1/72 Bristol Blenheim Mk1f Started 10 OCT 2019 Finished 19 APR 2020

[Boomerang]

 Started work on 1/72 Bristol Blenheim. I was undecided aboute how to finish it off but stumbled across a book on Australians in the Battle of Britain.
So it will be a Mk1f from 600 squadron RAF.
At a model show I picked up a Vac form canopy and turret ( cheap as chips) for a blenheim along with a few others.

Pictures etc as it matures.

Cheers

Gordon

[lastvautour]

The Blenheim Mk I is also on my to do list. Awaiting your photos.

Lou

[Boomerang]

Progress so far . Looks a bit rough but it sort of ,kind of looks like a Blenheim .

Work still needed on nacelles, cowls and cockpit.

Cheers

Gordon

[lastvautour]

Definitely a Blenheim. My model building lives through your progress reports. Keep them coming.

Lou

[lastvautour]

What wood are you using?

Lou

[Boomerang]

It's all Balsa except the fin/rudder is 3 ply and the stabiliser is basswood.

Gordon

[lastvautour]

Thanks. I thought so because of the grain in the enlarged photo. I have a few blocks in my stash but shutter at filling the grain.

Lou

[lastvautour]

Have you a way to duplicate the blisters on the nacelles. I was thinking of glue drops but wonder how to get them all the same.

Lou

[Gearup]

I have not had to make many duplicated parts such as the blisters on a cowl. But I do try to come up with solutions. I would try making a mold from silicone using a prototype carved plug and making multiple impressions in the mold. I have experimented with making silicone molds using silicon caulking + cornstarch + food dye. It works!

First, the silicone caulk must be the all silicone composition, not the latex type. Also it should have the note on the tube that it releases acetic acid (vinegar) as it cures. Open the tube up and if you have a very strong whiff of vinegar, you've got the right stuff.

Put a blob of silicone into a plastic container such as a chip dip container. Add a few drops of food colouring to the silicone. Now start adding the cornstarch to the mixture and start stirring it in. Keep mixing and adding starch until you get an even coloured mix about the consistency of pie dough. It takes perhaps 2:1 starch to silicon by volume. It should be fully incorporated and you will be able to handle the "dough" without it sticking to your hands. Roll it out to a consistent thickness and start making impressions with the previously carved plug (mounted on a stick for a handle).

Let the mold cure. It will probably get fairly stiff in a couple hours and will be like a silicon slab overnight. It is amazing that it does cure completely through. A blob of silicone alone without the starch and color will Be a skinned over blob next day.
Once it is cured, you could use whatever casting material you have on hand.since the blisters would be fairly small, PVA glue could work as the casting medium. Let it cure and pop them out to trim them.

I did use this method to make a cast of a wrench that I was able to cut open and  extract the wrench leaving a perfect casting mold as a test. There are various methods and mixtures on line using water, paint thinner etc. I just used silicone ,starch and food dye.

On my to-do list is to use this casting method to make a resin engine from a wooden plug.

Regards,
Fraser

[Boomerang]

Fraser,

I like your suggestions.

I might try it on a few other bits of airframe etc.., Look forward to your experiment with the engine.

Lou, One of Barry's projects involved blisters on a cowl . Done with PVA and maybe a mix of something he used template and dabbed it on. It will be in his projects somewhere.

Cheers

Gordon

[lastvautour]

Thank you Gordon.

Lou

[Oceaneer99]

Fraser, thank you for that method for making a mold. I have experimented with using silicone that way, but never thought of using it for a mold.

I have done some molds in the past using modeling clay or plaster.  Neither of these was a great solution, and the modeling clay only works for one casting.

I've used epoxy to make parts before. I have some larger epoxy bottles from woodworking and this type worked well -- it has low viscosity so fills in all the details. You do have to be careful to get all the bubbles out before you pour, I found. 

Do you know if the silicone could handle the high temperatures of a low-melting point alloy? I'm thinking non-lead plumbing solder, which is mostly tin with a little antimony, I think is the alloy.

Garet

[Gearup]

Hello Garet,

I've not tried Solder as a casting medium. .

Looking at the melting points of solder from kester.com it appears lead free solder has a melting range of 423-464f . Looking at an ikea high-temp silicon muffin mold it is safe up to 480f.

However looking at the MSDS for "LePage 2 in 1 Seal and Bond Kitchen and Bath Express Silicone" on line, it recommends avoiding prolonged heating to greater than 300f due to possible formation of formaldehydes. It does not state whether it is an uncured or cured silicon.

Additionally the mixing in of cornstarch would probably affect the temperature resistance and stability of the cured product.

So, I would think that it is a good mold material for resin or other cold casting material but it would probably not stand up to the temperatures of molten solder.

Regards,
Fraser

[Boomerang]

I have been busy with some other things . Managed to get some time on the Blenheim.

I wasn't happy with the engines so cut out a new pair out of block. The two brass tubes with a cutting edge filed onto them were used to shape the nacelles .
The large one is the right diameter for the cowling and the smaller one is right for inner diameter of cowling. The large one also makes a good hand hold for shaping.

Had to modify the tailplane shape and size . Still have to do the cockpit shaping .

Cheers

Gordon

[lastvautour]

Thanks for the tip on making the nacelles.  It is always a challenge to get them round.

Lou