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Author Topic: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed  (Read 1490 times)

DamienB

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HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« on: November 23, 2020, 11:34:40 pm »

This is - was - HMS Coventry D118, a Type 42 air defence destroyer. Launched in 1974 and commissioned in 1978, she was sunk by Argentine A-4 Skyhawks in the Falklands War of 1982, with 19 of her crew lost. My father was part of the crew (and still with us thankfully).



Last year I found a radio control model of a Type 42 (HMS Cardiff D108) on Gumtree for a reasonable price. It had been built from a Sirmar fibreglass hull and various resin fittings plus scratch built wooden superstructure based on, I think, Jecobin plans. The fuzzy pictures on Gumtree made it look better than it was in the 'flesh', but it was a good price, cheaper than buying just the bare hull. So I decided it would be a good basis for a refurbishment to turn into HMS Coventry.

The Type 42 was built to 3 standards, or batches - Coventry was a batch 1, of which 8 were built (including, ironically, 2 for the Argentine navy). She was the 6th ship to be laid down so benefited from some lessons learned as earlier ships were constructed and had some variations in fit. The 8 ships of batch 1 all had some obvious differences. The first of the class, Sheffield (also sadly lost in the Falklands War), along with the two Argentine examples, had 'Mickey Mouse' ears on her funnel; the Argentine pair had an upper deck extension amidships for mounting Exocet missile launchers. Sheffield had no upper deck sponsons for STWS torpedo launchers, though all subsequent RN examples did. Sheffield and Birmingham initially had a green deck and a boxier main mast than the other ships. The type 965 'double bedstead' radar was fitted to the early batch 1s, with - I think - Exeter being the first to get the less bulky type 1022 instead. For the purposes of this build I can ignore all the later modifications made to the type 42s except in terms of recognising what not to do!



So that's what I'm starting with. It's not a bad effort at all - certainly better than I could manage from chopping up bits of wood - but to turn it into HMS Coventry will need some work. Anyway the initial list of jobs was:

1. Remove the supports holding up the STWS deck and hangar deck (easy, hack hack)
2. Replace the funnel with an accurate one (not so easy but I soon acquired a Sirmar resin one)
3. Replace the type 1022 radar with a 965 (photo etched one acquired from Scalewarship)

But you know how it goes. The more you look, the more you find things that are wrong. So the main mast is the type that Sheffield had - that needs to go then. The superstructure on which that mast sits is wrongly shaped at its aft end. The kit on top of the hangar is mostly wrong. The aft 909 radar office and the forward end of the hangar are wrong. The bridge screen shouldn't have a railing right across the front. And on and on and on...
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #1 on: November 23, 2020, 11:52:08 pm »

Now skip ahead to the first coronavirus lockdown back in March. A partial set of scale plans was donated to me (thanks radiojoe!), and a quick shufti at those found that the boat suffered from a lot of over-simplified construction. I removed the type 1022 radar from its pedestal, but then found the pedestal was a solid block of wood, which would preclude having the type 965 from rotating, which is surely a must-have.

Now I'm not great at whittling wood, but I'm alright with computers. So, as you do, I've been teaching myself Fusion 360 3D modelling, bought a 3D printer (Elegoo Mars Pro, which uses UV cured resin), and got cracking with designing a replacement radar pedestal that would be hollow and give me some room for the gubbins necessary to have a rotating radar head. So here's the existing radar pedestal, and the first test print of my resulting 3D design:





The first lessons learned with this were that the printer was capable of some pretty amazing fidelity, but you have to balance that with the resulting fragility. Round the aft side of the pedestal, for instance, the diesel generator exhausts were so thin they crumbled away when I was cleaning the part up. And, of course, the more reference material I collected from various Facebook groups, Flickr, etc., the more detail I could incorporate on the design.



Broken exhausts on the first (left) print. I also found that, under a coat of primer, I was getting some horrendous horizontal steps in sloped surfaces. Some experimentation found that these were the result of how the slicing software deals with angled surfaces, and could be reduced by rotating the object on the printer's build plate (35 degrees worked for the print on the right above). The perceived wisdom on many 3D printing groups/forums is that you should angle things vertically too, but I like to start from a handy flat surface on the build plate where possible, and let the items 'grow' from that point.
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #2 on: November 24, 2020, 12:19:49 am »

The forward superstructure is easily removable for access to the batteries and motors etc. inside the hull, which makes working on the rebuild easier too. Here I've got as far as removing the inaccurate funnel and cleaning up some of the decks.  I now had a new resin funnel, which fits nicely. But we'll revisit that later. Another error found at this point was the fore mast, which is vertical when it should slope back slightly, and has a damping blanket wrapped around it which HMS Coventry did not have.

So, I designed some masts!


Each is broken up into sections for printing, and mostly hollow to save weight, use less resin, and you also have to avoid trapping any uncured liquid resin inside anything. The fore mast is made up of the base, main shaft, and everything from the disc at the top upwards. Plus the radar head. I initially had the disc upwards as part of the main shaft but it failed to print - that big flat disc just couldn't be held by the thin support beneath it as the printer peeled that layer off the exposure plate.

The main mast I broke up into the base (up to the second change in angle), the main section (all the way up to the top platform support), and the top platform with separate radar head again. I had to go back and separate out the railings around the lower platform as they made it too awkward to paint things.


...more to come.
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C-3PO

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #3 on: November 24, 2020, 07:54:02 am »

Amazing

Stunning work - not much else to say

Will follow this thread closely

Regards

C-3PO
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C-3PO

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #4 on: November 24, 2020, 10:50:01 am »

DamienB,

I have been Googling - is your printer the Elegoo Mars Pro or Elegoo Mars Pro 2

Think your post has cost me money :)

Regards
C-3PO
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radiojoe

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #5 on: November 24, 2020, 12:11:19 pm »

Beautiful work on the 3D printing Damien, so pleased the drawings were useful for you I'll follow your progress  :-))




Joe.
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #6 on: November 24, 2020, 06:48:03 pm »

I have been Googling - is your printer the Elegoo Mars Pro or Elegoo Mars Pro 2

Think your post has cost me money :)
Mars Pro, but I wouldn't recommend it due to issues with the light source it uses, which I'll cover in another post...! The Mars Pro 2 uses a different light source and is faster so probably a better option.
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #7 on: November 24, 2020, 07:07:13 pm »

Clearing the decks. I roughly penned in all the missing detail hence the black marker in places. To correct the rear part I cut away some of the wood and blanked it off with plastic card:

...and tried the new main mast for fit. Nearly perfect, but the ladder on the mast clashes with the roof, which makes me think the original builder has got the height of the superstucture slightly wrong. Also, the gap between the main superstructure and the hangar block is far too narrow. Hmmm...!


As to the hangar block, that had errors too. The 909 office was butted right up against the hangar wall, when in reality there is a gap. The hangar itself is also not a straight line at this edge - it's kinda L-shaped. So I started rectifying this by cutting out part of the rear wall:


...and drawing up a replacement 909 office:

The pipes are - I think - part of the pre-wetting system that sprays water all over the ship in advance of a nuclear attack, so that fallout can be more easily washed off afterwards.The big hole in the top saves resin and also lets it drain out during printing; I chose to put the bottom of the office on the build plate, because the pipe work makes starting from the roof or sides impossible.
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #8 on: November 24, 2020, 07:19:36 pm »

While I was at it, I thought the resin 909 domes (Sirmar I guess) looked slightly undersized, so I designed replacements. These printed from the base upwards, and I was conscious that would end up with a small amount of resin trapped inside when printing was finished, but I thought it would be a small amount and could be poured out when the part was removed from the build plate. I was wrong, it was a lot!

Office printed too - the pipe work is a bit saggy in place due to insufficient supports but that kinda matches photos of many real ships. A word on resin too; up to this point I was using clear resin, as it has the advantage that you can see if any solid bits have broken off during printing and are lying at the bottom of the vat when printing is finished. You can destroy your printer screen if the build plate comes down on top of anything solid and punctures the exposure plate, which is a very very thin and flexible piece of clear plastic film. However, clear resin is very brittle, particularly if you do a post-cure for too long. It also goes yellow very quickly if you over-cure it - which I have for these parts!
For a bit of light relief I moved on to replacing some fittings, namely the forward superstructure life raft shelves:

This is the 5 raft version that all the batch 1s were initially fitted with. What I didn't realise until one of the ex-crew pointed it out was that Coventry underwent a refit in 1981 where the forward two life raft stowages were cut off (the rafts had their occupancy ratings upped so fewer were needed onboard - in fact during 1980 she simply sailed with the forward 2 rafts removed, but the stowages still there).  I'll have to revisit this bit later!

The hangar area also has shelves for life rafts and other bits. The cage at the far right of each shelf is for fuel can stowage for the engines of the ships's boats. They're angled so that all the cans can be jettisoned into the sea by undoing a retaining strap - for instance in case of a nearby fire (and presumably when air raid warning red is piped?). It's not until you start really looking at photos that you find the little bits of unexpected differences - some of the early ships including Coventry had a smaller stowage area on one side, my first iteration of this missed that detail.
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frogman3

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #9 on: November 25, 2020, 05:56:09 am »

HI can we see a pic of the whole ship of what you have done so far ? as i love the type 42 has i have scratchbuilt   two batch 3  42's  HMS YORK D98 an HMS EDINBURGH D97 in 1/64 th scale an they sailed lovely an they are well balanced an nice looking ships on the wet stuff
chris :-))
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warspite

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #10 on: November 25, 2020, 10:40:56 am »

Does any one else have issues with seeing the photo's?
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C-3PO

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #11 on: November 25, 2020, 10:45:15 am »

Hi Warspite,

I can see them 100% in Firefox and Edge and can see them in Safari on my iPhone

I cannot see them in Chrome!!

Regards

C-3PO

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warspite

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #12 on: November 25, 2020, 10:49:21 am »

I only have chrome - so that explains it  :((
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RST

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #13 on: November 25, 2020, 11:25:00 am »

Can't see them on my smartphone. I have to press and hold for the option to open in a separate window, then they show up in the new webpage.  I was looking because the printers are sub 200quid now. Trying to convince myself I don't need a third one!
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C-3PO

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #14 on: November 25, 2020, 11:36:42 am »

Appears the images are stored on this web address .....could this be a trust setting?

http://www.hmscoventry.co.uk/model/....

C-3PO
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warspite

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #15 on: November 25, 2020, 01:53:43 pm »

As RST states when opened in a new tab they are visable, going to be a while to catch up
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #16 on: November 25, 2020, 04:37:47 pm »

Chrome was being fussy about security certificate signing; bit odd as the site wasn't https in the first place. Anyway hopefully fixed...
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #17 on: November 25, 2020, 04:38:29 pm »

HI can we see a pic of the whole ship of what you have done so far ?


Not right now, it's in bits all over the place :D
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #18 on: November 25, 2020, 10:17:29 pm »

The model's existing bridge. You guessed it - it's not quite right. The bridge's windowed area should go up in line with the 'screen' area below, and not have a hand rail in front. The windows are just black painted bits of photo etched metal too.


So, the most ambitious bit of design so far. Complete bridge and port bridge wing (no need to do starboard, it's a mirror image so I just print it mirrored). Hardest part here was finding reference photos - thankfully a couple of Facebook groups came up trumps.



Despite there being little chance of seeing much through those windows I did some basic interior shapes and some roof detail. Just because.

I've left the windows open and will figure out how to glaze them later. A couple of test prints gave me the right angle to park the windscreen wipers at so that they would print without needing to be separate bits.
However...


Some oddities when printed.

As with previous parts, I'd designed this to print from the ground up, i.e. the roof was the last bit to get done. The roof top, however, has lost some detail, namely the railing running from port to starboard behind the nav light stand. There's an odd 'step' just below roof level that isn't in the 3D model either. Also if you look closely at the bottom edges, there are some holes where no resin has been cured at all.

This is a problem with the Mars 2 Pro; it uses a grid of LED lights as a light source to cure the resin, and the plastic grid guide results in a cold spots where insufficient light gets through. Elegoo will provide a replacement grid and LED board if you contact their support, but it involves dismantling the entire printer to fit it and doesn't entirely cure the problem; I've since fitted my 'fixed' grid and while I no longer get holes in cold spots, you can still sometimes see indications of the grid pattern on large flat surfaces. A gentle sanding sorts it most of the time but there are types of printing - such as curved transparent lithos - you simply cannot therefore print nicely on this machine.
...more concerning though, is the recurrence of the weird piling up of resin in the roof interior:


It looks like uncured resin has collected and the roof has a sagged and melted look as a result. It took me some time after this to figure out what is going on. As the bridge was printed from the bottom up, it had nice solid walls and then the printer laid down a very very thin (0.02mm) layer of resin for the first lattice of roof reinforcement. That gets cured, then the print head moves up to peel the layer off the exposure sheet. It's not fully cured, so it's pretty flexible, and flaps like a sheet of paper in a breeze, being unsupported in the middle. When the print head moves back down to start the next layer, that flexible layer now flaps in the opposite direction, then a new layer is cured... with the previous layer not fully back in place. So over time this results in liquid resin trapped between ever wavier cured layers. Not good. The lesson is not to allow horizontal flat surfaces suddenly come into play as a design moves through the printing process.


Bridge wings - these worked better, though I'm not too happy with the contours underneath them and how they'll fit against the existing superstructure. Amazed that the little pipes on the outside faces printed OK, though they're incredibly fragile!
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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #19 on: November 26, 2020, 05:20:44 am »


Not right now, it's in bits all over the place :D


YES i see what you mean so exscuse me as im old school  an i really dont understand how this is bein built but this is 3D printing of the bridge isnt it ?
chris
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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #20 on: November 26, 2020, 10:39:41 am »

So printing the roof separately would have been better ?, to be glued on later,
Would creating holes for the little pipes and using copper wire might have been better assuming they were vertical and have sagged as they cured.
If the material is clear as in the earlier pictures (thanks for fixing it so we can see them by the way), in the 3D model would creating a recess and a layer of window have been easier, masking these areas off before painting or is it as previously mentioned that the resin yellows so would have been opaque later.
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #21 on: November 26, 2020, 01:14:45 pm »

I'll get back to the bridge shortly (it's already done, just need to do the write up) but yes, I went with printing the roof separately second time round.

I'm happy enough with the pipes in resin, if they get broken off I'll try wire though.
In attempt #2 (or was it #4) of the bridge I tried printing it in clear resin but the windows simply aren't clear enough; as they are all at an angle, you get slight aliasing on their surfaces which doesn't matter on a solid colour, but kills clarity on a clear part.
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #22 on: November 29, 2020, 08:17:27 pm »

Boat davits. Earlier in their career, type 42s carried a motor launch and a whaler either side of the funnel. Falklands experience showed that better defensive armament would be a wiser use of the space so these were done away with on later ships to make room (and weight capacity) for better cannon (and later CIWS). These were a pain to design as I couldn't find any good drawings or photos but I think they're roughly right.





Printed nicely first time so quick test fit - nearly right, cutting away the raised deck edge found them to be nearly dead on for spacing. I'll use a bit of brass or plastic rod to do the connecting shaft but for the time being these are being put aside while I work on other bits and pieces, such as this lot:



Hangar roof gubbins. From the top, clockwise... some sort of wooden mat (?), HF aerial (later ships had a mesh cone, early ones were solid with drain holes like this), gangway, RAS pipes (?) and some big blocky thing of which I know nothing. And the more I looked at the hangar and the tiny gap between it and the main superstructure, the more I got worried. Something was clearly amiss - but where?
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DamienB

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #23 on: November 29, 2020, 08:30:50 pm »

So I measured up the hangar compared to the scale plans. And it matched. And then it didn't match. And I got confused. And then I realised that the scale plans (from Jecobin) aren't even consistent with themselves.The length of the hangar is different in the side profile compared to the overhead one. Aargh!

Now, I already had the task of blanking off the bit of the hangar that I'd cut away to fit the new 909 office into, and the whole thing was lacking in detail, so I bit the bullet and designed the entire hangar superstructure block in Fusion. This was going to result in something significantly bigger than the build volume that the printer can handle, so it had to be split up into bits. And I didn't want a repeat of the roof problems I had with the bridge, either, so no building from the floor upwards this time.
Now, minus the life raft shelves etc., the rear portion of the hangar superstructure could fit within the printer's build area if I cut it just aft of the 909 office, and then used that cut surface to build up from. I wasn't sure how rigid thin resin would be, so I went for fairly thick walls but that still left a lot of internal volume to do something about. God knows what possessed me (gin probably) but I decided as it's going to have to be an empty shell to save resin and weight, it'd be a shame not to have *some* detail in there. Couldn't find any photos of early 42 hangars so it's all a bit speculative based upon the few photos I could find of later ships.




The printed result after a quick blast of white primer on the interior...


Success. Didn't clean off dust etc properly before priming but nobody will see. No soggy roof! It's a heavy chunk. If I were to go back and redo this I'd make the walls much much thinner.


Evidence of the resin-piling-up problem at the rear face. As this is all hidden it's no problem but I did have to go digging into this to release a certain amount of liquid resin trapped in the layers. Again, experience has told me how to better deal with this - support these surfaces like mad!
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RST

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Re: HMS Coventry D118 Type 42 destroyer - 1/96 3D printed
« Reply #24 on: November 29, 2020, 08:55:07 pm »

The model railways guys often tilt their prints, not only to pinch a bit more capacity but that the resin drips off to the end and makes a cleaner/ better print?
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