Sunday, 24 March 2013

by Bob McKenzie.

How many times have you made wing ribs by stacking and pinning and have the stack flex or the pins dig into the bandsaw plate and going off line?

Try this for a tapered wing. For this example, a Top Flite Nobler.....

As another member of our little group was also constructing the Top Flite Nobler, I offered to make a rib set for him, as all it would need would be to laminate some extra sheets and still only make use of the bandsaw once.

I cut and pasted paper templates of each rib size onto a suitable size sheet of balsa to maximise the number of ribs then cut 3 more blanks of each size.

Problem! As each rib stack consisted of only 4 pieces of 1/16” balsa, pinning was out of the question as small stacks of 1/16” pinned together do not remain firm and you have to cut the pins flush with the balsa to stop them snagging on things (which doesn't work – they still snag!).
How could I hold them firm enough to cut to the templates and accurately cut L.E. and spars?

First, I aligned each set of 4 sheets and applied super glue at each corner. Next I drilled a 1/4” hole in the centre of the lead out cutouts on each rib stack. A drop of super glue was placed in each hole on each stack. After the super glue had set, each stack was trimmed to its template, a final sand to shape and the L.E. notch and main spar slot were cut using a bandsaw.

If you have a small bandsaw like me, (a GMC 150), it would be best to make mirror images of the paper templates to allow the ribs T.E. to face the right hand side of the bandsaw so they don't foul on the relatively narrow throat of the bandsaw. I had to cut the spar slots on these ribs using an Exacto mini saw. If you have a larger bandsaw, no problem.

To separate the stacks of ribs when you are finished, cut out the leadout slots. I used an endmill to drill neat holes at each end of the slots then cut the remainder with a knife. See illustration 4.

This method could be used also on parallel chord wings.


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