How sharp is sharp enough

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Forum topic by Bureaucrat posted 05-28-2010 06:19 AM 1697 views 0 times favorited 20 replies Add to Favorites Watch
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18339 posts in 3617 days

05-28-2010 06:19 AM

Topic tags/keywords: question joiner sharpening

I went to use my 4” joiner today and discovered that it left a profile of some dent that got in the knives, I know not how. So I quickly went to the back up knives I took out a long while back. I could see a dent in both of those knives. I settled down in my chair by the table saw for the long process of sharpening the four knives. I put them through coarse, medium and fine diamond stones. I did have to remove quite a bit of metal to get rid of the dents.

I don’t have a jig for sharpening joiner knives, so I used my knuckle on the table saw as a guide.

After I went through all of the paces, I was able to raise a curly on my thumb nail but when I tried to shave my arm hair I was only able to irritate my skin and break off a few hairs. After 2 hours of work, I thought I’d be able to shave.
Do you think that these knives would be sharp enough for joining or do I need to do more work?

-- Gary D. Stoughton, WI

20 replies so far

View Kindlingmaker's profile


2656 posts in 3491 days

#1 posted 05-28-2010 06:29 AM

As a novice only, no. If your blades are that sharp then the first few passes will dull them if not the first. How many morning shaves do you get with one razor? Which is harder, hair or wood? Just a novice’s thoughts…

-- Never board, always knotty, lots of growth rings

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2656 posts in 3491 days

#2 posted 05-28-2010 06:41 AM

...chisels and knives are another thing all together… they love the scary sharp!

-- Never board, always knotty, lots of growth rings

View a1Jim's profile


117062 posts in 3542 days

#3 posted 05-28-2010 06:43 AM

I’ve never sharpened my own jointer blades so you’ve got me there.

-- wood crafting & woodworking classes

View Bureaucrat's profile


18339 posts in 3617 days

#4 posted 05-28-2010 06:52 AM

Do you think nicked blades or poorly sharpened knives constitutes a legitimate reason to upgrade to a 6” joiner? LOL!

-- Gary D. Stoughton, WI

View thatwoodworkingguy's profile


375 posts in 2895 days

#5 posted 05-28-2010 07:53 AM

Never sharpened my own either.

-- ~Eagle America~ ~Woodcraft~

View EricRFP's profile


106 posts in 3059 days

#6 posted 05-28-2010 08:59 AM

You need all of your knives to line up within a few thousands. If you don’t have a jig or superhuman skills I would say it’s near impossible to properly sharpen your own knives. At this point you may need to take your knives to a professional.

Try this instead, next time. Move one or two of the knives slightly over. You will have a perfect, clean cut now.

-- Eric, NorCal

View GMman's profile


3902 posts in 3662 days

#7 posted 05-28-2010 02:22 PM

Same answer as Jim

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Kent Shepherd

2718 posts in 3251 days

#8 posted 05-28-2010 04:03 PM

I do a lot of sharpening on my hand tools, but would not attempt to sharpen jointer knives. Even if there is no local company to use, there are places all over the country you can send them to. I keep 2 sets for all my jointers. That way I have a fresh set ready to go.

That said, I agree with Kindingmaker. If they are that sharp, they will only stay that way for a few boards.

And yes, you should upgrade. But why stop at 6”, or 8”—-I even have a 16”!


View David Craig's profile

David Craig

2137 posts in 3074 days

#9 posted 05-28-2010 04:09 PM

Maybe I get bad blades, but I have never been able to shave with the new jointer blades I purchased before. I do not believe scary sharp applies for use on machines. I would think it would make them a little brittle and vulnerable to chipping at such speeds. I think the best test would be to put them on the machine and try a test piece to see if the cuts improve. As mentioned already, jointer knives need to line up with each other. If you find the cuts are worse, then you might want to give up on the jig-less sharpening. If it improves then you can pat yourself on the back for a job well done.


-- There is little that is simple when it comes to making a simple box.

View Bureaucrat's profile


18339 posts in 3617 days

#10 posted 05-28-2010 04:54 PM

David: I’m going to build the Jig that fellow LJ, Garage Woodworks posted. Looked at it last night and I think it will take out the variability that my knuckle introduced.
Kent: I’d love to have an aircraft carrier for a joiner but in my 12×21 shop, space is a precious commodity.
Eric: On this little craftsman there isn’t much side to side adjustment, but will remember to try that before I launch into a sharpening frenzy next time.
Kindlingmaker and David: point taken, it’s a joiner not a razor.

Thanks all for the help

-- Gary D. Stoughton, WI

View PurpLev's profile


8534 posts in 3613 days

#11 posted 05-28-2010 05:02 PM

I see no reason why jointer blade would be any different than a hand plane blade. both should be as sharp, and both should be within reason to sharpen yourself. the jig you mentioned seems fantastic and will do the job! I don’t see why people are so scared when it comes to sharpening jointer knives… the mechanics are all the same.

spending hours sharpening does not warrant shaving hairs off – thats the honing part. from the sound of it you spend a lot of time taking off quite a bit of material to get the nicks off – which is a time consumer. once you have the blades cleaned up, honing should take a few minutes. good sharpening and inadequate honing will keep your hair on your arm ;) remember to hone both sides, until you don’t have the wire edge anymore.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View dbhost's profile


5705 posts in 3197 days

#12 posted 05-28-2010 05:22 PM


I have never sharpened jointer knives before, but I HAVE had nicked knives in my 6” jointer. Depending on your make / model, jointer knives are pretty cheap and easy to replace… The big problem is setting the depth…

With your size shop, you might want to stick with a bench top type jointer. Sounds like floor space is critical there…

-- Please like and subscribe to my YouTube Channel

View HokieMojo's profile


2104 posts in 3693 days

#13 posted 05-28-2010 05:24 PM

I think there are two things to consider and these are just my opinions, not facts.

1) there is a difference between types of knives. Some planers/jointers utilize blades that are set on pins. The height is not adjustable, so all the blades need to be sharpened to particular specifications. Other knives are meant for use with indexing adjustments. These can be sharpened by an individual and then you adjust the height of the blades so they are all the same.

2) With regards to sharpness, I don’t think the same level of sharpness applies to a machine. A spinning blad can make 100’s of thousands of cuts in an hour. You can’t assume that a blade would even stay “scary sharp” for 1/2 that many cuts (or even 1% of those cuts I’d think). Sharper blades will provide better cuts, but I don’t think there is a need to keep them at 100% all the time to get very good results. Remember, your objective with a jointer is to get a flat smooth surface. Not a finished surface.

View EricRFP's profile


106 posts in 3059 days

#14 posted 05-28-2010 06:40 PM

PerpLev. Are you serious? 4 blades that need to work together at 3200 rpms, that need to cut within a few thousands is not exactly the same as a single hand plane blade. If you don’t have a jig, don’t try to sharpen your own planer or jointer knives.

-- Eric, NorCal

View PurpLev's profile


8534 posts in 3613 days

#15 posted 05-28-2010 06:53 PM

my point was more about the fact that these are all blades, and can all be sharpened in the home shop.

I do agree with HokieMojo- planers that have replaceable knives such as the dewalt planer for example are not meant to be resharpened -but tossed once they’re dull, but jointer knives that can be set to height are usually meant to be resharpened. I believe these blades are those in question in this thread.

As mentioned above -there IS a jig to hold the jointer blades in place, you can find it on Garagewoodworks web page. there are also store bought versions of course.

now to put things in perspective – 3 jointer knives work differently then 1 hand plane blade, but all should be as sharp as can be – I see no reason to leave a jointer knife any less sharp than a hand plane #7 blade – which like a power jointer – is not supposed to leave the surface glass smooth – just flat. now, since you already have the blade in a jig, or in a sharpening session – the extra 1 minute it’ll take you to run it over the honing stone/abrasive is really not that big of a deal – and the surface of the edge will be cleaner/straighter.

yes. I’m serious. but it does not mean you have to agree with me

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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