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Hybrid Profile for Freehand Sharpening BU Plane Blades



The light bulb went on last night as I was planning how I would use my time in the woodshop today. I had two shelves to finish for one of the military chests I am building, and was aware that the blades in all my smoothers were dull.

When it comes to smoothers for hard, interlocked Jarrah, the best performance comes from the BU planes. Not only are these able to be set up for high cutting angles – at least 60 (included) degrees – but they are easier to push than the equivalent BD plane. The downside is that I really dislike honing blades for BU planes since my preference is to freehand, and BU blades have (until now) depended upon a honing guide when sharpening.

Briefly, it is easier to hone a camber if you use a high micro secondary bevel (generally 50 degrees) on a low primary bevel (generally 25 degrees). The article on the rationale for this method is here. This method requires a honing guide (and if you always use a honing guide for all your sharpening, and do not plan to change, then this article is not for you). Why is this article important for others? If you are like me - lacking the patience to use a honing guide (although I do own several and use them all) – then join me in discovering a simple method (gad, why didn’t I think of this before – now it is so obvious!).



Why is a special strategy needed for BU smoothers?

In a nutshell, the reason that one would be nuts to freehand a camber on a high angle 3/16” thick BU blade is that there is too much steel to remove. Don’t believe me? Go on .. I dare you.

Then it occurred to me that all one had to do is again – as with the honing guide method - remove as much steel as possible …. after all, it is not hard to freehand a camber on a Stanley plane blade. Removing steel simply means starting with a low primary bevel. How low? Well I thought of 20 degrees, but decided to first attempt this on a 25 degree primary bevel, which is commonly used by most BD planes. It is also one of the options of the Veritas blades. I planned to test this out with two Veritas BU planes, the BUS (Bevel Up Smoother) and the LAS (Low Angle Smoother).



Where to start ..

First I had to return the bevels to flat from the hollow grind I use. For this I went to my belt sander grinder jig I built several years ago ..





The next step was to add a 50 degree hollow grind on an area similar to the thickness of a Stanley blade. I chose to use a Tormek wet grinder but there is no reason not to use a high speed grinder … just carefully! If you do you a dry grinder, remember to first grind back the thin end of the bevel (otherwise it will burn).





The completed hollow grind is a little less that the thickness of a Stanley blade. I was concerned to go further at this point because the bevel still has a lot of steel behind it to camber. The blade is 3/16” thick.

Keep in mind that this hollow ground secondary bevel is 50 degrees, while the hollowed primary bevel of the Stanley is 25 degrees.





Time to hone the blade.

I used a set of three Professional Shapton waterstones: 1000, 5000 and 12000 grit.

With a hollow this narrow it is easier to freehand with a side sharpening strategy (that is, side-to-side). For this I essentially hone using one hand (I am right handed). Roll the hollow back-and-forth until it sits flat on the stone. I only need one, sometimes two fingers of my left hand to add extra downforce.

The train lines show the edges of the hollow are sitting evenly on the stone.

To camber the blade use 5 strokes with moderate downforce at each end on the 1000 stone.





Here you can see the high angle of the 50 degree secondary hollow grind.



The camber is created on the 1000 stone, and the 5000 and 12000 stones follow and polish the outline created.

I like to remove the wire edge after each stone (on the 12000 stone) – just a few swipes needed. This makes it possible to determine when a fresh wire edge is created after the next stone, which confirms one is honing fully across the bevel face.

There has been much talk about the wear bevel that forms on the back of a blade being particularly disruptive when honing BU blades. While I know it is formed, I have not experienced it interfering with further sharpening, as is alluded to by some. Anyway, to be safe, I have decided to include a micro back bevel that will effectively prevent the formation of a wear bevel at the edge of the bevel face.

The micro back bevel is added via David Charlesworth’s “Ruler Trick” …





This is the final result. Total estimated time for honing (after grinding) is under 2 minutes.

Below, hollowed, honed and cambered …





The proof of the pudding lies in the eating



Testing out the result is what this is all about. There are two objectives: firstly, the blade must be cambered so that smoothing does not create ridges in the wood. Secondly, the blade must be sharp and produce fine shavings typical of a finish smoother.

Below was the initial shaving as it came out the plane. The blade could do with a little adjustment (the shaving is not centred), but it is clear that the blade is cambered.





A thicker, wider shaving. Yes, the blade needs a fine adjustment.





And here are full width shavings and no trace of any ridging …



One of the shelves I was preparing today … The board has a shine and the plane is reflected in it.





After this appeared to be working well, I gave the same treatment to the LAS blade. This is 1/8” thick. Also hollow ground at 50 degrees …



And the same results from the LAS …







For my preferred method of freehand sharpening, this system works really well. It is easy to set up, takes as little time to hone a camber as on a hollow ground BD plane, all of which removes the one resistance I had for these planes. BU planes make exceptional smoothers, and a quicker, easier sharpening system makes it possible to access this performance more often.

I hope others find this as helpful as I have.



Regards from Perth

Derek



July 2011