Wood Ski Build Log. Minnesota, Summer 2013

Transcription

1 Wood Ski Build Log Minnesota, Summer 2013

2 Basic Plans The basic plan for the skis are from an article in Fine Woodworking, Cross Country Skis, The Easy Way 1981 #31 The skis are two thin laminations of hardwood for the base and top sheet, with a softwood core that gives the variation in ski thickness Being intended for loose deep snow, the skis were designed to be large and offer as much flotation as possible (240cm x 70mm)

3 Raw Material Selection Solid wood skis are often made from quarter sawn lumbar with the growth rings perpendicular to the base Since the core of the ski is solid, quarter sawn lumbar was used for the soft wood core. Pine was used, but spruce is preferred. The top and bottom hardwood laminations are thin enough that no special attention was given to their grain other than straightness and absence of knots. Red oak was used, but hickory or ash would be better.

4 Raw Material Selection Finding quarter sawn lumbar can be difficult so a wide 1 plank was found that had come from the center of a tree. The two sides yield matched quarter sawn blanks Ski Blank 1 Ski Blank 2 If this were a solid ski, a 2 plank would be required for adequate thickness

5 Mold Design An old ski can be traced out to give an approximate shape for a mold. An extra bit of camber built into the mold can be useful for counteracting camber lost to spring back If an old ski isn t available or a custom length is desired, an approximate shape for the mold can be designed as follows The green and red lines make the total length of the ski s camber. They are all equal in length. The green lines are straight and have equal but opposite slopes. The red segment is a gentle curve that matches the slopes of the green lines at their endpoints. The blue tip and tails are not counted in camber length and are simply curved to blend gently. A more gradual shovel tip can be desirable for deeper snow.

6 Middle Core Profile The middle core s profile was determined in a similar fashion. The length of the curved tip and tail was determined. The profile is 1/8 thick for those segments. Of the length remaining, the middle third was left at full thickness while the outer thirds taper linearly to meet it. 1/8 Tip 1/8 to ¾ ¾ 1/8 to ¾ 1/8 Tail 1 : 1 : 1

7 Trimming Blanks to Size The soft wood blanks were ripped on a band saw to width and one face joined flat, The opposite edge was planned down to ensure that it was parallel, Finally they were ripped on edge to give the proper thickness in the tips and under the foot. The hardwood blanks were also ripped to the proper width and planed to 1/8 thickness

8 Finished Laminations

9 Finished Laminations 1/8 Hardwood Tapered Softwood lamination

10 Steam Bender The tips of the laminations weren t flexible enough to fit the gluing mold, so they were first steam bent to shape. A wooden box with a metal pan filled with water was used to generate stem. A propane torch supplied plenty of heat. The opening in the box for the laminations was sealed with wet towels.

11 Clamping Steam Bent Wood After steaming the wood for a ½ hour, the tips were clamped in the mold to set. Non kiln dried lumbar works much better for steam bending, but this was just so that the tips could later fit the curve of the mold for gluing.

12 Gluing Up After the tip was bent to shape, the three laminations were glued together with waterproof wood glue (Titebond III). The more clamps the better

13 Post Glue Up Comments It is very difficult to align the laminations perfectly in the mold. It is much better to make the laminations thicker and longer than necessary and later trim them to size. Perhaps 30% of the mold camber came out upon removal. This should be taken into account when the mold is constructed

14 Trimming Skis to Size The skis were run through the planer on edge to trim sides. The tips were cut to shape using a coping saw. A router table was used to cut the center groove, but this was difficult due to the camber of the skis. This should maybe be done before gluing the laminations, although care must be taken to ensure that the groove comes out straight relative to the skis edges

15 Finishing Touches Helmsman spar varnish was applied in several coats to the top and sides of the skis. The bases will be sanded to give proper structure, de haired with a steel scraper and fibertex, and finally given a coat of pine tar

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17 Refs. Fine Woodworking on Bending Wood: 35 Articles, Taunton Press, 1989, #31