Topic: How do you make this? (Read 7281 times)

raflaunches · « **on:** February 10, 2016, 11:18:55 am »

hi everyone

I'm having problems with making the angled cover for the vents on the base of most funnels you see on warships, see attached photo. There is a matching item on top of the funnel which is easier to make to get the angles, etc, but how do you get the lower one to angle evenly and stay the correct shape?

I'd be interested in how other modellers have overcome this feature on their funnels, I've made round ones got my Gnat but they were perfectly circular do I used a piece of pipe and filed away, but these funnels are oval circles.

Colin Bishop · « **Reply #1 on:** February 10, 2016, 11:32:52 am »

That is a difficult shape Nick. I have not had to do it myself but my inclination would be to draw lines around the funnel at the levels of the top and bottom of the vent. Then make a thin (0.5mm) plywood cutout shelf which can be slipped over the funnel and stuck on at the lower level. For the straight sides of the funnel a small sloping strip of ply can be stuck with its top edge against the top line and its outer edge along the bottom of the shelf. Similarly a sliver of ply can be stuck in the same way at the centre of the front and back of the funnel. It is then just a case of filling in the empty sections with easy sand filler using the plywood as a guide level to rub down to. Use extra filler as necessary to blend everything in. If you make a mistake then it is easy just to add a bit of extra filler and rub down again.

You could probably do something similar using plasticard but in this situation I think ply and something like Ronseal wood filler would stick better and be easier to mould to the shape you need when rubbing down.

Colin

raflaunches · « **Reply #2 on:** February 10, 2016, 11:36:59 am »

Thanks Colin

It's certainly a difficult shape to get right, I'll give it a go and see what happens.
In the past on another model I made a square version but only because that was what the real vessel had.

Ian K · « **Reply #3 on:** February 10, 2016, 11:45:06 am »

Hi Nick,

I normally make these uptake deflectors from solid laminations of plywood. Just cut the inner and outer shapes using a fine jig saw or coping/fret saw to form the rings.
Next sand the chamfer on the outer edges, plywood is great at indicating the evenness of the angle, due to the laminates showing as a series of parallel lines.

Seal the ply rings and glue into position at the base of the stacks. I use a similar method for the stack top draft deflectors. On these larger ship models stability weight is not an issue! Good luck

Regards

Ian

raflaunches · « **Reply #4 on:** February 10, 2016, 11:54:23 am »

Thanks Ian

By sounds of things ply is the more forgiving material to use and like Colin says a bit of filler if you go wrong.

Thanks to you both, looks like I've got some practice to do over the weekend.

Colin Bishop · « **Reply #5 on:** February 10, 2016, 11:59:42 am »

Bob's method is likely to be more precise but will need a bit more effort. I'm a bit of a bodger rather than a model engineer so am usually happier with tinkering with something until it comes out right rather than depending on a high degree of initial accuracy. As a well respected modeller once said to me, looking at a block of wood. 'It's in there somewhere - you just have to find it...'

Colin

raflaunches · « **Reply #6 on:** February 10, 2016, 12:01:45 pm »

Quote from: Colin Bishop on February 10, 2016, 11:59:42 am

As a well respected modeller once said to me, looking at a block of wood. 'It's in there somewhere - you just have to find it...'

Colin

Too true Colin!

dreadnought72 · « **Reply #7 on:** February 10, 2016, 12:07:54 pm »

The funnels are flat-sided with semicircular ends.

You know ra, rb and ha. So...

hb = ha * rb / ( rb - ra )

rc = SQRT ( ( ( hb - ha ) * ( hb - ha ) ) + ( ra * ra ) )

rd = SQRT ( ( hb * hb ) + ( rb * rb ) )

The angle you need to cut to make this half-cone is alpha = 180 * rb / rd

Andy

Beagle1831 · « **Reply #8 on:** February 10, 2016, 12:09:52 pm »

Hi Nick

On Suffolk I made them out of plasticard - trial and error with cardboard templates first, then transfer to plastic and bend it gently to shape.

To get the shape of the template I worked out the shape needed for a round funnel corresponding to the ends, which is like a flattened out slice of a cone, then add in the straight bits needed for the flat sided middle of the funnel (if that makes sense?)

That said it's a massive pain and took about 5 tries to get right!! The plywood approach with the middles cut out sounds like the way to go...

Looks like a great model hope to see it at Wicksteed!

James

Beagle1831 · « **Reply #9 on:** February 10, 2016, 12:11:03 pm »

Just seen Andy's diagram - that's exactly how I did it.

dreadnought72 · « **Reply #10 on:** February 10, 2016, 12:11:24 pm »

Ummm ... my equation for rc has grown an unneccesary "+" at the end.

...oops. Bad markup. All fixed. :)

raflaunches · « **Reply #11 on:** February 10, 2016, 12:27:34 pm »

Thanks Andy

That takes me back to my engineering lessons at RAF Cosford, I'll measure it up and see how it works out.

Hi James

Good to hear from you, I've been told patience is a virtue and practice makes perfect!
Definitely see you at Wicksteed before I go back to Cyprus?

colin-d · « **Reply #12 on:** February 10, 2016, 12:37:12 pm »

Hi Nick,
i use three layeers of 1mm plastic...
just finished mine on the build that i am doing at the Moment...
i'll put some photo's up tonight when i get home..

managed to find one on my phone...

Bob K · « **Reply #13 on:** February 10, 2016, 12:40:09 pm »

Only just caught this thread. As a former draughtsman, and one who generally goes for a plasticard solution over wood for detail, Andy's well described solution is exactly what I'd go for. I have often used conic projections for sloping superstructure bases etc.

raflaunches · « **Reply #14 on:** February 10, 2016, 12:47:38 pm »

Wished I had asked this question years ago! Just imagine the models I could have built!

Thanks Colin and Bob, at least I've got the correct shaped funnels to work with so I'm going to have a play this afternoon drawing them up and then have a go making them at the weekend.
Brilliant response rate today!

Colin Bishop · « **Reply #15 on:** February 10, 2016, 12:56:34 pm »

Well, I think it is more interesting to respond to a specific query such as this rather than the vague ones we sometimes get. Very educational too to see the varying solutions which we can all learn from. I think a lot does depend on which materials you are most comfortable with but it's nice to know that there are alternatives you can try.

Colin

rickles23 · « **Reply #16 on:** February 10, 2016, 02:02:28 pm »

Hi,

For many tricky shapes I use a sheet of 200 gms/m2 A4 paper.

With a coat of paint you cannot tell that it is only paper.

Plus you can get a lot out of one sheet of paper.

Regards

Umi_Ryuzuki · « **Reply #17 on:** February 10, 2016, 08:35:42 pm »

As posed by others, I also cut a profile, and then horizontal cross sections at key points.
Then fill with pink or blue insulation foam, sand and sheet with balsa or plastic.

Paper or cardstock can be useful in making patterns if necessary.
You can wrap the form and draw cut lines to begin creating the pattern.
Then trace that onto your finish material.

For conical areas, a good Shroud Calculator app is usually available on Rocketry websites.

http://www.rocketreviews.com/shroudtransistion-calculator.html

http://rocketry.newcenturycomputers.net/shroudcalc.html

http://www.rocketreviews.com/shroudtransistion-calculator.html

ballastanksian · « **Reply #18 on:** February 10, 2016, 10:40:43 pm »

If you are concious of weight and are willing to spend just a little time on the mathematics then the plate method is the way to go especially if using brass or tinplate where the effect of plate seems to stand out

Otherwise, laminated ply, plastic or filler is perfectly sound. I will probably try the plate method in the future as these clever chaps have reminded me of what I forgot from 'GA' drawing at college years back, but will use plastic sheet and milliput as these techniques I use daily in my work.

Bob K · « **Reply #19 on:** February 11, 2016, 09:39:18 am »

Just noticed that HMS Abercrombie also has an angled funnel top deflector, so I will be using the projected cone plasticard method on that.

http://www.elbowroom.eu/ship_image/images/ships/Abercrombie%20HMS%207_1947%20Monitor%20W&L.jpg

Geoff · « **Reply #20 on:** February 11, 2016, 01:49:49 pm »

I usually build a ledge/platform round the bottom of the funnel to the correct depth and then wrap round a layer of plastic card vertically round the funnel for the correct height and fill the "L" shapes gap with car body filler and sand to shape.

I find this quick and easy to correct as you go - works for me!!

Cheers

Geoff

John W E · « **Reply #21 on:** February 11, 2016, 04:12:49 pm »

Hi there Nick
Just a thought; do you have the book ‘Scale Model Warships by John Bowen’
In that book there is a method of producing the cone assembly for the funnels also I have scanned a page from Model Boats Magazine which shows another method of doing this.
When I did the funnels for HMS Exeter, I used the combination of ideas which are show in the books and has also been mentioned on the Forum.
Where I originally started off using a solid plywood disc, sanded to shape, but this didn’t look right especially around the top of the funnel so I moved on to plan b; which was to use printers Litho Plate after making templates from paper which was transferred to the Litho Plate and cut out. Sadly, this failed for me again because the superglue (once dried out) delaminated from the Litho Plate causing the whole assembly to fall apart.
Plan c; I cut small triangles from Plasticard to the correct angle, glued them around the outside edge of the top of the funnel and then using paper templates, transferred them onto Plasticard and glued that into place instead of the Litho Plate which was more successful.
The thing I found with using Plasticard was that I could fill any defects with plastic fillers and sand down with Wet’n’Dry.
I have put a link on here to my Exeter build so you can have a look at the funnels.
Dont forget though, the funnels are 2 different diameters – they are of a smaller diameter both top and bottom.

http://www.modelboatmayhem.co.uk/forum/index.php/topic,33734.100.html

john

Unsinkable 2 · « **Reply #22 on:** February 11, 2016, 08:47:54 pm »

My method would be to take a piece of metal with a right angle corner and cut or file the corner at the same angle and width as the deflector, then mix body filler and place it around the bottom of the funnel. Then use the metal tool to scrape around and remove the excess filler. You should have left the shape you are trying to achieve. Make sure it's set and that it was sitting on something it didn't bond to. Remove it and hopefully all you need to do now is make a packer to raise it from the deck and possibly some light sanding!

This method may not give the same perfect finish as the afore mentioned methods but it may be of intrest to those who want a reasonable finish with minimum effort. U2

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Author Topic: How do you make this? (Read 7281 times)