How to make a wood toboggan Part 1

So, it has been a while since anything new was posted, but tonight I submit a post for your discriminating taste in wood working blogs.  First off is my newest brain child, actually the thought came to me 3 years ago but has since taken a hiatus. Steam bending for the purpose of building a toboggan. When we had our first snow fall here in Cowtown the inspiration hit me like a hard packed snow ball.  Both kids needed to get outside this winter and enjoy tobogganing like I did.

Making jigs has never been a real passion of mine but I did make three of them for this project.
While I am waiting for my Earlex Steam Generator to come by dog sled, I set myself to making the bending form.  Spruce plywood(the cheapest grade you can buy) was purchased and cut to make a 10" diameter bend. The width of the slats will be 2 1/4" wide so three pieces of 3/4" plywood were sandwiched together.  Now the dilemma was how to cut a curve the full width of the form. I do not own a band saw, however I have a router with one straight cut bit and one flush trim bit. I removed the plastic base plate that the router came with and attached the base plate to a scrap of laminate hardwood using good old double sided tape.

Drill the holes to match the spacing on the base plate and counter sink the holes. Attach the laminate to the bottom of the router and mark back from the straight router bit the radius you require. Secure the one end of the router and base plate to the form. Ensure the router is free to rotate around a pivot screw. You can change the position of the pivot screw to accommodate your desired curve.  Make sure you install stop screws in the form to contact the laminate in order to provide stops at both ends of the arc.  Make several passes through the arc increasing the depth each time. When you have hit your maximum depth, detach the router and flip the form over. Insert the flush trim bit and use the existing curve to guide your router as you cut the other half of the form.

Cutting the support brackets is easy just drill a hole through a pair of plywood blocks. When you straddle them across the form, insert a matching dowel to go through both pieces. Insert a scrap of wood that is the same thickness as the wood that you will be bending plus a wedge under the dowel and secure the support brackets. Next post regarding this toboggan will be on the steam bending.
Stay tuned...



Steam bending jig for a toboggan.  Mk I

 





The modified wood bending form Mk.II
Note : the latest version of this form does away with the two FA clamps at the bottom of the picture.



 

 

This update on the steam bending project reflects the modified wood bending form as seen in the above picture. Some observations on this process : Always leave the wood in the steam box longer than the minimum. The rule of thumb floating around is one hour for every inch of thickness.

I am now using 25 min. for 1/4" thick wood. The extra steaming time in this instance may reflect the kiln dried state of the wood at rest(before steaming).  The wood feels a lot more plastic when its bent around the form. The extra time in the steamer does not hurt the wood. The wood needs to be supported by a couple of cauls especially at the start of the bend and mid point through the form's circumference. See above picture for placement of the cauls.

 

 The drawback to using the form as I had originally built it is that the wood will expand along the width quite significantly will being heated and saturated with water.  If the form brackets are spaced out to accommodate the wood in an at rest state, they wood will be too wide to fit after steaming. This creates pinch points in the wood as it is bent around the form and the wood will crack.

One way to reduce the amount of spring back after you bend the wood , is to leave the piece in the form for as long as you can.  Essentially the bent wood MC should be as close as possible to the MC of the wood before it was steamed. I leave my wood in the form until the wood is cool to the touch and then remove it and use painters masking tape to retain roughly a 10.5" diameter in the end of the curved slat.

One note on the clamps in the form : this video explains how to make a speedy clamp.