Stretch or Trim a Primitive

The user can stretch or trim one or more dimensions of a primitive so that its ends are defined relative to ‘target’ locations.

1. Make sure that the CE is the primitive whose dimensions are to be modified.

2. Select Modify > Stretch/Trim > option, the following choices are available for selection:

   • All Sides... - Changes all dimensions of the current primitive by a specified distance.

   1. On the resulting form, enter a positive value to increase the dimensions or a negative value to decrease the dimensions.

      Remember, when using this option on, say, a floorplate (BOX), that the height (that is the plate thickness) is changed as well as its length and width.

   • ID P-Point - Changes one dimension of the current primitive such that a specified p-point moves by a given distance.

   1. On the resulting form, enter a positive value to increase the dimension corresponding to the p-point or a negative value to decrease this dimension.

      The user is prompted to ‘Identify P-Point to Stretch/Trim’.

   2. Use the cursor to pick the p-point to be moved (which must belong to the current element).

      

   • To P-Point - Brings a selected p-point on the primitive to coincide with a target p-point on another design element which the user picks with the use of the cursor.

     

   • To Pline - Brings a selected p-point on the primitive to coincide with a target p-line on another structural design element which the user picks with the use of the cursor.

   • Clearance to P-Point - Brings a selected p-point on the primitive to a specific distance from a target p-point which the user picks with the use of the cursor. The use can specify a positive or negative clearance, depending on which side of the target p-point the clearance distance is required.

     

   • Clearance to Pline - Brings a selected p-point on the primitive to a specific distance from a target p-line which the user picks with the use of the cursor. The user can specify a positive or negative clearance, depending on which side of the target p-line the clearance distance is required.

3. When prompted, use the cursor to pick the p-point on the current primitive that the user will use to define its new length.

4. If the user has chosen one of the cursor options, pick the corresponding target item to be used to define the new position of the p-point.

As a simple example of the stretch/trim concept, consider here the adjustment of a length of handrail (remembering that a complete handrail contains two separate cylinder primitives).

The following figure is typical of those occasions when the user may use the Stretch/Trim facility. A platform has been created, complete with handrails, and a step ladder has then been added to give access to the platform. The problem here is that a post and part of the platform handrail block the exit from the ladder, as shown in the enlarged view.

A procedure for correcting this problem is as follows (it assumes that both a 3D View similar the figure and the Members List are visible on screen):

5. Pick any primitive which forms part of the redundant post.

6. In the Members List, move up to the owning Structure (that is the complete post/joint assembly).

7. Use the Delete > CE option to delete the complete post.

   The result is shown in the following figure (a):

   

8. Pick the upper handrail (which is a single cylinder running from the top of Post 1 to Post 2).

9. Select Modify > Stretch/Trim >To P-Point.

10. When prompted, pick that p-point on the current cylinder which is at Post 2 and then pick, as the trimming reference, the p-point at the top of Post 3 (the top of Post 3’s vertical cylinder).

    Hint: The easiest way to pick a specific p-point is to position the cursor anywhere on the required primitive and hold down the lefthand mouse button as the cursor is moved. The p-points are shown as blobs and the cursor shape will change from to when it is over a p-point. Zoom in closer to the view if enough detail cannot be seen.

    The upper handrail length will be trimmed so that it now runs from Post 1 to Post 3, as shown in the following figure (b).

    

11. Repeat the previous Step to trim the lower handrail back to Post 3, as shown in figure (c).

12. Use the Create > Handrail > Only option (as explained in Create Handrails) to fill in the missing length of handrail between Post 2 and Post 4. (This option adds both the upper and lower rails in a single operation.) The result is shown in figure (d).

Note: At each step the user will have the opportunity to ‘undo’ the change after observing its effect in the 3D View.