Blades for Dewalt D27300 develop a bow when flattening the back
As the title states, when I attempt to flatten the backs of the blades for my D27300, they develop a bow. I’ve done this to 2 pairs of blades now. The first pair I worked on float glass with wet/dry paper and then the second pair I worked on a 10″ DMT diamond stone. Both pairs are Dewalt brand HSS blades
I’ve not found any information stating that the backs of these blades should not be worked and I can’t think of anything wrong with my method.
Apart from the fact that the bow makes it very tricky to seat the blades in the cutter-block, I found that the bow causes a problem for sharpening. Installing the blades into the cutter-block removes the bow but reveals concave curvature on the edge accross the length.
I’m sure I can figure out a way to clamp the blades flat for sharpening, but I’m pretty sure this shouldn’t be happening?
It’s been such a frustrating journey learning how to get this machine set up accurately – and now when I think I’ve got the thing useable, I’ve got this problem!
I can’t be the only person who owns a D27300 – but I’ve not found any mention of others reporting the problems I’ve experienced.
Replies
It's not a model sold in the US which reduces the user population considerably. Here, DeWalt planer blades are all of the reversible, disposable kind, which really don't allow for much sharpening. Even if these are conventional blades, why should they ever require a lot of blade flattening beyond a basic honing with a fine grit.stone or a quick pass to remove the wire edge after the bevel side has been sharpened?
Hi Steve, thanks for your reply.
When you say blades should only ever need a basic honing/wire removable on the back, are you suggesting that new blades should be pretty much perfect and ready for a quick hone before use? In my experience, blades (including chisels, hand-plane blades) are never flat enough for proper sharpening - they always have slight dips that you can see after a quick polish - either from machining marks that are still there or by covering the back with marker pen first.
I've not come accross any mention of blades warping during prep/sharpening and Dewalt said they couldn't help me. I'm hoping there's a steel expert or two hanging around here who can offer some advice...
Lee.
I take it these are thin high speed steel knives for a jointer or planer. The rapid cooling of the quenching operation that hardened this steel left residual stresses in it as the outer faces cooled slightly ahead of the core. Correctly done, the two faces cool at the same rate; and the steel that was flat to begin with is still flat, but only because the stresses are balanced. The two faces are equally in compression while the core is in tension. Grind material off one face, and you unbalance the stresses. The compressed material at the unground face will push the piece into a new shape where the forces are again in equilibrium.
When a thin section like this has to be ground after heat treating, it is necessary to grind both faces equally--and cautiously.
If your goal is to refine the cutting edge, think of this as a lapping operation, not grinding. You are not trying to remove material, only to produce a finer surface finish only where it matters. Apply steel blue to the face so you can clearly see where material is being removed. Use a narrow hone that will conform a bit to high and low spots and work along the blade a bit at a time. Raise the back edge of the blade the least little bit or focus the pressure on the front edge so only the cutting edge is being polished. Don't overdo it.
Great answer, thank you!
Perhaps it's just basic common knowledge about HSS? Dewalt said they couldn't give me an answer and told me to visit a dealer. There's also no mention in Lie-Nielsen's Taunton book 'Sharpening' (that I found anyway).
Should there be a warning with hss blades about sharpening?
I've read plenty of forum posts about people looking for good sharpening services or talking about doing it themselves but no mention of people warping blades.
Thanks for the help,
Lee.
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