Detail Drawings

By | April 2, 2017

A detail drawing is one that shows each part of the machine separately. The parts are fully dimensioned and there should always be enough views of each shown so that the fabricator or machinist can make the piece without other instructions. If needed, notes are added to the drawing to make the construction clear.

The details are sometimes drawn on the sheets in a logical arrangement that they are assembled on the machine; that is, adjacent parts in the machine are drawn adjacent to each other on the detail sheets. Sometimes the details of parts that are to be made and perhaps assembled in one part of the shop are grouped together on the detail sheets. In other cases, it may be best to group together the details of similar parts that are to be made by the same machinist or department. In one group you may see all the details of the shafts required; in second group all the gears; in a third group all the gear guards, and so on. The choice of any of these methods can be determined mainly by the conditions that the manufacturing of the machine takes place in.

The image above shows the details of the crank end of a connecting rod. This is a simple bolted strap end that resists the tension of the rod by the shearing strength of the bolts and the friction set up between the stub end and the strap by the tightening of the bolts. It’s a very firm and solid construction.  Open end type of construction like this is always necessary on a center crank motor.

In assembling this end, the boxes are placed over the crank pin, the strap placed around the boxes, and the wedge secured in position by means of the cap screws. The stub end is then moved into position between the jaws of the strap, and is secured by the bolts.

Because of the heavy service that the rod is designed for, there’s no allowance made for play between the boxes. The boxes are made of cast iron, babbitted, with flanges to prevent lateral movement. The babbitt, which forms the rubbing surface, is an anti-friction metal, sufficiently fusible to be melted in a common ladle. Its use is very desirable because of its property of forming a perfect bearing easily without the need for re-boring. The boxes are held in place by a wedge that’s raised and lowered by means of two cap screws passing through the strap and tapped into the wedge.