Armortek

With the introduction of the .50 Ranging Machine Gun and the .30 Browning coax on the Mk 5/1, the 20 pdr barrel required counter-weights to balance the gun. Between one and three mild steel strips 13" long, 1" wide, and of varying heights and numbers (1 - 3 strips) were welded to the top of the fume extractor.







Tanks varied in their configurations, hence the need to identify which pattern was applied to a particular tank. This is 064, note the centre strip is shorter:



Finished fume extractor:





The bolt was a modification to allow crews to drain the fume extractor by depressing the barrel.



Regards

Stephen

I'm sure I'm not the only one having a last minute panic to get ready for the big show on Saturday. Despite the tailstock clamp breaking and getting a centre stuck in the headstock, my little lathe has come good in turning one half of the 20 pdr barrel. Creating this out of the 105mm kit barrel has involved extending the breech end by 4cms with an insert, increasing the taper between the breech and the fume extractor and reducing the barrel diameter overall. Although it is often wrongly claimed that the 105mm L7 was just a bored out 20 pdr barrel, they are in fact quite different.

In the time available, I haven't been able to attack the barrel forward of the fume extractor but the photos below represent a halfway house which shows the difference between the two.

Boring out the breech end to take the extension:



Turning the new taper:



Reducing the barrel diameter:



The bits ready to assemble, with the breech end insert in place:



The (half) finished article, with the 105mm for comparison:










Now for TankMOD at the weekend.

Regards

Stephen

The Guinness Record application is almost done, time to get back in the workshop. Next is the rifling for the barrel.

This is the method I invented for the Panzer III, which Mike Stannard copied. His photo etched part is far better than I achieved by milling and I'm pleased to think a bit of his legacy will live on in the Cent. First stage is to true up the part, particularly the mating edges, and turn a mandrel to size:



Then the part is annealed and rolled in a mini-pinch roller:



Although Mike's part was intended for an 88 and should be over-size for the 84mm 20 pdr, it turned out to be a bit undersize. No matter, I added a small brass strip with the lands milled and encased it all in a brass sleeve barrel insert:



Finally, a comparison of the kit 105mm (which is exactly to scale) and the new 84mm 20 pdr:



Regards

Stephen

Hi Stephen,

Lovely rifling! Very informative photos on the taper turning. Is the offset fitting on the Warco tailstock a Warco or third party item?

Thanks and congrats on making TankMod such a great success.

cheers Fabrice

Hi Fabrice.

It's a trick I learnt from a former toolmaker to avoid having to offset the tailstock with the concomitant risk in restoring true. It's an offset boring head:

http://www.warco.co.uk/boring-bars--bor ... -head.html

The other important benefit is that the boring head gives you much greater offset than that available from offsetting the tailstock. Just as well, as the offset needed to turn the taper for the 20 pdr was right on the limit.

TankMOD was fun but a lot of work.

All the best.

Stephen

Stephen

Outstanding job on the gun barrel rifling, this is something that I have been thinking about trying. I am in the process of buying some new tools so when I have sorted these out I will give it a go.

Thanks for the inspiration.

David

The front half of the barrel is too long to turn on my lathe. Deep breath, out with the hacksaw.....

Having faced the two cut ends to maintain true, next step to turn the much less severe taper forward of the fume extractor. It needed a small end cap to be turned in order to locate the fixed centre:



This is an interesting comparison between the diameter of the 20 pdr on the left and the unmodified 105mm Armortek barrel on the right:



Boring out a recess for a brass insert to rejoin the two cut halves. The fixed steady inevitably marked the barrel, so some careful surface dressing needed:



Two halves joined and polished:



Gaps filled, primed and reunited with the rear half. The fume extractor will now sit in the correct position:



From this:



To this:







I'm pleased with the way the 20 pdr has turned out because it's quite characteristic of the Mk 5/1 but it wasn't without its moments.



Regards

Stephen

Niiiice!
Chris

Breath taking work Stephen. Just the thought of hack sawing my barrel section in half scares the life out of me.
Still,following religiously, even if I've been a bit quiet lately........
Kevin

looks a bit like it means "look out" if on the receiving end of that barrel,very nice stephen, yeovilton on saturday, see you if your there, regards simon.

This is an amazing job, wonderful .... I do not know what else to add!
Congratulations, Stephen....Also for your courage!
Ciao,
Iacopo

Thanks chaps. Simon, looking forward to Yeovilton on Sat.

Every tank deserves to have its own identity. 064 is no exception. Over the last few weeks, three of her first crew met for the first time since leaving Vietnam at the end of 1969. Following David Hay's visit to UK, when he signed the model, I now have the privilege of being able to add the signatures of three other former crewmen, representing the B Sqn, 1st Armd Regt operational tour in 1969 and the A Sqn tour in 1970:








It means a lot to me to be able to connect the model directly with the crews who fought in the original.

Having completed the barrel, it's also time 064 acquired the barrel name adopted by B Sqn. This alludes to the province of SVN in which the Australian Task Force mostly operated. The crew commander, Barry Bennier clearly remembered it was painted on by David Hay, sometime after the battle of Binh Ba, (June 1969). There is only one really clear photo but it is visible in a couple of others, enough to give me the pattern, which I created in Powerpoint:





I then cut a stencil from Friskfilm and airbrushed the colour:









Original:



Model:



Regards

Stephen

Hi Stephen.

Excellent as ever see you at Yeovilton on Sat ..... only kidding
Cheers Paul.

nice one, you'll have to explain what that means to me on saturday, translate! all the best simon.

It doesn't need translating, it's phonetic....

Adrian.