restoration mk6 cromwell

[ferrettkitt]

Flying tank Cromwell

 

http://www.britishpathe.com/video/tanks-take-off/query/tanks+take+off

Edited February 24, 2013 by ferrettkitt

[Old Git]

that's right it's fitted with the 15.5" track and not the earlier 14" or the comets 18"

 

Thanks for the reply Rick. I had often wondered if there was any discernible difference between the 14" tracks and the 15.5" tracks and from the picture above it would appeat to be so!

[Billruston]

Hi rick, hows it going?

 

Bill.

[ashtonpete]

It should not be too long now, the electrician and I have been doing the wiring today (I should add I am assisting him under his instructions) So we should be starting on the button any day soon.

[eddy8men]

electrics are pretty much done now and once the oil pressure gauge is fitted we can start the engine

[happydayz123]

That will be a great day, for u mate.

Regards

stu

[ajmac]

Rick,

I presume that bottom photo is a power take off gearbox; generator on the left, starter on top.....but what is that on the right?

Edited April 11, 2013 by ajmac

[eddy8men]

you're right alastair, the crankshaft drives the dynamo on the left, with the starter on top and the turret traverse hydraulic pump on the right but the pump is redundant as we will use the hand traverse to move the turret round.

 

speaking of turrets we are now focusing on getting it together, the roof had taken a hit at some point in it's life which required cutting out and replacing, the hatches were also missing. i had managed to obtain the commanders cupola but the loaders hatches had to be fabricated. i'm also on the hunt for interior fittings like 19 set equip, besa ammo boxes, water cans and anything else i can nail to the inside !

 

 

 

 

rick

[Old Git]

Fantastic Pictures Rick, I'm loving these mate!!!

[the_shadock]

fortunately, the loader's hatches are easier to fabricate than the commander's cupola (I guess).

 

P-O

[eddy8men]

the loaders hatches are quite straight forward to fabricate, unfortunately when the turret roof was damaged it also bent the brass rainwater channel that fits beneath the hatches and a new channel has had to be fabricated. as for the commanders cuploa that is cast so would prove costly to have made but i was lucky enough to find one

[Old Git]

That's a lovely close-up of the commanders Cupola Rick, not often we get such a good pic of an essential piece of the Cromwell. Got any more close-ups? Those brass rainwater channels for instance, or shots of the underside?

 

Rgds

 

Pete

[eddy8men]

no worries pete, i've been meaning to go to bob's yard for a while so it's as good an excuse as any to go over this week. i'll put some pics up when i do.

 

rick

[andym]

Any engine noises yet?

 

Andy

[Bob Grundy]

Any engine noises yet?

 

Andy

 

Only the metalic turning over of the engine............

[fesm_ndt]

What's the armour like to drill, i.e. is it something like bisalloy wear plate with a hardened martensite type surface but not so hard interior? Or back in them days was it just through thickness high hardness?

 

I wonder if through thickness hard as that would be a bugger to tap new threads etc and any structural welding would need a bit of care.

 

I doubt it could be too finicky as it was originally welded up in a fairly rudimentary manner but I wonder if there was many weld failures given it was all new in them days and cold cracking and brittle fracture were unknown back then. reminds me I have a war related video on brittle fracture..........

Edited May 3, 2013 by fesm_ndt

[eddy8men]

i've heard a few things about drilling holes in armour but i've not tried it myself yet. one tip was to heat the area until almost melting then knock a sharp punch in to make the hole, another tip was to use masonary drills instead of high speed steel but as i said i haven't tried either. anyone else know of another way ?

[rnixartillery]

An APDS Round will do the trick,especialy if its just left the end of a 17 pdr !

 

Rob.................rnixartillery.

[rippo]

I think it'd just be a case of getting the right drill. A carbide tipped masonary drill may go through, but a coated HSS drill would be better, a colbalt or a miracle coated drill.

 

If you need anything drilling i'll have a go at it. Be intersting to see how tough it is.

 

Regards

 

John

[Adrian Barrell]

There is armour and there is armour........ I've drilled some armour very easily with HSS and I've failed with other armour using cobalt drills. The easiest was early war US rolled homogeneous and the hardest was last week on a piece of Czech pre-war plate. I gave up on that and made a new plate!

 

Face hardened can be difficult as used on White half track and scout car. The best way is to drill it from the soft, inside face until the drill starts to give up then punch the hard face out.

[fesm_ndt]

There is armour and there is armour........

 

yep I guess that was what I was curious about ie back in WW II was it a through process of thick and all hard or were they dabbling in face hardening, but you have said loads of different variations so they were trying loads of ideas so must of been a lot of research after WW I.

 

Bisalloy is a term we use for wear plate in Australia and it is a face hardened plate on both sides. I made the mistake of making a roo bar mount out of it, all was good until tried to drill holes in it.

 

Interesting about the White halftrack comment as hardening on one side I believe is done to have hard exterior for obvious reasons and a softer inside surface to reduce spalling. You can normally pick this concept as it is typically all welded from the inside.

 

edit ... I forgot to ask, do you find much obvious cracking in the welds when you been rebuilding? Curious as it was all new tech and a mad rush in them days.

 

An APDS Round will do the trick,especialy if its just left the end of a 17 pdr !

 

Rob.................rnixartillery.

 

Most likely shouldn't remind Rick as I think he had to bondo a few of them already

Edited May 3, 2013 by fesm_ndt

[ferrettkitt]

Rick Bondo-ing it not likely to expensive when you can use plaster that's readily available

[Adrian Barrell]

yep I guess that was what I was curious about ie back in WW II was it a through process of thick and all hard or were they dabbling in face hardening, but you have said loads of different variations so they were trying loads of ideas so must of been a lot of research after WW I.

 

Bisalloy is a term we use for wear plate in Australia and it is a face hardened plate on both sides. I made the mistake of making a roo bar mount out of it, all was good until tried to drill holes in it.

 

Interesting about the White halftrack comment as hardening on one side I believe is done to have hard exterior for obvious reasons and a softer inside surface to reduce spalling. You can normally pick this concept as it is typically all welded from the inside.

 

edit ... I forgot to ask, do you find much obvious cracking in the welds when you been rebuilding? Curious as it was all new tech and a mad rush in them days.

 

 

Face hardened was more common in European production but most British and US was homogeneous. The US were more willing to try welding than the British, Sherman went over to fully welded by mid 1942, Cromwell wasn't welded until early 1944 and then only some models, old habits die hard!

 

Though White used face hardened, IHC used homogeneous in their halftracks. Early US armour was quite soft, 1943 saw some improvements I understand.

 

As long as the welding is chrome or nickel based, cracking is not a problem. There is a heat affected zone adjacent to the weld but the ductility of the cooling weld metal allows for this.

[eddy8men]

i'm glad you asked that question mike as i was wondering what method you would use to make a piece of steel armoured. my churchill has one or two holes from 84mm law and around some of the holes the steel which is 3 inches thick has delaminated into what looks like thin sheet less than a 1mm thick. is this the face hardening coming away ?

thanks for the tips adrian, drilling from the soft side out is the way ahead. simple when someone shows you how to do it.

 

rick

[David Herbert]

Several people have refered to the hardness of armour as if it is a good quality. In WW1 the only way to make steel plate tougher was to have a relatively high carbon content and to heat treat it in a way that left it relatively hard. This made it nicely proof against small arms which was the perceived threat but when hit by anything big it shattered. look at the WW1 tanks at Bovvy to see what I mean. Between the wars there was no money for development and no one could believe that there could be another war so we went into WW2 with almost the same technology as 20 years previously.

 

In WW2 it rapidly became clear that tanks were required to fight other tanks and defend against anti tank guns, both of which fired relatively large, high energy projectiles. It was simply not possible to make the projectiles bounce off in the way that you could with a rifle bullet, and instead it needed to be 'bogged down' and stopped progressively before it penitrated the armour. To do this the armour needed to be very strong, but at the same time ductile. Hardness was a very negative feature because it lead to shattering in which very little of its strength was used. A high melting point was a good thing because when hit a lot of energy is turned into heat and it is better if as little of the armour melts as possible (not very strong when runny). We now have aluminium armour which provides perfectly good protection at the cost of being 2 1/2 times thicker than steel and is not at all hard.

 

The ultimate in hard armour could be thought to be the ceramic layers in Chobham armour but actually they contribute almost nothing to the protection against projectiles as they just shatter, absorbing little energy. What they do very well is deflect the jet of very high temperature plasma from a shaped charge so that it does not burn its way in.

 

In conclusion most WW2 and almost all later armour is deliberatly not very hard. However it is quite often made of alloys that work harden in the same way that stainless steel does, and that can make it very hard to drill and particularly to tap threads into. Also many people think that the nickle based welds are somehow much stronger welds than normal. The weld itself is actually not particularly strong but the point is that as it cools it does not contract and pull cracks in the surrounding armour plate as ordinary arc weld would.

 

David