Boeing Y1B-17 Project--1/48th Scale

[Second Air Force]

Excellent tip, Nico! That's the kind of information I hope comes out in the vacuform discussion.

I still remember the very first vacuform kit I purchased and how near-impossible it looked to me. After working with the stuff, and learning from others, I got to a place where I didn't mind building with vacuformed parts. I must confess that I never did finish the old 1/72 XB-35 Flying Wing, though--the styrene kit came out before I ever got up enough intestinal fortitude to build my vacformed one!

Scott

[Second Air Force]

It's raining today so I did a little sanding. Here's a photo of the left fuselage half after removing most of the flash. You can see a little pigtail of material on the edge, a sign that you're just about at the correct sanding depth. From this point on you have to use a very light and even pressure on the part so as not to go too far:

Boeing Y1B-17 Project--1/48th Scale

A couple of shots of test-fitting of the two halves after sanding. Notice that there is a tiny bit of a gap at the vertical fin/fuselage juncture--I still needed to touch up the top of the vertical fin to finish this part of the process. On larger parts it is sometimes difficult to uniformly sand all the surface at one time because vacuform pieces are usually a little bit more flexible than their styrene molded cousins.

Boeing Y1B-17 Project--1/48th Scale

Boeing Y1B-17 Project--1/48th Scale

The same process, this time on the horizontal stabilizer halves. I usually start by sanding the entire half as a unit, keeping it on the sandpaper with even pressure (providing that the part doesn't have dihedral, of course).

Boeing Y1B-17 Project--1/48th Scale

After getting through the flash it's time to fine tune the process. For this part I sand only the left and right halves of each piece individually so as to get a uniform leading and trailing edge thickness.

Boeing Y1B-17 Project--1/48th Scale

Boeing Y1B-17 Project--1/48th Scale

And here are the two halves after sanding and finessing.

Boeing Y1B-17 Project--1/48th Scale

Boeing Y1B-17 Project--1/48th Scale

You can see from the last photo that the trailing edge is still a bit thick. With careful sanding you can achieve a knife-edge on most vacuform surfaces, especially on a Koster kit. In this case I'm going to be cutting the elevators and trim tabs loose from the stabilizer later and I'll finish the thinning of the trailing edges then.

More later,
Scott

[No.1]

Amazing work mate! Is there any need to add framing inside, to keep shape precisely?

[Second Air Force]

Yes, I'll be adding some extra reinforcement to the horizontal stabilizer. Since I'll be removing the elevators I'll be able to add the spar in the same area as the close-out for the elevator well. On that F-89 I built years ago I made an aluminum carry-through spar in order to keep the wings from drooping in later years. It worked quite well in that application.

Planning a vacuform kit is really harder than building it. On this project I cut out and sanded all of the major pieces before starting to modify them. The fuselage halves need to have a lot of work done around the waist windows, for example. I'll temporarily assemble the two halves before I start cutting so as to keep everything stable and dimensionally accurate.

Scott

[Nico Braas]

For fuselage vacform part I advise to strengthen it with internal bulkheads.
Just one will give an enormous improvement of stiffness.
As glue you can try regular polystyrene plastic cement, especially for wing and horizontal tail parts. For fuselage halves I would advice polyacryl glue. It gives a good bond and excess can be easily sanded away.

[Second Air Force]

I tend to agree with Nico on adding transverse bulkheads in the fuselage. On this model I won't be able to add any full bulkheads as I want the entire aft fuselage to be open for viewing. Instead I'll build up several frames with longerons and stringers to help beef up the fuselage much like Boeing did it. Fortunately the Koster kit is molded of sturdy plastic and can be built without much additional strength.

Here's another little update. One of the modelers on WIX, Steve Nelson, posted a suggestion to use a marker pen to outline where cutouts are to be made and around the perimeter of parts when cutting from the sheets. I added that process into the update.

I followed the tip that Steve posted about outlining cutouts with a Sharpie and it is a nice guide for trimming, indeed. On a Koster kit there is a light outline molded into the parts such as where the horizontal goes through the aft fuselage. I simply ran the marker around the perimeter of the molded-in guide marks in this instance.

Boeing Y1B-17 Project--1/48th Scale

I should mention for those who haven't done much vacuform modeling that you have to be careful when cutting holes into the fuselage halves for wings and stabilizers. Study the particular kit you're building to make sure that the left and right halves agree with one another. I once built a Wyvern that was molded with the left wing opening 1/4" further aft than the right. If I hadn't done some measuring first I would have made a mess of it. Today's kits, and especially the products I've gotten from Koster, are very accurately molded but some of the old vacuforms weren't quite so precise. It makes building vacuform all the more satisfying when you are able to build a poorer quality kit into a presentable model, but it can also be exasperating to make cuts that don't line up. Measure twice, cut once!

Here's the stab cutout during trimming. Lots of filing and test fitting, but the process isn't anything difficult.

Boeing Y1B-17 Project--1/48th Scale

After making both cutouts I slid the horizontal into the fuselage. Notice that it isn't 100% perpendicular to the vertical in this photo. A tiny bit of tweaking will make this come into line. I'll probably build a little fixture so that I get it just right.

Boeing Y1B-17 Project--1/48th Scale

Just because I could, I assembled the sections together for the first time to get a feel for how the airplane will look someday. I haven't built a 1/48th B-17 for twenty years---darn it's big!!!!

Boeing Y1B-17 Project--1/48th Scale

Boeing Y1B-17 Project--1/48th Scale

Scott

[No.1]

Great work and good point on marker use. When I need to mark anything I use CD label markers, they are very thin and can write on almost all surfaces. Must say that I am impressed how the shape is well positioned and how it fit to the rest of the airframe!

[Second Air Force]

I am sure I've already done so, but here is another shameless plug for Koster vacuform kits. The fuselage halves fit perfectly into the original Monogram forward section with only a very minimum of work. I've never been disappointed in anything Mr. Koster has produced and can hardly wait to start working on the PB4Y-2 modification that I photographed earlier.

Scott

[Sall]

 

[Letipapa]

Very,very informative and useful, Scott, thank you for that!

[Second Air Force]

Very quick update--a couple of pictures of the waist and ventral gun openings. Next will be making the die for vacuforming the actual blisters.

Boeing Y1B-17 Project--1/48th Scale

Boeing Y1B-17 Project--1/48th Scale

Scott

[Sall]

Great job!

[draken35]

Find so too

[Second Air Force]

This evening I tackled the problem of making the gun blisters. I first got out the calculator and calipers, figured the size of each emplacement in 1/1 and copied No.1's profile view of the lower blister, scaling it to 1/48. Here's some of my math project and the final size of the lower blister:

Boeing Y1B-17 Project--1/48th Scale

I then laid the drawing up against the fuselage to get an idea of the dimensions before committing to making parts:

Boeing Y1B-17 Project--1/48th Scale

Here is the first mold being made for what will become the male master that'll go in the vacuform machine:

Boeing Y1B-17 Project--1/48th Scale

The first male die just after being popped out of the mold. Now I will start the shaping and fitting process, and once I'm happy with the result, I can use this piece of resin to vacuform the clear parts. If I make a mistake, I can always pour as many more pieces as needed to get the four enclosures.

Boeing Y1B-17 Project--1/48th Scale

Scott

[Profa]

Almost like building a real thing...