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The job is easier if you can design your mortise to have the same exact width as your chisel (or just a hair larger). That way, as long as you keep to your line on one side, the other wall should also be at a same distance.

The job is easier if you can design your mortise to have the same exact width as your chisel (or just a hair larger than the chisel). That way, as long as you keep to your line on one side, the other wall should also be at a same distance.

You can go by feel, and by sound. The mallet's sound will change as you reach the bottom of your previous "run". When you hear the mallet sound's deadening, it's an indication that you should move the chisel over and start a new "run". This way will save you energy too.

Example:

(from popular woodworking )

Example2:

(from woodworking masterclasses )

You can go by feel, and by sound. The mallet's sound will change as you reach the bottom of your current "run". When you hear the mallet sound's deadening, it's an indication that you should move the chisel over and start a new "run". This way will save you energy too.

^{Example 1: End grain jig (from popular woodworking ). The angle can be arbitrary. Here, the 87degree jig creates a taper that will accommodate a wedge.}

^{Example 2: Jig for side walls (from woodworking masterclasses ). Longer chisels help.}

Twist

The twist can sometimes be due to the direction of the grain being different between the two corners of the chisel. The presence of small knots or denser wood around where there used to be a branch can "slow" down one side of the chisel more than the other, and so it twists. The twist is normal, but you can minimize it. It mainly causes your mortise walls to slightly move to one side or the other. Definitely reposition if you feel the chisel twisting.

Place your body behind your chisel, and visually ensure that your chisel is perpendicular to the work surface. Human eyes and brain excel at determining whether two lines are parallel. To take advantage of that, at the end of your piece, place a clamp on your workpiece as a visual aid (and verify with a square that your clamp is held plumb). Then visually refer to the clamp to ensure you chisel parallel to it -- this will ensure your side walls are parallel and straight down.

To make sure that the walls are plumb, you can place a combination square inside the mortise. You can also use it as a depth check.

The bench chisel works best when you take small bites with it (compared to a mortising chisel). You'll feel it sink more or less easily along the bevelled slope until it hits the bottom of your mortise, and then you'll be able to go one, maybe two, "hits" deeper. This causes the pyramid-shaped peak at the bottom of your mortise.

You can go by feel, and by sound. The mallet's sound will change as you reach the bottom of your previous "run". When you hear the mallet sound's deadening, it's an indication that you should "move the chisel over" (belly forward) and start a new "run" down. This way, you'll save some energy too.

When you scribe your lines on opposite faces (e.g. with a mortise gauge), do the measurement from the same reference face. This way guarantees that at least one of the mortise walls will be kept at the same distance from that face. Also a good idea to double-check that your work-piece faces are square to one another if you use a mortise gauge.

If you design your mortise to have the same exact width as your chisel, then as long as you keep to your line on one side, the other wall should also be at a same distance regardless of if you flip it around.

If you already have tenons for the mortise, you can sometimes remove the gap around the tenon by gluing a sliver of wood on the tenon, and paring it down to match the adjusted mortise dimensions.

Twist

The twist can arise because the grain differs from one corner of the chisel to another. The presence of small knots or denser wood around where there used to be a branch can slow down one side of the chisel more than the other, and cause twist. The twist is normal, but you can (and should) minimize it. Definitely reposition if you feel the chisel twisting.

Place your body behind your chisel, and visually ensure that your chisel is perpendicular to the work surface. Human eyes and brain excel at determining whether two lines are parallel. To take advantage of that, at the end of your workpiece, place a clamp as a visual aid (and verify with a square that your clamp is held plumb). As you chisel, visually check that you are parallel to the clamp -- this will ensure your side walls stay parallel and straight down.

Along the way, you can use a combination square inside the mortise to see if the mortise walls are 90deg from the reference face. You can also use the square as a depth check, which is especially useful in the corners.

A bench chisel works better when you take small bites with it (compared to a mortising chisel). You'll feel it sink more or less easily along the bevelled slope until it hits the bottom of your mortise, and then you'll be able to go one, maybe two, "hits" deeper. This causes the pyramid-shaped peak at the bottom of your mortise.

You can go by feel, and by sound. The mallet's sound will change as you reach the bottom of your previous "run". When you hear the mallet sound's deadening, it's an indication that you should move the chisel over and start a new "run". This way will save you energy too.

When you scribe your lines (e.g. with a mortise gauge) on a through mortise, do the measurement for both openings from the same reference face. This way guarantees that at least one of the mortise walls will be kept at the same distance from that face -- and your hole should line up better when you flip the piece around. It is also a good idea to double-check that your work-piece faces are square to one another before you start digging.

The job is easier if you can design your mortise to have the same exact width as your chisel (or just a hair larger). That way, as long as you keep to your line on one side, the other wall should also be at a same distance.