Morningstar's Musings: A bigger bang for your Buck

Now i've been playing around on and off with Autodesk Inventor, trying to create CAD model of bits I want for my railway or models.
Now like all modeling you need good source material to work from, pictures, blueprints, sketches etc.
I'm not very artistic I can't draw freehand for toffee, the only picture I ever really liked that I did in art at school(cough 30 years ago!) was of BR Class 31, and that was more a tech drawing than freehand it was 3/4 view from the top.

Now i've been looking at WW2's wonder weapons, and have a few of them in kit form to make, Germany's large Railway gun, America's Atomic Bombs. In the World of 1:144 there doesn't seem to be much of a selection of British Wonder Weapons, I did find this one https://www.shapeways.com/model/844351/1-144-panjandrum.html, https://www.youtube.com/watch?v=a-MBgkSijcc
great for scaring the odd dog it would seem....

To that end I decided to have a look at the RAF's munitions, some of the Upkeep Prototypes were quite interesting shapes, especially the the giant golf ball! Would the Lancaster crews have had to broadcast on their radio's "Fore" to Germans below as they dropped it?? Barnes Wallis the designer of the Upkeep bomb had originally proposed to make a huge 6 engined Victory Bomber to carry a 10 tonne earthquake bomb to shatter the dams from high altitude. The bomber never came to be but the 10 tonne bomb eventually did.

The 22000lb (10 tonne) Grand Slam Bomb was eventually carried by a heavily stripped Lancaster B1(Special), all armour and armament removed except for the tail gun. They only dropped 42 of these most notably on the Bielefeld Viaduct raid where along with its smaller sibling the 12000lb Tall Boy Bomb, another Barnes Wallis design, manage to shake down 100 yards of the viaduct. The Tall Boy was able to drop from an almost unmodified Lancaster, it just had to have bulged bomb door to accommodate the bomb in the bay. Four Tall Boys eventually did for the Tirpitz, three direct hits and near miss, and over she rolled in the Tromso Fjord. The Tirpitz had already survived two previous raids with Tall Boys, in the first raid one went clean through the bow deck and out of the keel before exploding, in the second raid her one rudder was disabled and severe flooding caused by near misses.

Well thats the preamble, no back to the point.....
I found a nice diagram of a Tall Boy bomb with some key dimensions on it to work on a little learning project on Inventor CAD package. Dimensioned Tall Boy Bomb (the diagram is about 1:25ish)

Drawing the the actually bomb body was quite easy, a simple profile sketch that then gets rotated to make the solid body shape. I was intending on drawing the bomb at the final intended scale of 1:144 directly, I'd already drawn up a table of the dimensions derived from the diagram with a vernier, but as it's good CAD tool I drew it full scale.(This would prove a problem later!!!)
Drawing the fins was a nightmare, I couldn't get the CAD package to draw them as I wanted, Inventor has feature call Loft that lets you extrude for one shape to another, much watching of YouTube video tutorials ensued and I figured it out, you needed 3 sketches of the aerofoil shape to make it work, the tip, root(in my case bomb center line) and another one in between the two. Now once you have one fin you get the CAD tool to produce 3 more to complete the circular pattern.
Right, forgot to off set the fit so quick manipulation of the three aerofoil sketches and everything recalculated and then redrew itself.
Now heres where I cocked up taking the full scale CAD model down to 1:144.... Curse you decimal points!!!!
1/144 = 0.006944444444...
So using the Inventors Derive tool, I selected my finished model and typed in the scaling factor....
Great everything looked ok still.
Now come the next big thing, lets see if I can get a 3d print of it from one of the on line 3d fabricators.
I upload it and got a warning back your item is too small to print....
Hold on an minute it should be about 44mm long and 7mm in diameter that miles bigger than their minimums.
Gah, found a mistakes in what I'd done, I'd used 0.0006944 as the scaling factor so now the bomb was 10 times smaller, hence why no print!!
By chance while looking for more dimension for the Grand Slam I found another modeller stating all you need to do is multiply a Tallboy by 1.2 and you end up with near enough a Grand Slam, actually it needed to be 1.23 to within a millimeter or 5 on the full scale drawing, by the time its 1:144'd you'd never know!!
So folk's if you want some small model large bombs they can be found here
Tallboy http://shpws.me/rknf
Grand Slam http://shpws.me/rkGV
Hopefully in early April I will receive my initial prototype prints.....