Bizarre event with a Sherman

[Adrian Harris]

A very odd thing happened today whilst running the BARV.

I've just put new connectors on the motors and was running it around the garden to check the wiring was OK. It slewed to a halt with no drive on one side and, when I checked the tracks, it had thrown off the outside sprocket ring on one side.

There were no bolts left holding it in place, with a couple sitting in the track where it had stopped.

I was fearing the worst for the sprocket centre but, having collected together a new set of bolts, the ring went back on and all the threads seem intact.

I can only assume that the bolts had worked loose and today was the day the last one came out.

Anyone one else ever had that happen on a Sherman ?

Adrian.

[chris fry]

hello Adrian,
so you bought the barv??, "loctite" hope you used this with the bolts you put back in, this will stop this happening again, and before you ask no mine has never done this but i do use loctite on anything that looks like it can work loose,
take it easy,
Chris.

[Armortek]

Hi Adrian

Is the sprocket bolted on with the original Armortek supplied high tensile bolts, or have "more authentic" replacements been used. These bolts are highly stressed and soft replacements could easily stretch and come loose. This would cause such a problem.


regards
Mark

[Adrian Harris]

> Is the sprocket bolted on with the original Armortek supplied high tensile bolts,

David will be able to answer but they look like standard M3 x 6 hex heads to me.

> These bolts are highly stressed

I did wonder that, but they're only held in with 3mm of thread in an aluminium sprocket centre, so I would have thought the weakest part would be the aluminium thread, rather than the steel bolt

Adrian.

[Adrian Harris]

> so you bought the barv??

I'm afraid so. I did have plans for making my own but David did such a wonderful job on this one that I couldn't pass it up.

I'll be adding my own mods to the running gear over time, so will add Loctite to anything that looks like it might need it.

Adrian.

[David Skeldon]

Hi,
I got the Sherman second hand ,So do not know the history of the bolts,

David

[Fabrice Le Roux]

Adrian,

Apologies for picking up thread late.

FWIW When I detailed my M32 sprockets some years ago (The oxen are slow but the Earth is patient!) I put a small counter sink into each 3mm hole in the laser cut steel sprocket ring, but slightly deeper on the inboard ring. I considered that this would serve to centre and lock each bolt in position, preventing "creep", much as the chamfered edge of the wheel bolts on a car wheel does. I used good quality countersunk hex socket M3 bolts and fitted each with studlock adhesive. The inboard ring therfore cleared the final drive housing without further modification. The outboard ring with the shallower countersink allowed me to turn down the edge of the bolts by 0.5mm to give the appearence of scale cap screws as used on the M4A3. I added some other details based on Rich Stinchcomb's super photo ref CD (never bettered) and this is the result:

Modified Sheman Sprocket

I have run this for some 3-4 hours with no problem but I wish to emphasise this mod was not approved by Armortek and anyone copying this does so at their own risk! If you plan on playing hard with with your model, stick with the designed tolerances and components.
Cheers, Fabrice

[Fabrice Le Roux]

Just a small addendum to above post this is it the sprocket fitted filled and painted:

Finished Sprocket

The model is still unfinished, but now has working winch. It will be exhibited on the Malden and District Society of Model Engineers (MDSME) stand at Sandown Park Model Show next month if any of you are attending.
I plan on doing a detailed retrospective build account when I finish her!
Cgheers, Fabrice

[Adrian Harris]

> some years ago (The oxen are slow but the Earth is patient!)

Too true - I have pictures of it from the 2009 Armortek Open Day, to which I still refer

Yours looks a good compromise for these fixings. The only way I can see to truly replicate them would be grub screws but the only way that would work would be to thread the sprocket gear and centre at the same time, so the thread was continuous. I'm still amazed at how small the full scale parts are, given the forces imposed upon them by the tightness of the Sherman tracks when turning and cornering.

I'm off on the 2nd so may pop over to the show.

Adrian.

[Fabrice Le Roux]

Adrian,
Was it really THAT long ago! Crikey !
This is the type of sprocket I was modelling.. there does seem to be small variations even between Shermans of the same mark though.

Stinch's Vermont Sherman

Hope you enjoy the show if you make it.
cheers, Fabrice

[colin fairweather]

hi all

is it me or does it look like theirs a plate / locking tab behind each set of two bolts on the sprocket centre hub ?

colin

[Fabrice Le Roux]

Hi Colin,

Agreed. I had to take a second look before uploading that shot. Rich did the photoshoot in the rain a few years ago. The photos all show exaggerated texture as a result of glint. The flash makes it even more pronounced. In another shot of the same sprocket, slightly out of focus, you can't see anything definate. I came to the conclusion that the rectangular marks are not something rusted into the surface, but some artifact of the casting process.

This pic, taken at the Cobbaton collection, in slanting direct sunlight, shows that the nuts on the centre ring of studs were locked with spring washers. At least at the end of this vehicle's service life!

Cobbaton Sherman Idler

Just to confuse things further I found a single photo of a Sherman type sprocket with the outer small bolts linked in pairs Panther style! Weird.

cheers Fabrice

[Adrian Harris]

I built up quite a collection of sprocket photos when getting the design ready for my late style sprocket rings and I don't recall any with locking tabs. From memory, most of the sprocket centre caps seem to use a locking nut similar to a castle nut but with a tapered end.

I'll have a look through when I get in tonight and post a selection.

The Cobbaton M4A4 is handy as a reference as some of the bogies have been shot to pieces, so you can see the internal structure of the different parts.

Adrian.

[Fabrice Le Roux]

Adrian,

Came across this on the G104 Sherman Group site. Looks like you don't need to worry about sprocket nuts at all, just model seventy years of rust and paint!

Nutless Sherman!

They are in for a nasty surprise if they ever try and move the old girl...
cheers Fabrice

[Adrian Harris]

> just model seventy years of rust and paint!

BTDT with the M4A3 prototype thanks very much

If they do move it, it'll look like this M4A4 at the Omaha Beach Museum:

Sorry it's a bit "false", I had to Photoshop it to get rid of the shadows.

All joking aside, that one you posted looks exactly like I would expect if you could completely countersink the M3 bolts round the edge. Not sure there would be enough meat in the sprocket ring though

Adrian.