Lugs (Modeling)

The option to represent lugs was initially added to BikeCAD so that certain paint schemes could be represented. For example, one might like to paint the lugs one colour and the tubes another.

Since aesthetics were the driving factor in adding lugs. The option to display lugs is found in the paint dialog box accessible from the Paint icon.

There are two paint schemes that display lugs. The Lugs scheme uses the first of four frame colours for the tubes of the front triangle. The second colour is for the seat stays and chain stays. The third colour is for the bottom bracket lug and seat lug and the fourth colour is for the head tube lugs and rear dropouts.

The Lugs with Panel scheme uses a single colour for all the tubes of the frame. The second colour is for the panels on selected tubes. The third colour is for the trim on the edges of the panels and the fourth colour is for the lugs and rear dropouts.

You may not be able to capture every nuance of the contours of your lugs with the controls available. However, you can edit values of E, F, G and H to approximate the basic appearance of your lugs.

The angles of the lugs will always change to accommodate the geometry of your particular frame design. Similarly, lug diameters will change automatically with changes in tube diameters.

When building a TIG welded frame, it is common to define the attachment of the down tube to the head tube by the distance the head tube extends below the bottom edge of the down tube mitre. Meanwhile, lugs are often sold with a published value for the down tube / head tube intersection point measured along the head tube centre line. Be aware that you can toggle between these two alternate dimensioning schemes in the Primary dimensions dialog box. When one of these dimensioning schemes is selected, that dimension will remain constant while its counterpart may change with other changes in frame geometry. In this exaggerated example, note how the 13mm dimension will remain constant as the bottom bracket is raised. Meanwhile, if we switch dimensioning modes, and raise the bottom bracket again, it is the 49mm dimension that remains constant.

For more on designing a frame for lugged construction, see Lug Angles (Building a frame to suit predefined lug angles).