Using a corner chisel?

[Wade Lippman]

I cut a rectangular hole in a 1/2" cherry panel with a jig saw and then straightened it out with router. That left me with round corners, when I want rectangular corners. I have a corner chisel like http://www.woodcraft.com/Product/143717/Quick-Cutting-Corner-Chisel.aspx?refcode=10INGOPB&gclid=CN7kq_nQkcMCFSwLMgodnwwASQ that I have used to square hinge pockets. Would it be useful here? How exactly would it be used?
Is there a better tool? Would a scroll saw be worth a try? A file maybe?

[Rod Sheridan]

Hi Wade, that chisel is meant for very shallow cuts.

I use a chisel and mallet to square inside corners..............Regards, Rod.

[John Vernier]

I agree that this is a job to do by hand with a sharp chisel. I might not even use a mallet depending on the hardness of the wood. For cherry I probably would. The hinge gain corner chisel you link to might just mark out the corner for you, but I haven't tried that.

[Peter Quinn]

The device you link is for squaring butt hinge mortises that are 1/8" deep, and they do a lousy job at that, too much slop, impossible to sharpen, not great ImO. I have a proper "corner chisel" which is a paring chisel with a long handle and steel ferril, you can strike it with a mallet, works well enough but tough to sharpen. The other issue is you really don't want to mash your way through 1/2" of material. I just use the same template that guided my router to guide my chisel, I don't generally cut them out with a jig saw, instead make a glue up using strips of plywood or MDF , this leaves you a good rectangle, bearing surface for the router that is flat and clean, and square inside corners to guide your sharp chisel as you pare out the corners....while the template is still attached to the work in its original location.

[Jim Matthews]

I think you're on the right track.

Score a fine knife line where you want to cut.
If there's more than 1/64" to remove, saw most of the waste.

File to the line and check your fit.

Something like this, you want to "sneak up" on the dimensions.
If you put some blue painter's tape around the edges,
you might save yourself some trouble when it comes time
to apply finish.

[John Gornall]

I recomend this tool for squaring mortises:

https://www.lie-nielsen.com/product/floats/1-fm-1-2-mortise-floats?node=4081

[Dave Zellers]

All good advice here but if possible don't square up the corner from the top, come at it along the sides (even on the end grain side) and as pointed out, sneak up on it. SLOWLY.

Removing the iron from a block plane can give you a short 'chisel' if needed in a tight space. The idea of using the router template as a guide for the corners is a winner.

Sharp tools and tiny bites.

[Jim Matthews]

Removing the iron from a block plane can give you a short 'chisel' if needed in a tight space.
Sharp tools and tiny bites.

That's clever, inexpensive and will probable work.

Wish I had thought of it.

[Bill White]

I had an extra chisel from an extinct mortising attachment for a DP. Sharpened it up well, turned a handle, brass ferule, epoxy, VOILA! A mortising chisel that didn't cost an arm and leg.
Bill