Mortise problems.

[Knotty_Pine]

I've been trying to get the hang of M&T joinery, and I keep having a seemingly simplistic problem; my boards keep busting when I try to chop down.

Here's how I do it, then maybe you fellas can tell me what I'm doing wrong.

1. Mark it out. For this example I'm going to describe doing a 1"x3" Mortise.
2. Bore holes at each end just a smidgen narrower than the mortise will be, since the next smallest Forstner I have is 7/8", that's the one.
3. Remove the material between the holes. Normally, I first square off one end of the mortise and then work my way to the other. But some time during the chopping down with the chisel going with the grain, it will bust along the grain.

So, what might I do to prevent this? My chisels are scary sharp, but it just seems like I'm either going too deep per chop, trying to take off too much at once, or it's sucky wood. The last seems like the least likely as it's not like every board I own is badly weak, lol.

TJ.

[HAMMER23H]

TJ I'm not sure what size board you are using but the general rule of thumb is to make the mortise 1/3 the thickness of the board. In inch and half material the mortise should be around 1/2",¾" material would be ¼". Use a drill and remove most of the material with multiple holes.

[pgeer]

Without the benefit of seeing what happened, I'm going to suggest "C"clamping a couple of pieces on both sides of your mortise to support it during the clearing. A chisel cuts and pry the wood away so it needs room to do so, maybe a smaller chisel might be better in your case.

[TDHofstetter]

I'm inclined to thing the issue is trying to grub it out in too-large chunks. Even mortising is pretty much a paring operation... chop-pare-chop-pare.

-- Tim --

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[dcarter636]

I avoid any splitting action along the grain when ever possible, but lacking a 1" mortise chisel I suppose some chopping parallel to the grain may be unavoidable. A bench chisel can be used much like a mortise chisel if it has nice sharp sides that will cut the side walls of the mortise.

When using beveled bench chisels to make a mortise, splitting can be reduced or avoided by deeply chopping the cross grain direction first then plunge in the long dimension shallower so that any splits terminate at the cross cut/chop. I recently hacked out four large (1 1/4" x 7/8"x 1/2" deep)blind dovetails in soft maple this way with no splitting.

[Bruce50010]

If I'm reading right, you're drilling two 7/8" holes with the centers 2 1/8" apart, and trying to remove everything in the middle with a chisel? Everyone's suggestion of going slower and removing less material at a time with a chisel makes sense, but if I'm reading right and you're only starting with two holes, I think you can make things a lot easier on yourself by drilling a series of overlapping holes so that you only have to square up a little 'triangular' shaped piece between each one.

Here's a picture I found online showing a drilled-out mortise ready for chiseling:

http://www.flickr.com/photos/carljoseph/3449795034/

[Cody Colston]

TJ, Bruce has the answer for you. That's the reason for using a Forstner bit, the ability to drill overlapping holes.

Once you drill out the mortise, there's not much left to do except square up the ends and pare the sides.

Cody
Tyler, TX

[center]He is no fool who gives up what he cannot keep for that which he cannot lose.

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[mapleman]

what everyone else said plus - bench chisels do not have the same thickness and rigidity of a mortise chisel and they will deflect and twist a little bit. and that could help cause the chip out that you will have...

later, John

[rhull]

>I avoid any splitting action along the grain when ever
>possible

Ditto. I think this is your problem. Do as much of the chopping as you possibly can across the grain, and perform paring operations with the grain.