The first thing before designing am item is to be well aquainted with the capabilities of your printer, because this will heavily influence your design.
For the UP printer, these are the following constraints which need to be considered:
Minimum wall thickness (XY): 0.7mm
Minimum trench (sharp definition) (XY): 0.4mm
Minimum trench (XZ): 0.2mm (rounded edges)
Minimum trench (sharp definition) (XZ): 0.4mm
Minimum thickness for things like mudguards (XZ): 0.6mm to avoid a lacy finish.
Prefered Zaxis step 0.2mm ( to suit UP Mini)
These numbers will determine what details need to be omitted, or beefed up overscale to print.
It is easiest to work off a good set of 2D drawings. However, many of these drawings are wildly innacurate, so picking good ones is essential. Checking known dimensions against the drawings is a good start. I tend to favor the later issues of Panzer Tracts and the Speilberger books for German vehicles. For US vehicles, the Hunnicutt series is the go-to set of reference. The Bradford books of scale plans are a good starting place especially for British and Russian vehicles, but often contain minor innacuracies. (Given the overscale effect of adjusting the model for printability, this is often not a real issue.) Also there are now many specialist modeling books like the Nuts and Bolts, and Kagero books which contain nice and accurate drawings.
( I have all the Speilbergers, most of the Panzer Tracts and Hunnicutts, plus over 200 reference books (including 30+ Jane's)... )
Once you have a good drawing, you need to establish the scale it is printed in by comparing the drawn size vs a known dimension. (Good drawings have a scale bar.) Just because the drawing was meant to be printed at 1/35, say, doesn't mean the printer got it right. The Bradford books especially suffer from this.
Usually there will be a 20ft bar ( or similar).
20x12x25.4 / measured size = scale factor
To get to 1/200, I then divide the scale factor by 200.
This resultant number is used to multiply every dimension measured off the drawing to give the 1/200 size.
Remember to double-check the real size/200 vs the measured size x resultant scale factor. They should be the same...
Drawing the unit, I always start with a side-on sketch showing the track outlines, wheels, and hull profile.
Sizes are adjusted to fit the parameters above, especially track thickness 0.6mm for delicate tracks, 0.8mm for heavier, 1mm for very heavy. Wheels are positioned so that they intersect the track by approx 0.2mm to ensure that there's something holding the tracks together.
See pic1
I tend to fully draw one side of the vehicle, where symetrical, and mirror all the events when done, then add all the assymetrical details.
This is the time where lots of reference photos are required, to see if that bit goes in, or out, and at what angle... this is where you'll find the errors in the drawings. Minor ones I ignore, major ones I go with the photos.
Try to keep XZ axis gaps 0.5mm or bigger if you need to remove support from them. My most used cleaning tool is a chunky Xacto holder with an old blade which I have filed off the cutting edges from. This makes a fine prodding tool with a 0.5mm thick, strong blade which is too blunt and unpointy to stab myself with.
Pic2 shows many of the above discussed points, ie thick trackguard brackets, wheels intersecting tracks, slightly exaggerated gap above track for cleaning out supports. It also shows one trick for making finer detail that the printer thinks it is capable of. Detail, either raised or recessed, with a 45 degree chamfer to its edges will print. You can get away with a mere 0.4mm wall on XY as long as the sides of the inside slope inwards at 45 degrees, same in XZ with raised detail as you can see on the tool boxes of the Luchs.
Model, pic3
I prefer to print my gun barrels parallel to the build table ie flat, which is why I draw them with flat bottoms, to give the support something to build on. At 1:200 you really can't see the difference.
One final note: on the Up, at any rate, for some reason you get nicer XZ surface finish AND far better results with the bottoms of wheels if you rotate the part 45 degrees in XY on the build table.
Post's attachmentsluchs1.jpg 326.92 kb, 1 downloads since 2014-09-12
luchs2.jpg
luchs2.jpg 107.24 kb, 1 downloads since 2014-09-12
luchs3.jpg
luchs3.jpg 61.31 kb, 1 downloads since 2014-09-12
You don't have the permssions to download the attachments of this post.