Black Prince Scratch Build

This section is for builds that are not strictly Tamiya or Heng Long. For instance, replacing the electronics from a WSN or Matorro, or even a scratch-build.

Postby enginepeter » Sun Dec 27, 2020 3:57 pm

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.
Attachments
BP 7_resize.jpg

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Postby enginepeter » Sun Dec 27, 2020 8:37 pm

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.
Attachments
trk 1_resize.JPG
hull concept_resize.jpg

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Postby 43rdRecceReg » Sun Dec 27, 2020 10:38 pm

Hello, Peter!. I'm still indebted to you for the excellent job you did on the Comet RT aerial bases. :thumbup:
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. :D :thumbup:
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Postby enginepeter » Mon Dec 28, 2020 9:23 am

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

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Postby enginepeter » Mon Dec 28, 2020 10:00 am

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!
Attachments
susp 1_resize.JPG
Turning, rough shaping and drilling hole or cutting thread
susp 2_resize.JPG
Shaping in the jig
susp 3_resize.JPG
All the finished inner and outer wheels

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Postby enginepeter » Tue Dec 29, 2020 11:00 am

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.
Attachments
susp 4_resize.JPG
Tube bearings for Swing Arms
susp 5_resize.JPG
Drilling suspension side plate holes
susp 6_resize.JPG
Soldering side plate to top
susp 10_resize.JPG
Aligning second side plate for soldering

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Postby enginepeter » Tue Dec 29, 2020 11:08 am

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.
Attachments
susp 7_resize.JPG
Filing template
susp 8_resize.JPG
Completed side plates
susp 9_resize.JPG
Testing wheel/swing arms
susp 11_resize.JPG
Fixed wheel brackets

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Postby HERMAN BIX » Tue Dec 29, 2020 11:32 am

Magnificent engineering Sir, and for a very rare *& worthy subject machine :clap:
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Postby 43rdRecceReg » Tue Dec 29, 2020 4:00 pm

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

:O 8O :D ...I'm not surprised in the least, HB.
Great images -and they remind me I love the smell of swarf in the mornings, Peter :clap: These pics take me back to the workshop at school...
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Postby HERMAN BIX » Tue Dec 29, 2020 10:48 pm

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 :wtf:
I remember him vividly, and during my later apprenticeship, anyone in a grey shop coat traumatised me !!
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Postby enginepeter » Wed Dec 30, 2020 4:32 pm

Thank you for your comments. Herman Bix - I wear blue overalls if machining a mucky Job such as spraying smelly cutting oil everywhere- else old clothes! No need to worry about grey men!

The next stage was to complete the inner hull. As the inner sides were thin alloy (1.5mm) strength would be needed front and back to hold and keep everything rigid.

The front armour and rear panel were made to scale thicknesses. The front proved more complex in view of both the size and shape with differing angles, so to save material and make the job easier it was made in two parts. Even so it took some time to first machine then drill the holes for all later fittings such as the mg mount and drivers port mounts. Especial care was taken with the holes that would be used for the two alignment pins to hold both parts in the correct position before drilling and threading holes for their securing bolts.

Large surfaces were left to fix the hull side plates to and then surplus material was roughed out wherever possible.

An extra thick panel was used at the rear beneath the scale back panel to provide strength and a good mounting point for the side walls, with some surplus material milled out.. To join these two pieces I experimented with Aluminium solder. The process appeared a bit rough and ready compared to using usual solder, but providing the pieces were strongly held in a jig to ensure continuous alignment it worked well enough.

Side and floor panels were then cut and the inner hull assembled. Diagonals were measured at the top before drilling all screw mounting holes to ensure everything was square. No problem at he bottom as the floor plate was square.
Attachments
IMG_9880_resize.JPG
Machined front
IMG_9883_resize.JPG
Rear plates
IMG_9889_resize.JPG
Side walls and floor

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Postby enginepeter » Thu Dec 31, 2020 1:06 pm

Next the sponsons either side of the inner hull.

I acquired some alloy channel section that I cut and machined to size. Front and rear bulkheads were added, held in position by soldering and the 'box' closed with the addition of a roof. Holes were drilled in the floor of the sponson to mount the suspension, these mounting points using 3D printed top hats on the underside to locate/hold the swing arm springs.

The outer sides were rebated at the front so the horns could be mounted flush to the outer wall.

The next stage involve making the four horns and these were first sawn then shaped by filing to a 3D printed template. Thin brass was used to line the axle bearing slots, held in place using dummy bolts glued into the alloy.

The axle blocks were drilled and slotted to run in the grooves. To adjust the track tension the axles for the idler wheels were drilled and threaded 2mm and long socket headed screws were used to adjust the tension. To hold the axle blocks etc. in place, steel bar was used, bolted to the ends of the horns like to original tank. The socket head screws were a variation from the original but I wanted strong screws that could be easily adjusted.

Holes were drilled and threaded in the ends of the horns to hold the steel fittings, the steel studs (12ba size) being thread locked in place. Yet more dummy bolts were used to complete them. (By the end of the project I had spent a fortune on buying dummy bolts (0.8mm, 1.0mm and 1.5mm from Kupfner in Germany) as well as small BA bolts down to 16ba (1.35mm head) size.

Caps were fabricated from brass to fit the outside of the axle blocks and soldered in place.

The horns were then fitted to the sponsons.
Attachments
sp_1.JPG
Completed sponson shell
sp_2.JPG
filing the horn to a template
sp_3.JPG
Tension adjustment on the horns
sp_4.JPG
Fitting horns to sponson
sp_5.JPG
Completed bearing blocks

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Postby BarryC » Thu Dec 31, 2020 2:46 pm

Fantastic engineering and machining skills! :clap: :clap:

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Postby EAO » Fri Jan 01, 2021 3:06 am

BarryC wrote:Fantastic engineering and machining skills! :clap: :clap:

Barry


Exactly what Barry said! Amazing skills! :thumbup:

Regards,
Eric.
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Postby enginepeter » Fri Jan 01, 2021 1:56 pm

Barry and Eric - Thank you for your comments. You might feel differently about my skill level if you could see the number of pieces in my scrap bin!

After fitting the horns to the sponsons, holes were drilled in the inner hull to mount them to it.

The Idler wheels were turned from alloy, miniature bearings being used for the axles. Tyres were 3D printed using a flexible filament.

Support pieces were added to the sponsons to hold the roof before track guides were also milled then bolted in place.

After fitting the suspension supports and top hats for the springs, the final pieces were the outer skins where holes had to be drilled through this and the sponson for the side hatches. In view for their size these were cut by chain drilling and then filing.
Attachments
sp_6.JPG
Drilling holes to fit horn to inner hull
sp_7_resize.JPG
Suspension support fitted. Note top hats for springs.
sp_8.JPG
A few road wheels in place
sp_9.JPG
Machined Idler
sp_10.JPG
Tyres fitted to idler and track guides on top of sponson.
sp_11.JPG
Starting to fit outer skin
sp_12.JPG
Chain drilling hatch hole

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Postby enginepeter » Sun Jan 03, 2021 1:42 pm

The next stage involved the fitting of the motors. Before getting to this point the drive cogs had to be made. The panther ones that fitted the track were too big a diameter so two lumps of steel bar were machined for the inner parts and steel plate used for the outers, steel pins being used to keep alignment. Slots were then milled for the cogs before filing to shape.

Housings were made for the small bearing that would be fitted to both the walls of the hull to support the shafts.

A word or two on motors. I bought a 5:1 in the mistaken impression it would be better for a very heavy tank – also they would just fit inside the inner hull with very few mm to spare. I connected everything up for a trial run to check how the tracks ran true as well as to see how the gear boxes coped with the weight. Extra lumps of metal were added as temporary weights to get near the final weight. All was well on the solid floor but it struggled on carpet.

Back to the drawing board and the acquisition of a pair of 4:1 gear boxes. The only problem was these would not fit by a couple of mm. The problem was solved by moving the drive motor on one of them to a different position, by adding a small mounting plate.

This worked fine even on carpet. Later on, however, I reduced the power to the engines to 60% as this would give me a scale road speed and of course this resulted in problems again on the carpet. I have left it for now but at some stage I will probably try to build a pair of gearboxes to give me lower speed but keep the torque.
Attachments
mot_1.JPG
Fitting 5:1 motor with panther cogs to check alignment
mot_2.JPG
Bearing Housing
mot_3.JPG
Machined gear cogs
mot_4.JPG
Gearbox with moved motor

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Postby Will01Capri » Mon Jan 04, 2021 1:41 pm

Fantastic work, looks great
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Postby 43rdRecceReg » Mon Jan 04, 2021 1:58 pm

Following on with a mix of envy, admiration, and sheer astonishment, Peter. :clap:
Note to self: must find a decent mini-sized lathe one of these days. :problem: :)
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Postby enginepeter » Mon Jan 04, 2021 3:52 pm

Thank you Will01Capri and Roy. I think I use the drill and file more than anything else. The major problem is eyesight and the size of parts, particularly when they fly off the work bench!

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Postby enginepeter » Mon Jan 04, 2021 3:58 pm

To finish the sides, the side hatches were made with working hinges as well as drilling numerous holes for various sized bolts scaled to match the originals.

The top deck was cut from sheet alloy, held in place with a lug at the front and rare earth magnets used at the rear. A hole was cut for the turret ring and a further ring added for the turret rollers, that give clearance over the mudguards.

A rebated frame for the front hatches was made by soldering two cut/filed pieces of brass before work started on fabricating the hatches themselves. This involved some intricate work with the soldering iron and a fair bit of cussing! They were made up of numerous thin pieces of brass and head sinks were the order of the day to stop everything disintegrating.

The air intakes for the rear were also fabricated, using sides and back made of steel that had been silver soldered together. Various pieces of sheet brass added to create the top and grill. Brass lugs were then shaped and soldered to the ends.

To complete the top deck various handles, covers and dummy hinges were added as well as a working barrel lock. The mountings for the periscopes were machined with the rain caps and dummy prisms to be added after painting. Holes were later drilled to mount the traverse motor.
Attachments
top_1.JPG
Completed side panel and top plate
top_2.JPG
Hole and support ring for turret
top_3.JPG
Completed front hatches with holes also drilled for periscopes
top_4.JPG
Rear air intakes
top_5.JPG
Completer top deck

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