Hi Ralph, if you can post your cylinder 3DM model file it would help a lot to answer your question more specifically, it's pretty hard to know what might be going wrong just from a written description alone.

Some general things to watch out for though - for 3D printing you want your original object to be a solid before you export it to STL. The first thing to check is whether it's reported as a solid in MoI or not, to do that select it and then look at the object type indicator in the upper right corner of the window, here:



If that say something other than "solid" (like if it says "Joined srf" or "surface") then it means your object does not form a completely closed volume and has some open edges in it that are not glued to other edges. That can mean missing surfaces or some places that need to be repaired. To find the particular problem areas you will need to set up a keyboard shortcut with a script on it that will show naked edges, check here for how to do that:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6051.2


> So How do I fix the hole or how do I build a cylinder correctly?

For fixing the hole the exact steps kind of depend on the specific problem, that's why it's very helpful to post your model file. If it's a big missing surface then you need to construct a surface and get it joined in to the other model, if it's a missing end cap then selecting the cylinder and running Construct > Planar is the easiest way.

The easiest way to build a cylinder is by using Draw solid > Cylinder, that will create a solid cylinder directly from the start.

- Michael

First thing re: Cylinder thats not a Cylinder it is a Slug. A Cylinder is open there should not be closed ends. The is like a Piston which goes inside a Cylinder.

It should ask for Radius, Height, Base and Wall Thickness.

I am trying again I should be able to do this with simple extrudes.

Thanks for the reply.

edit......................................................

Well I know that is what's called a Cylinder but it's not the kinda Cylinder I am looking for.

Here is how I am drawing a closed end Cylinder (Can)

Drawing a Cylinder using MOI

Desired a one end closed Cylinder (Can):
20mm outside diameter
14mm inside diameter
3mm base

Start from Bottom view
Draw a Outside Circle name Outside (20mm)
Draw a Inside Circle named Inside (14mm)
Select both circles
Extrude 20mm Cap both ends
Select just the inside circle
Extrude 3mm
Boolean Union
Select all
Delete Inside
Delete Outside
Select all confirm Solid

Hi Ralph, another possibility is if you start with the base solid cylinder (draw solid > Cylinder), you can then use the Construct > Offset > Shell command to hollow it out and give it wall thickness.

To do that, after you draw your base cylinder, before doing the Shell select the top face (click once on the cylinder and then click a second time to "drill in" to select the face). Shell will make openings in the thickened result on the selected faces. So then run Construct > Offset > Shell and put in your thickness. The same thickness will be used throughout so you'll need to tune up the base still with that way with another extrude and boolean union.

Also instead of shell you can select the top face and run Construct > Offset> Inset , which has an option in it for making the inset depth to be set separately from the wall thickness. That's probably the overall least number of steps way.

- Michael