I happen to like the unusual/ rare varieties of allied tank used during WW2.

Superb work so far

I see you are using sketchup, something I'm "wrestling" with myself

How did you get the imported drawing to the correct size?

I'm trying to do something similar, I created a shape (aircraft canopy) based on 2 scans of the original, then traced 2 different shapes in Y and Y planes, but these were composed of dot-to dot trace & I can't get this as a solid so I can use this to cookie-cut the correct curves from my solid shape?
Hope that makes sense.

I have used Sketchup to output .Stl files & cnc milled them at Uni (I have some priveleges working here)
I could get this cut for you?
nb non-profit 1 copy each?

Iain,

It's a reasonable start, but I don't think you've quite captured the shape of the bustle at the back of the turretor how the rotor bulges blend (or don't) into the front part of the turret.

If you look at the photos Roy posted, you can see taht theh turret sides slope gently from bottom to top and that the radius if curvature wher ethe sides meet the roof is relatively consistent and relatively small (i.e.tight corners).

In plan (overhead) view, the front of the turret, forward of the transverse centreline, follows the outline of the turret ring, i.e. it round. It's only somewhat aft of that transverse CL that the turret elongates into the bustle.

If you need more photos, I have a bunch of the three remaining turrets.

Not trying to dump on you, just pointing out things so you can capture the intricate shape.
Paul

Think I may have bitten off more than I can chew, but determined to get it done.

A suggestion I might make from many years of 3D modelling (I'm a mechanical design engineer by trade and have been doing 3D CAD modelling for 12 years) is to get the basic shape of the turret correct first, omitting any radii where any two surfaces meet, like where the walls meet the roof or where the rotor bulges meet the turret face. Put those in only _after_ you get the basic shapes correct. Otherwise you're messing with those details and allowing them to change how you view the model before you get the actual basic shapes correct.

The photocopies overlap, but do contain all the information from the original, it's just a b!tch to stitch it all together properly for measurements, and the like.

Also, I'm, not sure what you are using to define the side of the turret up near the bulges, but something wonky has definitely happened there to throw off the shape at the outer end of the lower bulge.
Paul

Are you doing this all as surfaces? It would probably work better doing it as a solid and then, when everything is finished, shell it out to a rational thickness.