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Rubbertree 08-20-2012 12:04 AM

Quick Mortising question
 
Hi Folks...right to the question...
I'm playing with mortise and tenon joinery for the first time, using my friend's hollow chisel mortiser. He has been told to leave a space between each hole when creating a mortise and then do a second pass to take out the remaining wood. I find this counter-intuitive as it means that the outfeed on the bit is blocked with every press on the first pass. I'm following his rules (his machine) but am smoking up a storm...something I think would be prevented if I just created the mortise in one pass. I know my terminology may be off but I hope someone understands what I mean.
Any thoughts or advice is greatly appreciated.

notmrjohn 08-20-2012 06:51 PM

I dunno if I unnerstan what your sayin. Here's the way I do it I do each end, using positioning and limiting jigs if I can , then I go to the center or maybe not perhaps between the center and the ends. The idea is to have each plunge cut through solid wood and not ovelap a previous hole. once you've cut out all the 'soild' holes you can, then you try to center your plunge as much as you can between the ones you've already done with the least overlap as possible, but with as much equality on each side as you can ( cause we don't wanta show no bias, wood is so sensitive.)When you start cutting those in betweeners you'll notice that the round drill bit wants to go off to the side of least resitance, sometimes so much that it hits the inside of the square chisel. Not good for bit chisel or mortise, go slow. Infact the whole holing should be slow, from first outside cuts to the last, don't force the chisel, let the drill do the work with the chisel following. Don't try to make the entire motise with th machine. Once the mortise is almost done you'll feel how easy it is to clear it out. Do a lot of easing up on the bit all the way out of the hole to clear the chips.Blow out the chips, air compressor is good. You can lean over and blow them out, but look out for that spinning chuck, as the foreman said to the boss when I got my hair caught in the drill press " I tole you not to hire them damn hippies."The boss said , " But the kid sure knows how to clean up a mortise." Cause now you gotta clean it up, lots of folks try to use that square hollow chisel to clear out them lttle tits. Not what it's made for , the bit removes wood the chisel squares it. Buy youself a good SHEFEILD 1/2" Chisel use it to shave off them tits, keep it sharp never hit with a mallet, don't hit with nothin, keep it razor sharp, enuff to shave with. Course as a hippie I aint shaved since 19 ought 67.
But no not one pass start at each end, nibble away between. In fact some times it's not all the way thru.

jcrack_corn 08-20-2012 11:44 PM

the bit deflects if all sides are not supported. you will get a bad mortise and reduced bit life.


yes, you have to go slow and make sure you are sharp to avoid the heat/smoke.

so yes, do full holes with about 1/4" space between them, then come back and take those 1/4" bridges out on pass 2.

very standard.

Rubbertree 08-22-2012 09:01 PM

Alright...now I have to tell him that he was right...again.
Thanks for the input guys, I appreciate it.

Keith Mathewson 08-22-2012 09:09 PM

When the bit started smoking you drew the temper out of the metal,you need to buy a new bit. Most likely the drill bit was not deep enough. The bits are not sharp enough from the store, they require honing.


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