Haven’t printed the new doors yet. But I have been busy. I nailed down the turret curved back with all the doors, hinges, latches, foot rungs and bolt heads. I did it at least five times until I got it right. Each time I thought I had it all tied down, I’d put the STL version into the slicer and then would see something was wrong. Either some details were imbedded too deep or not deep enough, or they tilted in some way. The I saw that I didn’t use enough segments on the curved surface and it looked terrible. Then when all that was done, I found that somehow the pieces was about 3 scale inches too narrow. So I to fix too. All told it took much of yesterday and today to get it right.
SketchUp does not actually draw curves. It draws a series of straight lines that approximate curves. For circles the default is 24 segments. That’s quite clunky and in 1:48 would be very noticeable. To fix it you’d have to sand all the peaks down to curves, but all the details are part of the print and they would get in the way. For the tools that make curve parts, the default is 12 segments. When I’m doing a surface that I want to print almost a true curve I go minimum 48 and even better 96 segments. SU’s computational engine works harder the more segments that curves have. For graphic display purposes, SU smoothes the curves, but the segments are actually there and when you export as an STL, there they are.
Here’s an example:
The drums are R-L 24, 48 and 96 segments. With the curve smoothing they look like perfeect cylinders and if I were to print or render this, it would look great.
When I turn on “Show hidden surfaces” you see the segments, although the surface is still smooth.
But after STL conversion and loading into the 3D slicer, this is what the cylinders actually look like. In 1:48 that flats will be very noticeable.
One of the most difficult aspects of drawing the back wall was putting the details onto a curved surface. SketchUp works on an X-Y-Z coordinate system with X being the red axis, green the Y axis and blue the vertical Z axis. It is always best for many reasons to orient your drawing with the these axes which facilitates moving things around. That works great on a rectangular object with 90 degree corners. With a curved surface like this wall, only one spot in each quarter turn aligns with the axes. I drew all the details off the model, ensured they were each printable solids and then embed them in the curved wall’s surface. I actually push them into surface just a bit to ensure that the details don’t form detached in space. I they have separate supports, which many will, they could completely form, but not part of the print. When the wall surface is not on axis, when you move the object in the x or y direction it moves in an angle. So if I wanted to put the part in a specific location, I had to zig-zag and creep up on it. It took a long time.
Then about 3/4 the way through the exercise, I decided to copy and paste the completed wall to the master drawing. When I placed the wall against the rest of the gun house I drew previously. It didn’t fit! Frankly I don’t know when the size change. I say “changed” because the original curved wall was that gun house’s back wall which I copied and then added the two scale inch depth. This image shows the first wall I drew superimposed over the corrected wall. This difference was unacceptable. The side walls have to intersect with the 0.040" thick side walls with no gaps.
Here’s a vertical look at the wall over the main frame. Again, the wall has to key into the frame correctly. The new wall is on the frame and the incorrect one behind it.
I couldn’t just stretch the wall to fit. I had to start over. However, I was able to take all the details off as a group and preserve them. That sounds easier than it was since they were on slightly different distances from the center and lying on slightly different radii. Lots of trial and error. Notice I’ve thought ahead for a change. I included the mating flange that will connect to the straight side walls. There is angle brackets on the real turret that do the same thing.
Here’s how the finished product will look. Notice also the curved angle bracket that secures the floor and back wall to the frame. This is not the fianl look for this part. I have to study the pictures and drawings more.
And the finished front.
And in a more rendered way.
Here’s how the wall fits on the printer.
I’m using heavy supports on the wall itself and a lot of them. It’s not that there’s that much surface area, but it’s a bit heavy and that weight starts to play a part in the support scheme. All the details are supported by fine supports. Notice how fine the facets are on the surface using 96 segments. Very light sanding will remove them entirely. In 1:48 you can include ALL the detail.
While the attached foot rung will print, I’m worried about thier longevity, especially the ones hanging down below the lower edge. I will surely break them off. I am printing them in bulk so I can replace them if necessary. I’ve included a 0.020" stub on them that will fit into a drilled hole. Each rung has to be supported separately. I can make many of these fairly fast.
We’re heading back East on Tuesday. I may do some work tomorrow, but after that we’ll be gone a week.