mortise depth

[Curtis Niedermier]

I recently assembled a mortise-and-tenon frame for a tool chest lid. I have been having trouble chopping a "clean" bottom in my mortises, and I usually end up going too deep. I went too deep on each of the mortises on this frame as well.

Is there any problem with this? I can't imagine there is, but I figured I'd pose the question anyway.

[Judson Green]

Not at all. I usually go deeper than necessary. Even when I cut with a machine I've always gone just a bit deeper (say ⅛" or little more). But guess you need to judge how deep is too deep.

[Chris Griggs]

Judson covered it. Totally fine as long as you dont blow through so a show face or somehow interfere with another joint. BTW, one thing I have found is that 1/4" chisel can get down into a mortise and easily take light paing cuts in the bevel down orientation to help level off any high areas. I find this quicker and easier that doing a bunch more chopping just to get out a little bit of a high area.

[Jim Koepke]

Going deep on a mortise provides a place for extra glue to escape.

jtk

[Bruce Haugen]

I recently assembled a mortise-and-tenon frame for a tool chest lid. I have been having trouble chopping a "clean" bottom in my mortises, and I usually end up going too deep. I went too deep on each of the mortises on this frame as well.

Is there any problem with this? I can't imagine there is, but I figured I'd pose the question anyway.

Short answer: yes.

Before I learned to provide a little room at the bottom and make M/T joints that weren't piston fit (or a smidge tighter), I blew out several joints, split the side of the wood on the mortise shoulders or blew out the backside of the end..

[Terry Beadle]

Having a bit of space below a tenon in a mortise is not a show stopper. But having a 1/4 inch space is border line IMO. Mr. Kingshott, a world renowned furniture maker would cringe at having more than a 1/16th I think.

Some tips:

Use a bit of masking tape on the chisel to avoid this problem.
Use Japanese bottom cleaning chisels to get the bottom flat.
Use forstner bits to pre drill in a couple places in the mortise hole to give your self an edge at bottom control.
Liter taps with the mallet as your near depth.
Cheap plastic calipers from Harbor Freight will give you good feed back as you go, OR make your own depth checker
with a bit of dowel in a small block of wood with a sheet rock screw to hold the dowel at the targeted depth.

The mortise hole should match the tenon very closely for maximum mechanical strength and for aesthetics.

YMMV and this is IHO.

Enjoy the shavings.

[Chris Vandiver]

Japanese bottom cleaning chisel(soko-zari-nomi);http://www.toolsfromjapan.com/store/index.php?main_page=product_info&cPath=312_634_635&products_id=2188

[Warren Mickley]

I generally make the mortise depth 5/16 of an inch less than the width of the stile. For instance if the stile is 2 inches wide I make the tenon 1 11/16 long and the mortise depth the same. This gives some room to overshoot the mortise a bit and not break through the far side. Leaving 3/8 of an inch leeway might be safer for someone without much experience. Or you could make a through tenon which is somewhat easier.

The best glue surfaces are the side walls of the mortise and the tenon, so it does not matter if the end grain of the tenon is not nicely mated to the bottom of the mortise.

[Jim Koepke]

There is also a western chisel for this. Often called a lock mortise chisel since making mortises in drawer and cabinet doors for locks was a regular task at one time.

Here is a search result:

http://www.google.com/search?q=lock+mortise+chisel&client=safari&rls=en&tbm=isch&tbo=u&source=univ&sa=X&ei=Cee1UuarD4XcoASk-4CwBA&ved=0CGAQsAQ&biw=1320&bih=863#q=swan+neck+chisel&rls=en&tbm=isch&imgdii=_

These are also sometimes called swan neck chisels.

jtk

[Jessica Pierce-LaRose]

Lock mortise chisels always seemed like they'd be easier to use than the Japanese style, but I've never used either. It seems like there would be a natural rocking motion with the swan neck chisel, where it looks like the Japanese chisel would be moved perpendicular to how it is held? I doubt either tool is one I'm going to be purchasing any time soon, but anyone have a comparison in use?

[Jack Curtis]

Lock mortise chisels always seemed like they'd be easier to use than the Japanese style, but I've never used either. It seems like there would be a natural rocking motion with the swan neck chisel, where it looks like the Japanese chisel would be moved perpendicular to how it is held? I doubt either tool is one I'm going to be purchasing any time soon, but anyone have a comparison in use?

The Japanese shoji chisels are designed so you can clean out a 1/4" x 1/4" shoji mortise, not likely something anyone could do with the swan neck chisels.

[Chris Vandiver]

The Japanese shoji chisels are designed so you can clean out a 1/4" x 1/4" shoji mortise, not likely something anyone could do with the swan neck chisels.

Soko-zari-nomi is but one of three specialized chisels used for cleaning up mortises in door construction(and other similar construction)in Japan. Of course these three chisels are used in conjuction with a mortise chisel. They come in several widths from about 1bu(approx. 1/8") to around 4bu(1/2"). They are invaluable when doing a mortise where a very thin remainder of the stile is left at the bottom of the mortise. The left over is thin enough to see through and needs to be very clean and uniform(this is where the soko-zari-nomi is so handy)and when the mortise and tenon are assembled, the tenon endgrain(rail) can be seen through the back side of the mortise(stile). This is done only on very high class work.


I always thought the swan neck chisel(lock mortise)was designed for digging out the deep mortises found in mortised lock sets, you know, too deep for a standard mortise chisel to have any leverage. Isn't it designed to remove large amounts of material as opposed to smoothing out the bottom of a mortise(like the Japanese soko-zari-nomi)? I've never used one but that is what I've always thought.

Specialized Japanese mortise tools as seen below;

[Brian Thornock]

I was given a pair of swan neck chisels by my dad and they are very handy for deeper mortises, especially getting into corners. Honing is a little tricky because of the leverage relative to the bevel, but they are good to have. I wouldn't necessarily buy one, though.

I leave my mortises a little deep, especially when drawboring.

[Matthew Hills]

You can see how Paul Sellers approaches making an even bottom:
http://www.youtube.com/watch?v=q_NXq7_TILA

The glass is a bit of a cheat, as easier to gauge where you are and to check for shallow spots. Also, longer mortises are easier than smaller mortises.

Matt

[Brian Holcombe]

I cut very thin tapered mortises and found Paul's method to be almost impossible to use for it. Though it seems to work very nicely for what you would typically find in most case goods or chairs.

I suspect that in practical terms a flat bottom near to the end of the tenon is not important, and may end up being a hinderance. A mortise and tenon works because of all of the long grain engagement, not the end grain.

[Jim Koepke]

I always thought the swan neck chisel(lock mortise)was designed for digging out the deep mortises found in mortised lock sets, you know, too deep for a standard mortise chisel to have any leverage. Isn't it designed to remove large amounts of material as opposed to smoothing out the bottom of a mortise(like the Japanese soko-zari-nomi)? I've never used one but that is what I've always thought.


I think you are correct about the lock mortise chisels. It is doubtful western craftsmen worried much about the precision of the bottom of a mortise.

jtk

[Jim Koepke]

To me it is kind of interesting that Paul Sellers is a proponent of a convex bevel on edged tools but if you look at his mortising chisel it has a flatter bevel than most mortise chisels.

My feeling was the video didn't have much to do with getting an even bottom to the mortise so much as it was demonstrating the use of a bevel edged chisel for doing mortise work.

jtk

[Chris Vandiver]

Chopping a mortise where one side of a bevel edged chisel registers against a piece of plexiglass, couldn't be easier. Too bad all mortises don't have a plexiglass sidewall.

[Hilton Ralphs]

To me it is kind of interesting that Paul Sellers is a proponent of a convex bevel on edged tools but if you look at his mortising chisel it has a flatter bevel than most mortise chisels.


Isn't that because he prefers to keep the hollow grind on bench chisels to save time with sharpening whereas micro bevels are not that important when chopping mortises with a pig sticker?