Jakko’s 1:35 Sherman Crab Mk. I — seeing double?

[Jim R]

Hi Jakko
That is a real tribute to your research, skill and patience. I think it is superb. You have got to be pleased. Looking forward to the next steps.
Jim

[Guest]

Me too

This still needs some bits added, mainly some kind of structure at the front, of whose purpose I’m not certain at all. Then it’s more work on the upper turret interior …

[Guest]

Great internals Jakko, looking good .

[Mickc1440]

Just had another catch up Jakko, some wonderful scratch building skills on show, a real credit to your patience.

[Guest]

Thanks, but it looks better in the photos than in the flesh, I assure you

[Guest]

The fun never stops …

My M4/M4A1 manual says there are different types of gunner’s controls in the Sherman: electric or hydraulic. Photos I found of a restored M4A4 show the electric type, but would my subject have had the same? When I showed my father the last photo I posted of the turret basket and mentioned the different turret drives, he said, “we used to turn a handwheel” — referring to his playing in this exact tank in his youth, when it was on display outside the war museum (see the start of this thread). However, he couldn’t remember if this wheel was vertical in front of him (as per the electric drive) or horizontal on the right (the manual controls for the hydraulic drive).

Then I decided to check the M4A4 tech manual that is available online, and happily, that only shows the electric type. Great, because that probably answers the question and it’s the easier one to scratchbuild. Here is what it looked like:

[ATTACH]370117[/ATTACH]

But how big is it? The hands in the photo don’t provide enough of a clue, but the manual also included the following illustration, a bottom view of the turret drive and how it meshes with the ring gear:

[ATTACH]370113[/ATTACH]

I photographed the ruler with it because that provides almost all the information needed to work out the size for your own model, if you’re stupid enough crazy enough in a mood to add it to your own model.

It may not be immediately obvious how, but notice the two bolt heads drawn on the turret ring … because there were 32 bolts on the ring, you can work out what the distance between two bolts should be on your model:

[ATTACH]370118[/ATTACH]

This because the sine of an angle in a right-angled triangle can be found by dividing the length of the opposite side of the triangle by that of the hypothenuse — thus, if you know the length of the hypothenuse and the angle, you can work out the length of the short side.

Since there are 32 bolts, the angle between them is 11.25 degrees; we need half that angle, though, to get a right-angled triangle of which one side is half the distance between the bolts and the other important side is the distance from the bolt to the centre of the turret. You can just measure that last one on your model — on my kit, the diameter turned out to be almost exactly 50 mm, so halving that gave me 25. Multiplying that by the sine of half the angle results in half the distance between the two bolts, so it just needs doubling to get the full distance. In this case, that’s 4.9 mm.

Measuring from the top of one bolt to the top of the other in the drawing found that this was nigh on exactly 20 mm, meaning all I needed to do was divide measurements I took in the drawing by 4 to find how big all this needs to be in 1:35.

But we’re not there yet! How tall is the thing?!

That’s where the left-hand photo in the manual (page 330) came in. From photos, I judged that the handwheel’s left side is pretty much even with the left side of the gearbox. Other illustrations showed its axle to be offset to the right a little, so more measuring now that I knew the width of the gearbox, gave me a diameter of about 9 mm in 1:35 scale. That, then, let me work out sizes in the photo by measuring vertically using the wheel’s size as a reference. The gearbox, according to that method, is about 13.5 mm tall and the motor housing (the round bit at the top) about 7.5 mm excluding its pedestal.

[ATTACH]370115[/ATTACH]

This is the basic shape of the gearbox, built from 2 mm square plastic rod and some 1 mm card. I quickly decided against trying to build it hollow, because getting everything square would be a nightmare. Much simpler to build a solid block and file and cut that to shape:

[ATTACH]370116[/ATTACH]

The motor housing is two diameters of tube one inside the other (the outer is 7.1 mm) with a unched disc for a top and a bit of sprue as the basics of the pedestal.

There still needs to be plenty of detail added, as well as some basic shapes, well, shaped, but I’m getting there, I’d say

[Guest]

Calling the turret drive done:

[ATTACH]370169[/ATTACH][ATTACH]370170[/ATTACH]

It’s not quite the right shape, but I can’t put my finger on where the mistake is. I suspect it’s too tall, as on test-fitting in the turret, I had to reduce the height of the round pot on top (the electric motor housing) and then also found I had made the upper half of the bottom part too tall, so I then had to saw and carve off bits on the right side so the whole thing sits lower on the turret ring. In any case, it looks convincing through the turret hatch:

[ATTACH]370171[/ATTACH]

Here is the turret basket as I have it now, with the drive in place as well as the turret switch box (the rectangular box next to the cylinder attached to the basket) that’s just visible past the drive:

[ATTACH]370172[/ATTACH][ATTACH]370173[/ATTACH]

Still to do are the gunner’s seat and the structure at the front that I still can’t work out what it is, what it’s for, or how it’s constructed …

[Jim R]

Hi Jakko
Run out of superlatives. Looks really good. Another most interesting update.
Jim

[Guest]

A bucket load of amazing detail going into this Jakko

[scottie3158]

Jakko,
Lovely additions.

[stillp]

That turret basket is a model in itself Jakko!
Pete

[Guest]

Thanks, guys, and you’re right, Pete, it is starting to feel like a model in its own right … Not that much longer and it’ll be done, I hope, as I really want to get on with the rest of these two models, but this needs to be done first of course.

[Guest]

I set about building the gunner’s seat, and when trying track down more photos of it, I found a site with extensive photos of the interior of a restored Sherman V — typical, of course, that I couldn’t find that when searching for variations on M4 Sherman interior but it does turn up for M4 Sherman gunner’s seat. Thanks, Google Image Search :rolling:

Anyway, that showed me what the unidentified structure is: a rack for .30 calibre machine gun ammunition boxes, stacked three high and three deep. And, of course, that let me build it for my turret basket, because it means dimensions are easy to get correct. Here it is, in place:

[ATTACH]370361[/ATTACH]

The gunner’s seat is also done, but leaning back a bit because it’s not glued yet. I may have to move it forward and down a little, though — the commander has very little room for his legs this way.

(Incidentally, the photos on the site I linked to above show that I indeed built the turret controls too tall so it sits too far back on my model. Not going to change it anymore, though )

I also put some stuff on the turret side wall by the commander’s seat based on those photos:

[ATTACH]370362[/ATTACH]

The holster is actually a Verlinden resin German pistol holster minus its magazine pouch, but it’s far too big for 1:35 and about the right size for the flare pistol it would have held in the tank. I also added a third seat (for the commander, like the one below), but folded down so it doesn’t obscure the view. This came from my other Asuka Sherman V, where it was spare, on a scratchbuilt bracket. I also added a cable from the commander’s intercom box to the rear (it goes nowhere except out of sight), and baseplates for the binocular case (in front of the intercom box) and the torch (behind the seat). There won’t be a binocular case in the tank because I can’t imagine it would have remained there for long The torch mounting still needs its brackets, though, and I also need to add some brackets to the wire, as well as some more stuff to the wall in general.

Nearly there!

[Guest]

The turret drive mechanism was so much fun I’ve decided to do it again!

[ATTACH]370730[/ATTACH]

The basic shape of the gearbox on the left, the motor housing on the right. I started again because after looking at the model and photos of the real tank more, I felt that what I had just didn’t look right. It’s far too tall, meaning it has to sit too far back and is obviously too far up. Using the site with interior photos I linked to above, I could estimate the height of the part above the turret ring far better: you can tell in one of the photos that the top of the motor housing is above the three screws that hold the side of the mantlet to the turret, but below the screw in the upper right corner. Measuring that distance on the model with the kit’s M34 mantlet part in place, gave me a height of 11 mm above the turret ring, and therefore a total height of about 16 mm. For comparison, the turret drive I had is 22 mm high, and that’s after I already sawed about a millimetre off the motor housing from what I had originally built.

I’ve also been slightly more sensible in construction/laminating of the gearbox now because I wasn’t quite clear on the shape when I started my first attempt, so I didn’t take the hollow bit at the bottom of the rear face into account at the time, which as you can see, I have now. I also didn’t bother with the extension at the back, because that won’t be visible anyway. Now I need to wait for the glue to dry so I can file the sides flat.

[Guest]

The replacement turret drive is now nearing completion:

[ATTACH]371104[/ATTACH]

Better dimensionally and detail-wise than the previous version, and I decided to scratchbuild the handwheel too. I had used the one from the previous attempt mainly because it was the only one of the correct diameter in my scrap box, not because it looked so much like the real thing. I now began by making a piece of 7 mm plastic tube into a ring:

[ATTACH]371103[/ATTACH]

This using a lathe, first with files to round off the outer side, then almost cut it off with the lathe’s cutting tool. The centre is a punched plastic disc, the spokes are plastic strip, with a cross cut from thin card as a backing for strength. I then puttied all the gaps, because the real thing was cast.

Still to do is the wiring on the drive, scraping down the putty on the handwheel a bit and adding the knob on the wheel. Plus, of course, sticking the handwheel to the drive. Then all I need to do is build the elevation gear onto the gun, and I can (hopefully) start painting the interior …