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Sharpening: Help me understand hollow grinding.

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Forum topic by Schoffleine posted 10-07-2013 02:29 AM 980 views 1 time favorited 11 replies Add to Favorites Watch
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Schoffleine

45 posts in 1547 days


10-07-2013 02:29 AM

Sharpening takes forever and half a day and, frankly, I’m kind of tired of spending almost as much time sharpening chisels and planes as I am working with the actual wood. I was looking at getting a grinder to speed things up a bit but the whole process of grinding doesn’t really make sense to me. I made a crude picture to illustrate my hang ups.

So how do you get a straight edge if the surface that you’re grinding on is curved? I thought maybe people were using the side of the grinding disc but watching YouTube videos reveals that’s not the case. I did find one where a guy turned the disc sideways and ground his planes/chisels that way, but that doesn’t seem to be the norm.

Seems that it’d also produce an edge/face that’s incompatible with honing on a flat stone as well? Also I imagine you’d still have to flatten out the back with flat grinding? But since so many people do it, I reckon I’m missing something somewhere.


11 replies so far

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Mosquito

4651 posts in 930 days


#1 posted 10-07-2013 02:40 AM

In short, you don’t. You just hollow grind, and hone the edge. The hollow grind is in place of the primary bevel, and then you hone the edge like the micro bevel.

http://tomsworkbench.com/2012/02/01/the-right-grind/

-- Mos - Twin Cities, MN -- Stanley #45 Evangelist - www.youtube.com/MosquitoMods

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bobasaurus

1239 posts in 1821 days


#2 posted 10-07-2013 03:10 AM

Typically when you hollow grind, you don’t go all the way to the cutting edge… I leave about 1/32 or 1/64”. This keeps the edge from burning and ruining the temper, and the edge stays straight from the previous honing. So you don’t have to worry about grinding a perfect line. Then the hollow grind makes a really nice baseline to start freehand honing, since you can rock it and feel exactly when the two upper ends of the bevel’s hollow are against the stone. I lift it a couple degrees and hone on the coarse stone until a burr appears, then go to the finest stone, lift a few degrees higher than before, and hone again. Finally, remove the burr on the flat using the finest stone.

-- Allen, Colorado

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Deycart

381 posts in 895 days


#3 posted 10-07-2013 04:15 AM

If your spending that much time sharpening, you may want to take a look at how you are sharpening. What are your steps? Mind you that sharpening is a road with many paths. There many was to get to a sharp tool. Just depends on your budget and inventiveness.

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Schoffleine

45 posts in 1547 days


#4 posted 10-07-2013 04:24 AM

Well for chisels I use those 1” x 4” diamond stone strips from DMT found here: . I can do up to a 1” chisel with them and I just do the back edge until it’s shiny up until the edge on the blue stone (coarse one), and then on the fine and extra fine I just kind of have to guess because there’s no obvious differences in shininess at that point.

Then for the bevel, I tried free hand sharpening them but that wasn’t working because it’s too easy to rock it one way or the other and screw up the angle, so I bought a Veritas Mk. II jig and use that now instead. Seems to work fairly well. I sharpen through the three grits and then test to see if it’ll cut paper/hair and if so, I’m done. If not, I start over since something went wrong somewhere.

For plane blades I do pretty much the same thing but I go perpendicular to the length wise direction that I’d do with chisels to accommodate the wider blade.

I know a lot of people buy those crazy 8000, 12000, and beyond grit water/oil stones but frankly I don’t have the money to do that, and they seem too easy to screw up (and require a $200 diamond lapping stone to correct) so I don’t bother. I’ll buy the larger diamond plates that DMT has once I can afford them, but for the moment the above items are all I’ve got in the sharpening department. I do have some lapping film on the way (should get here Tuesday) and am interested in giving that a go to bring it beyond what the diamond stones can do.

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waho6o9

4859 posts in 1214 days


#5 posted 10-07-2013 04:28 AM

http://www.youtube.com/watch?v=WO_M95qDdAQ

Enjoy another sharnening technique from Mr. Burns.

You might want to check scary sharp, tormek, Japanese waterstones,
oil stones, and find what suites you best.

I hollow grind on the tormek and then use Japanese waterstones for
the secondary bevel, the back gets flatten as well.

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Deycart

381 posts in 895 days


#6 posted 10-07-2013 04:28 AM

Well you got the right idea. I might add you should try to polish the back of your blades as well as the bevel. Try to imagine a smooth surface on one side and then the other side you have deep gouges. This is not exactly the ideal shape for a blade to be in. Second note is that you DONT have to go through all your stones every time you sharpen. If you don’t have any chips missing just use the finest stone you have. I go up to 8000 on my water stone with a veritas mk II and then strop it free hand a few time on a bit of leather with green paste Chromium oxide. I usually just strop it a few times before I get started in the morning and then maybe once in the mid afternoon and sharpen about every two or three days.

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Deycart

381 posts in 895 days


#7 posted 10-07-2013 04:32 AM

Depending on the tool the back may not need to be “flat” a plane blade is one example where it need not be flat. You can put a back bevel on it to save a lot of time from trying to get it perfect and its a great technique for a really old pitted blade because the back bevel can quickly get though the gunk to good steel. Of course most back bevels are between 5 to 1 degrees. It really does not change the performance of the plane much. In fact in a bevel down plane (most planes) it makes for a better surface with less tare out at the expense of ease of pushing it through dense wood.

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crank49

3380 posts in 1608 days


#8 posted 10-07-2013 04:59 AM

The biggest mistake I see folks make when sharpening is to start out with too fine of a grit and then skip too many grades between grits..
I have heard of people spending hours trying to flatten the back of a chisel on a 400 grit when a couple minutes at 100 then a couple minutes at 220 and so forth till you get to 400 would get the same job done in about 8 minutes.

Hollow grinding will greatly speed up the process as well because after you create the concave surface you are only having to hone the micro bevel.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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Don W

14922 posts in 1205 days


#9 posted 10-07-2013 12:02 PM

I hollow grind on an 8” aluminum oxide wheel. I go straight to a hard Arkansas stone. I’ve got a set of DMT’s that only get used for flattening the back of the irons.

I agree with polishing the back. Its a must do. http://lumberjocks.com/donwilwol/blog/33653

I freehand, so its a little quicker and takes some practice, keep trying, you’ll get there.

-- Master hand plane hoarder. - http://timetestedtools.com

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kaerlighedsbamsen

474 posts in 351 days


#10 posted 10-07-2013 12:21 PM

If you use that much time sharpening your technique needs a closer look. Or your tools is way too soft in the steel…

I use a Tormek (garage sale, 20€), a quick brush on an Arkansas aluminium oxide stone and finaly a quick hone on the leather weel. When going through my most used tools for brus-up-sharpening i can grind them all (5 chisels, 3 planes, 2 knifes, and a scissor) in about 20 minutes including setting up the planes. That leaves them razor sharp and ready to use.

Find a system that you like and get good routine using them. That will get your time back making projects in stead of sharpening.

I think the hollow grind issue is covered good i the above posts. My only addition is to say that on turning tools hollow grind is often really good – especially if you are after a cutting rather than scraping action and flat stones should then be avoided.

-- "Do or Do not. There is no try." - Yoda

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12strings

402 posts in 1022 days


#11 posted 10-07-2013 12:38 PM

I tried using a regular (high-speed grinder), and kept burning my tools, so I have switched to using very rough (60-80 grit) sandpaper on granite for grinding, It works fast enough for me, since I don’t grind every time. I then move up to 220 sandpaper, then 1000 waterstone (6×2”) followed by a 6000 waterstone…All the equipment I use for sharpening cost less than $50, since the 1000/6000 waterstone is a dual-sided thingy that was $30…but it works well and is easy to flatten by just rubbing it on the 220 sandpaper on the granite.

-- I'm strictly hand-tool only...unless the power tool is faster and easier!

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