Author Topic: B-25 Mitchell  (Read 10088 times)

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Balsabasher

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Re: B-25 Mitchell
« Reply #15 on: March 31, 2011, 05:51:27 PM »
Thanks Ken for the excellent description,I will give your idea a try sometime as it does look most effective.
Barry.

Ken Pugh

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Re: B-25 Mitchell
« Reply #16 on: April 02, 2011, 11:36:27 AM »
Gave the B-25 to my granddaughter last night and she loves it.  They went home today and we got this snap.  I asked her what she would like me to build her next and she asked for a bomber.  She likes all planes but especially those that blow things up.

I had bought her a snap together plastic kit just in case she wanted to give that a try.  We were up together until midnight putting it together.  Her dad came in when it was almost finished and I was trimming the decals for her.  I finally told him that she actually built the model and he was stunned.  After a while of holding his mouth open he told her, "You can't believe how proud I am of you right now."  Overall, a great day.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5556

Ken Pugh

Balsabasher

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Re: B-25 Mitchell
« Reply #17 on: April 02, 2011, 02:42:40 PM »
She is lovely Ken,what a little sweetie ! she is so lucky to have you do this for her and will always remember these days,the model is a true gift in every sense as it was hand crafted with love,you can see the way she is holding it that it will be looked after and treasured,it will certainly outlive any plastic model for sure.
Barry.

Mark Braunlich

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Re: B-25 Mitchell
« Reply #18 on: April 02, 2011, 04:47:48 PM »
Great job Ken.  Bravo!  I still have a wooden toy soldier my grandfather carved and painted for me when I was about seven.  He passed away when I was eight.  It's the only thing I have from him other than my middle name.

Mark

Ken Pugh

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Re: B-25 Mitchell
« Reply #19 on: April 21, 2011, 01:52:15 PM »
I haven't been posting anything here to date because I wanted to see how some things turned out first.  I did take pics along the way so all will be caught up, eventually.  As Lou is now starting a B-25 I figured I better get to posting in case any of my trials can help.

First off, my finishing technique.  I am still not a master of it yet but it is getting better.  I realized that woodworker finish techniques did not really try to get rid of wood grain showing through.  A trip to the library produced a book just on woodworker finishing methods.  It was filled with the methods used in different desired results and using different types of products.  I focused on water-based products because I would be using water-based paints and I want to keep my solvents the same.  A small section of the book was dedicated to what was referred to as "piano finish."  This was the description they give to a completely smooth finish with no grain visible at all.  They showed the way to do it with all the products and I learned the water-based way.

"Piano finish," water-based style.

The key to understanding the technique is that you are filling the pores of the wood.  Filling the pores and filling low spots are two completely separate issues and are dealt with separately and with different products.  Don't worry about filling your bad spots during the early stages, though small problems can be addressed.

Since you will be working with water-based products, the first step is to raise the grain of the wood.  I keep a spray bottle of distilled water on my bench as it has many handy uses and this is one of them.  Spray or wipe water over you part and let dry.  When dry, sand off all the raised grain.  If you get carried away with sanding in later steps and sand down below the surface you have now, you will have to raise the grain again.  Develop a light touch with your sandpaper.

When the grain is raised, you can now apply water-based wood filler.  I could not find the exact product recommended and can't remember the name of the stuff, but I was stuck using Elmer's Carpenter's Wood Filler.  When I first used this product it was not getting into the wood the way I wanted.  I now thin it some with distilled water.  The filler now flows into the grain of the wood nicely.  Because of thinning, it is imperative that you raise the grain first.  Wood filler only fills about 80% of the pores, so two passes is not a waste of time, though you can probably get by with just one.  One thing is critical.  If you are going to use a wood filler, DO NOT USE SANDING SEALER.  You can't fill the pores if you can't get to them.  Apply per the instructions and sand off.  Once this is done it is important to vacuum out the part.  You are actually sucking the dust out of the unfilled pores.  This is important for future steps to get into those pores.  When applying this stuff, just apply what is needed to go over the surface of the wood.  Any extra you put on there has to be sanded off.  I use a small stainless steel spatula to apply, then scrap off most of it.  Remember, you are not filling bad spots, you are filling the pores.  Sand this surface lightly.  Don't sand past the filler and into the wood or all your work turns into dust.

After you finish using the wood filler and have vacuumed out the part, it time to apply a finish.  Use your favorite water-based polyurethane.  I like the Minwax Polycrylic.  It is a good finish that I will experiment with using as a clear coat.  I have used it to seal silkspan and to apply fiberglass and it works great.  When using water-based polyurethane (not oil-based products) use a synthetic bristle brush.  This Polycrylic will completely remove the nice tip you have on a natural bristle brush and it will get sloppy.  I don't think it is permanent, but it makes application a pain.  Use the synthetic brush and the tip stays intact.  Polycrylic dries to sand in 2 hours.  They recommend three coats but I find two works fine in this process.  Sand with 220 grit sandpaper between coats.  When you are done, let dry 24 hours before next step.  At this point, if you have any low spots that need filling, do it now.  I use Bondo glazing putty.  This is an automobile product for filling small areas.  In our models, even our big areas are small to the car guys.  When this is finished, you should have a nice, smooth surface sanded over with fine sandpaper that is ready for finish.

Once you have your polyurethane coats done, you can now spray on a primer.  I like Dupli-Color Filler Primer.  This is a high build primer used by the auto paint industry to fill the scratches in the bare metal before painting.  You can spray that stuff on as thick as you want and it just builds up.  Follow the directions for whatever product you decide to use.  You don't really have to sand between coats with filler primers and can just lightly sand the final coat.

Once this is dry, paint with your favorite water-based acrylics.  If done properly, there will be absolutely no grain visible at all.  If you are like me, there will still be a little, but you will have a very smooth surface.  I haven't tried it with balsa but I bet it would work well.

Ken Pugh
« Last Edit: July 23, 2011, 05:48:09 PM by Ken Pugh »

Balsabasher

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Re: B-25 Mitchell
« Reply #20 on: April 21, 2011, 02:15:36 PM »
Excellent tips here Ken,the biggest problem this end is the un-availability of the products that you mention in the UK,no doubt there are similar products out there just waiting to be tested that would give similar results to your own findings.
One of the best ways to fill balsa is to use the cling film technique,suitable primer is applied to the wood and cling film is pulled in all four directions across the surface,once cured the surface is like glass and requires very little sanding,the edges of the cling film are simply wrapped underneath say the wing until the curing has been completed,by doing different components at a time it can be more labour intensive but the end results are worthwhile in my opinion.
You can use a variety of materials including conventional sanding sealer which works really well applied as a generous coat,the cling film smooths out and forces the sealer into the surface.
Barry.

dave_t

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Re: B-25 Mitchell
« Reply #21 on: April 21, 2011, 02:44:35 PM »
I don't know their methods for making the masters for resin models, but if you scroll down on this link for Unicraft models and take a look at the photos of the master model http://www.unicraft.biz/germ/do19/do19.htm the results look a bit like what you described.

Of course, it is possible that it is not made of wood, but a laminated man-made material.
« Last Edit: April 21, 2011, 02:50:03 PM by dave_t »

Ken Pugh

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Re: B-25 Mitchell
« Reply #22 on: April 21, 2011, 04:55:21 PM »
That cling film method sounds like the latex method a German uses for fiberglass on model boats.

I may have to find that book again in the library and see what it says on oil-based products.  They may be more available in the UK.

Another thing to consider, this is done to the parts after they are glued together.  This wood filler can make a weak glue joint.  I fill some parts before gluing together, but I leave the joint areas untouched.

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #23 on: April 21, 2011, 04:59:25 PM »
Thanks for the link, Dave.  I have considered making resin kits before and that site shows a lot of kits broken up into parts.  Something to consider when one is a solid modeler.

Ken Pugh

Balsabasher

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Re: B-25 Mitchell
« Reply #24 on: April 22, 2011, 01:15:50 AM »
I quite often partially pre fill the grain on the parts before assembly, especially with awkward types like biplanes etc when it is virtually impossible to sand at times.
Experimentation is the answer to try out different methods,and we are all learning things along the way as well.
Barry.

Ken Pugh

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Re: B-25 Mitchell
« Reply #25 on: April 22, 2011, 12:45:54 PM »
The way I will build this one is slow and overkill for 1/72 scale but I am learning new techniques.  The tail and wings will be built up with separated surfaces that will not move.  This is done for strength.  I like very strong and durable models.  This also allows me to get the grain of the wood going to the best benefit of the part.

First up, marking out parts for cutting.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5644

I use some of the points already on the templates for peg locations.  The fuselage is built in two halves so I have a perfect centerline from above that does not go away.  Notice that I marked on the template the thickest part of the airfoil.  This is also drilled out.  A peg will go through and will be used to align the wings and provide a stronger glue joint.  It will also provide clamping but I will show that when the time comes.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5650

Here is another trick I use.  The outside of the line is in heavy black ink.  The inside is in red ink.  When the parts are glued together, I have an indicator when I am getting close, black ink, and an indicator when I am at the line and going too far, red ink.  Because the parts are pre-drilled for pegs, the ink will be inside at the centerline and will be visible as you carve.

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #26 on: April 22, 2011, 12:56:51 PM »
The nacelles are made up the same way as the fuselage.  Here are some tricks I use to shape them.

When making square stuff round,  I draw in the round shape in the front then carve that in.  This then becomes the guide for the rest of the nacelle.  I also mark where it changes from round to a ventral shape.  The front is a little long and will be trimmed off and shaped later.  Up is marked early because the aft end of the nacelle is not round and orientation of the part is important.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5653

I noticed on the Japanese solid model sites that they sometimes had a lot of vertical lines drawn on the fuselage.  These did not match the cross section points of their plans.  I still don't know why they did it, but it occurred to me this can help.  As I am finalizing the shape of a curved part, I draw some contour lines in.  They don't have to have perfect spacing and they are done free hand.  When you rotate the part around and look at it on end, you can see how your contour lines are lining up.  This is great for determining what shape you have along the part.  You can get your shape right and symmetrical this way.  As you carve/file/sand down, just draw in some more lines.  The closer the lines the finer the contour you can see.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5651



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5652

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #27 on: April 22, 2011, 01:10:05 PM »
The tail is built up of several parts as will be the wing.  This eliminates carving of lines and makes the part stronger.  When you get to the stubs, the grain needs to be in a different direction than the tail, so I used square stock for this.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5645

Notice the diamond drill bit is chucked up in a handle.  This can be used like a burnishing tool to shape your parts.  I mainly use it when digging out the front of nacelles.  This works great with diamond tools because there is not directional cutting surface and you take off less material at a time compared with using a moto tool.  You can do some intricate carving like this, a trick I learned from the ship modelers who need to do ornamentation carvings.

I cut the parts separately instead of making one part and cutting it into two pieces.  The stubs are marked so I can put square stock there.

Here is the rough part.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5646



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5647

And here is how the part looks cleaned up a little.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5648

And now the built up tail section.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5649

When gluing on the vertical to the horizontal, I first made sure everything was squared up.  Instead of wood pegs I am using brass nails, which are stronger.  When you can get everything to line up without a lot of pressure and fiddling about, you are ready to glue.  If you need to put pressure on something to get it lined up, the drying glue will shift the part.  Everything must sit together nicely with no aligning pressure needed.  To glue up the parts, put wood glue in the joint, but CA on the peg/brass nail.  Press the parts together and hold until the CA sets.  This will provide the clamping pressure needed for the wood glue, which gives the strongest joint.  I do this with wings as well and don't have to set up clamping rigs.  The peg and CA glue provide plenty of clamping pressure.

Ken Pugh

Balsabasher

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Re: B-25 Mitchell
« Reply #28 on: April 22, 2011, 03:06:10 PM »
Very neat workmanship Ken and your second B-25 is coming alive,the ring idea is excellent and I use a variation of this whilst carving,slip a piece of string around say the fuselage and eyeball from the front/rear as you carve,slide the string along checking for high spots etc,you will see them appear like magic as you do so ! simple and effective as your drawn rings are.
Barry.

lastvautour

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Re: B-25 Mitchell
« Reply #29 on: April 22, 2011, 03:09:12 PM »
Excellent tutorial on your project. Have you looked at my one piece wing?


It should give lots of strength to the finished model.

Lou