Chopping out mortise - should I be crushing the side walls?

[Minh Tran]

Hello,

I'm cutting out 1.5" x 2" x 1.5" housed mortises and have noticed that I'm crushing the walls of the mortise. I try to hammer my chisel while removing 1/8" - 1/16" of waste with a 3/4" wide chisel. The wood is pine 2x4s.

This can't be right since the crushing is causing blow-outs inside the wood, making it weak on the surface and prone to dents.

I'm making mortises using a Dewalt chisel. Perhaps it needs sharpening but it might just be that I'm using the wrong technique.

[Jon Grider]

Might be a combination of technique and a dull chisel. I find coniferous woods need a very sharp chisel to cut properly. Also I wouldn't 'hammer' out the waste but take small passes, shaving the wood fibers off gradually until you creep up on the mortise lines.

[Wayne Lomman]

It is a pine problem. You need a really sharp chisel and take smaller cuts. Persistence and patience required. Cheers

[Jon Endres]

I have done a fair amount of traditional timber framing, mostly in pine, and I can tell you that you need to have a razor sharp chisel. You should be easily able to pare a thin slice off end grain with hand pressure alone, if your chisel is sharp enough.

[Minh Tran]

I put off sharpening my chisel until just now (because I've never done it before). The chisel didn't properly fit the honing guide but even with a crappy sharpening job, I managed to get a sharper edge.

I tried chiseling the mortise again and noticed a world's difference!

:( I'm going to have to properly learn how to sharpen my chisels now.

Quick question: When I started sharpening my chisel, I started by flattening the backside with 1000 grit water stone (and followed up with an 8000 grit stone). The backside, although flat, loss its factory-mirror gloss and took on a cloudy-opaque gloss. I thought as you move up in grit, you get a more glossy finish. 8000 grit it super fine!

[Floyd Mah]

Here's the way to keep the outside of the mortise orderly. You must realize that the sharp end of the chisel is like the prowl of a ship. You need to compensate for this. Deep, continuous cuts won't end up where you think. Just placing one side of the chisel parallel to the desired wall of the mortise doesn't mean that the chisel will travel in that direction. The chisel will try to under-cut the marked lines when you strike the handle, since it will deviate in the direction of the midplane of the faces of the chisel. The best way to combat this is to take smaller chops when removing the waste.

Another consideration for me is that the pencilled lines usually turn out to be wishful thinking: chopping with the chisel will often wander over the line. This is often a problem with the softer woods. The best way for me is to use a sharp razor (utility knife works) and carefully scribe the pencil lines, at least 1/8" to 3/16" depth. The razor will will give you vertical cuts (vs. just trying to whack it out with a chisel). Then carefully use the chisel to remove the waste. Don't set the chisel edge in the scribed line or it will bruise your opening. Tap adjacent to the scribed line to raise the chip first. Now you will have a pre-cut depression, like a template, on the surface to guide the rest of the waste removal. You can then increase the depth of the mortise slowly, with either a sharp chisel, or with a router plane (hand tool). At this point, you might want to use a drill, drill press and a forstner bit or other wide bit to remove waste down to the depth of the mortise. It should cut a hole slightly smaller than the mortise so that you can finish up with a sharp chisel. Use a small adjustable T square to make sure your cuts are perpendicular to the face of the wood.

[Floyd Mah]

If you want to end up with a mirror finish on your chisel, get a piece of leather (old boots work) and some polishing compound. Strop the chisel as your last step in the sharpening process.

[Frank Pratt]

If you want to end up with a mirror finish on your chisel, get a piece of leather (old boots work) and some polishing compound. Strop the chisel as your last step in the sharpening process.

If you use a leather strop, glue it to a piece of wood so it says nice & flat, & be super, super careful not to round off the back edge of the bevel at all. And as Floyd said, it should be mirror shiny.

The chisel should be sharp enough that you can shave the hairs on your arm with it. Don't try shaving the hairs on your face with it, trust me.

[John Blazy]

Glad you figured out how to sharpen. If you have a grinder, use it to hollow grind the face bevel to make sharpening faster. If no grinder, the rounded end of a belt sander works great too.

If you are doing several mortices, I would hog out the majority of the wood with a router first, getting a flat bottom and go near (not to) your lines. Then your chiseling time will be reduced significantly, and the square sides and bottom from the router bit gives a great guide to chisel straight to, especially for the end grain.

[Ken Fitzgerald]

Sharp, sharp, sharp.

Literally, you should be able to shave thin slices with your chisel after you have drilled out the hole. Two key words, thin, sharp. Don't be afraid to go back a touch up the chisel's edge during or after one mortise and beginning another.

Sharp, sharp, sharp

[Stan Calow]

The way I was taught, was to not hold the chisel straight up and down but tilt at a slight angle to pare down the sides of the mortise a bit at a time. If I don't I'l get really wide uneven sides.

[Greg Hines, MD]

I use waterstones and a Worksharp 3000 to sharpen, and it makes a world of difference. Though, when I made a table using big timbers like that, I used a router and jig to guide it.

Doc

[Minh Tran]

Sharp, sharp, sharp.

Literally, you should be able to shave thin slices with your chisel after you have drilled out the hole. Two key words, thin, sharp. Don't be afraid to go back a touch up the chisel's edge during or after one mortise and beginning another.

Sharp, sharp, sharp

I took more time to make sure to get a sharp chisel edge and it cuts a lot better!

The corners were very difficult to cut square at first (it took me 1 hr to square a 1.5" x 2" x 1.5" mortise) because I tried to cut it out by hand. Once I got over my fear of rounding off the chisel tip, it took me 30 seconds to square a corner. :)

I smacked the chisel butt hard and did a prying motion and that does a nice job chunking out pieces of wood. A sharp chisel ensured that when I struck with my hammer, the chisel would dig a clean planer-cut downwards. A dull chisel (when I tried this technique) blew out the walls.

I'm not sure if this technique is bad for the chisel but the blade seems to be holding up so far. I also tried slowly paring the rounded corner until it was a small square column (at which point I used the above technique) but this dramatically increased the time it took to clean a corner.


Here's the way to keep the outside of the mortise orderly. You must realize that the sharp end of the chisel is like the prowl of a ship. You need to compensate for this. Deep, continuous cuts won't end up where you think. Just placing one side of the chisel parallel to the desired wall of the mortise doesn't mean that the chisel will travel in that direction. The chisel will try to under-cut the marked lines when you strike the handle, since it will deviate in the direction of the midplane of the faces of the chisel. The best way to combat this is to take smaller chops when removing the waste.


For a housed mortise, isn't it ok to cut the inside of the mortise a little over the line? This gives room for glue, and the tenon slips in a little bit better, albeit it won't be a tight fit.

For a through-mortise, where the fit needs to be tight, it seems I might need to score the edge of the mortise on the opposite side, in a way similar to your description, so that blowout doesn't occur. The idea here is to pre-cut the wood fibers so that when the chisel (and drill bit) comes through while paring (drilling), it only blows out the section inside the mortise hole.

Please correct me if I'm wrong though :)


The way I was taught, was to not hold the chisel straight up and down but tilt at a slight angle to pare down the sides of the mortise a bit at a time. If I don't I'l get really wide uneven sides.

This makes sense for the walls of the mortise. It's pretty difficult to do when you're working on a corner. Can't fit a straight edge against a curved one :).


Glad you figured out how to sharpen. If you have a grinder, use it to hollow grind the face bevel to make sharpening faster. If no grinder, the rounded end of a belt sander works great too.

If you are doing several mortices, I would hog out the majority of the wood with a router first, getting a flat bottom and go near (not to) your lines. Then your chiseling time will be reduced significantly, and the square sides and bottom from the router bit gives a great guide to chisel straight to, especially for the end grain.

I have a benchtop grinder. I haven't tried hollowing out the face bevel. My 1/2" chisel actually has a slight convex face bevel (between the microbevel and the rest of the face bevel) and it seems to be holding up. Perhaps the extra material in the convex region of the face bevel is reinforcing microbevel.

I don't have a great clamping set up for a router so I've been using a drill press with a 1" brad-point bit (the thing is a monster!)


I use waterstones and a Worksharp 3000 to sharpen, and it makes a world of difference. Though, when I made a table using big timbers like that, I used a router and jig to guide it.

Doc

That thing looks awesome. At first I thought about the space it'd take up but then I realized that I dedicate that much about of footspace for a sharpening station anyways.
The $200 price tag is a bit off putting though.

[Marshall Mosby]

Yeah well, you rightly did sharp the chisel. One thing I would like to add though. Maybe you're already doing it this way but still I am gonna write this. You should keep the plain side of the chisel facing outwards and the tapered edge side faces inwards. Also I really should say that you've managed to do it quite right until now seeing the difference in the pictures of mortise you posted earlier and now. Good Job!

[Greg Hines, MD]

That thing looks awesome. At first I thought about the space it'd take up but then I realized that I dedicate that much about of footspace for a sharpening station anyways.
The $200 price tag is a bit off putting though.

I would tend to agree that sharpening can be expensive. When I got it, I was looking at a Tormek, and did not want to spend the $700 that it costs. But you do need to plan to sharpen your hand tools, and often. To me, the speed of the WorkSharp is a big part of why I got it. It is also easy to touch up an edge in the middle of a job, such as a turning gouge or plane iron.

Doc

[Floyd Mah]

I might be guessing wrong, but it sounds like you are just using one width chisel for your work, hence your worry about the corners. When I work on a mortise, I end up using several chisels. I use a wider chisel for some of the work, but the larger widths are good for defining the general area of work. Narrower chisels work faster because they work less material. I might use 1/4" chisels in some areas, since the density of the wood differs. Skewed chisels are very useful for defining corners. Right and left-handed skewed chisels let you approach a good corner without eating up the wood that you want to leave behind, as well as using the skewed edge to pare the cavity. I have a heavier mortising chisel, but haven't found much use for it. By the way, you can make a nice skewed chisel just by grinding the leading edge of a regular chisel. Be sure to make them in pairs: a right handed skew can't be substituted for a left handed one, and vice versa. I've found all widths useful. They are also useful for dovetail work, where the angles may be particularly acute.