Author Topic: Halifax MkIII  (Read 1044 times)

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Model Maker

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Halifax MkIII
« on: January 17, 2017, 09:48:15 AM »
Starting a batch of 3 - Halifax MkIII's in 1/72 scale. Two will be gifts for friends whose father flew in an RCAF Halifax Mk III.

Fuselage and wings are rough cut. Station lines for cross sectional templates have been penciled in on one fuselage Not sure yet how on approach for attaching the wings to the fuselage. One fuselage is drilled for tenons. The other is cut out to accept a single wing combined with a fitted filler piece. Also not sure yet how to go about shaping the tail turret. I've left sufficient material in the cut out to carve it as part of the fuselage. Or alternately, I may shape it separately and then glue it in place.

I've shown the tools used for laying out the wings and fuselage. The vernier is much easier to work with than a ruler when transferring some dimensions such as centrelines from the templates to the wooden blocks. The fuselage incorporates a tang used for clamping in a vice for shaping and sanding. It will be removed near the end of the build.

A few of the requirements such as the nacelles and smaller diameter impellers will no doubt stretch my abilities. I've tested making 3 blade plastic propellers using Lexan which seems to be promising and creating a first row of cylinders of a faux Hercules engine. Once the build is ready for these items, I'll provide pictures.



« Last Edit: January 17, 2017, 11:52:46 AM by Model Maker »

lastvautour

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Re: Halifax MkIII
« Reply #1 on: January 17, 2017, 03:37:34 PM »
Looking forward to your progress.

Lou

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Re: Halifax MkIII
« Reply #2 on: January 18, 2017, 11:19:22 AM »
Have started to rough finish the fuselage and wing.

Photo 2 shows the the fuselage with the tang in the carving clamp and the dust collection tray underneath to collect the shavings.  The fuselage cross section is very boxy and the lines from the cockpit to the tail are very straight so I opted to use a chisel to true up the lines after bandsawing. Thin slices were removed to crop the high points as well as remove some of the kerf lines left from the bandsaw blade. I could have used a plane, but the grain was a little rough and I was afraid of the wood tearing rather than being shaved. Didn't want to use sandpaper yet, as residual aggregate particles can dull the edge of chisels.

Photo 3 captures the trimmed fuselage with the template stations added for reference during shaping.

Photos 4 & 5 illustrate the use of a low angle block plane with a bench hook to rough shape the underside of the wing and wing leading and trailing edges. A sharp low angle block plane makes quick work of this. Since the wing has a dihedral shape I was not able to utilize the plane to rough finish the top wing surface.

Photo 6 shows the chisels and bench hook used to rough shape the wing's upper surface. Due to the size of the surface I opted for chisels similar to shaping the fuselage but a little wider ( 3/4" & 1" - 18 mm & 25mm). Due to the width of the wing, a longer chisel was used to allow the chisel back to "float" on the surface and control the thickness of the shavings. The grain was a little tricky and I had to be careful not to allow the chisel to dig in. The key to this method is to hone the chisels before use to ensure the cutting edge is very sharp.
« Last Edit: January 18, 2017, 11:30:24 AM by Model Maker »

lastvautour

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Re: Halifax MkIII
« Reply #3 on: January 18, 2017, 12:58:08 PM »
I also prefer a wide chisel for shaping all parts. Thanks for the update.

Lou

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Re: Halifax MkIII
« Reply #4 on: January 20, 2017, 03:14:14 PM »
Since the fuselage is rather straight forward, I thought I would start with the wings first.

Photo 7 shows the reference lines for the air foil shape. Typically I  pencil in the chord line on the side. The Halifax airfoil chord is lower to the underside than the top side. I also pencil in the high point of the air foil top and bottom and key points were the curves take a sharp change in direction. These reference lines aid me in creating a uniform shape along the length of the wing.

Photo 8 captures the rough shaping of one half of the wing. I'm opting for a single wing design rather than two half wings for this particular model. Although not finished, the leading and trailing edges are taking shape and aligning with the top surface reference lines.   The initial shaping was performed using a chisel and my new vee block bench hook which cradled the wing very well. Once the initial chiseling was complete, the surface shapes were refined using a couple of files. My trusty honing board to touch up the chisel's sharpness can be seen to the side of the vee block bench hook. Nothing more dangerous than a dull chisel!!

Photo 9 shows both sides of the wing rough shaped. The bow sander with some rough sandpaper (80 grit) was used to smooth the surface. I'll start to use a couple of templates from this point to create the final shape. Files will be used from this point onward to fine tune the wing shape.
« Last Edit: January 20, 2017, 03:16:58 PM by Model Maker »

lastvautour

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Re: Halifax MkIII
« Reply #5 on: January 20, 2017, 04:35:31 PM »
Nicely taking shape.

Lou

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Re: Halifax MkIII
« Reply #6 on: January 21, 2017, 06:56:23 PM »
Thanks Lou - It's getting there slowly.

Continued work on shaping the wing and fitting it to the fuselage.

A cardboard template was used to continue shaping wing airfoil. The wing has been left a little thick to allow sanding to the finished thickness and profile. I certainly enjoy the new bench hook vee block for shaping the wing using chisels. In the past I was always concerned about the wing jumping the backstop or moving sideways using a standard bench hook. With the increased height and vee shape of the backstop, this is no longer a concern.

The fuselage wing slot was finished using a razor saw, chisels and file. It was cut a little narrower than the width of the wing to facilitate a tight fit. The skew chisel is a great tool for creating sharp clean interior corners. Once the fuselage slot was finished, the wing was fitted using a chisel to remove fine shavings from each edge. The wing has a slight angle of attack so each edge needs to be slightly angled rather than being square to the fuselage centreline.

With the wing fitted to the fuselage a filler piece has been cut and fitted lengthwise. Prior to shaping the fuselage in this area, the wing and filler piece will be glued in place. The filler piece will then be shaped with the surrounding fuselage profile to hopefully create a seamless profile. If not, a little filler will address any imperfections.
« Last Edit: January 21, 2017, 07:06:45 PM by Model Maker »

Model Maker

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Re: Halifax MkIII
« Reply #7 on: January 24, 2017, 08:53:01 AM »
On to rough shaping the inboard nacelles and fitting to the wings. The inboard nacelle is located on a horizontal part of the wing and it will be straight forward to cut out the wing profile. The outboard nacelles will require an angled wing profile cut out to account for the dihedral.

Blanks for the nacelles were cut on the bandsaw. Additional length was included for a tang to clamp the nacelle in the carving clamp for shaping. The tang will be removed after final shaping and sanding is complete. I am planning on 4 components for each of the completed assemblies - nacelle section + cowl flap section + engine cowl section with faux engine + engine cowl front section.

The wing profile was fine tuned using the nacelle template and the fuselage centreline.  This was an iterative process involving material removal and checking the nacelle template against the fuselage centreline. The wing chord is not parallel to the fuselage centreline but has a slight upwards incline (angle of attack) of approximately 3.5 degrees. The picture shows the final fitting with the template having a slight upwards tilt compared to the fuselage centreline.

The nacelle template was used to layout the nacelle outline on a blank. The outline and wing profile were cut using a scroll saw. But if a scroll saw is not available,a coping saw can be used. With a coping saw, it may be advantageous to first drill a hole of the appropriate diameter at the wing tip contour rather than trying to cut the tight radius by hand. The wing profile of the nacelle was adjusted using a combination of round (rat tail) and flat files with the tang clamped in the carving vice. This is an iterative process involving repeated material removal and installation of the nacelle onto the wing to check contact and orientation to the wing chord. Since the wing chord was set up parallel to the top surface of the wing section which fits into the fuselage, the top of the fuselage section it can be used as an initial reference for parallelism. Final fitting and check for parallelism / alignment to the fuselage centreline will be performed after finished sanding of the wing is complete.



« Last Edit: January 24, 2017, 09:04:03 AM by Model Maker »

Boomerang

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Re: Halifax MkIII
« Reply #8 on: January 24, 2017, 02:54:18 PM »
 

  Looking good Ken.

  Gordon

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Re: Halifax MkIII
« Reply #9 on: January 27, 2017, 12:59:33 PM »
Thanks Gordon. I'm slowly making progress. This model is a little more challenging than the Spitfires and Mustangs which I've previously completed.

Fitting the outboard nacelles to the wing profile is a little more complicated than the inboard nacelles. The wing tip has a compound angle (dihedral and leading edge taper) while the wing profile has a dihedral angle and a thinning cross section to account for.

A scrap piece of wood was planed on opposite sides at an angle equal to the dihedral of the wing.  This piece will be used for cutting out the wing profile from the nacelle and drilling the wing tip in the nacelle. Slots were cut into each tapered section to minimize the thickness of material to be cut by the scroll saw when cutting out the wing profile shape. To account for the wing leading edge taper, a small piece of wood was cut with the same angle as the wing taper. This small angular piece will be used with the base for drilling the wing tip at the correct compound angle in the nacelle.

The blank with the nacelle outline is placed on top of the wing taper section and base ready for drilling. The combination of the base and the tapered section on top results in a mirror of the compound angle. I have found it is easy to become confused on the required orientation of the blank when dealing with compound angles. To minimize errors,  I  placed a pencil indication of the required directions on the blank to ensure the blank is correctly orientated.  I also apply the rule "check twice, drill once".

Once the leading edge hole was drilled, the rest of the wing profile was cut from the blank. For this, only the wing dihedral angle needed to be accounted for, so the blank was placed directly onto the tapered base with the wing profile section placed over top of the base cutouts. The underside profile was cut close to the line, but the top surface profile was cut inside the line to provide some removal material for fitting.

After cutting out the profile, final shaping was performed using several rat tail files. As with the inner nacelles, fitting is an iterative process of filing, test fitting, identifying areas for further material removal and repeating until an acceptable fit is achieved.

An alignment and paralleness check was performed with all nacelles placed on the wing. The tang extensions provide a means to check the parallelism of the four nacelles by sighting over the top surfaces. If a wing contour is incorrect, the sighting will show the nacelle to be lower or higher than the others. I purposely incorporated a little looseness in the nacelle wing profiles to allow minor movement when they will be glued in place. Any gaps will be filled using wood filler.
« Last Edit: January 27, 2017, 01:39:13 PM by Model Maker »

lastvautour

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Re: Halifax MkIII
« Reply #10 on: January 27, 2017, 05:15:30 PM »
Good job on the nacelle mating.

Lou

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Re: Halifax MkIII
« Reply #11 on: January 29, 2017, 01:52:31 PM »
Thanks Lou - The joints are not quite as tight as I would like. But I have two more wings and sets of nacelles to fit so I'm sure my skills will improve.

Now that I have the nacelles rough shaped and fitted to the wings, I've moved over to the faux engine. The plan is to complete the faux engines, cowlings and air vents before finishing the nacelles. Because I will be fabricating the engine cowlings from wood, the outside diameter of the engine will be smaller than a scale engine to allow for the cowling thickness. The Hercules engine incorporated 2 rows of 7 cylinders but I an not sure the second bank will be very visible. During one of my surfing sessions I came across a build of a Revell model  Halifax. In this particular kit, only the first row of cylinders was modeled. So for this model, I'm opting only for one row of cylinders with a non scale diameter to provide the false (faux) impression of an installed engine.

There are 7 cylinders in each cylinder bank so the drilling and shaping etc. is based upon a heptagon (7 sided shape). To facilitate fabrication some templates were created to facilitate drilling cylinder holes, shaping the crankcase cross section and winding paper around a wooden toothpick to obtain a scale cylinder diameter.

The template for drilling cylinder location holes is taped to the dowel which is placed in the vee block for drilling. The length was determined by multiplying the dowel diameter x 3.14 (pie). This length of the centreline was then divided into 7 equal section.  The side lines will be used later as guidelines for cutting the dowel to the correct width.

After the holes have been drilled, the dowel is re-clamped in the vee block. The sides of the vee blocks provide a guide to cut the pieces square to the axis of the dowel. AS previously mentioned, the side lines on the template provide the guidelines for cutting to the correct thickness.

I initially struggled to find material which could be used to model the cylinder and also incorporated an extension to mount the cylinder into the crankcase for positioning and strength. After some playing around I opted to use a wooden toothpick as the base for mounting into the crankcase and winding a strip of paper on the outside to obtain the cylinder diameter. It took a little trial and error to obtain the required length of paper. But once the correct length was determined, a template of paper strips was created. The template strips of paper are cut to the correct length and width. Each strip of paper is passed through a pool of carpenters glue and then wound around a toothpick. Once dry, the cylinder assembly is mounted in the vee blocks and cut to the correct length.

To obtain the crankcase cross section, a paper template of a heptagon with centrelines was glued to the end face of the drilled crankcase using a glue stick. The centrelines are visually aligned with the centreline of the previously drilled holes around the circumference of the dowel. A sharp chisel is placed along each segment of the heptagon and struck with a single blow. Since the material is thin and a softwood dowel was used, the waste material is easily cut. Once shaped, the template is easily removed as the gluestick does not provide strong adhesion. The paper covered wooded toothpicks are inserted into the location holes to create a cylinder bank. If I had opted to go with two rows of cylinders, I would have created a second cylinder bank and then glued the two banks together with the rear cylinder bank rotated to align with the gaps between the front cylinder bank.


 
« Last Edit: January 29, 2017, 02:33:13 PM by Model Maker »

lastvautour

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Re: Halifax MkIII
« Reply #12 on: January 29, 2017, 03:57:58 PM »
Awesome engine build up.

Lou

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Re: Halifax MkIII
« Reply #13 on: January 29, 2017, 06:04:21 PM »

 It's a real pleasure to watch everything come together. Well done Ken !

 Gordon

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Re: Halifax MkIII
« Reply #14 on: January 30, 2017, 02:14:05 PM »
Thanks Lou and Gordon for the positive feedback. Hopefully there's a few tid bits of the build which folks will find interesting.

Switched over to making the parts for the engine gearbox and assembling the faux engine.

The gearbox portion of the engine is comprised primarily of two circular sections so I opted to model these using 5/16" and 1/4" diameter dowels. To facilitate alignment and the future propeller installation, holes were drilled axially in short sections of each diameter of dowel. The dowels were clamped using using the V blocks orientated in the vertical direction. Holes were drilled in each end to maximize the number of components which can be cut from each dowel. The drill bit's tend to wonder, so a centre drill was used to start the holes.

After drilling, the ends of the 1/4" dowel were rounded per the corresponding engine component.

Because the engine parts are short and must be squarely cut to consistent lengths, I put together a jig with a movable stop which can be positioned to facilitate cutting the dowels (or any other material) at different lengths.  The  fixed vertical guide and movable stop allow consistent lengths to be cut when multiple parts of the same length are required. When cutting the drilled dowels, minimal downward pressure is applied due to the thin walls. Otherwise material tearing occurs. - I learned that lesson the hard way!!

The two gearbox parts were glued together to form the gearbox. This in turn was glued to the crankcase. I am a little worried about mounting the propellers due to the scale, so a 3/32" outside diameter brass tube was installed. The tube extends beyond the gearbox to mirror the engine shaft. The propellers will be attached to the shaft using a 1/16" diam. solid brass rod which fits inside the 3/32" brass tube. With the 3/32" tube temporarily installed, the faux engine is complete and ready for a light sanding. Just prior to mounting the propellers, I will position the 3/32" tube with the correct length extending and epoxy it into position. 

After sanding, the engines will be placed into a container of shellac. The shellac should impregnate the paper and act as a long term bonding agent as well as providing a sealer / primer for painting.
« Last Edit: January 30, 2017, 02:30:49 PM by Model Maker »