Complex beveled cuts

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Complex beveled cuts

Postby Steven Phillabaum » Tue Apr 19, 2005 2:05 pm

Thought I would throw this out for usage. I used a bench mount, 6 inch disc and belt sander by craftsman for making all my angle cuts in the wood framework. Could even do the complex angles.
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Postby 10kDA » Sun Apr 24, 2005 7:31 am

Disk sanders are great, aren't they? I worked on the restoration of a history-making wood glider some time back and we had to build the monocoque fuselage from scratch. Being constrained for time (had to get it done for display in a museum) we rough-cut then finished nearly every stick on a sander. By my recollection I would say the tools we used most were single-edged razor blades or box cutters and a disk sander. It's hard to choose between the disk sander and the Sawzall when picking the Crowning Achievement Of Mankind.

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Postby Steve J » Sun May 15, 2005 3:34 am

I have been using my disc sander in this way for many years.  I am now concerned about what I recently read in AC 43.13-1B as well as The Wood Handbook (USDA).

I sure hope that this is relevant and applicable to the older style adhesives that were in use before the current species of expoxy adhesives.  It woul be good to hear some comment.

Extract from AC 43.13-1B :

1-6. PREPARATION OF WOOD SUR-FACES FOR BONDING.  It is recommended that no more time than necessary be permitted to elapse between final surfacing and bonding.  Keep prepared surfaces covered with a clean plastic sheet or other material to maintain cleanliness prior to the bonding operation.  The mating surfaces should be machined smooth and true with planers, joiners, or special miter saws.  Planer marks, chipped or loosened grain, and other surface irregularities are not permit-ted.  Sandpaper must never be used to smooth softwood surfaces that are to be bonded.  Sawn surfaces must approach well-planed sur-faces in uniformity, smoothness, and freedom from crushed fibers.  It is advisable to clean both joint surfaces with a vacuum cleaner just prior to adhesive application.

The do however continue to say:

a. Roughening smooth, well-planed sur-faces of normal wood before bonding is not recommended.  Such treatment of well-planed wood surfaces may result in local irregularities and objectionable rounding of edges.  When surfaces cannot be freshly machined before bonding, such as plywood or inaccessible members, very slight sanding of the surface with a fine grit such as 220, greatly improves penetration by the adhesive of aged or polished  
surfaces.  Sanding should never be continued to the extent that it alters the flatness of the surface.  Very light sanding may also improve the wetting of the adhesive to very hard or res-inous materials.

The wood handbook shows magnified pictures of cell structure damage due to sanding - I could not clip an extract (it is a pdf) so I attached the whole chapter.

Does anyone know where I can download extracts from ANC-18, Design of Wood Aircraft Structures.

Take care
ch09 Adhesive Bonding.pdf
Note page 9-4
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