Mortising problems

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Forum topic by rjack posted 12-13-2007 01:29 AM 1125 views 0 times favorited 5 replies Add to Favorites Watch
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110 posts in 3851 days

12-13-2007 01:29 AM

I have a drill press with a mortiser attachement. Normally, it works pretty well, but now I’m trying to create a 5/8 inch wide mortise that is 3 inches deep in Ash. I’m using a 5/8 mortiser bit/chisel. I would use a smaller 3/8 or 1/2 inch chisel but they are not long enough to go 3 inches deep. I feel like the pressure that I have to use will snap the drill press arm.

Any suggestions?

-- Roger - Havertown, Pennsylvania

5 replies so far

View Max's profile


56000 posts in 4269 days

#1 posted 12-13-2007 01:34 AM

I would check the sharpness of your drill and the chisel they could be dull. Also on a mortise that wide and deep you might want to work two holes side by side going in say 1” or so one after the other until you reach depth. Then you should be able to do the rest with no problem. But make sure every thiing is sharp first.
Hope this helps.

-- Max "Desperado", Salt Lake City, UT

View Karson's profile


35120 posts in 4396 days

#2 posted 12-13-2007 01:42 AM

There is a mortise sharpening diamond cone at Rockler (I believe) they are great for sharpening the chisels. The chisel should have about the thickness of two dimes between the shoulder of the chisel and the collar on the mortising attachment.

Lightly tighten it at that point, then raise the bit as far as it can go and tighten in the chuck. Then loosen the chisel and raise it up to the mortising collar. This should give the correct clearance between the drill and the chisel. If they are sharp you might be able to drill it out. If not do as Max suggested Drill down 1/2 to 1” and then move to the side 1/2 of the chisel width and go down again. You might be able to work you way across the total width and the depth doing it that way.

You should not have any smoke from the bit, cut slowly and let the chips come out of the chisel.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia †

View Dorje's profile


1763 posts in 3992 days

#3 posted 12-13-2007 10:26 AM

I used to have an attachment, now have a mortiser, and both machines/set-ups struggled with getting through dense material, even when the chisels and the bits were honed and pretty darn sharp.

If it still feels uncomfortable to do after tuning up the bit and chisel, there’s always the old forstner bit to drill out the waste and a chisel to clean it up square strategy…

Good luck – let us know how you fare. Are you working on your bench?

-- Dorje (pronounced "door-jay"), Seattle, WA

View Olaf Gradin's profile

Olaf Gradin

73 posts in 3835 days

#4 posted 12-14-2007 01:04 AM

From what I understand of the mortiser setups, you have to exert more force than you would think. It can be quite a workout. The models with longer pull arms give you more leverage. You might be able to extend yours, but the machinery may not be built to tolerate the force you can put on a longer arm. I don’t have a mortiser, so I had planned on doing this same thing with the forstner drill bit and a chisel to clean-up afterwards.

I recently took a Rob Cosman all day workshop in which I learned the proper way to chop mortises with a mortise chisel. They looked fantastic, but chopping a 5/8” mortise by hand doesn’t exactly sound like a fun way to pass the time!

-- It takes a viking to raze a village. &mdash Blog'r:

View rjack's profile


110 posts in 3851 days

#5 posted 12-14-2007 11:48 PM

Thanks for the advice everybody!

Karson, I made the adjustment that you suggested and that helped, but I still had a problem with the initial hole.

What I ended up doing is drilling 2 holes with 1/2 inch bit about 1/2 inch apart and 3 inches deep in each mortise. Then I used the mortising attachment on my drill press to clear out the wood between the 2 holes. This created my starter hole. After that, I just did partial pieces adjacent to the current whole and everything worked great.

-- Roger - Havertown, Pennsylvania

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