chisel question

[Matt Hunstiger]

So today I finished my joiners mallet and I had a question about chiselling. When I was chopping out the moritise a couple days ago I had trouble with shallow humps along the slope on each side. I'm wondering if people have advice for avoiding that. In this first picture you can see the angles that I was following from top to bottom, and it was about half way or two thirds down that I seemed to have the hump/rounding. I was chopping from both top and bottom, and I first cleared out a channel from both sides with brace/bit. It was a very slight hump, but it just seemed to take forever to get it to go away so the handle would seat all the way, as it was so shallow so that I had a hard time getting purchase on the chisel business end. The mortise is 3/4" wide and I was using a 3/4" chisel. Thanks for any advice.

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Here's the finished product. I bought a hard maple "bowl blank" that I cut in half for the head, and the handle is ash from a tree that came down in my in-laws' yard. When it's had time to acclimate itself after a few weeks, I'll shave down the handle a bit so it seats lower, i.e. not sticking out much above the top. This is a Paul Sellers youtube project.

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After a coat of boiled linseed oil.

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[James Pallas]

Matt, Your mallet looks good. A longer chisel would probably help when reaching that deep.
Jim

[William Fretwell]

The 3/4” chisel you used is not a morticing chisel so flattening the mortice sides with a wider chisel speeds things up. It’s an unusual mortice so you just improvise.
The mallet will last you a lifetime, worth the effort!

[Luke Dupont]

I'm not really understanding your question. Do you mean that the walls of the mortise are fat in the middle, resulting in gaps at the top and bottom?

When chopping a mortise without pre drilling, the waste against the bevel of the chisel helps to keep it "flat against the wall", but when pre drilling the holes, or sawing out the wast of dovetails, etc, the empty space on the bevel side means that the chisel can want to pop out of the cut, especially in hard wood, resulting in a "hump" in the middle of the mortise. When this is the case, it can be useful to try to ever so very slightly under cut the middle (create a very very shallow hollow rather than a hump), or at the very least check with the side of your chisel or something as you work, and see if it rocks or is straight.

Humps also form if you use any kind of tool with a "sawing" motion, such as a file or rasp. Beginners often try using a file or rasp on end grain, ie to clean the base of dovetails or tenons or something, but this almost always results in a rounding of the surface leaving a hump in the middle, even if you're really careful. So, the chisel is definitely the most capable tool of solving this problem.

It may help to make sure your chisel is really sharp. A lot of times when mortising, a chisel will get duller than we realize.

[Jim Koepke]

Nice looking mallet Matt. After making a few the problem you described is familiar to me. While working in the shop today it seemed like another mallet build would be fun, but there are so many other things to get done. Maybe next fall.

One thing learned is if a 1" mortice is being made for the handle some of the clean up is easier with a smaller chisel. Another thing is chisels with a 90º bevel are very helpful at removing humps or other waste.

A powered sharpening system is needed for this. With a regular wheel grinder set the tool rest to cut at a right angle to the blade. Have the underside of the chisel facing up. This should produce a clean 90º edge on the chisel. It works like a mini-scraper or a one tooth float.

Here a 1/2" one is in use:

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Start with a small bevel and it will grow with resharpening.

This worked so well I found some long 1/8" & 1/4" chisels to modify to 90º bevels.

jtk

[Matt Hunstiger]

I'm sorry I was confusing. I drew a little sketch on the kids' white board. So the mortise when looking down from the top of the mallet head is 3/4" wide, which is my chisel width. The left and right sides of the mortise in the top view are the sloping sides in the side view, and it was where the purple was that I seemed to be getting the "hump."

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[Matt Hunstiger]

Thanks everyone for the useful suggestions. The responses are helpful.

[Rafael Herrera]

Pare the high spots, use a straight ruler to check. It doesn't need to be perfect, in fact, ever so slightly hollow to ensure no gaps when you fit the handle.