How to use Hollow-Chisel Mortiser

[Pete Brown]

This may be technique or quality of the chisels or sharpening, but I have had poor results with my Powermatic mortiser (benchtop model)

1. the hold-down always sticks at a bit of an angle, so I can never get good downward pressure on both sides of the mortise. It may be defective, I'm not sure. That also prevents me from being able to move the wood along adequately to complete the mortise.

2. The chisels tend to wander when cutting. I have everything squared up, but it still leaves less and decent mortise walls.

3. The chisels visibly crush the wood as much as cut it. This is soft maple, but to me this points to having to sharpen the chisels. I just haven't gotten around to that yet. I'm using the Powermatic chisels.

4. Getting any two mortises within about 1/4" of each other causes the chisel to crush the wood between them. Originally I thought I could use the mortiser to cut the 4-square craftsman pattern seen on so much furniture, but this prohibits that.

Any suggestions?

Pete

[Mike Cutler]

Pete.
First you need to hone and sharpen those chisels, then work on the drill bit and get the leading cutting edges, and outside cutters sharp. I have yet to get acceptable results with my mortiser alone, and always end up cleaning up the mortises with a chisel. I'm getting ready to try some Fisch, or Clico chisel and bit sets. WL Fuller is reputed to make nice chisel and bit sets also.

The hold down on my Delta 14-651 was a waste of metal. You are better off using a sliding clamping arrangement and clamp the wood to the fence. A lot of people have added an aftermarket XY sliding vise to their mortiser. This makes the mortising go quicker.

Is your chisel absolutely square to the fence. It has to be square.

Is it the chisel wandering, or is the entire mortising head twisting? The ways may need to be adjusted if the whole head is moving.

You should be able to punch two mortises right next to each other, and leave a very thin wall in between the two holes. I have done it many times. I suspect the combination of the dull chisel and bit are the majority of the problem.

Good luck and post back. A lot of people use these benchtop mortiser with success. Someone should be able to help.

[Doug Shepard]

Everything Mike said + I learned long ago not to trust the holddown (also on a Delta). I always use 2 QuikGrip clamps to hold it to the table. Tedious to be sure, but it works.

[Jim Becker]

One other thing...the bit is supposed to do the work and should extend below the chisel by 1/6"-1/8" or so...about the thickness of a nickle. The chisels should just be cleaning up the cut, not doing all the work.

[Pete Brown]

One other thing...the bit is supposed to do the work and should extend below the chisel by 1/6"-1/8" or so...about the thickness of a nickle. The chisels should just be cleaning up the cut, not doing all the work.

Thanks. The Powermatic has a spacer that sets the bit to the correct height, so no problems there.

Thanks to the rest of the folks. I'll hone those chisels and see where I end up. It's good to know that the mortiser should be able to cut mortises close together without crushing the wood around it.

[Larry Rose]

I have the Jet morticer and except for the totaly useless hold down it's a good machine. Has any one tried to modify or replace one other than the xyz clamp. You would think that reputable companys like Jet, Delta and others could do better. Any ideas?

[JayStPeter]

This is a good article on honing mortiser chisels

http://www.popularwoodworking.com/blog/Hollow+Mortise+Chisel+Tuneup.aspx

[Gary Keedwell]

Definetly invest in quality chisels. Jet has good ones and Lee Valley is good. Get the best steel so they won't lose temper (Dullness). Don't know if you can get HSS.

Gary K.

[Gary Keedwell]

Definetly invest in quality chisels. Jet has good ones and Lee Valley is good. Get the best steel so they won't lose temper (Dullness). Don't know if you can get HSS.

Gary K.

[Chris Jenkins]

Pete,

Not quite sure how to fix that hold down without a better visual, but I agree on the chisels. I've worked with several different brands and they all come as sharp as a donut. I've used a DMT Fine / Ultra Fine (600 / 1200) grit diamond stone in the past with good results. This works great on outside of the chisel.

Then I used a rat tail file wrapped in sandpaper to clean the inside of the chisel. I've seen some pretty bad boring on these. Work the ejection port sides to so that chips come out smoothly and don't catch on the burr that is left behind by the factory.

Then use the diamond cone that is on the Powermatic Mortiser to sharpen the inside of the chisel points. Once you are happy there take it back to the extra fine grit and remove the wire edge burr left behind. Chisel is done.

As far as the bit goes. Work the triangular point edges. Not the point so much as you don't want to take it out of center. Also work the lip so that there is a good cutting edge there as it is the part that contacts the wood first. Last spot to work is the first part of the auger. This is the flat spot at the bottom of the bit. File that from the bottom at the same angle it is already ground at.

This whole process takes me about 25 - 30 min per chisel for new ones. Even less when you just need to touch them up.

Hope that makes sense. This method has been working for me. You need to touch the chisels up often on real hard woods to keep a clean wall cut.

BTW, I learned this method from the Taunton website. Their is a video on it if you have membership there.

Chris

[Ken Milhinch]

I use a Delta Mortiser, and once I bought some quality chisels, I had no problems whatsoever. (The hold down works just fine.) What Jim said about the bit extending beyond the chisels seems to be the salient point here, because from your description, you seem to be doing the cutting with the chisel rather than the bit.

[Pete Brown]

I use a Delta Mortiser, and once I bought some quality chisels, I had no problems whatsoever. (The hold down works just fine.) What Jim said about the bit extending beyond the chisels seems to be the salient point here, because from your description, you seem to be doing the cutting with the chisel rather than the bit.

Thanks. The bit does do the cutting (it is set per Powermatic spacers), but the chisels, when squaring the edges and corners (they do have to cut a little) weren't doing a good job. I'll sharpen them up and see how it goes.

Pete