Mortise troubles

[john davey]

I am still building my bench and am at the mortise chopping stage. This is the first time I am using the 1/2 mortise chisel from the Narex set. I am having a few issues. First I flattened the back of the chisel but did not grind the bevel before sharpening it. The leading edge was weak and broke down. See pic below. This is not a big concern to me as I have heard others say this and after grinding they were fine. Second problem is a little more troubling. I had the side of the top of the mortice blow out on my while prying. See pic below (repaired but you get the idea). I am assuming this is a combination of my poor technique and the fact that the legs of the bench are laminated pine. The dimensions are 3.25 x 3 and I am chopping through the 3.25 side. My guess is I am so how twisting the chisel to cause this but am not sure. To be honest this is my first time chopping through mortises and this happened when I was about 3/4 of an inch into the cut on the second side. Meaning I already chopped about an inch and a half of out of the other side. This pine also feels very brittle. Almost like some kiln dried 2x4's I purchased a while ago that just disintegrated when you drove a nail into them. The legs were laminated from the straightest 2x12's I could find at the Borg and ripped to size. If it just technique I am fine with it just need to know if this is common with pine or I should practice a bunch before I continue..... Thanks, John....

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[Jim Foster]

I used my 1/2 inch Narex Mortise chisel to cut a 1 1/4" deep by 3" or 4" long mortise in White Oak and it stayed pretty sharp. The only thing I did to it was flatten the back a little and add a 35 degree microbevel to the front. From the pictures, something seems a little excessive. Did you find a knot when you were prying?

[David Posey]

I used the same chisel in SYP on my bench. The primary bevel on that chisel doesn't need to be reground, but you want to put a steep secondary one on it. I think mine's about 35 degrees. Even if you never use secondary bevels on other chisels, I would do it on this type. I do think the tips tend to be a little brittle on the Narex, so if you kept the original angle, I'm not suspired it broke.

I also had that blowout happen a few times with the pine on my bench. I was using pretty deep mortises, and I was sure it wasn't going to make it any less structurally sound, so I just glued it back and counted it as a learning experience. There's a chance that if you are twisting the chisel you could have caused it, but I think it's more just the hard-soft-hard nature of that pine.

Did you score the sides of the mortise first? I can't quite tell from the picture. Do this, and do it deeply, and you won't have to worry too much about blowout.

[Jessica Pierce-LaRose]

The secondary bevel is rather important on these chisels - if I remember correctly, they come with a quite shallow bevel; so as you drive the chisel it can sink into the wood deeper more easily, but you want at least a narrow secondary bevel with a higher angle (I like 35ish degrees as David mentions) so that it holds up to the heavy duty pounding it receives.

Also as David says, marking your sides deeply helps prevent tearout. I use a mortise gauge for this.

Also, particularly if you're making a through mortise, avoid prying when you can. A trick I picked up from the Woodwright's shop is to slice down the middle of the junk in the mortise with a heavy knife so it pops out easier. I often pry out stuff, if I have to, with an old screwdriver. If you're doing a through mortise though, you can usually get the mortise done and then push out the junk with a mallet and a little block of wood. I think Roy Underhill said something along the lines of "there's very little prying in woodworking".

There's a recent episode of the Woodwrights shop here :

http://www.pbs.org/woodwrightsshop/video/3100/3104.html

At the tail end he does his "mortise under glass", which shows a technique that works quite well.

[James Owen]

As others have said above, you want a good secondary bevel on your mortise chisel. 35˚ is a pretty good place to start, and you can easily go as high as 40˚ or so, if your chisels tell you that they want it (by continuing to crumble at the cutting edge). I'd also suggest making your secondary bevel rather stout: I put a 1/8" to 3/16" or so wide secondary on mine; it keeps plenty of metal behind the edge to support it, and makes honing a bit easier. I've also found that a flat bevel seems to work a bit better than a hollow ground bevel on mortise chisels. YMMV

You should be able to cut mortises by hand with a minimum of prying. Try this link for a demo on one technique: http://pfollansbee.wordpress.com/2011/08/11/mortising-under-glass-thanks-roy-frank/ (A photo version of the same technique shown in the link that Joshua posted above.)

If you're going to be chopping a lot of mortises, you might want to take a look at getting an English Oval Bolster Mortise Chisel ("pig sticker") in the size(s) you regularly use. These have some features that make chopping mortises accurately and cleanly very easy. Vintage or new will work just fine......

[Jim Neeley]

Second problem is a little more troubling. I had the side of the top of the mortice blow out on my while prying. See pic below (repaired but you get the idea). I am assuming this is a combination of my poor technique and the fact that the legs of the bench are laminated pine. The dimensions are 3.25 x 3 and I am chopping through the 3.25 side. My guess is I am so how twisting the chisel to cause this but am not sure.

John,

First, although I've taken hands-on classes including M+T construction I'm not a "tenured mortiser". In those classes I was taught to be extremely careful when prying to not put any twisting or lateral force on the chisel. Additionally I was taught to start the cut in from one end and work to the other. With the central body of the mortise cleaned out and a central cavity, shift to thin shearing cuts for the ends such that your front hand can provide the small amont of "prying" necessary to evacuate the material.

Also, when prying, it has been recommended to me to use a mortising chisel one size smaller than the chopping chisel, to protect the walls from blowout.

This is just my $0.02... The approach has worked for me when mortising in pine. YMMV.

Jim in Alaska

[Joe Fabbri]

John,

From my limited experience with chopping mortises, I've found pine (yellow pine) to be a little problematic in terms of chipping out and splitting. I think the only solution to that is to make sure you've scored down deeply enough. If you're using a marking/cutting guage, try following up with a razor blade knife. Go slowly, so as not to veer off of the original scored line. Also, I mark the ends of the mortise with a chisel, only pressing down, not striking the chisel. I found this helps to keep the wood chipping out past it.


Joe

[Jessica Pierce-LaRose]

Jim brings up a good point - you can actually get by with a fair bit of prying if you need to (although if these are through mortises, you may very well may not need to) but any twisting action when prying is what gets you - any time I've chipped a corner of a chisel, it's from twisting more than prying.

[john davey]

Thanks for all of the replies. I will re grind the chip out tonight and add a secondary bevel to it. Since I have the set I may actually try the 3/8 chisel as well since that was suggested. I am scoring the sides. I am using my 2 inch chisel and tapping it in on the lines. I think I was prying to much and with some twist which is what got the chipout. They glued back fine so I will be back to it tonight. I am also thinking of trying my luck at drilling some waste away. I have 8 of these to do. 4 at 3.5" by 3.5" deep and 4 at 2.5" by 3.5"deep. At this rate it will be my retirement bench :). Thanks again...John.

[Joe Fabbri]

When the mortises get too big, then drilling is probably the best bet. If they're through mortises, drilling half way from both sides will probably make alignment easier.

You might want to be careful tapping the 2 inch chisel to score the lines. It's possilbe to split the wood a little.

Joe

[Jessica Pierce-LaRose]

1/2" is right on that hairy line for me between chiseling and drilling and paring - it's big enough that mortising starts to feel like work, but small enough that clearing out all the waste from drilling paring can be kind of a pain. I can also mortise a lot straighter than I can drill . . . . But if you've got a drill press and a forstner bit that can handle most of the work, drilling is definitely going to be easier if you've got 8 of them to do.

[john davey]

OK, I was able to fix the chisel and complete the first mortise. Actually I need to clean the mortise up but the chisel made it through the 3.5 inches of pine and cut much better. After regrinding I added a secondary bevel as recommended. I also used my 220 Norton stone to grind out the chip instead of the bench grinder to keep a flat bevel as suggested here. Pic below.....John

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[Floyd Mah]

I've had a lot of experience pushing needles into patients for spinal taps (for spinal anesthesia). In any case, using a beveled tool is not a totally obvious process. If you consider a beveled tip of the chisel, one side being in-line with the handle and the other side beveled relative to the long axis of the chisel, one's first instinct is that when you tap the end of the chisel, the chisel will move forward, in line with the axis of the chisel. That is not the actual case. While the majority of your forces move the chisel in that direction, the chisel will try to deviate in a direction that is the average of the two sloping faces. It's similar to sitting in a boat and using the oar on one side. The boat will try to obey the force on the side with the oar, but the other side of the boat will meet resistance and deflect the boat away from the straight ahead direction.

When you hold a chisel in a perfectly perpendicular direction above the wood and tap, the chisel will try to move in a perpendicular fashion until the beveled side deflects it. In your case, if the non-beveled edge follows the outline of the mortice, the inside face (beveled) will try its best to push the chisel outward. This causes your chisel to blow out the side of the mortice, especially if the grain in the soft pine traps the chisel and overcomes your ability to keep going straight. I've found the best way to avoid this is to scribe deeply (as mentioned above) with a razor knife and to take out the initial layer of wood longitudinally by paring with the chisel. Don't use the mortice chisel until you've gotten deeper into the mortice. Also, I pre-drill the waste wood and use a wide chisel to cut the wide face of the mortice as much as I can. The mortice chisel works best for removing wood at the bottom where you can't apply leverage to pry the wood out.

Also, at the narrow end of your mortice, if you scribe deeply and tap the wood with the chisel 1/8" away from the end, you will cause that wood to lift up along the cut and provide you with a very clean edge. Then you can use that to brace your chisel as you go deeper.

Anyway, my main recommendation is to carefully outline your mortice with a razor and then pare down before tackling the rest of the mortice with other chisels.

[john davey]

I finished another mortise and this time knifed in the lines and the results are much better. So the combination of a secondary bevel and knifed lines seems to have me 2/3rds of the way there. Obviously the final 1/3 is practice. Good think I have 3 more legs to do. now blow out but I did do a little prying at one end and messed up that edge slightly. A few new pics below....

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[Charlie Stanford]

You are, almost without a doubt, overpowering the chisel. Don't pound it like you're crucifying Jesus. Ease off. Change your mindset - you're sculpting a rectangular hole, not bludgeoning the poor workpiece to death as the photos indicate. Finesse and restraint are in order. Figure out how big (or small, actually) a bite you can take and have the mortise look clean as you work through to the other side. Let the tools do some of the work. Mortising is kind of like sawing - pressing the saw hard only slows you down in the end. Taking gigantic hunks with a mortise chisel (because you've heard you should) will result in less than desirable results. If you are using the chisel correctly, you'll need to do very little prying. Very little. Maybe none. It would take me longer to cut a clean mortise in pine that it would in hickory.

Joinery grade (construction grade) timber will never cut as cleanly as fine hardwoods commonly used for furniture. Getting neat, crisp results is not always easy when you're using lumberyard pine.

You could also consider the drill-and-pare method, especially if you own a dowel jig (Stanley 59 for instance) that assures upright boring.

[john davey]

Thanks for the insight Charlie. Yes I am smashing them pretty hard. I believe I might just try drilling then as they still take quite a bit of time to cut at the rate I am smashing them. Lighter taps will take longer I presume. I agree about the hardwood comment as i am able to make cleaner mortises in cherry. Thanks again...John

[Charlie Stanford]

Thanks for the insight Charlie. Yes I am smashing them pretty hard. I believe I might just try drilling then as they still take quite a bit of time to cut at the rate I am smashing them. Lighter taps will take longer I presume. I agree about the hardwood comment as i am able to make cleaner mortises in cherry. Thanks again...John

Chopping mortises is often presented as an exercise where an uninhibited free-for-all, let our your animosity, pounding is in order. It's definitely not in my opinion. I'm frankly not sure where this notion came from. It's never worked for me, I can honestly say. I think there was a point in time where I THOUGHT I was doing it right by doing it this way (though this never "felt" right). It may have been a day when the arthritis in my shoulder was acting up or maybe I was just really tired and I took smaller bites, came up with a beautifully cut joint, and frankly in about the same amount of time it would have taken by wailing on the chisel and having to dig the jammed chips out instead of watching them happily eject themselves as I proceeded at a more sane pace through the joint. It was a real eye-opener and more importantly the work was of much better quality. Much better.

You also need to check the geometry of your chisel. Is it square in section, or a slight parallelogram? If a parallelogram it will stand a bit of a harder hit than a perfectly square chisel.

It can be frustrating doing a lot of chopping, which feels like hard work, having to be followed by even more digging and levering which is even harder work. If you, or anybody else, feels they do as much digging and levering as you do applying power with the mallet then the chisel is definitely being overpowered and it will take LONGER doing it this way than slowing down and letting the chisel eject the material and move through the joint at a rate suited to the implement being used. Really, it's no different than running a mortising machine. They can only cut as fast as they can cut and pressing them does not help production time.

[Joe Fabbri]

Although I have two mortise chisels (a 1/4" Narex--which I haven't really used yet--and a larger 1/2" socket mortise chisel), I've only really used a regular bench chisel. Since I don't want to break it by diving in too deeply and prying out a lot, I've gone gently with it. With the smaller bites, like Charlie describes, I get pretty nice results, even in some difficult pine. So, if you find that you have too much to do slowly, maybe you should give the boring method a try.

Joe

[john davey]

Thanks again. I will be gentle tonight and see what happens :)

[Jim Matthews]

In Ice Hockey, you may employ your stick to disrupt your opponent's possession of the puck.

If your stick is brought into play from waist level downwards, play continues.
If you bring your stick into play from overhead, you go to the penalty box and feel shame.

Mortising by hand is tiring, and the impulse is to apply more force to get it over with, already.
The only way that works is tedious - a little at a time.

Have a look at Ian Kirby's primer (http://www.woodworkersjournal.com/Main/Articles/Skill_Builder_Hand_Cutting_Mortise_and_Tenons_8080 .aspx) on the method.
Note that he leaves plenty of clearance "North" of the mortise to prevent blowout.
This is trimmed away after the mortise is complete.

[Jessica Pierce-LaRose]

I like to work in the middle, and get to full depth rather quickly, working outwards as needed - that's really the majority of the heavy chopping is at the beginning there - once you get to depth, it's almost more of a paring cut as you slowly widen the mortise. If the mortise isn't particularly large, often time hand pressure is enough. If it's large, I'm really only using the mallet to allow me to take a bigger bite, but at that point it's still a "paring-esque" cut. Regardless, my last few bites on each end as I'm squaring up the ends are pretty much hand pressure only.

Although being driven by a mallet, a super keen edge isn't needed, I keep a piece of MDF with green compound and a drop of oil on it nearby; frequent stropping makes the job easier.

To start, I like to take careful small bites, followed by gentle paring almost parallel to the surface to get a show surface (particularly on through mortises, where it's not hidden by a tenon shoulder) looking nicer. This also helps guide the chisel. I find it useful to line up the chisel carefully, and then lean on it a bit to bite it into the wood to keep in place before I whack it with the mallet - it can be hard to keep it in place while positioning for that first whack before you've got a little depth to keep it in line. If doing a door or something it's nice if you can to size the mortise and panel's groove to match, as that groove helps line things up in the begining.

[john davey]

Thanks for the link Jim. I'll read that at lunch today. I did some more chopping last night and I was obviously pounding to hard before. It is strange that with light taps it still went at about the same pace as when I was banging the crap out of them. I will try to post some pictures later as I didn't take any yesterday but the results are getting better. I think with more practice and all of your help I am starting to get the hang of this. Thanks again all...John

[Jim Koepke]

Have a look at Ian Kirby's primer on the method.

Jim,
Thanks for the link. It is downloadable and can be saved as a .pdf.

Though I am not in 100% agreement with Ian Kirby's method and opinions, that is just different opinions.


It is strange that with light taps it still went at about the same pace as when I was banging the crap out of them.

One of the mysteries of life is knowing when extra effort will not change the results appreciably and when just a little more will make an outstanding difference.

A steady, sustainable pace is often quicker than going all out and having to stop for a rest before the finish.

There are a few stories in my life that are good examples of taking a little more time to save time. The best saying on this still comes from learning to type with out an instructor. One of the books said, "strive for accuracy and let speed emerge on its own."

jtk

[Tom Vanzant]

Jim K,
Applied to a 5-hour drive, by staying within 2 MPH of the limit instead of "more", we arrived in the same ellapsed time with 1+MPG increase in mileage, and weren't as tired, probably from not having to be looking over our shoulders.

[Jim Matthews]

The lighter force allows the shank of the mortise chisel to register against the side walls.

Driven harder, the bevel will try to follow the grain in the path of least resistance. This may not have any relation to the side walls, previously cut.
I must confess, when I cut something this deep, I bore out the center with a brace and bit. The screw does the work easily and a sharp chisel cleans up the sides.

You can even glue up a template to guide the various size bits you own. Clamped in place, something around 1" thick will get me started straight from - the start.

Bob Rozaieski tackles this in a solid video (http://logancabinetshoppe.com/blog/2010/01/episode-14/), without quick edits. 16:48 the fun begins. 22:09 he mentions the guiding action of the mortise sides.
Note that in the comment section, it is suggested that boring out the mortise is helpful when larger holes are needed.

[john davey]

Thanks again Jim. Bob's videos are fantastic. I don't know how I missed this one.... I believe I have all of the concepts down. I also read Ian Kirby's PDF that was mentioned here. I had a spare glue up that was going to be a table leg in cherry that never got used. I tried both of Ian Kirby's methods and in cherry I was getting much better results. Granted I was not going 3.5 inches either. Bob basically did one of those methods in his clip. I believe I will drill the rest of these out since I need to get moving on this bench and I believe the pine is problematic going 3.5 inches. Thanks again for all of the help. I actually am planning a M&T project in my head and will start that as soon as the bench is complete....John