RC Tank Warfare community hobby forum

After completing my Cromwell Scratch Build using 3d Printing for a lot of the upper hull I decided that my next project would be all metal to give different challenges. This was some 18 months ago, since when all my tank time has been committed to this project - hence I have been quiet on the forum.

When I started research the Black Prince prototype (Number 4) was readily accessible at Bovington so I was able to take photos and a number of measurements. On my second visit to Bovington I went to the research centre hoping to find some plans and technical details. ! was forewarned the the file was 'thin', containing little more than a report on some of the trials and a series of photographs. No plans or scale drawings.

Back home I started to use CAD to draw up some plans to work to and soon realised that I needed more measurements so back to Bovington (some 200 miles away).

Part of the CAD exercise was to work out how I could make the hull from aluminium, so that the minimum of bolt heads were visible and that it would also be strong enough to hold together.

I wanted to build it using scale dimensions for the armour. From the scant details at Bovington I guessed that the armour thicknesses were similar to the MK7 Churchill so based my plans on those measurements.

Before getting into detailed planning I needed to sort out what tracks I could use. Discarding options to have them cast for me as too expensive I first 3D printed some and then tried to sand cast some. When this gave mixed results I then tried printing using a wax type filament and then lost wax casting. Both methods worked to a limited extent but with fettling the results and drilling pin holes I decided to try another approach.

Dave Allerton at Forgebear generously gave me some Panther G track links to play with and a bit of grinding and filing gave a track link the correct scale width albeit the pitch was a little short. The photo shows the correct sized printed track alongside the adjusted taigan track.

Firming up on the dimensions I then produced a 3D model before ordering various thickness of alloy sheet and some 'U' section.

The serious work of sawing, filing and machining could then begin.

Hello, Peter!. I'm still indebted to you for the excellent job you did on the Comet RT aerial bases.
Having looked at your website, and other bits and bobs, I'm sure this project should yield an enviable result.
Now that my Comet and Cromwell projects are pretty much complete (Cromwell 99%- Comet 90%)- I'd actually considered getting a Ludwig Churchill kit. The Black Prince would be a possible later development...
The Black Prince looks to have pretty much the same turret as the Comet, at least at first glance. Having an external mantlet certainly makes the job of fitting a cannon much easier than shoehorning one into a Cromwell, with its internal mantlet.
Following along, and looking for inspiration.

Hello Roy

Yes, I have been watching your progress with the Cromwell and Comet - you have your hands full! Yes the mantlet for the Black P appeared similar to the Comet - I think I used some Comet photos to try and get a decent working shape. At least the Black P is bigger than the Churchill but even so I did not have a lot of room for the gearboxes as you will see later.

regards. Peter

With the tracks sorted I could get the spacing right for the road wheels and size the suspension swing arms to fit the scale width of the side plates. I decided to make the wheels from alloy to save weight, so I started with a length of 1 inch bar that was turned to size. I set myself up to cut rebates, and hubs as part of the first operation as well as drilling 2.5mm holes for the axle pins. A 2.5mm thread was cut in the outer wheels in the first stage before fitting the wheels in a jig to hold them whilst cutting the profiles and later milling the slots in the hubs. The axle pins would be 2.5mm bolts thread locked in place through the swing arms. 48 wheels proved a little repetitive and there was a fair amount of swarf to dispose of!

The suspension swing arms had to fit between the suspension side plates, hold the road wheels the right distance apart to fit the tracks, provide a solid base for the springs as well as actually move. To get this right a number of prototypes were 3D printed before considering what material to use to make them. Again I experimented with white metal casting but in view of the failure rate I reluctantly decided to make use of 3D printing. I acquired different types of filament to make samples before subjecting them to destructive tests and found that the ordinary PLA worked best in terms of strength and ease of printing.

To provide an anchor point for the springs a round lug was added to the swing arm and to protect it from wear, brass tube was used to house the pivot and axle pins.

The side plates for the suspension were made from brass sheet. A plan was produce showing the location of all the holes required for the suspension swing arm mounts as well as the original weight saving. The 4 side pieces were clamped together and the milling machine used to drill the holes using their coordinates from the plan. Two further pieces of brass were machined to provide shoulders and the correct profile so they could be used to hold the side pieces that would be soldered to them. These were made over long to give clamping points and were later trimmed to size.

It took some time to solder each set of 3 together to be both the correct distance apart and to align the various holes. Spacers were machined to size and drill bits through holes used to align parts before they were clamped together.

Once soldered the surplus on the side plates had to be sawn/filed away. To make this easy 3D templates were printed and held in position using the axle and pivot holes as the cut lines were marked out.

Once the sides were completed it was time to assemble the wheels and swing arms then try them in place and adjust clearances. Ordinary nuts were used to hold the pivot pins for the trial. Printed fittings scaled on the original had threads cut in them and were used for final assembly. There is no lateral stress on these pivots so threading and gluing was felt more than adequate.

Finally a pair of fixed mounts were fabricated from brass for the fixed wheels.

Magnificent engineering Sir, and for a very rare *& worthy subject machine

HERMAN BIX wrote:Magnificent engineering Sir, and for a very rare *& worthy subject machine

...I'm not surprised in the least, HB.
Great images -and they remind me I love the smell of swarf in the mornings, Peter These pics take me back to the workshop at school...

My Engineering teacher at high school was one Mr Green, he was a Royal Marine Commando .
In the winter in New Zealand which was not far short of snowing most days in the north island at least, he used to sneak up on us dumb asses and catch some ‘tard with his hands in his pockets. Then the entire class had to run across two rugby fields which were white with heavy frost, barefoot, and back, apparently to take our minds off our cold fingers
I remember him vividly, and during my later apprenticeship, anyone in a grey shop coat traumatised me !!