Hi Alligator, there are a few different ways to do it, but possibly the most simple way is to draw in a line that's 40mm long and then snap on to the other end of the line when you're creating the other cylinder. Sometimes it can also be easier to with 2D curves first, so maybe draw in circles instead of directly creating cylinders, then extrude those circles into cylinders when they are all positioned. Or if you were going to be using the cylinders for subtraction there is actually no need to extrude them, you can just subtract the 2D circles directly inside the boolean command. It's usually easiest to work with 2D curves when possible.

In order to draw a line of a specific length, type in the length while you are in the line command. That will activate "distance constraint" which makes the endpoint of the line to be that specific distance away from the start point.

So the steps for that are: Run the Draw curve > Lines > Line command. Place the first point of the line and then before you place the second point and finish the line, type in 40 and push Enter. Now you can place the second point in the direction you want and the endpoint will be located 40 units in that direction. Usually when drawing you'll want both "Straight snap" and "Object Snap" to be enabled on the bottom toolbar, if they are not highlighted in orange then enable those so you will get various snaps to help you out.

Then draw your circles snapped on to the ends of that line.


Another way you could do it would be to place the first circle where you want it, then select it and run the Transform > Copy command, then pick the center point of the circle as the base point, then activate distance constraint (type in 40 and push enter) to make a duplicate of the circle 40 units away. You can use distance constraint anytime you're in a command that picks multiple points.


Also another different way is to use "relative coordinates". For that, draw in your first circle, and then start up the circle command to draw your second circle. For the center point of the second circle, type in: r40,0 and push Enter. (that's the letter R at the front there, then 40,0 as x and y coordinates). That will set up an offset of 40 units in the x axis direction for the current point pick, so now go snap on to the first circle's center and the new circle that you are drawing will start at 40 units over from that one.


You can also use distance constraint with object dragging if you enter in the distance before doing the drag, so another approach would be to make one circle where you want it, select it and then duplicate it using Ctrl+C / Ctrl+V, now type in 40 and push enter and then click and drag on the circle and it will drag around but in an increment of 40 units from it's start position.


Let me know if you are still stuck.


- Michael