Landships II

Ironsides · Legend

Tank armour and methods of drilling holes

Ironsides · Legend

Hi All, Correction to the above I now think the armour on training tanks was unhardened plate rather then boiler plate... any ideas....
To follow on to my original question there does indead seem to be a method of treating armour plate by locally softening with an electric arc before drilling/punching holes, it does seem that at least in thin plates punching was a practical possibility...

Menne describes burning holes in thick armour using an electic arc, curiously enough this is fairly local to me Kreuztal is about 10km away, and�many of my neighbours are called Menne....

Cheers smile

kieffer · Commander in Chief

Hi Ironsides,

I read that somewhere too, that training tanks were made of soft steel. I think David Fletcher stated that in one of his books.
The patents you mentioned are very interesting stuff!
Must look it up, but I read somewhere that cutting and drilling was done before hardening, with the British tanks. I wonder how they performed the drilling, on a multiple machine may be?

regards, Kieffer

Ironsides · Legend

Hi kieffer, most of this refers to heavy armour but�I would think the technique could be applied equally to any hardened steel plate as�i understand it the British Didnt use face hardened armour of the Harvey type as it doesnt appear to be possible for using this technique on thin plates... still looking though...
The main problem as I see it is heating would distort any accurate work done drilling holes, so this and cutting was done at the hardened stage to allow for any accurate fit, however this applies to warships where the mass of metal would create bigger problems, thinner smaller plate would have less problems in this regard but may�well still warp significantly.....
I expect the drilling was done using a jig, the fit doesnt have to be that exact as the"frame" behind the armour need not be hardened steel and therefore can be drilled in situ, although this may cause some weak spots.....
I found the "Machine for Punching Holes" very interesting it does appear easier to do then drilling on thin plates(german reversed bullet comes to mind)...

I have to say its very difficult to evenly heat a sheet of metal consistantly any difference in the heating�and cooling or slight uneveness in the plate itself would cause distortion and�the number and size of holes could effect this, and the metal needs to be quenched quickly otherewise all you do is soften it....
Of course it may simply be the drills were of a harder�steel then the hardened armour plate... someone had to develope those tungstone carbide bits....

Cheers smile

-- Edited by Ironsides on Monday 15th of March 2010 01:51:24 PM

Rectalgia · Legend

Ironsides wrote:

...
Of course it may simply be the drills were of a harder�steel then the hardened armour plate... someone had to develope those tungstone carbide bits....

Cobalt-steel alloys emerged as something of a wonder material for hard and heavy cutting just prior to WW1. I can find nothing specific but 'cobalt' drills would have to be a possibility. I think they could do the job. Certainly various cobalt alloys were coming into favour for machine tools even before the start of the war. The war only hastened developments - associated research into longer-lasting gun barrels or liners wouldn't have hurt the promotion of that metal either.

kieffer · Commander in Chief

Hi gentlemen,

the technique of drilling by arc was already existent during the Great War, according the patents Ironsides mentioned (great research Ivor!) So technically this could have been practised in the production of armour plates.
But...there is still the given fact that cutting and drilling was done before hardening...
at least with all British Mark tanks and even so with post war Mediums.
And it makes sense to me:
You don't have the problems which were hardly overcome (in the last war years) with hardening armour plate.
Drilling armour plate with special hardened drills is costly, tool bits are expensive. And it takes more time, it's the old rule of every lathe, mill and drill: the harder the material, the slower the speed of the machine. Almost every handbook on steel handling has that economical aspect mentioned, about labour time and costs of tools, the electric energy used and so on. Speaking for the "arc" one could say that this method is probably cheaper than conventional drilling, though you need specialised crafts men. Serial plate drilling is usually done on machines which are an investment much bigger than arc flames. The same for punching thicker plates, these were huge installations.
It would be interesting if there were any pictures of steel works where you could see some of the tools and equipment. The only ones I saw were merely the assembly lines in tank work shops but may be there are other pictures?

regards, Kieffer

Brennan · Lieutenant-Colonel

One of the reasons cutting & drilling was done before Hardening was that there was virtually no experience in hardening large sheets of thin (as compared to ships) armour. A range of techniques was apparently used often quite arcahic! It has been suggested by several well regarded authors that these experiences effect the inter war & WWII Brit decisions to work on Homogenous cast steel armours & forgo face hardening? Something that is often forgotten is that untill quite modern (ie post WWII) processess were developed,�facehardening vehicle armour plate�was slow & expensive - & its impact on cost & pace of German (WWII) tank production is recorded (though generally ignored by the "fan" clubs).

CharlieC · Legend

WW2 armour wasn't quite that simple - the Germans started out with face hardened plate for the Pz III and IV but went to homogeneous plate for the later tanks - lots more at http://yarchive.net/mil/ww2_tank_armor.html.

I think the WW1 plates would have been drilled possibly even as the plates were assembled prior to riveting. The build accuracy on the WW1 tanks was fairly bad, especially in the French tanks, so pre-drilling the plates prior to offering them up to the frames would cause lots of problems with aligning the hot rivets.

Regards,

Charlie

-- Edited by CharlieC on Tuesday 23rd of March 2010 02:51:02 PM

Ironsides · Legend

Hi All this 1940 armour patent is interesting from what it infers of the problems and the information that it gives on previous procedures for the manufacture of thin armour plates in this case up to 1" thick...

Cheers smile

-- Edited by Ironsides on Wednesday 24th of March 2010 01:08:59 PM

kieffer · Commander in Chief

Hi all,

pre-drilled or not, that's the question (sounds like Shakespeare..)
According to David Fletcher and other authors, plates were drilled and cut in soft state by the manufacturer before hardening. You can read that in the Osprey volumes about the MkI and Mk IV as well in Armoured Fighting Vehicles in Profile Vol.1.
Mr. Fletcher states that the MkIV plates were brought in the assembly line as sub-assemblies.
I quote freely: the inner frames with all connecting panels being assembled on jigs with the aid of power riveters before coming to the erecting shop where hand riveting was employed to attach them to the floor and lower body panels. Same procedure for the outer frames.
All authors consequently name drilling, no punching. Though punching was common practise in ship building.
But that's another story. I don't know how far machinery standards were during the war, but multiple drilling was practise in the 20's, I think they even started experimenting with using water as they do now with plasma cutting.
I don't think they drilled in situ, just to get holes aligned with existing ones. That would be even more inaccurate and time consuming, opposite to standardization. And drilling a hole in 10mm plate, you don't do that just on mere eye-sight not to mention by hand.

regards, Kieffer