i checked the diameter and they were perfect to fit over the panther sprocket just leaving the teeth visible and were nice and snug where the track overhang sits where the sprocket engages , obviousy way too wide but i decided to cut them in half and thin them down a bit and glue a half reversed onto the panther sprockets, they came out quite well i think.
Still needs more work on the wheels.
Next rear idler wheel tensioner.
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Postby Sub » Fri Oct 29, 2021 5:38 pm

Hi,
Rear idler wheel adjustment completed.

1/16 thick steel bent to 90 degrees to the height of the axle and drilled to bolt to the hull and for a 2ba brass bolt to pass through with 2 nuts either side of the steel bracket, a further 2 ba nut soldered onto the end of the bolt head which the 4mm axle is a good snug fit with no play, to adjust the tension on either track just undo and tighten the corresponding nuts, which moves the axle and lock it up.
Prefer this than the original set up as its inboard the hull away from any muck, mud etc and is so easy to adjust, and its so simple. ( i operate the K.I.S.S. system where i can)

It may look a bit agricultural to some but this design has been in use for decades on motorcycle rear wheels to adjust the chain drive and it will be ok for years of use.
Few pics.
Cheers.
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Postby tankme » Fri Oct 29, 2021 6:58 pm

That track adjuster is the same concept I use in my 1/6th scale tanks and it works great. Nothing wrong with that design. My old Suzuki SV650S worked that way to align the rear wheel.

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