Sharpening Jointer Knives on Surface Grinder

[Benjamin Miller]

Hey guys,
I've lurked for many years and never created a thread. I thought you might like to see some pictures of how I sharpened my jointer knives on my little surface grinder last night.

I got a glorious old Yates-American 12" jointer a few years ago, and I don't think the previous owner had ever sharpened or replaced the knives. They're a somewhat unusual size -- 12" x 1 1/2" x 1/8", but 1 1/4" deep ones would also work. I priced a replacement set at $60 -- ouch!

I called around locally and could get the knives professionally sharpened for $27. That's still too expensive, and I have a surface grinder in the garage (I'm more of a metalworker), so I decided to try sharpening them myself.


My grinder has a magnetic sine chuck on it, which means it can tilt to any angle by placing gage blocks under the front ground roll. The rolls are 5 inches apart, and I measured the primary bevel of the knives to be 35 degrees, so sin(35) * 5 = 2.868". I stacked 2.868" in gage blocks under the front roll of the vise and locked it down:
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I placed the knives on the chuck, using some parallels to space it from the back edge. The back edge of the chuck has been indicated parallel to the grinder travel within about .0003".
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Here's a picture of the dull knife before grinding. Notice the huge nick on the edge. The edge is very dull, and the knives have been ground inconsistently -- some have a secondary bevel, some do not, and they are not consistent in depth.
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After grinding. That nick at the end isn't actually a nick, but part of the wire edge that needs to be honed off.
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I made a honing block on the table saw to hold the knives for a 40 degree secondary bevel. You could grind more or less bevel based on the type of wood being cut, just like a chisel.
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And finally, after honing the secondary bevel and removing the wire edge, here are the extremely sharp blades.
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I reinstalled the blades in the jointer and took a pass over some figured maple I have. There is zero tearout, and the surface is glassy smooth.

[Bruce Page]

Very nice! I really like your magnetic sine plate - wish I had one!!

[Marty Gulseth]

Yes, you are indeed a metalworker! Very nice indeed!

Regards,

Marty

[Tai Fu]

I don't have a surface grinder, so I gave mine to someone who does to sharpen it... cost 6 dollars.

[Chris Fournier]

I have a surface grinder but not half of your flair for fixturing and grinding! Very nice work. I don't use my surface grinder everyday but when I do use it the precision that it affords me always leaves me in awe.

Again, nice work!

[Bob Wingard]

NICE WORK ... (oozing jealousy) ... wish I still had access to a nice surface grinder ... that's what retirement will get you if you don't have your own equipment.

[Jeff Duncan]

First clue that you are a metal worker was when you described the "huge nick" and "dull knives", with the pic. You should see the knives that come out of my 16" when it's time for sharpening if you think those are bad:D

FWIW the prices you got both for replacements and sharpening are pretty cheap. If your only using your jointer occasionally as in weekend projects here and there, a set of knives will likely last you several years or more between sharpenings. So $27 goes a long way. My 16" knives cost about $51 to sharpen the set of 4. But obviously you have the means to do it yourself and sometimes that's the best way to go! Not to mention I'd bet those are significantly sharper from your methods than anything your local shop would do;)

JeffD

[HANK METZ]

I sharpen my Delta 6" blades on a fixture I made for my Radial arm saw, which is much like a surface grinder in operation. Did it just last week in fact, local shop wants $18 to do it @ a buck an inch per blade.

[Ronald Blue]

Do you run coolant when you grind? HSS is very susceptible to heat in a thin piece like a blade. I sharpened some planer blades for a friend years ago and flooded with coolant and had excellent results. What grit wheel do you use? When I was doing tool and die work we used Norton wheels and for the best results and a wheel that maintained a profile we used a 100 grit. For stock removal a softer 60 grit worked best. Do you have jo blocks to set the angle? You have a nice grind on the chuck surface. Is this grinder hand crank or powered? Sorry for all the questions but it just brings back memories.

[Tai Fu]

Wow, you guys pay a lot for services for sure. My 12" jointer blades (3 knife set) was sharpened for 6 dollars, and it was a really good grind, hollow grind with a coarse stone followed by a secondary bevel with a finer stone. Result is very straight and sharp edge, looked better than new for sure!

[Benjamin Miller]

Thanks for all the compliments, guys.


Do you run coolant when you grind? HSS is very susceptible to heat in a thin piece like a blade. I sharpened some planer blades for a friend years ago and flooded with coolant and had excellent results. What grit wheel do you use? When I was doing tool and die work we used Norton wheels and for the best results and a wheel that maintained a profile we used a 100 grit. For stock removal a softer 60 grit worked best. Do you have jo blocks to set the angle? You have a nice grind on the chuck surface. Is this grinder hand crank or powered? Sorry for all the questions but it just brings back memories.

This machine has drip coolant that works well for heavy grinding, but I ground these knives dry. I have an infrared thermometer, and measured about a 10 degree Fahrenheit rise, so that means the steel could have expanded 1.5 * .000006 * 10 ~= .0001". I can't think of many circumstances in woodworking where a ten-thousandth of an inch would matter, but I know some people on here are nuts :)

I use a Norton 5SG46-JVS wheel. This is one of the new seeded gel wheels that Norton makes, and it's the cat's meow. It's fast cutting, long lasting, and cool grinding. I did cringe when I spent $80, but this wheel works great on everything, so I only had to cry once. 46 grit, J hardness. I have some higher grit wheels, but they tend to burn the surface and don't leave a finish much better than this one.

I have a set of Starrett Weber gage blocks that I bought at a swap meet for $100. They came out of a GM factory that shut down, and are in excellent condition and more accurate than my best micrometer can measure.

The grinder is crank powered, and I ground the chuck in with drip coolant. Talk about a tiring job! Three hours of crank, in .025", crank, in .025", repeat. I took about .002" off the bottom, flipped it over, and took about .003" off the top (in .001" passes). I measured about .0003" in deviation on my surface plate on some test pieces, and that's good enough for me. This is more of a tool & cutter grinder, and I am more a hobby machinist.

I have some stepper motors and a driver circuit to automate the thing. I need to rig up some sort of mount and write the code, but that should be easy enough.

[Mel Fulks]

The SEMI high speed steel fraudulently sold as high speed is MUCH more sensitive to heat than the real stuff. To order high speed steel without a specific grade is often an opening to being cheated.

[Ronald Blue]

I have been out of true machining for nearly 20 years now. As in all things advances are made in the the tools we use. Norton was always a high quality product and it's good to hear they still excel. We had one manual Brown and Sharp surface grinder and the rest were power. I remember grinding the sine chuck on that one by hand a few times. That is a tiring process. Fortunately though in light use it shouldn't be needed very often.

[Bill Orbine]

Machinist stuff aside, I love the honing block you've created. I see in the background you used the wet/dry sandpaper laid on the marble or granite slab. That's a very nifty idea and I'll say I learned something today! This is the sort of method to use when needed to touch up the knives if not quite ready for grinding. Thank You!

[Benjamin Miller]

Thanks, but I copied the honing block from somewhere on the Internet. It will be nice to touch up the knives between sharpening. If you make one, 45 degrees will work perfectly fine and won't require any crazy setups (mine was 40 degrees, so I had to tilt the table saw 40 degrees and cut it on its side).

I got the granite tiles from Menards for about $2 each. They're pretty darn flat... perhaps not as flat as my Starrett surface plate, but flat enough for sharpening purposes.

For this honing job, I used 220 and 500 grit sandpaper to create the microbevel. Anything sharper than 500 isn't necessary here.