Riddle me this

[Chris Knight]

When I plane the edge of plywood, I always have to set the blade much coarser than when planing an ordinary piece of wood in order to make shavings of comparable thickness but I have never understood why.

Grateful any insights!

 

[Adam]

Does the mixture of grain direction give some "springy-ness" due to the wood fibres standing on edge that must be overcome to take a shaving (e.g. you have to push down harder) or, alternatively, take a deeper cut?

Adam

 

[Evergreen]

Perhaps the presence of the glue between the laminations makes the edge of plywood more resistant to the cutting action of the plane iron? Rather like when you plane some pine and the resin from a knot can make your plane skid off that patch?

Regards.

 

[Chris Knight]

Adam,

That is the only reasonable sounding explanation I could come up with myself but I haven't convinced myself it's right, for one thing, even pushing down very hard doesn't compensate fully by any means. Also the vertical fibres are after all, glued to the horizontal ones next to them and I think that should keep them stiff.

Evergreen, I don't think the glue makes a difference in being tougher to cut - it's not noticeable for instance when planing laminations with grain all running the same way. Also simple resistance to cutting would encourage me to reduce the blade setting, not make it coarser.

 

[Scrit]

Have you tried planing with a low angle plane instead?

Scrit

 

[Anonymous]

Chris, no answer to offer but I too find this to be true :?

 

[mudman]

Perhaps it is due to the vertical wood fibres of the end-grain portion of the plywood. Perhaps they are bent over by motion of the plane which then causes them to be cut shorter than if they weren't. The plane may start off at the correct depth of cut but then rides up on the forward bent fibres to give a shallower cut and continues at this level.