Got back to the 25 pdr for a day. Still a lot of farm work and a beautiful day. But needed a quiet day in the shop playing with Armortek. Soon enough, the snow will arrive and I'll have LOTS of time. But Just needed to tinker.
So I love this kit, but without a doubt, this is the most peripatetic build I've ever been involved with... I am helter skelter all over the place trying to get one thing done to fit to another and back again... because everything is such a system! And I had to go an build myself a recoil system which, to parahrase Doug Neidermeyer (Faber College '63) "involved more than two dozen individual acts of engineering perversion SO profound and disgusting that decorum prohibits listing them here..."
I am adding details as I go, but also thought I'd throw in some thoughts that would help with folks get the gun working like the finely-engineered artillery piece it is. And for those familiar with 'real' artillery, it is just wonderful that you can turn beautiful, oily handwheel and feel a ton of metal rotate with the balance and tolerances of a fine Swiss watch. An Armortek kit should (and can) do the same!). Just takes some care and attention to detail during assembly
But first... some updates. Almost 2 months ago, I got the breech finished up and put together barrel and breech. The breech was modified to take a brass 28 ga shotshell, which is an almost perfect scale replica of the 25 PDR casing. They have to be shortened, but they are right on and go perfectly with Dave Dibb's resin shells and shell carriers!
Here is the breech, though I needed to to a tiny bit of machining to get the breech block sliding as smoothly as I wanted it. This was due to my new chamber lip being a tad taller than the factory one.
This was an idea taken from Dave Dibb's build at Armorpax... the top of the breech is not a nice, smooth machined piece. More likely a large casting or forging. I would guess a casting. So I took a cue out of my Rolls-Royce engine build and used my plenishing hammer to roughen up the piece all over. I think Dave did it with a spray-on coating, but I decided to put it right in the metal. Note that before plenishing, I smoothed and softened up the edges and rounded things so it doesn't look so 'machined.'
And it's on to the recoil system. In an earlier posting, you could see my 'gen 1 attempt.' And it was worthless. Springs were either so strong that they snapped the barrel forward hard enough to break things (and made 'pushing the barrel back' almost impossible) or they were so weak that if you elevated the gun, the barrel would flaccidly sag backwards in its recoil channel. The answer was compound springs... with variable rates. In fact, I ended up using 12 springs, 4 of small diameter and relatively soft. 2 of small diameter and much stronger. And 6 larger diameter outer springs, all the same rate. On sliding guides fitted to a pair of brass rods. I don't even want to think about the time it took to get it right...
The result far exceeded my expectations. And I'll try and post a video. But the barrel goes back smoothly about 1.5 inches. And then goes forward just like it's running on hydraulics. Smooth as silk! Shuts at the front just like it should and makes no noise or snap. I'll try and post a video of it tomorrow. Oh and because the actual barrel carrier on the original has rows of rivets on it... I added rivets. Hard to see in the above photo. But they are there. Soldered in and smoothed up on back.
And on the subject of 'smooth...' next came fitting up the barrel trunnions. As a restorer of 'real' artillery, I can tell you that this is one of the most critical parts of any piece. So when it came to assembling the trunnions, I opted to build around the actual trunnion piece and then make the rest of the carrier 'fit' the aligned cups and caps.
The first thing was to true up the trunnions theselves. They were actually true from Armortek. But the cheeks had some material in them that was creating a tight fit on the gun carriage trunnions and caps. So set the whole thing up in the Monarch and trued up the edges, but without removing anything from the actual bearing surfaces. I actually debated replacing them with brass or bronze as 'aluminum on aluminum' is a rather tough choice for long-life smoothness. But decided that since we're not headed to El Alamein with this one... it won't get hard use!
Before machining the trunnions, I had assembled the cheek plates and the cross 'bar' (where the pivot bolt goes) and epoxied them together. I did this with the trunnion block tapped into place. It would not move, but it also aligned my 'top' trunnion cups perfectly while the bottom pieces were locked together with cap screws and epoxy.
Next, the trunnion caps were fitted (and stamped to mark them... always stamp them!) and then line-reamed.
I was lucky enough to have a decimal reamer close enough to 10MM that I could ream them in a line and then lap in the actual trunnions in. Which worked out absolutely perfectly! They were 'almost' perfect and a few minutes with medium lapping compound left our top
Here we have the assembly 'together' and being lapped. Lapping compound can is in the back. Took fewer than 5 minutes to get it moving completely smoothly with no binding or tight spots.
Here we see the trunnion caps (with their stamps) in place and lapping compound squeezing out of the gap.
With the Trunnions now in perfect alignment, it was time for the 'base' to get some attention. Because as careful as the alignment process was at the trunnions, it still left the 'base' about 1/2mm out of alignment. Which means that when it goes on the trails, it will have big trouble turning smoothly. Everything has to be in perfect alignment in order to elevate and slew correctly and smoothly. So the whole unit was fixtured to the mill table and set up to take a skim cut off the bottom rails. A digital readout (DRO) makes this much easier!
Here is the fixtured piece ready to take a cut.
And making a cut down the 'high' (technically low) arm to put it in alignment with the other side. About 1/2mm removed which does not seem like a lot but would have made the process of trying to get the barrel to slew really difficult. This is what I mean about going forward and backwards a lot with this kit! It's easy looking, but there is a lot of small stuff to make it really come out to its highest potential!
That's about all I got done today... Or at least photographed. Lots of little bits of back and forth on axles, seat, armor-shield, etc. But all these bits are requiring some 'steps back' to re-evaluate. One of which is trying to 'squish' copper rivets and get them to dome. I thought my pneumatic brake riveter would handle it. Well... didn't even move the shank. So I annealed it. And... nothing. So off to get some aluminum rivets to use on the armor. And on the Rolls-Royce armored car. Because properly dollied rivets are... properly dollied!
Cheers,
RPR
P.S. Anyone got a line on 1/6th scale Broadarrow stamps? Because just about every part should have one! And I bet the Centurion folks would like to add some Broadarrows. Job for someone who has die- and stamp-making skills???? Because I surely would love one!
And luckily my work space is underground and soundproof as not to scare my neighbours in whatever way......
