In general, the building frame is made of two squared battens, about 1¼ inch square for an 18-foot canoe. These, sometimes tapered slightly toward each end, are fitted with crosspieces with halved notches in each end to fit over the top of the battens. There may be as many as nine or as few as three of these crosspieces, with seven apparently a common number. Where ends of the long battens join they are beveled slightly on the inside face and notches are cut on the outside face to take the end lashings. Each crosspiece end is lashed around the long battens, a hole being made in each end of the crosspiece for this purpose. The lashings, commonly bark or rawhide thongs, are all temporary, as the building frame has to be dismantled to remove it from the canoe. Sometimes holes are drilled in the ends of the crosspieces, or in the long battens, and in them are stepped the posts used to fix the sheer of the gunwales. The methods of construction, using the building frame, varied somewhat among the tribes. Since the gunwale was both longer and wider across than the building frame, the posts for sheering were set with outboard flare. However, some builders made the gunwales hogged by staking them out when green, and then set them above the building frame with vertical posts. These gunwales would not be fitted with thwarts nor would the thwart tenons always be cut at this stage. The bark was lashed to the gunwales while they were in the hogged position with the ends secured; the gunwales were then spread by inserting spreaders, or stays, between them, after which the thwarts were fitted. This method required knowledge of just how much hog should be given to the gunwales, and it must be stated that not all builders guessed right enough to produce a good-looking sheer. Judging the hogging required in the gunwales was complicated by the fact that most of these canoes had laminated ends in the gunwales at bow and stern, and a quick upturn there as well. This method of construction persisted, however, because the straight sides made easy the sewing of gores and side panels. In some Alaskan birch-bark canoes the building frame was, in fact, part of the hull structure and remained in the canoe. In these, the building frame was hogged and then flattened by the ribs in construction so as to smooth the bottom bark by placing it under tension. In some canoes the posts for sheering the canoe rested under the thwarts rather than under the gunwales. In most canoes the building frame was taken apart and removed from the canoe when the gunwale structure was complete and in place, sheered.