9

I've been trying to sharpen plane blades and jointer knives for a long time now but never was able to get a really sharp edge. I see most people can achieve this, some can cut a paper by using the paper's weight against the blade, others can shave hair out of their hands with the blade.

I really follow a simple process in sharpening, I have a stone with coarse/fine sides and I have a honing guide. I've been using this one from veritas for the jointer knive so the blade edge is touching the stone at the right angle. I do the coarse side first to remove any dents in the blade and them move to the fine side. I've tried doing this for:

  • The length of the blade
  • And a microbevel

Both didn't give me the required result, in one instance the blade was so blunt that it showed burn marks while planing the surface.

This is giving me a lot of grief as I have the same problem with sharpening hand plane blades, what I want to know is:

  • What am I doing wrong?
  • Is a stone with coarse/fine surfaces enough for what I am doing?
  • How much sharpness is good enough? What do you do for testing the sharpness of your blade?
  • Did you sharpen it to the point where the burr fell off in a little wire edge? – grfrazee Mar 1 '16 at 20:45
  • I would also like to know more about your technique. What was the grit count of the stones you were using. Did you use honing compound when you were done? – Matt Mar 1 '16 at 21:12
  • @grfrazee no, I didnt know I have to do that. – OKAN Mar 2 '16 at 2:06
  • @Matt I dont use a honing compound, is it necessary? – OKAN Mar 2 '16 at 2:06
  • Honing compound is used on strops, not stones (usually). – grfrazee Mar 2 '16 at 2:06
4

It's hard to diagnose a problem like this without at least good photos of everything so the following involves some guesswork.

Is a stone with coarse/fine surfaces enough for what I am doing?

Impossible to say with certainty because of the variables. Unfortunately stones (diamond abrasive plates as well) graded as coarse, medium, fine etc. are by no means equal. One maker's 'fine' will be very similar to another's 'medium', something that has tripped up many of us buying sharpening products from different makers :-(

In the product photo you link to the honing guide is being used on abrasive paper on glass and I was thinking there was every reason to suppose they would go to a finer grit than the 'fine' side of many stones. Looking further down the Product Highlights underneath say they include a piece of 15 micron film, which is approximately equivalent to 1000 grit. Unless you know the grit ratings for your stones and the 'fine' is 1000 or finer that's likely part of the issue here (but see Note at bottom).

Just in general, a simple combination stone like this can be good enough as the core of a sharpening system... I should mention that many people with elaborate (and expensive) sharpening setups would disagree with this! But for planer knives how fine the 'fine' side is could be critical, although other issues including how you're sharpening may be as important or more important. Which leads us to...

What am I doing wrong?

Possibly nothing, but let's see. If you didn't begin by lapping the unbevelled face of the blade flat as per the instructions then do that first. As in all similar sharpening operations creating a uniformly flat surface along the edge on the other side of the blade is vital to creating a sharp edge.

Then, when sharpening the bevel, the PDF includes this:


Hint: Apply pressure on the push stroke only. This will prevent a thin wire edge from forming along the leading edge of the blade. Continue this action until a satisfactory finish has formed on the bevel.


If you haven't been using push strokes only when sharpening do that also.

Final point, check your stones for flatness. For this operation it's vital your stone (both sides) is completely flat. If you check with a straightedge and you find there's even a slight dish on either or both sides then flatten the stone before you try sharpening again.

Stones can be flattened in numerous ways, the cheapest for you now is to use a sheet of coarse wet-and-dry abrasive paper on a very flat substrate. A good surface for this in the typical home is a kitchen countertop, generally made of thick, stable material held reliably flat by how it is installed. But don't assume it's flat, check it first before use.

How much sharpness is good enough?

As a general principle no edge used in woodworking can be too sharp. Obviously there are complexities, but all other things being equal sharper is usually preferable to less-sharp (again, see Note bottom).

What do you do for testing the sharpness of your blade?

I've never tested a planer knife for sharpness but think of them as a sharp edge, not just a planer knife and test accordingly.

If they aren't good enough to pare wood as you'd use a chisel for example then they're definitely not sharp enough. Arguably you should aim for them to be sharp enough that they'll neatly pare pine end grain, although in practice this may not be required for a planer knife. Related: How can I tell if wood turning (lathe) chisels are sharp?

This is giving me a lot of grief as I have the same problem with sharpening hand plane blades,

Although the goal is obviously the same sharpening planes irons can be approached slightly differently. There are some previous Questions on sharpening that might be of some help:
Is there a 'best' way to sharpen an edged tool like a chisel?
How does one aggressively sharpen chisels and plane irons when damaged?
Does it matter what kind of diamond stone I get?
Sharpening grits -- naming and selection

If you'd like further help with your handplane irons start a new thread to get more specific answers on that.


Note on grit size and sharpness: there is no absolute need to sharpen to 1000 grit, although it gives very good results. Many Western woodworkers now sharpen both their chisels and plane irons to well above this but you can actually get a good, workable edge on abrasive as coarse as 250 as long as the sharpening is done well and no wire edge/burr remains.

This is NOT to say the edge is as sharp, it isn't, but it can be sharp enough for the job at hand. For best results though you should go sharper, especially on chisels.

-2

Sharpening is an art.

I recommend buying The Razor Edge Book of Sharpening by John Juranitch. It explains the basic principles correctly. Other books like the ones by Leonard Lee and Ron Hock are either worthless or have a lot of distracting misinformation. For example, if you read the other answer posted above you can get a sense for the irrelevant and incorrect mumbo jumbo in those books. Juranitch's book is simple, clear and correct. If you remove the anecdotes from his book it would be 5 pages long.

You only need three grits, a coarse grit (60-80), a medium grit (120-160) and a fine grit (250-400). You can sharpen with just two, coarse and fine but it is more time consuming. Ideally, each grit should be double the screen size of the previous one.

The error you are undoubtedly making is that you are applying the abrasive to both sides of the edge. If you read Juranitch, it makes it clear why that is a mistake. He very clearly explains how to sharpen a plane blade.

Another book that has reasonably correct information is "Japanese Knife Sharpening: With Traditional Waterstones" by Rudolf Dick, who is one of the few I have read with any deep knowledge of sharpening. This book applies to sharpening knives (two-edged blades), however, so it may be less applicable to your situation.

  • 3
    Instead of just dismissing another answer as "mumbo jumbo", it would be more helpful for everyone to either point out inaccuracies in comments on that answer or use your answer to help dispel myths and confusion. – FreeMan Mar 2 '16 at 20:47
  • @FreeMan Well, for example, the other answer suggests "lapping" the bottom of the plane. Lapping is for mating two pieces together, not for making something flat, so just to begin with the post is using terminology incorrectly. Secondly, flattening the bottom of a plane is usually unnecessary and has nothing to do with making it sharper. The other answer has a long dissertation on the supposed importance of a flat stone. You could sharpen a chisel or plane with a stone shaped like a pigeon egg. Also, the post uses the word "honing" with no understanding. Honing is not a synonym for sharpening. – Treow Wyrhta Mar 2 '16 at 22:09
  • 1
    Sorry, @TreowWyrhta, but "to lap", in this context, legitimately means to flatten and polish metal, glass, or similar materials. Very common usage in the English-speaking woodworking community, and I believe in machining . Flattening the back of a plane iron or similar knife -- at least the back of the bevel -- is an accepted part of modern sharpening technique. – keshlam Mar 3 '16 at 3:37
  • First off thank you so much for your polite critique of my Answer :-| As far as the use of lapping in this context, it may be an incorrect use of the word in your opinion but in case you missed it that is how it is used in the Veritas PDF I linked to. It repeatedly uses the term: "Prepare the lapping surface", "Lap the face of the blade" etc. It also appears you misread what I was saying about that anyway, I didn't state the entire surface needed to be made flat, I stressed it needed to be flat along the edge (as the PDF also makes perfectly clear in an illustration, fig. 3). – Graphus Mar 3 '16 at 11:03
  • Re. the importance of a flat stone, I said "for this operation" — because of the type of jig used the stone must be flat, just as it must be for the initial lapping of the flat of the blade. I am also not at all confused about the difference between honing and sharpening thank you very much. – Graphus Mar 3 '16 at 11:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.