Plywood veneer surface planing, production imperfections. What is acceptable?

 

This Koskisen 1mm Birch plywood stamped as AB/B  was sold with an inference as GL2 by a supplier back when I purchased this. The website was recently changed showing that GL2 was available for order. The AB/B  has areas that may meet the GL2 criteria, but I still must determine what an AB/B quality actually is relative to a Germanischer Lloyd graded plywood.

I have cut and discarded large areas of the AB/B plywood. A GL2 product is shown as available for order from Koskisen, but this is not what I have. The stamp on the wood is attached. I just like learning and someone must have an idea regarding this! Come on EAA tell me I'm not having to learn this on my own, now that my plans building is an oddity! By the way I am not trying to single out any supplier discussing this. I understand one mill closed last year when I was talking to a distributor regarding quality and grading a few months back. The cost to send an inspector to grade plywood as aircraft quality is no small cost (I have the actual numbers!).

Aircraft Spruce posts a Germanisher Lloyd criteria booklet for the GL graded ply (which this is not). According to Table I in that information a 0.1mm deviation (about the thickness of a laser print paper) is acceptable in a ply layer of 1mm metric plywood. That means that some, but not all, of the planer tearing on the AB/B plywood would fall within a GL specification for aircraft grade plywood.

 

Very General information sheet on the Koskisen Birch plywood

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B9spnpVnhZLCMjI0NTkzNjUtZDg4Ni00ZDM1LWFkMDYtZjc2N2IxNDMxYjll&hl=en&authkey=CP7Mu9gC 

Photo information sheet with photos roughly showing the visual qualities of the Koskisen grade.

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B9spnpVnhZLCZDRkNDA1YWQtNmQwOC00Mjc3LWEzOTktNjE5NDMzMWZiOTE0&hl=en&authkey=CJbUlbIK 

The Germanischer Lloyd booklet “Rules for Surveying and Testing of Plywood for Aircraft”

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B9spnpVnhZLCNmRlMTJjOTYtZjE1Yi00MTAwLTk1ZWQtYTE1MTJjZDc0YTli&hl=en&authkey=CJ-4_YUC

 

 

 

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Having only experienced the edge chipping, I feather the chip with 220 grit and maybe a dot of epoxy if the chip spread but did'nt break off.  If the plys are not delaminating I would use it.  The surface appearance means nothing.  I was going to comment yesterday but I had to keep re-logging in for some reason and gave up.  Hope this little bit helps.  Bob 

Hello Bob,

We have a winner! I have a response, thank you for the comment. I have done something like that in the past when the edge pulled up just a little. I know another builder that uses something such as an epoxy clear coat to make the ply more solid before cutting. I have not done that before. The batch of plywood I received today was better than the previous batch from another supplier. This plywood was made by Mahogany oy.

Thanks,

Clarke

Sucks to duplicate work when the first piece goes in the scrap box, does'nt it.

Yes, it is frustrating when a hidden defect appears. Maybe I should I say hidden to my eye which is slowly learning what to look for. I buy non aircraft graded materials because it is what I can afford and I don't need to spend the money on "Aircraft Grade" ply for my project, so I can hardly be upset. I'm actually really thankful there are a few suppliers despite my questions. Discarding a part learned on is really not so bad, and better now than potentially a failure later.

 

I guess that is part of the fun of it, learning to spot details and feeling good about the work. The Koskisen plywood had a more pleasing surface texture than the Mahogany Oy brand I received yesterday. The Mahogany Oy was much cleaner on each sheet in general but the order was smaller and they may have felt the need to more selectively ship sheets. Regardless I still want to learn more about what to look for. I guess that means reading standards and learning by discarding. The bottom line is my wife loves seeing the smile on my face in the workshop and I can't beat that!

 

Thanks again for your response!