Forum: woodworking.stackexchange.com
Tags: <chisel><mortise-and-tenon>
Title: How to avoid damaging the ends of mortise holes when chiseling?
Question: I've watched a couple of videos of making mortises.     What technique should I use to remove (bulk) waste from the hole without damaging the ends of the mortise hole?   Clearly levering against them will bruise or dent the wood.  I'm really looking for a technique which allows me to reliably clear the debris without risking damage.   I'm especially looking for answers more specific than "be careful".  Edit: I'm not talking about the paring stage, I'm talking about bulk waste removal.

Answers:
sents: text: First, as Aloysius says above, you should stay away from the ends of the mortise during bulk removal.
text: 1/16 of an inch or 1-2mm should be sufficient.
text: Now, when you have done a bunch of chopping, and you have chips clogging the mortise, you need to clear them out, as you said.
text: Use a bench chisel that is one "size" below your mortising chisel.
text: For example, a 1/4 inch if you are doing a 3/8 inch mortise.
text: Guide the chisel with the thumb and forefinger of your non-dominant hand as you work it into the chips.
text: Then, still lightly pinching the chisel, rest your non-dominant forefinger on the board and use it as fulcrum as you lever the waste out of the hole.
text: The chisel should not touch the end of the mortise if you do this correctly.
answer_details: author: woodworking.stackexchange.com/users/600/Mr. Kevin
score: 5
sents: text: Don't lever.
text: Pare straight downward into the opening, taking it in multiple passes if necessary, and letting the chisel act as a wedge to do the work.
answer_details: author: woodworking.stackexchange.com/users/91/keshlam
score: 4
sents: text: Paul Sellers is a master craftsman, author of several books and some very good video tutorials.
text: He does several on cutting mortises - this one probably being most relevant to this topic.
text: https://www.youtube.com/watch?v=LPBkO2chZxk
text: I've learned a lot from watching his videos, still dont have the skill to implement the lessons very well as yet - very much a novice at this.
answer_details: author: woodworking.stackexchange.com/users/1637/FreudianSlip
score: 4
sents: text: Are you looking to use only hand tools?
text: If you have a router, this can get the majority of the mortise bottom flat with a flat bottom bit.
text: Then the corners will be easier to chisel out.
text: A drill with a forstner bit can be used to accomplish this as well.
text: If you have a drill press, that would be ideal.
text: There are also hollow chisel mortising attachments you can buy for drill presses that will make perfectly square mortises, and many woodoworkers will "drag" this along the bottom to achieve a relatively flat mortise bottom.
text: If you want to use only hand tools, a router plane would be capable of achieving this, coming from both directions to get into the corners.
answer_details: author: woodworking.stackexchange.com/users/2753/Jacob Edmond
score: 1
sents: text: Borrowing from my own answer about this very topic : Auger Bits Whether you are going for traditional techniques or powered/hand hybrid auger bits would be a tool of choice for this.
text: Using auger bits that are the exact width of you hole you are trying to make, in a brace and bit or drill, you can easily remove waste and not have to worry about going "outside the lines".
text: Stagger the holes and you will get a similar shape like that of the ones you have pictured. From Chris' Project Page As you can see from the above image (mortise in a workbench)
text: most of the wood was removed with auger bit.
text: The screw tip and the shape help to naturally create straight holes.
text: I'm really looking for a technique which allows me to reliably clear the debris without risking damage Be careful when/if you are exiting out the other side.
text: To mitigate damage you can Used waste/scrap wood (clamp well) Count
text: the rotations it takes until the screw (eye) just shows proud on the other side (A Roy Underhill suggestion).
text: Mark
text: the depth of your bits using masking tape.
text: Feel for the screw/eye coming out
text: Most of those suggestions will work in tandem.
text: This way you can turn the work over and have cleaner edges on the outside.
answer_details: author: woodworking.stackexchange.com/users/128/Matt
score: 1

Summary of the answers:
to avoid damaging the ends of mortise holes when chiseling you can use a bench chisel one size below the mortising chisel. A router will certainly be a big help as would a forstner bit. There are also hollow chisel mortising attachments fro drill presses. If using only hand tools, a router plane would be able to do it.
When using chisels, stay away from the edges during bulk removal in a mortice. Use a bench chisel one size below your mortising chisel. Don't lever. Pare straight downward into the opening, taking it in multiple passes if necessary, and letting the chisel act as a wedge to do the work. A router can get the majority of the mortise bottom flat with a flat bottom bit.  A drill with a forstner bit can be used to accomplish this as well.  A drill press would be ideal. Hollow chisel mortising attachments  for drill presses make perfectly square mortises, and many woodworkers "drag" this along the bottom to achieve a relatively flat mortise bottom.  If you want to use only hand tools, a router plane would be capable of achieving this, coming from both directions to get into the corners.