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11th April 2004, 07:07 AM #1
Chopping Mortises – A Quick Tutorial
In a small response to years of subtle but predatory marketing on our Public Broadcasting Station that has newcomers asking about mortising machines for their early projects involving a dozen mortises or fewer, I prepared a short primer this morning in the shop to answer a younger man’s question. The entire session, including stock preparation and photography, took 30 minutes. The actual mortise chopping took 4 minutes, and I wrote this up on my lunch break.
First, you need mortise, not paring or firmer chisels. These Japanese ones below I bought from Highland Hardware when they first opened more than 2 decades ago to replace the badly worn family ones.
Note the flat bevels in the photo above; not hollow ground and no secondary bevel. These are laminated blades designed for striking, and they come in the exact width of your intended mortise, ¼, 3/8, and ½ inches.
Also note that the backs are hollow ground to facilitate easy flattening as you hone them during their life. You can see the hollow above the edge.
Their bevels should be touched up on the hone every time you use them; your stones ready for use should be a permanent fixture on a corner of your bench. Honing these is easy; just index the flat bevel on the stone. You also need to hone the back dead flat, and I also hone the sides lightly on the fine stone to remove any burrs. I use a set of 4 Arkansas stones all the way to the finest “black” grade, but you can use what you normally sharpen with. I wiped the oil off the stone and chisel for clarity; don’t hone them dry or the stone’s pores will clog.
I do a final stropping on the stitched muslin wheel with Knifemaker’s Green Rouge. Hard felt wheels are the best for this, but they are expensive.
Then I lay out the mortises on the prepared stock. First, the mortise gage double tines are set to the width of this half-inch chisel. Then the mortise gage fence is set for mortise location on the stock, and lines scratched. Want to have the mortises dead center? Simple, just run the fence down the opposite face of the stock, compare the marks, and adjust the fence until the marks are identical.
It’s a simple matter next to mark your mortise width with try square and marking knife. I’ll cut a simple blind double mortise and have used a pencil to make the lines clear in the photograph. You need to leave your pencils in the drawer for this and other joinery marking, as they are insufficiently precise.
Index your mortise chisel plumb in the end knife cut, and strike with a wood mallet. Do all four ends.
Continued on Part II
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11th April 2004, 07:08 AM #2
The next chopping sequence is from the center of the mortise, and the waste merely levered out…splitting rather than cutting the wood along its long grain. My training aid today is a 2 X 2 of sopping wet Douglas Fir from the scrap pile out in the weather…. hard, tough and splintery. Your dry cabinet hardwoods will be easier. When working with highly figured wood such as Birdseye Maple you are afraid to split, then simply strike the outline of your mortise lightly with a paring chisel, first.
I repeat chopping from end and center, levering out the waste until I reach the desired depth; then I reverse the chisel and use it bevel-down to clean up the mortise bottom.
The final result is a little furry because of the wet wood, but entirely satisfactory. There is a small chip-out at the top of the right mortise, but this will be completely hidden by the tenon shoulder when assembled. If you desire a neater edge, simply chop a 16th or so inboard and pare to the final line. Not necessary at all unless you are using a two-shouldered tenon where that edge will show.
Frankly, even working in large, commercial, 3-phase shops, I never found many mortising machines that were entirely satisfactory. The bits are difficult to sharpen so you need two sets of them for production work, and the over arm design likes to flex under pressure, especially when the bit is getting dull, which also tends to pull your work piece out of alignment with the fence.
Why bother? These few simple, inexpensive tools and a shop-made mallet are all you need to do mortise and tenon joinery on one-off projects for the whole of your lifetime.
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11th April 2004, 11:05 AM #3
Bob,
I agree that it is absurd for someone who simply wants to cut a dozen or so mortices to consider buying a morticing machine, and that, if that is all they want to do, then using morticing chisels is the way to go. I also agree with you that morticing machines that use square chisels are not entirely satisfactory. However, mortising chisels and chisel morticing machines are not the only options. If you need to cut mortices for small-shop production, then router-based morticing machines such as the Matchmaker or the Multirouter are probably the way to go.
The amateur furniture maker who needs to cut a fair number of mortices, and who does not have the time or inclination to cut them by hand, can use a hand-held router equipped with a solid carbide spiral-upcut bit to do the job. If he spends a day or so building a precision morticing jig, he can cut a precisely sized and precisely positioned mortice in a couple of minutes. See
http://www.woodworkforums.ubeaut.com...&threadid=5633
and
http://www.woodworkforums.ubeaut.com...&threadid=7272
Rocker
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11th April 2004, 11:20 AM #4
Bob
Your tutorial is one of the best I've seen. It's clear, comprehensive, easy to understand and illustrated with excellent photos. Well done and thanks for taking the time.
ColDriver of the Forums
Lord of the Manor of Upper Legover
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11th April 2004, 12:35 PM #5If you need to cut mortices for small-shop production, then router-based morticing machines such as the Matchmaker or the Multirouter are probably the way to go.
The guidance he gets here is that this is traditional joinery business is mystically difficult and he needs to line the machinery company coffers with money his young family could better use for something else.
We'll teach him to use the plunge router after he has some competency with his basic set of hand tools, develops a lasting interest in craft, and is ready to move on to greater production.
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11th April 2004, 02:13 PM #6
Well done Bob
You have certainly been busy lately with your picture-laden tutorials (at Wood Central and Traditional Tools. Extremely clear and well written. I hope you find time to keep them coming.
I think that they are not really for the novice seeking a reduced-tool method of building, although you state this is the audience at whom you are aiming, but perhaps the more adventurous or old-world-orientated woodworker (these days working with hand tools seems to have unfortunately acquired an aura of the fanatic). Not many beginners or tool-deprived would-be woodworkers are going to have mortice chisels. And the price of one good mortice chisel is about the same as one cheap/entry level router here in Oz (such as the GMC). Which tool would you choose as a novice woodworker? Still, you will find many friends on this Forum (and I am one - owning at least a half-dozen morticing chisels that get used alongside my routers), and hopefully your baring of the mythology around one of the "black arts" of hand joinery will inspire others to try something new.
Regards from Perth
Derek
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11th April 2004, 09:41 PM #7GOLD MEMBER
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Question arising
Thanks for the tutorial Bob. Your effort is appreciated. One question arises though. I notice you recommend flat bevels on your mortise chisels. I have seem this stated from time to time, but have never known why. Is it something to do with the action of the chisel in wood, or is it to do with sharpening ?
cheers
Arron
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11th April 2004, 09:58 PM #8
Arron
It doesn't have to be a flat bevel - it can also be a rounded bevel. It just must not be a hollowed bevel since this is weakest and the tip may break off when prizing out the chips. Remember, the mortice chisel is for chopping and levering out, not for slicing timber. It needs to be strong. A rounded (convex) profile would certainly be strongest and provide the best "scoop" but may be harder to cut with. I think a flat bevel is the best compromise of strength, sharpness, and scoopability.
Regards from Perth
Derek
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20th June 2005, 07:20 PM #9Member
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Photos?
Just wondering where the piccies have gone.
antisense ^_^
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20th June 2005, 07:23 PM #10
Bobs got this posted on another forum somewhere. Do a search...................................
Cheers,
Adam
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I can cure you of your Sinistrophobia
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20th June 2005, 11:30 PM #11
OK I did the search and could not find any other versions. It looks like the picture pincher, pocketed the photos and ****** off.
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21st June 2005, 12:35 AM #12
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21st June 2005, 08:10 PM #13
Thanks Schtoo