Tuesday, May 19, 2009

Sharpening Q&A

A reader from the Netherlands asked a number of questions about a previous post on sharpening. Below are his questions (in black) and my responses (in blue). But, because there are so many excellent sharpening techniques and preferences, and more than one answer to his questions, please share your opinion on the subject. 

1. What is the purpose of a microbevel? If your plane is 25 degrees and you make a microbevel a few degrees higher, why not just make the plane 28 degrees? The micro bevel makes honing faster. Rather than having to re-sharpen the entire bevel when it gets dull, you just need to hone the small section that is 28º.  The extra 3º also adds some beef to the cutting edge. That's helpful, especially if you hollow grind the 25º bevel.

2. A few weeks ago I bought a Stanley sharpening set which includes oil, a jig, and oil stone. 
I started sharpening my blade and then noticed that certain parts were getting a different look. This is when I realised that the shape of the stone was changing and that I need to keep the stone flat as well. What is the best(cheap!) method of keeping the stones flat? I flatten all my stones on fine grit drywall screen that sits on top of thick plate glass.  Keep the stone flat, apply even pressure, and scrub it back and forth until it has a uniform surface.  Flatten your stones often.

3. The higher the grit one uses for honing the blade, the sharper the blade gets? Click here for Chris Schwarz' detailed explanation about this.

4. I still don't understand the differences between diamond, water and oil stones. Does one need to keep all of these stones flat? Or is the diamond stone so hard, the shape never changes? Also if I spray water on an oil or oil on a water stone, what happens then? I will defer to other readers since I've only ever used waterstones (which must be kept flat).  

5. I do get the blade at 25 degrees with my jig and sharpening stone, but it never really gets sharp.  "Sharp" means that two surfaces meet so precisely, the edge disappears. If you see light reflecting off the cutting edge, your blade is not sharp.  Is your jig/guide working well? It should not let your blade "rock" at all.  Another thing to look for is little nicks along the edge--does it look jagged?  Are you sharpening/honing with progressively finer stones? I flatten the back and establish the bevel on 1,000 grit and finish with 8,000.  Other people add 4,000 grit in between those two.  Ideally, you want a mirror finish on the back (approx. 1/2", not the entire back) and the bevel.  Also, the cutting edge must be 90º to the sides.  The problem might not be the blade, but your jack plane.  Is the sole flat? If not, then even the sharpest blade won't be able to make your plane work well.  See Chris Schwarz' post here.

6. Does the back of the blade need to be completely flat? I have seen some vids on youtube where they are putting a thin ruler under the blade while flattening the blade. I assume this changes the angle of the back slightly. This is debatable. I flatten the backs of all my irons--dead flat. If they're in bad shape, I start with an 80 grit diamond stone. I have never used the ruler trick, so cannot comment on its effectiveness.

7. I have only recently started using a jack plane. The Jack plane fell on the ground a few times and the shape of the blade changed and it lost it sharpness. Since then I have been trying to get a sharp blade without much success.  If the blade is nicked or skewed, you'll need to regrind the cutting edge so that it is 90º to the sides of the blade. Some people put a slight camber on the blade's edge, but you still need to start with 90º.  If your plane fell on the ground, it might also be damaged, so check the sole for flatness.

I'll add that until I took a class on sharpening, I was very confused (and I'm still learning new things).  This is a deep subject with lots of choices, preferences, and strong opinions, but if you're looking for an inexpensive sharpening method, I recommend the Scary Sharp technique. 

Let the debate begin! 


Geemoney said...

Let the debate begin, indeed! I would only add a couple of things. First, whatever method you use, it is like any other handtool skill. Take some time to practice it; you will see an improvement. Second, for all the scary sharpness you can achieve on a particular piece of metal, going to a better piece of metal can be very, very helpful. Take a look at aftermarket blades from Hock or Clifton (including chipbreakers); they're not super cheap, but you'll be glad to have upgraded. And as long as I am at it, take a good look at the chipbreaker, and make sure that it mates well with the blade. I think you need to make sure that you aren't getting confusing results from a non-optimal setup.

Good luck!

Woodbloke said...

Hi Kari - you've unleashed a 'kettle of worms' here but this is what I do. There are many variations, all of which achieve the same end, a razor edge, which, strange as it may seem, is so sharp that it doesn't seem sharp when you test it.
Firstly, primary bevels are ground at 23deg on the Tormek. A secondary bevel is then honed using an eclipse honing guide (Charlseworth modified)at 30deg on a DMT diamond stone with a 'projection board' so that repeatability and angle accuracuy is assured each time. Then a micro-bevel is honed 2deg higher on a 10000g Spyderco ceramic. The 'ruler trick' is used on plane irons but not chisels and I also use a leather strop loaded with Jewellers Rouge and Vaseline (petroleum jelly) for a bit of luberication.
It's not a difficult process but everyone develops their own preffered method to achieve the same end. There's a good piece in F&C this month about using the 'Scary Sharp' method which is econmical in the short term but could prove costly over a longer period.
I tried waterstones some time ago, but unless you're totally dedicated in your flattening regime, it's all too easy to start to sharpen on a concave stone...which I found out to my cost! - Rob

Eric said...

Quick follow-up question: When you go back to touch up your microbevel, what stone do you start on and how high up do you go?

The Village Carpenter said...

Geemoney and Rob, thank you for your recommendations! Rob, petroleum jelly???? Never heard that one before.

Eric, you only need to go back to your finest stone for touching up the microbevel. I use an 8000 grit waterstone.

KevinKuehl said...

From my reading, oil on waterstones falls into one of two types. There are some man-made waterstones that can use either water or oil, but once you've used oil, you can never go back to water. The natural and other man-made waterstones only work with water. I'm not certain what happens if you use oil, the instructions just say don't do it.

MackTheKnife said...

I sharpen only with diamond and ceramic stones. They never dish and you don't need to used water or oil. After a session on my diamond stones I use a stiff brush on the surface and knock it against the sole of my shoe to dislodge filings. On the ceramic stones I clean them up with hot water and Comet or some other cleanser. I never use a jig (been doing it more than 40 years so the proprioceptive memory is hardwired in), so I put on my microbevels with a strop. Jeweler's rouge is really too soft, IMHO. Use the "green stuff" or something with aluminum oxide in it. Japanese plane irons and chisels have the backs dished out very near the edge (the edge is dead flat). This cuts (hah, I made a funny!) down on the friction and gives a smoother cut.

Woodbloke said...

Hi Kari - "Rob, thank you for your recommendations! Rob, petroleum jelly???? Never heard that one before."

Petroleum jelly or Vaseline is the sort of stuff you rub into chapped lips in the cold weather, best otained from a chemist (drug store in the US) if you're unfamilair with it. When you rub in a bit of Jewellers Rouge the blade is still difficult to draw accross the leather but rub in a finger full of Vaseline to form a nice 'goo' and it'll just glide over the surface...works a treat, but you must wipe off the accumulated gunk on the steel if you need to go back to a stone (clogs it a bit!)I'll probably do a entry on the Blokeblog shortly on how I sharpen blades - Rob

Metalworker Mike said...

Here's an entry on sharpening from my blog.


I actually use a lubricant with the diamond and ceramic stones, though you certainly don't have to.


Mitchell said...

Personally, I think the subject of sharpening should be included with politics and religion as the third subject that should never be discussed in polite company. Ask 10 woodworkers the same question about sharpening and you will end up with roughly 14 different answers.

I will, however, step into the fray with a question that has come to light with my own sharpening experiences. It seems to me that it is easier to turn a straight chisel into a skew and a skew chisel into a straight than it is to keep them in their original configuration. What's up with that?



The Village Carpenter said...

I use King brand waterstones but I don't know if they're manmade or not. I've only used water with them.

I use ceramic stones with my chip carving knives and they are great, as Bob (Mack the Knife) says. I've tried them with my plane blades, but am happier with the edge I get on my waterstones.

Rob, I've used vaseline just not for stropping--I'll look forward to reading your post about it!

Mitchell, you're right about sharpening choices--there are many and all seem to give the same or similar result. You just have to find one or several you like and then keep at it.

Gary Roberts said...

I have to admit that I follow the Homer Simpson school of sharpening. I use diamond plates to flatten the back, rough the edge on a hand powered grinder, clean it up on a fine diamond plate followed by a series of three ceramic stones lubricate with whatever is at hand. Then I form a microbevel by eye. My math skills are abysmal, so I don't subject myself to figuring out things like angles. Duhoh....

Woodbloke said...

Kari - "I've used vaseline"...apologies for straying into the 'egg sucking' area! - Rob