thetyreman":3scv9a5n said:
I've been chopping some dado joints today and noticed that the piece of oak seems even harder than normal, I heard somebody on here saying that this is the result of it being kiln dried? is that true, can it change the hardness of oak. Ben.
As others have already noted, oaks, as is the case with all wood species, can vary in hardness because of a variety of factors, e.g., growth conditions, such as climate, soil, location, and so on. In every Bell curve the majority fit somewhere near the peak of the curve, with outliers at either end, and in this case we're talking of hardness, with the majority of pieces of oak of a particular species fitting somewhere close to the curve's peak. Yours may simply be an outlier at the hard end.
However, you mention kiln drying being a potential cause. It's true that wood kilned to a low moisture content (7% ±2% MC being the standard American target for furniture grade material) becomes stiffer and harder than when the wood was green, i.e., at fibre saturation point (FSP) and above. It's also true that kilned wood allowed to regain moisture from its kilned MC condition up to and above FSP will never be quite as soft and flexible as it was before in its original green state and before it was kilned. This is one form of hysteresis. I also suspect that the kilning of the wood in itself hasn't made it especially hard, but again, it's possible.
So, in your case I suspect you have a hard outlier, as I discussed earlier. I suppose it's also possible that your chisels aren't as tough as you think, and maybe they weren't tempered correctly; I suspect this is unlikely, and they may just be softer in general compared to other chisel brands and the steel they choose to use. I've no real information about that last bit as I've never investigated the subject of steel properties, e.g., hardness and its suitability for woodworking tasks. And lastly, as others suggest, maybe you might benefit from using a steeper sharpening angle on your chisels which should help with edge retention, at the cost of requiring a bit more force to drive the cutting edge through the wood, i.e., whack harder or more frequently with the mallet. Slainte.