# Hollow-Chisel-Mortiser Tune-Up



## NBeener (Sep 16, 2009)

I didn't know, originally, that virtually EVERY chisel that you buy needs to be sharpened, before you use it.

Neither did I extend that reasoning to my Grizzly Benchtop Mortiser's hollow chisel mortiser bits.

But … after a LOT of use of the thing, and after always watching Norm Abram use what seems like SIGNIFICANTLY less effort, to make mortises with HIS Delta unit than my Grizzly seems to require …. I did some poking around.

I found an old test that compared like seven different hollow-chisel mortiser/bit sets, with the most expensive (Clico) being roughly TEN TIMES as expensive as the cheapest set.

The seven were:

...1) Woodcraft, 
...2) Hartville, 
...3) Lee Valley, 
...4) Guildcraft, 
...5) Clico, 
...6) Shop Fox, and 
...7) Fisch

Two clear conclusions:

...1) You really DO NOT get what you pay for, on this one.

In fact, the two MOST expensive sets were among the three considered "not recommended." Shop Fox was the 3rd;

...2) Proper preparation of both chisel AND bit makes a WORLD of difference.

So … armed with this knowledge, and … thinking I should spend big $$$ and replace my OEM Grizzly bits … I, instead, went to the shop and did tune-up work.

Some of the instructions I worked from were found here. The rest was a combination of glancing at NUMEROUS sources, and … what I'd learned about sharpening, generally.

I ran all four outside faces of each chisel through the sandpaper gauntlet, starting with 150 grit, and-pretty much without skipping a grit-working my way through 1200 grit. What started as dull finishes, rough with milling and finishing marks … ended up as pretty much mirror-polished sides.

I then used the Rockler 220 and 600 grit diamond cones, made for sharpening the inside of the chisels.

The chisels have a 5/8" shank, so … using my Forstner bit … I drilled a 5/8" hole in a scrap of wood, and used that as the 'stand/clamp' for each chisel.

Centering it under the drill press chuck, I lowered the diamond cones, at the lowest speed my drill press will turn, and took a light pass at each of the chisel interiors for a few quick seconds.

I followed THAT with a quick de-burring process on a whetstone.

Look … I don't have ANY before/after measurements, or ANY quantitative data to convincingly prove the difference that all this effort (maybe a total of an hour) made.

But here's the deal.

The difference was *staggering.*

I had done a LOT of mortises in African Mahogany, so I knew THAT wood fairly well.

My newly-tuned bits flowed into and out of the wood MUCH faster, MUCH easier, without EVER getting "stuck" on the bit (so that the fence clamp had to 'push the wood back off').

The chip ejection was picture-perfect, smooth and steady, with smaller chips.

I made it a habit of holding my DC's hose, with a reducer nozzle (ShopVac would work fine here, too), to keep the holes free of debris that would only slow the process.

After the mahogany, I mortised some SPF, some Red Oak, and some Maple-all with the same results.

To ME, the difference was night and day.

Truly.

The edges were cleaner, smoother, more even, and … the process took MUCH less time. It was FAR less of a wrestling match with the lever than before … and I HAD already greased the gears on which the head travels.

I did NOT take the time, yet, to properly sharpen the auger bits that come with the chisel sets.

That's next.

If THAT makes ANY difference, then I'm going to be one tremendously happy mortise-making camper.

I also did NOT (yet) take a triangular file to work the inside corners of the hollow chisels, as the article linked above recommends. I will. I may also do what I can to polish the insides of the hollow chisels, figuring … can't hurt, and may help chip ejection.

Two more learnings:

...1) The recommendation is that you point the OPEN face of the chisel _in the direction of the movement of the workpiece," and

...2) Many sources recommend that you have the thickness of a nickel or a dime between the flat of the auger bit and the points of the chisel.

Testing revealed that MORE is better.

According to one test, a gap the thickness of a nickel-roughly 0.072" thick-results in operating temperatures roughly *40 or 50 degrees higher* than if you increase that gap to 0.117" (the gap provided by the built-in spacer, on the Powermatic PM701 mortiser, used in their testing.

I have a 0.125" gage block that I will NOW use to set the gap between bit and chisel.

Going any further than that, obviously, creates fairly significant risk of breaking the bit.

Hope this helps.


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## richgreer (Dec 25, 2009)

Thank you for this great post. I had never thought to sharpen my mortising chisels. Now I am going to sharpen them right away. This post gets an A+ for "valuable information provided".


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## jbertelson (Sep 26, 2009)

Good post Neil. If I ever get a mortiser, I'll get back with you. I had read the business about sharpening the chisels someplace else, don't know if it was a magazine or what. I think I read it in some magazine though. So it definitely seems to be the thing to do…................


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## sbryan55 (Dec 8, 2007)

Thanks for the post, Neil. Even though this seems intuitive I would not have thought about sharpening the chisel on my mortiser. Now you have given me something else to do!!


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## Beginningwoodworker (May 5, 2008)

Thanks for posting, Neil. I am learning a lot about my benchtop mortiser.


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## BobLang (Feb 2, 2009)

It would be nice if you gave credit to your source. Most of this post is taken from an article from Issue 7 of Woodworking Magazine.. The back issue is still available for anyone who would like to read the original, or you can download just the article from Woodworking Now.

Bob Lang


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## NBeener (Sep 16, 2009)

You're right, Bob, and-for that-I apologize.

What I came across was a copy of an article that-only later did I realize had been excerpted from "Woodworking Magazine-" just as you said.

Again, my apologies.

The article, by the way, was quite well written, and informative. Since-when I posted this-I didn't HAVE the info about sourcing-I couldn't give the proper attribution.

I should have added it, today, though.


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## grizzman (May 10, 2009)

gee neil…what a great reminder that we need to sharpen these little devils…sometimes these things just slip right on by , cus were so into the project, we forget the obvious..but ,,,good ole bob lang isnt cutting you any slack…almost down right plagiarism…lol….you do a good thing and get knocked down a notch…but it was some good training…...your becoming quite the wood worker…..im proud of ya buddy…grizzman


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## TopamaxSurvivor (May 2, 2008)

Nice info Neil. Thanks, I don't have one of these, but now I know what the deal is


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## 559dustdesigns (Sep 23, 2009)

This is good stuff Neil, Thank you


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## Timbo (Aug 21, 2008)

Thanks Neil, Thanks for taking the time to post I have a new benchtop mortiser sitting in the box and this is information will come in real handy. I think I will dig out the bits and sharpen them all.


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## lumberdustjohn (Sep 24, 2009)

Thanks for posting.
I thought they would be ready to go out of the pack.


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## PetVet (Nov 7, 2008)

Oh oh, another project for me. I just finished cutting a bunch of mortises for a step stool. I am wondering now how much easier it would have been if I had sharpened the chisels and bit. Thanks for the heads up!!


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## stefang (Apr 9, 2009)

Great post Neil. There are also some very good sharpening/set-up articles on Fine Woodworking.com for members in the link below:

https://www.finewoodworking.com/skillsandtechniques/skillsandtechniquesarticle.aspx?id=33099


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## patron (Apr 2, 2009)

thanks neil ,
i got this bookmarked .
now i need to get the proper sharpening stuff for up to my 1" chisel too .
if anyone knows where ,
i would appreciate it .

good post neil !


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## mtkate (Apr 18, 2009)

This is a really great post and reminder. I just broke my first mortising bit yesterday so I managed to find your words of wisdom again and this time they stay in my favorites.

It always happens on a Saturday afternoon (in my area, the stores to get a decent replacement are all closed Sundays…).


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## Geedubs (Jul 23, 2009)

This is great information. I just picked up a Delta 14-651 this week, used, and am in the process of reconditioning the machine and the four hollow chisel sets. I also had found Bob Lang's article and used it as a guide. I have tried using various grits of sandpaper on the sides of the chisels but still have not been able to achieve a consistent mirror finish. I did pick up the sharpening kit from Woodcraft, however, and that seems to work great. Now I am trying to find good information on sharpening the auger bit.

Thanks again Neil (and others) for the valuable information.


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## Gator (May 2, 2008)

Thanks Neil, 
My plan this week was to have a look at the chisels that came with my General, and now I know where to look for the information to get it done.

Great post.

Gator


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## bbrown (Sep 3, 2008)

I just snapped two 1/4 inch bits. I forgot to set up the big gap at the tip! Always happens at the worst time it seems. Moved on to using a drill press but it's a lot more work to make mortises that way - lots of hand chopping, etc.
It looks like folks are using a bigger gap between the mortise points and the drill bit tip than I ever have done. 0.125" is a sizable gap.

I know this post is now 7 years old, but the info is very helpful!

BTW, I ordered two new replacement bits (just the inner drill bit part) on-line: Fisch (Austrian made apparently). Only $10 each with free shipping on Ebay. Does anyone know if there is much difference amongst the different makes?

One other thing: what's the logic for keeping the opening for expelling the wood chips in -line with the movement direction of the wood?


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