Author Topic: B-25 Mitchell  (Read 10112 times)

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Ken Pugh

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Re: B-25 Mitchell
« Reply #30 on: April 22, 2011, 03:31:48 PM »
I'm going to keep that string idea in mind for quick and easy spotting.

I tried carving a one-piece wing with fairings on the P-47 and had several things I didn't like about it, including carving up so much wood.  Getting the wing of the B-25 lined up and symmetrical is a task I shy away from.  Plus, I am still developing ways of making larger models but on a small scale.  Big chunks of wood get hard to find.  I had so many glue joints fail on my first B-25 that I almost gave up and carved a new wing, but then I found the solution and all was well.

Ken Pugh

dave_t

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Re: B-25 Mitchell
« Reply #31 on: April 22, 2011, 03:48:22 PM »
I draw reference lines all over my fuselage while carving. I tend to carve one half of the fuselage completely up to the center line and then carve the other side to match, using the pencil lines to let me know if I am close to the right shape.

I like the one piece wing Lou.

lastvautour

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Re: B-25 Mitchell
« Reply #32 on: July 03, 2011, 02:59:05 AM »
Saw your pictures in the gallery. I like the way you made the wing to nacelle fairings. This is a problem area for me, but your method has given me new hope in this area. Are these pictures from the this Mitchell or your new one?

Lou

Ken Pugh

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Re: B-25 Mitchell
« Reply #33 on: July 03, 2011, 06:37:54 AM »
Pics are of the new one.  I made a big post of pics but have not gotten to posting here yet.  The methods used here will definitely be explained in detail, though I am already thinking of new ways to do some of these things!

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #34 on: July 03, 2011, 07:17:40 AM »
Sorry it has been so long since I have posted on this build but there have been many challenges here that interfered.

From the previous post, I got the aft end of the nacelles made then moved to the front.  The front circle was carved out as a guide for the rest of the shape.  Up needs to be marked because at the rear end there is a definite up and down that is easy to lose track of.  An error was made here that I had to correct later after the nacelles were glued to the wing.  Since the blanks are cut over-sized, one has to be careful to get things down to size as carving proceeds. I forgot to do this and had to saw off the front end.


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

With the front of the nacelle shaped, I then drew in the inside of the engine fairing.  Notice I use two pieces to make the nacelles just like I do with the fuselage, so the centerline is permanently visible.  Just need to mark the other centerline and the center axis of the engine is easy to find for drilling later.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5986

From this point I carved in the prop transmission.  I just hollow out around this and do not bother with engine cylinders because they can't be seen at 1/72 scale with my spinning props.  Cylinder area is just painted black but the transmission is painted gray because it is very visible.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5987

Completed nacelles.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5988

Ken Pugh

lastvautour

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Re: B-25 Mitchell
« Reply #35 on: July 03, 2011, 07:23:05 AM »
Please make as detailed as you can. I keep the putty makers in business  around here.

Lou

Ken Pugh

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Re: B-25 Mitchell
« Reply #36 on: July 03, 2011, 07:41:30 AM »
On to wing construction.  The B-25 originally had simple dihedral on the wings but there was a nasty dutch roll tendency that would have made bombing especially difficult.  This was corrected by using several fixes, one of which included breaking the wing outboard of the nacelle and re-attaching straight outwards.  It is an optical illusion that there is anhedral in the wing at this point.  The taper of the the outboard wing makes it look like it is drooping down when it is actually straight.

On the model, the inboard dihedral was sanded in with the same angle sanded on the outer surface of the inner wing panel.  The outer wing is then glued straight on with the aid of a spacer until the glue dries.  With care, the taper can then be shaped to get the distinctive B-25 wing shape.  On my first version of this model all of my wing joints failed no matter what glue was used.  I then used proper joinery techniques used by carpenters and they are now very strong.  All joints along the wing are reinforced, just as all parts glued to flat surfaces now have pegs.  It makes a tremendous difference in strength and also aides in alignment.  Get it right then glue and your parts won't shift while the glue is drying.  Boy, I hate it when that happens.

The individual wing components were cut out.  Make sure you have the grain running in the direction of greatest strength, another benefit of building in pieces.  The outer tips cut here were not used and I later made them of thinner material with the grain running perpendicular to the span.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5989

After the parts are shaped and the airfoil is complete, I drew in the control surfaces and carved them out.  The dihedral is also sanded in at this point.  Test them against the fuselage to make sure all is correct and make sure you hold both wings on at the same time to make sure everything is symmetrical.  Remember, get everything to fit now with no effort so the drying glue does not distort things later.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5990

I use Swiss chip carving techniques for my control surfaces.  This requires a special knife and a specific technique to do it easily.  You cut along your line at an angle, the cut along the other side at an angle.  The sliver then pops out and you have your engraving.  This knife is made so you can have the tip of the blade inserted like in the photo and have your thumb running along your wood as a guide.  Look where you want to go, not where you have been and you will get surprisingly straight lines.  When you get used to holding the knife the same way every time, your grooves will get very uniform, though it is a little difficult at this small scale.  One can also do this with other knives but it is more difficult and slower.  If your knife gets dull it will tend to come out of the wood and could end up in your hand (trust me on this one).  If you have to force it, sharpen your knife.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5991

Here is a comparison of two chip carving knives.  The top one is made by Two Cherries.  They made excellent knives but this is not a Swiss-style chip carving knife.  The bottom on is a Wayne Barton model.  He is a proponent of Swiss-style chip carving.  He specified this knife and has several books on the subject.  Just search for Wayne Barton if you are interested.  The top one does not properly align your hand and thumb, making the job more difficult.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5992

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #37 on: July 03, 2011, 07:51:32 AM »
Wing joinery.  You will use a key piece with the grain running along the span.  Test your saw blade on scrap would to see how big your kerf is.  If you are lucky, it will match a standard thickness of wood.  That is how it works out for me.  In this picture, carefully notice that both pieces of the wing panel are lined up and held together.  You then saw in the slot that will have the key.  Two work best to keep alignment.  These do not have to be perfectly aligned with the wing span, just make sure you cut them together.  Since they are not perfectly aligned, the keys really hold the joint tight and alignment is easier.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5993

Check your work and clean up your slots, if necessary.  Cut some keys with the grain running along the length of the slot.  You will glue along the joint and inside the slots.  This makes an extremely strong joint that does not shift as the glue dries.  Notice the spacer wood under the inner panel to hold in the dihedral.  This holds everything so tight I don't have to keep things clamped for a long time.  The slots are tight to the keys and not perfectly aligned, so the joint holds together nicely.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5995

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #38 on: July 03, 2011, 08:08:54 AM »
Nacelles to wings.  As I said before, glue joints need reinforcement.  Using two pegs assure the parts will not shift as the glue dries and keep everything aligned.  Hold the parts together and drill through.  Make sure everything fits well before applying glue.  If you have to use force for your parts to align, don't be surprised if they are not right after the glue dries, even with clamps.  I use a simple Clark Y airfoil though the original had a semi-symmetrical.  This gives a flat surface for the nacelles to glue against.  One could just cut in a flat area if the proper airfoil is used.  At this point the nacelle is too long, a problem I corrected later.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5996

Once the glue was dry I drew in the nacelle top fairings.  All of these areas are filled with wood.  Some just use filler, but I like to use as much wood as possible for durability.  You will use filler over this later, but get all this blocked in nicely with wood.  Just glue on scraps until all areas are filled.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5997

This view shows the fairing as assymetrical, though it is more symmetrical after I carved it out.  If you make sure there is plenty of wood, then you can just carve off what is not necessary later.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5998

The leading edge of the wing is only a little more challenging.  You can carve and fit these areas, but I just fill in with square stock until all the areas are filled.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=5999

At this point the top nacelle fairings are carved in and the wing tips are installed.  They are small but they still have two keys.  If you don't do this, don't be surprised if they pop off later.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6000

All is glued up and ready for scrutiny.  I still wasn't pleased with the shape and further refined it.  Remember, carve first, then file, then sand.  With a nice, sharp knife, you can slowly carve off extremely fine thicknesses and get the shape you want.  This is an area the beginner easily neglects.  When carving, you get to where it looks right.  Leave it laying around for a few days and you notice it is still rather thick.  There is more wood that needs to come off.  Shave it off thinly and slowly until it looks right.  After I reached this point with everything glued up, I still fiddled with it another couple of hours getting the shape to look right.


http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6001

Ken Pugh

Balsabasher

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Re: B-25 Mitchell
« Reply #39 on: July 04, 2011, 02:36:30 PM »
Excellent advice Ken on the carving sequence,I like the way that you have done those engine nacelle mid portions,the shape is tricky but you have pulled  it off well,the pegs and plugs are most effective and make for a tough model,your enjoyment of building solids comes through.
Barry

Ken Pugh

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Re: B-25 Mitchell
« Reply #40 on: September 20, 2011, 02:50:47 PM »
Now it is time to detail the nacelles.  The exhaust ports of the engines had individual covers in later models of the B-25.  This gave a significant performance boost.  The first time I did these I glued on pieces of wood and carved them down.  Unfortunately, the wood would frequently split halfway through.  For the other one, I planed the wood down to the proper thickness.  You then curve the leading edge, glue on the nacelle with CA, then cut it off.  Before you do any of this mark out the locations of the covers, including guide lines to show where they start and finish lengthwise.  In this shot you can also see the cowl flaps are carved in.  They are carved too deep, but the filler putty that fills the wood grain will fill this in some and bring the detail down some.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6316

Here is a completed nacelle.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6317

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #41 on: September 20, 2011, 02:52:35 PM »
The wood added in a previous step is carved down and filler smooths everything out.  At this point, I also filled the grain as done previously.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6318

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #42 on: September 20, 2011, 02:53:53 PM »
In this shot you can see the cheek gun fairings and the nose drilled out.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6319

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #43 on: September 20, 2011, 02:58:59 PM »
The tail has been slotted in and the wings drilled.  Everything is mocked up and checked.  If it doesn't want to stay in the proper position without glue, keep working on it.  If you glue it up without proper fits things will shift as the glue dries, even if clamped.  Take the time to get good fits then gluing is a breeze.

This was the first time I took the time to use my marking knife.  I marked out the tail location with the marking knife then started carving the slot.  I was quite surprised at how the tail fitted in nicely without needing to square up the hole.  My marking knife and I are now very good friends.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6321

Ken Pugh

Ken Pugh

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Re: B-25 Mitchell
« Reply #44 on: September 20, 2011, 03:04:35 PM »
There she is all primed up and waiting for paint.  She will have an intricate paint job and all markings will be painted on, no decals.  I have standardized my mounting method so I made up mount for building and painting.  The brass pins are made long so I can paint around the mounting holes while using the mount.

I usually don't post anything about the steps of construction until I am well past those steps to make sure that the method posted is the method that works.  I am now quite far along in painting and am working on the markings at the moment.  I have used a couple of methods for the markings and hope to have a good method to describe for those hating themselves so much as to want to paint markings in 1/72 like I do.



http://smm.solidmodelmemories.net/Gallery/displayimage.php?pid=6322

Ken Pugh