Landships II

CrashandBern · Field Marshal

RE: What's on Mr.X's work bench...

CrashandBern · Field Marshal

Hoorah... the track unit is finished I must admit I'd been procrastinating about starting it but once I got it under way it all went very smoothly.

I tried a different method for the tracks on this one, normally I'd cut a full length track run then scribe in each link division and add the surface detail. This time I basically made one very wide track link and cut it into individually links... there's merits to both techniques but the latter worked well in this instance.

�

Happy New Year�

Bern

baldwin · Hero

Bernie

A work of art-outstanding.

Roger Todd · Legend

That is shaping up superbly.

CrashandBern · Field Marshal

Thank you kindly gentlemen... I'm off for a well deserved sherry and mince pie now!

TinCanTadpole · Legend

Very nice - and the coil springs are great.

CrashandBern · Field Marshal

Masters finished and onto the moulding stage... thought you may be interested to see some of the moulding process...�

CrashandBern · Field Marshal

TinCanTadpole wrote:
Very nice - and the coil springs are great.

�Thanks TCT :o)

TinCanTadpole · Legend

Bern, since you've posted some pics of the moulding process, what material do you use for the mould - is it something flexible and rubbery? Do you use a two part mould that can be reused, or do you need to take a new impression of the master parts for each kit?

Roger Todd · Legend

Having done a fair bit of mouldmaking and casting myself, I'd guess RTV silicone rubber, they look like two-part moulds for the track units and one-piece (open-backed) moulds for the other parts, and you should be able to get anything from 30 to 50 sets of castings from a mould before it deteriorates noticeably (so I'm given to understand, I've never made that many castings from any of my moulds).

TinCanTadpole · Legend

Ah! Part of the reason I ask is that the fuel tank, being a drum on a stand, looks like it would need to be tipped on its side to be removed easily from a mould - a two-parter, anyway.

Roger Todd · Legend

Fair point! RTV silicone comes in many grades of hardness, from very firm (used for white metal, for example) to very soft and elastic. I've used a very elastic one and believe me when I say you can cast something like that drum in a one-piece mould (as long as it is in contact with the surface it rests on, which may call for a bit of compromise when making the pattern) and pop it out when it's cured without tearing the rubber (although how many you could do over a period of time without it tearing is another matter). I did a small waterline battleship hull several years ago based on the Yamato which had massive undercuts near the stern and had no problems popping it out of a one-piece RTV silicone mould.

Roger Todd · Legend

Aye, it's called 'keying', hence my (possibly cryptic) reference earlier to 'keying-dimples'. Basically, if you're making a two-part mould, you need to blank off half the pattern/master with clay to make the first half of the mould. Because you're using clay it's easy to use a spherical bead pressed into the clay to make hemispherical indentations, which become raised hemispherical bumps in the moulding rubber. On the second half of the mould, those rubber bumps will form corresponding hollows into which they will fit when the rubber has cured. You make lots of keys in flexible moulds as it ensures the two halves lock together perfectly and keep the mould's shape so as to create as flawless a cast part as possible (on the other hand, with a rigid mould, say plaster, for casting flexible objects, such as rubber masks, you only need a few keys as the mould halves keep their shape anyway and the keys are solely to ensure they're correctly located in relation to each other).

I've seen some two-part moulds that were poured as one piece and then cut apart using razor-sharp blades in an irregular pattern to create the keys but I've never tried that approach myself and it looks a bit risky, plus it looks more likely to damage the pattern/master.

-- Edited by Roger Todd on Tuesday 22nd of January 2013 05:18:56 PM

CrashandBern · Field Marshal

As Roger says my moulds are made of RTV, anything on a dimpled white base (plasticine) is a two parter and the mould with the engine cover, seat, fuel tank etc is a single piece open backed mould.

I use a medium shore hardness RTV which is pretty flexible so you can get away with reasonable undercuts but is less prone to deform than the very soft RTVs. The number of pulls varies but PU resin hardens the surface of the RTV over time so even moulds with no undercut tend to deteriorate after 20 or so cycles.

When I get a chance I'll post more pics as the moulds and the first set of castings are now done.

�

Cheers

Bern�

Roger Todd · Legend

You make your moulds in a very similar way to mine, even down to the keying-dimples! When I was casting (haven't done so for a while now) I used a very crude centrifugal casting technique: put the mould in a stout plastic carrier bag and spin it at arm's length around a rod held in both hands, with the carrier bag being short enough not to hit you on the chin as it goes by! Sounds ridiculous but it works, castings made that way tended to be air-bubble free. You need a big 'plug' at the top of the pour channel so that as air bubbles rise, they only ruin the plug and not the part itself.

baldwin · Hero

This is all fascinating.It looks simple but there again it can't be.

Bern,keep us up to speed.

CrashandBern · Field Marshal

I've heard of people doing the centrifugal bag trick with resin castings but I've never tried it, I'd be worried about my moulds leaking... knowing my luck the air would come out the top and all the resin out the bottom!!!

�

So here are the finished moulds... if the next time I post I'm picking resin out of my hair you'll know I've tried Roger's method� smile

CrashandBern · Field Marshal

baldwin wrote:
This is all fascinating.It looks simple but there again it can't be.
Bern,keep us up to speed.

Barry it can't be that hard if I'm doing it� wink

Cheers

Bern

TinCanTadpole · Legend

Aha, the dimples are for aligning the two halves of the mould! Wasn't sure last night.

CrashandBern · Field Marshal

Recently I've seen a lot of resin parts that have been cast in a two piece mould that started life as a single piece and was cut apart with a razor (you can see the mould cuts in the flash). I guess it's got the advantage that there's no potential for the RTV to creep into the second half of the mould also it's a lot quicker than having to prepare a two piece mould but like Roger the lack of proper keying and the potential to damage the master and the mould puts me off trying it.

�

So as promised here's the first set of castings... I did these last weekend but have only just got around to downloading them from my camera.

I may modify the track units so that the bogies are separate parts, you'll lose less detail around the idler wheel and return rollers this way.

�

Roger Todd · Legend

CrashandBern wrote:
I may modify the track units so that the bogies are separate parts, you'll lose less detail around the idler wheel and return rollers this way.

I wouldn't bother if I were you, I suspect you only think you're losing detail because it's very hard to appreciate the surface detail of bare resin castings, especially when the resin's cream coloured. I bet if you paint it up in the intended colours it'll show more detail than you think is there and look just fine.

mike_m · Major

Interested to hearing your resin pouring technique especially for the track units.� Do you use a slow cure resin?� Do you pour all in one go?

I have done a fair bit of resin casting of ship models but nothing this complex, you look to have a very good method for those complex parts

Cheers

Mike

CrashandBern · Field Marshal

Roger Todd wrote:
CrashandBern wrote:
I may modify the track units so that the bogies are separate parts, you'll lose less detail around the idler wheel and return rollers this way.
I wouldn't bother if I were you, I suspect you only think you're losing detail because it's very hard to appreciate the surface detail of bare resin castings, especially when the resin's cream coloured. I bet if you paint it up in the intended colours it'll show more detail than you think is there and look just fine.

Hi Roger, I know where you're coming from�as it is sometimes hard to see surface detail on pale resin�but in this case there is an actual loss of detail as I had to fill the void between the idler wheel and the bogie for the mould to release without tearing apart. There's also some void filling�under the return rollers.

Don't get me wrong the single piece track units look fine but the moulds will be prone to premature breakup and�clean up will be easier�in separate�parts... I may just run the current moulds until they need replacing then split the parts for the next set.��

CrashandBern · Field Marshal

mike_m wrote:
Interested to hearing your resin pouring technique especially for the track units.� Do you use a slow cure resin?� Do you pour all in one go?
I have done a fair bit of resin casting of ship models but nothing this complex, you look to have a very good method for those complex parts
Cheers
Mike

Hi Mike,

I use Biresin G26 PU resin, it's a fast cure resin with ~ 5-7 minutes pot life depending on the temperature... if it's really cold you can get perhaps 10 mins but it cures as you mix it on a hot day (if we ever get one!).

I bond tubing into a syringe and inject the resin as I get better results that way�also there's precious little time for pouring and yes I fill the mould all in one go... other than that there's no special technique and it's usually a lot of�trial and error!

Cheers

Bern

�

Roger Todd · Legend

Ah, fair enough! It'd be interesting to see how many pulls you get from the moulds and still retain quality. I also use Biresin G26 (from Alec Tiranti Ltd), it's the best PU resin I've used so far. I started with Smooth-On but I never liked it, pot life was too short making pouring a stressful nightmare (and resulting in more hit-&-miss castings) and curing time was too long, the worst combination! I'm lucky in that I live in London on the Victoria line so Tiranti's shop is a mere 20 minutes away from me and I can get all my mouldmaking and casting supplies there.

Do you dust your moulds with talcum powder before pouring resin? I find that helps as it disrupts the surface tension of the resin and enables it to get into the mould's nooks & corners more effectively. Also, with large parts (such as a ship's hull) I use a latex-surgical-glove-clad finger to smear a small amount of resin into every corner of the mould first so there's a good detail layer before pouring in the rest.

CrashandBern · Field Marshal

I tried Smooth-On too and like you didn't like the results. Pot life on the grade I tried was longer than G26 but it foamed at the slightest amount of humidity and didn't flow as well as G26.

I�dust some moulds with talc but not all of them, generally only the larger ones with lots of rivet detail... occasionally�I forget and to be honest I haven't noticed a difference.

I used to�prefill the detail on�some of my moulds but I've found the force of injecting the resin�works it into the�nooks and crannies�so I�start with a sealed mould now.��

TinCanTadpole · Legend

This discussion is very interesting; would anyone care to comment on the strength of resin castings? I'm thinking in particular of whether or not it would be strong enough for workable track links in a reasonably large scale (up to 1:16, where links would have a pitch of about 12mm).

Roger Todd · Legend

I wouldn't like to use it for a model that large, though you might get away with it if the model only ever runs on a perfectly smooth level surface (which rather defeats the point of building a working model Great War tank!). The problem is that resin is fairly brittle and not really designed to withstand any kind of shock or loading, which is fine for static display models. You could probably get away with using it for tracks on a 1/35 scale model, as the links would be thick enough for strength but the model as a whole would be light enough not to put undue strain on the tracks. But a 1/16 scale model would, all other things being equal, weigh more than 8 times the 1/35 model whilst the parts would only be around 4 times stronger.

I could be wrong though.

Roger Todd · Legend

Also, I forgot to say earlier, you wouldn't want to use resin for connecting the links at any scale, it would simply break. You would only use resin links as shoes attached to some kind of chain, the chain bearing the stresses of being driven by the sprockets.

CrashandBern · Field Marshal

I'm with Roger on this, I'm not sure what the all up weight of a 1/16 RC tank would be but I'm pretty sure a PU track wouldn't be up to the job.

As Roger says you possibly could get away with a PU track plate attached to stronger drive links but you'd probably want to encapsulate some form of metal mesh within the resin casting to give it some strength. �

mike_m · Major

Thanks for the tip Bern, I must try the syringe method.� I think the resin I use is the same just under a different name, G27 is a little faster curing but not a lot different from G26.� I use an aerosol mould release which is more of a help in giving a longer mould life than any noticeable improvement in flow.�

Cheers

Mike

Roger Todd · Legend

Is it one of the wax releases, or silicone-based?

mike_m · Major

I use Smooth On Universal mould release, which I have found to work well

�

Mike

CrashandBern · Field Marshal

So with the Flying Elephant, Mk.I Supply tank and Tadpole nearing completion I thought it was time for something a little more colourful and as this has been sitting around for about three years it was high time I got on and built it.

PDA · Legend

That's your Renault Porteur, isn't it? I've been meaning to get one of these for some time.

Looking forward to seeing this build, Bern.

CrashandBern · Field Marshal

It is indeed Phil, the fuel tank, tracks, radiator, winch capstan and engine cover ventilator are only just sat on for the pics it'll be much easier to paint with them as separate parts.

CrashandBern · Field Marshal

That's the basic camo on. Needs black outlining and a light blow over with some light tan or base yellow to tone it all down and blend it in a bit but that's the main part done.

Makes a change from brown tanks!

I haven't done the load area as I'll be making a planked bed with side rails as seen in many of the period pictures.

-- Edited by CrashandBern on Tuesday 2nd of February 2016 09:46:29 PM

CrashandBern · Field Marshal

Camo outlined, needs a bit of touching in here and there but that's pretty much it.

As you can see I've made a start on the wooden bed, there will be rails on both sides. I also need to decide what's going to either sit on it or get towed along behind?

CrashandBern · Field Marshal

In between times I've been doing a bit on the FB.

The tracks have been weathered and fitted and I've finally finished building the planked bed platform, the side rails were very time consuming as there are 30 individual styrene strips in each one.

Each side of the bed has been drilled with seven 0.6mm holes which were then opened up with the tip of a no. 10 scalpel blade into rectangular slots for the side rail uprights to drop into... at the moment they're just sat in the holes to test the fit but will be glued in once the painting is completed.

CrashandBern · Field Marshal

Bed and side rails painted, needs weathering, a unit decal making for the front of the fuel tank and some sort of heavy load to pull.