|Musings with coffee|
Sitting here with my morning coffee while cleaning up the current mesh a bit. One of the things that becomes more and more important with a Sketchup construct as it becomes – more and more complicated is to divide it up into sections. This allow you to modify/affect one section with affecting the others. A Sketchup mesh can be pushed and pulled much like warm taffy .. pulling on one bit stretches the part you are pulling on and everything that is attached to. While this might be exactly what you want – often it is not. An example is the bit in the distance in the pic here .. the shaft support. I made the hole for the gate control approximately 1/2″ dia as that seems to me to be a logical size for the mechanism. If it is determined that it needs to be .. 3/4″ dia then it would be much easier to modify the gate control for that new dimension before adding back to the entire gate.
Doing something like that .. enlarging the shaft hole from 1/2″ to 3/4″ becomes more involved since you have to always keep in mind that the end purpose of this is to create a 3D mesh that can be uploaded for printing. Since I am designing for FUD I have to keep in mind then the design guidelines for that material.
I said ‘approximately’ 1/2″ dia shaft. In 1:48 1/2″ equals 0.0104~” .. more or less .01″. That is 0.264~mm. I made the hole 0.254mm dia. Am I crazy? lazy? .. nope. If and when I have this printed I will want to use a nominal wire size. I have some 0.010″ music wire .. which is .. .254mm .. that’s the sort of thing you have to keep thinking about.
So. Look at the pic. The shaft hole is 0.254mm. The surrounding boss is 0.8mm and everything sits inside the casting that measures 0.853mm tall. Do a little math and the wall thickness is 0.273mm .. OOPS. That is already a ‘fail’ most likely. The FUD design guidelines specify a minimum wall thickness of 0.3mm .. meaning that this needs to be fixed. It *might* slide by the automated software checks .. but things like this are a lot simplier if I just make the walls thicker now. The gate control is MUCH easier to modify as a separate mesh. Note that I need to increase the thickness of the walls by 0.027mm .. not much at all .. about 0.001″. Silly yes .. what does 0.001″ matter? Probably not much and possibly would slide through the automated checks. Probably though can get you in trouble (if you have a map for passage through a minefield .. that is *probably correct* .. you might regret following it .. for a bit)
If Russ informs me that .. a 3/4″ dia shaft would make more sense then more radical measures would be required. In 1:48 – 3/4″ equals 0.015~ .. or .. 0.397~mm. If I was going to use this dimension then I would use the 0.15″ dimension exactly (.381mm). That would calculate to 0.72″ dia .. ‘close nuff’. Adding the 0.3mm wall thickness would then give a boss measuring 0.981mm. That’s larger then the current height of the shaft casting shown (0.853mm) requiring the made larger also.
The point of all this is that .. I can modify this gate control as I need and when finished I can then ‘stick’ it back to the top of the rest of the model.
I put some dimensions of the bits and pieces
Here’s something else. Looking at the pieces of the gate separated into individual sections, I put dimensions of them. The minimum size of an object printed in FUD is 5x5x5mm. This is simply that a human has to pick them up and Shapeways considers this the smallest that their workers can reliably handle (find). Notice that the gate shaft casting at the far end only measures 4.667mm .. meaning that is too small to be a separate printing. That’s no problem here because (probably) it will be part of the center barrel-like object. Just pointing out that you have to keep in the back of your mind these things.
The reason the near vanes are while and the rest of the mesh is green was that I am cleaning it up. Going though bit by bit .. fixing holes in the mesh; removing un-needed lines and so on – and coloring it white as I finish each piece. This makes it easier to keep track of where I am. Color has noting to do with printing in FUD .. this is simply a visual help while designing.