Curving tubes

Tubes can be bent in BikeCAD using the Curved check box. For tubes in the front triangle, you'll find the Curved check box in the Tubing dialog box.

For chain stays you'll find two Curved check boxes in the Chain stays dialog box. One check box curves the stays in a way that is visible in the side view and the other check box curves the stays in a way that is visible in the auxiliary view.

Similar controls are found in the seat stays dialog box, with one check box for curves in the side view and another for curves in the auxiliary view. Note that if you select a wishbone seat stay you will gain an additional option for curving the seat stay in the side view.

This option is called Raked. It is meant to accommodate an approach to curving the seat stays that was used in an older version of BikeCAD. Because raked stays are controlled using a different dimensioning scheme, this may still be an option you'll want to explore for current designs.

If our design includes any extra tubes, the curved check box for those is found in the Extra tubes dialog box.

When bending tubes, it's helpful to display the dimensions used to control those curves. For most curves in the side view, you'll find the dimensions in the Tubing tab of the Dimensions dialog box. Here, for example, we see all the dimensions controlling the seat stay curvature in the seat stay tab, which is a subtab of the Tubing tab. Dimensions relating to curves visible in the auxiliary views are controlled in the Stays (auxiliary view) tab. Here, for example, we see all the seat stay curve dimensions in the Seat stay subtab.

Curvature dimensions for Extra tubes are found in the Extra tubes tab.

The actual mechanics of applying bends to tubes is the same for all tubes, so I'll demonstrate on the top tube. If we apply a single bend, dimension A is the distance along the line connecting the two end points of our tube, where the deflection occurs. Dimension A can be expressed as an actual distance in mm, or as a ratio of overall tube length. Dimension B is the amount of deflection applied to the tube. Dimension B can be either positive or negative. Dimension R is the radius of the bend. If we set the radius to 0mm, we'll see that dimension B goes all the way to the corner of the bend. Notice that as we increase the radius of the bend, dimension B still points to the theoretical corner of that bend. Notice also that you do not have the option to directly input the angle of the bend. However, the bend angle is one of the dimensions that you can show on the screen. If you are looking to model a bend with a particular angle, you can play with dimensions A and B until the desired angle is achieved.

If we opt to apply two bends, we gain dimension C, D and small r. Similar to A, B and R, dimension C locates the point at which the deflection occurs, dimension D defines the amount of deflection and dimension r defines the radius of the bend. Like dimension B, dimension D can be either positive or negative.

When curves are applied to any of the tubes in the front triangle, notice that the icons defining the extension of the seat tube above the top tube as well as the extension of the head tube above and below the top tube and down tube becomes locked in the mode of defining this extension as the distance along the centerline of the seat tube and head tube. The option to define the extension by a distance measured along the edge of the tube is no longer available. When modeling bends in tubes, it can be helpful to turn on the problem curves checker. For more on the use of this tool, see the video on identifying problem curves in BikeCAD Pro.