Cleaning out mortises with chisels. - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 04-09-2015, 12:19 AM Thread Starter
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Cleaning out mortises with chisels.

I have used a Forstner bit to hog out 6" x 1 3/8" through mortises in the verticals (fir) of a trestle table I am building. Now I am cleaning them out wth a chisel. I think my chisels are very sharp as I hone them regularly but I am finding it difficult to clean up the ends where I must cut across the grain as opposed to the sides where the chisels shave through like a knife through hot butter. Is this to be expected or are my chisels just duller than I supposed?
I can shave away my thumbnail so it seems the chisels are harp. Maybe technique? Any links that address this problem would be appreciated.
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post #2 of 10 Old 04-09-2015, 01:30 AM
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Cutting across the grain is always more difficult than cutting with it. A quick sanity check for the sharpness is try slicing through softwood end grain. If it cuts clean, its sharp

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post #3 of 10 Old 04-09-2015, 08:01 AM
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Make sure they are flat on the back side and without any kind of bevel on that side. Chopping down a mortise will be difficult if the back isn't truly flat. If you lay it on your stone and it doesn't sharpen the tip while flat. This is the first place to start.

For me if I can shave hair off the top of my hand it's sharp. You can probably get a screw driver to shave the top of your thumb nail.

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post #4 of 10 Old 04-09-2015, 08:26 AM
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We all have ways of testing the sharpness of our chisels - all my body parts are out of the testing zone - I use paper.

To the question at hand - with Al, check your chisel bevel, besides the back being flat (100% flat), what angle are front bevel at? Most factory settings are wrong. As for technique, those are rather large mortises, so I would take my widest chisel and score as straight a line as can be but with the cross grain (especially with soft woods), I use maybe a 3/8 chisel for the bulk of the work. With soft wood cross grain, my wider chisels are only used to start the cuts and to finish cleaning the cuts.

Its' never hot or cold in New Hampshire... its' always seasonal.
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post #5 of 10 Old 04-09-2015, 08:51 AM Thread Starter
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Quote:
Originally Posted by Al B Thayer
Make sure they are flat on the back side and without any kind of bevel on that side. Chopping down a mortise will be difficult if the back isn't truly flat. If you lay it on your stone and it doesn't sharpen the tip while flat. This is the first place to start. For me if I can shave hair off the top of my hand it's sharp. You can probably get a screw driver to shave the top of your thumb nail. Al
Ok,
That will be my benchmark. Thanks!
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post #6 of 10 Old 04-09-2015, 09:04 AM Thread Starter
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Quote:
Originally Posted by BernieL
We all have ways of testing the sharpness of our chisels - all my body parts are out of the testing zone - I use paper. To the question at hand - with Al, check your chisel bevel, besides the back being flat (100% flat), what angle are front bevel at? Most factory settings are wrong. As for technique, those are rather large mortises, so I would take my widest chisel and score as straight a line as can be but with the cross grain (especially with soft woods), I use maybe a 3/8 chisel for the bulk of the work. With soft wood cross grain, my wider chisels are only used to start the cuts and to finish cleaning the cuts.
What would be a proper angle for this type of work? It looks like mine are about 25 degrees.

Thanks Bernie!
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post #7 of 10 Old 04-09-2015, 09:21 AM
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I have my chisels at 28 - 25 is sharper but not as durable. Most chisels are between 22 and 30 so your chisels are fine.

Its' never hot or cold in New Hampshire... its' always seasonal.
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post #8 of 10 Old 04-29-2015, 01:11 PM
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For endgrain mortise cleanup:

1. Perfectly flat back.
2. Extremely sharp.
3. Use light mallet if needed.

Not directly related to your question, but a paring block is a great help just to keep things square.
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post #9 of 10 Old 04-29-2015, 09:01 PM
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Squaring up mortises on the end grain side is tough if your trying to control the actual length of there mortise. In addition to all of the good suggestions when you get your chisel "right" for the job, you can add a block to support the back of the chisel. I use very dense wood with adhesive backed wet/dry paper on the interface side clamped right at the square line to guide my chisel back.
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post #10 of 10 Old 04-30-2015, 02:45 PM
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Also, if you're using Douglas fir, it's going to be a LOT harder than pine. I'd almost rather put mortises in oak... My experience with doug fir is that it tends to be almost stringy, and severing the grain takes a lot more effort than I had expected. A good sharp chisel will work, but be prepared to hone (or strop) often.
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