Having created a cylinder with a hole through it, I want to select the flat face at each end. For cylinders in which this face is wide (a large difference in diameter of inner and outer circle), there's no problem either clicking on it with the mouse, or selecting it using find. However, if I make a thin walled tube, the end surfaces can't be selected with either the mouse or the search option. Is there a simple way to solve this problem?
Having made a circle to extrude, there is a lower limit on the extrusion depth (the diameter is 20m, whilst I want a depth of only
In your second example, with a cylinder diameter of 20meters(20x10^3mm), and a thickness of .03mm the ratio difference is approx .03/(20x10^3 * 1.414) = 1.06x10^-6.
I use the diameter multiplied by the diagonal of a bounding box to find the approximate longest fiber.
1.06x10^-6 is the approximate RELATIVE accuracy required to create this feature, I believe.
For example, if the relative accuracy is set at the default of .0012, with the 20m diameter cylinder the minimum length would be about 1.414 * 20x10^3 * .0012 = 34mm
Remember this is the smallest the feature may be, if this is not the first feature of your part, the real result may be larger.
Several articles have been written in the last 3 years with respect to accuracy, and the PTC knowledge base has an OK explanation.
You may be able to create and use the features you outlined.
You cannot go lower than 1x10-6 for accuracy values.
BTW, PTC is probably well aware of accuracy issues for long, thin parts (piping), because the piping module uses a different accuracy to work around this.
Surfaces seem to be unaffected by this, and you may be able to make this feature a surfaces, although you may not be able to knit it to a solid.
I tried the above example, and with my RELATIVE accuracy set to .0001, I could create a protrusion of diameter 20000 only with a thickness of 0.5 . If I tried to make it .1 thick, the system complained that the minimum thickness of the feature had to be larger than .47319.
I then changed the relative accuracy to .00001 and the system complained now if the thickness was thinner than .047319 (good, the change is linear)
By changing the accuracy to .000001 (1x10-6) I was able to make the thickness .03 .
BUT, in my first example .47139 / (20000 * 1.414) = 1.67 x 10^-5, or approx 1/6 smaller than my accuracy value of .0001 relative.
AND, when I change my accuracy by more than 6x coarser, the feature fails.
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