Planer Thicknesser Blade Query, Tolerances etc

[El Barto]

I just got back some blades I sent to Saw Tec to be sharpened and one of them has come back with a slight hollow in the middle. Enough that when setting up the blade it doesn't register on the small piece of wood I use to make sure the blade is even across the width of the planer.

So that leads to me to ask, what are the tolerances here and what can be gotten away with? I've attached a couple of photos where you can clearly see what I'm talking about (spot of light just underneath my thumb), and I've also checked it against a couple of other straight edges to make sure it isn't the planer bed.

It's a very small amount, I can just about get a 0.08mm feeler gauge through it. Should I send the blade back or will the discrepancy not make a difference?

 

[El Barto]

It also occurred to me that because there are two other blades, a small error with this one might not make a difference...

 

[El Barto]

For those interested, I installed the above blade and ran through a test piece. It came out fine. Square and accurate.

 

[Steve Maskery]

8 thou is the thickness of two hairs, which, whilst not great, is not dire either. I once had cause to complain about a 28 thou hollow, that is almost half a millimetre, which is a different kettle of fish altogether.

 

[El Barto]

Yeah that wouldn't have been ideal...! Good to know though that a minimal hollow doesn't cause any problems.

 

[RobinBHM]

Surface planer beds arent perfectly flat generally.

Also planer knives can change shape when they are tightened into the block.

I would say upto 1/2mm can be ok, if not ideal. And with a diamond stone, its not that difficult to improve it. I hone surface planer knives maybe 3 or 4 times before sending off for re sharpening. It can be done in the machine, takes 10 mins.

 

[transatlantic]

I hone surface planer knives maybe 3 or 4 times before sending off for re sharpening. It can be done in the machine, takes 10 mins.

If you keep them honed, why would they need to go off to be sharpened?

 

[dzj]

If you keep them honed, why would they need to go off to be sharpened?

Because of nicks in the blade edge. You can deal with a nick or 2 by laterally moving the blades,
but for more than that, re-grinding is necessary.