<-- Mosquito FB.VI - Twin Engined Aircraft of WWII

[Airframes]

Thanks Hugh !

I've finally got the RTV mould underway, having first botched it.
Mixing very small volumes of the RTV silicone rubber, with the catalyst, is slightly tricky, as the ratios are very small ( and the instructions not totally clear), with around a 3% ratio, catalyst to RTV, required at the temperature I'm working in.
I used a pipette to add the catalyst, but miscalculated first time around, as the compound had virtually cured as I was mixing it !
Second attempt, with greatly reduced catalyst, seems OK so far - the pouring was slow and easy, and it was evident that the catalyst works quickly, even in small amounts, as the compound poured very slowly, compared to the 'raw' RTV.
Curing time is around 4 to 6 hours, so I'll just leave the 'mould', and hope I've got it right !

Pics show the already set mix at the first attempt, and the second attempt, with the RTV poured over the masters, inside a split, half shot glass, to form the mould.

Given that this cures OK, the shot glass will be pealed off, and the masters carefully removed from the mould.
The two parts of the resin will then be mixed, and poured into the RT mould and left to cure.

 

[Wurger]

 

[Airframes]

Thanks my friend.

Well, it worked, despite having concerns about getting the mix ratios right.
The 'masters' were easily removed from the fully cured mould, and close inspection strongly suggests that the moulds have formed perfectly, without any air bubbles around the frontal detail.
The pics show the cured mould, with the 'masters' still in place, and a close-up showing the open moulds, with the detail, including the little 'pimples' for the air vents on the 'Gee' indicator, nicely formed.
Next step is to mix the two-parts of the polyurethane resin, and pour it, carefully, into the three mould cavities, which I'll do later this evening.
Curing time to de-mould is suggested as 15 to 40 minutes, depending on ambient temperature, so with a bit of luck, I might have something to show later. Keeping my fingers crossed that the first attempt works without air bubbles of deformities.

 

[Wurger]

 

[Crimea_River]

So far so good.

 

[Airframes]

Yep, and thanks, Wojtek and Andy.
Going to stretch out for a couple of hours, as I've been 'on the go' for around 16 hours so far, and feeling a bit sore and stiff, and then I'll mix and pour the resin.
Darned sleep pattern is up the pictures at the moment, due to this damned shoulder and neck problem, Get to sleep OK, but wake up after an hour at the most, thinking I've been asleep for hours, due to the pain.
Hoping to get a steroid injection soon, to ease things a bit, but it won't be until after the Christmas holiday period.
With a bit of luck, I might be able to post pics of the first lot of cast resin parts later tonight.

 

[Airframes]

The first attempt at casting the resin parts has been made, and they've turned out reasonably well, with just two air bubbles, and not very large, on a couple of the cable connectors. If I was going to get bubbles, this is where I expected them to be, due to the shape, and very small size of the connectors, which stand proud of the 'body', and at an angle.
I haven't cleaned the parts yet, so I haven't inspected these areas closely, but I think that, when trimmed, they'll be OK.
Given the very small amounts of resin used, and the difficulty getting the mixed resin to pour slowly, and accurately, into small openings, in order to prevent air bubbles, from a large container (in relation to the size of the mould openings) I'm quite pleased with the results. The smaller mould openings are just 4 mm across, and I had to pour close to the openings, to prevent the resin going all over the place (which it still did !), so next time, I'try feeding it in from a pipette - the amount of resin needed is small enough to allow this to work,I would think.
The two parts of the resin have to be equal by weight, and, even mixing about ten times more than required, the container, with the resin, only weighed 6 grammes - mixing anything less wasn't enough for it to register on the digital scales !!

PIC 1 Shows the mould with the resin poured, and on the right, is the small plastic 'shot' glass it was mixed in, with the remaining resin already set ('pot' life is only 3 to 5 minutes).
PIC 2. The cast parts immediately after removal from the mould.
PIC 3. A close up, showing how they look. The part on the left, which is upside down, is the receiver and combined R/F unit, and the 'bubble', at bottom left in the picture, is a cable connector, so not a major problem, as a cable will ..... be connected here. The 'bubbles' on the part at the right are also cable connectors, so again, no major loss of detail.

So, all in all, I'm pleased with this first attempt, and have learned from the experience. When I cast the next sets, I'll arrange to pour either from a pipette, or get a very small glass pouring jug, with a spout.
Once the parts are cleaned of the release fluid from the 'masters', which remains in the mould, and the raw edges trimmed, they'll be painted, and fitted into the rear cockpit, when 'cables' will be made, from two gauges of lead wire, and attached to the relevant connectors.
Once that's done, the cockpit can be finished, and the tail wheel painted, assembled and fitted, and the fuselage joined.
Thanks once again for your continued interest, and I hope to post another up-date very soon.

 

[rochie]

Turned out reasonably well Dogsbody

 

[Crimea_River]

I'd say so as well. Nicely done Terry.

 

[Wayne Little]

Top stuff Terry!

 

[Airframes]

Thanks chaps.
Those 'bubbles' aren't as bad as they looked at first. The 'flash' broke off easily, and the connectors are quite reasonably formed. The angled parts haven't cast very well, but there's a small depression in each one, which will allow the cables to be fitted easier, and the 'angle' can be created when this is done.
I'm going to cast another couple of sets today, using a pipette to pour the resin this time. I'll also leave them in the mould a bit longer, as the 'Gee' indicator, the largest part of the three, was slightly soft around the edges. Not that this matters much - it can still be used, as the affected areas won't be seen.

 

[Wurger]

This is a work I like the most. Great Terry, just great !!!

 

[Airframes]

Thanks very much Wojtek.

I've done another casting, and, working on the 'SISO' principle, given the original 'quality' of the 'masters', these have turned out much sharper, and probably as good as they're going to get.
This time, I mixed the two parts of the resin 'by eye', checking for equal levels in the pots, and then assessing the colour when mixed. I used a pipette to pour the mixed resin into the mould, and left it to cure for an extra half an hour.
The parts virtually popped out of the mould when removed, and where nice and clean, with minimal flash, which has yet to b cleaned off.
There's some loss of detail on the carry handle of the 'Gee' indicator (the vertical line on the left of the front face), where an air bubble formed, but this can be removed, and a 'proper' handle fitted, using stretched sprue.

The lighting in the photos kills some of the detail, but they're much sharper than the first attempt.
The first set, which are still usable, will be used on the Lancaster build, as they will be back in the Nav station, with the smaller boxes under the table, and not quite as highly visible as in the Mosquito cockpit, whilst this second set will be cleaned up, a little extra detail added (which was the original intention), then painted, before fitting into the FB.VI cockpit and 'wired up'.

 

[Wurger]

 

[rochie]

Really nice Terry

 

[Airframes]

Thanks Karl.

 

[T Bolt]

Lovely work Terry. I've got to buy the supplies some time and do some casting myself as I have a few things I'd like to make.

 

[Crimea_River]

I bought some resin a while back bit it's clear. Do you know if there is any ingredient I can add to make the casting opaque?

 

[Wurger]

... Do you know if there is any ingredient I can add to make the casting opaque?

Depending on the resin type, epoxy or polyurethane, there are offered pigments. E.g. Pentasol ...
You have to look around in Canada net. I'm sure you can find equivalents.

 

[Gnomey]

Lovely work so far Terry!