Mortises with router

[Bryan Rocker]

Good afternoon folks,

After quite a number of tests, LOML finally decided on a kitchen cabinet door patern. I made a template out of 3/4" plywood to hold the rails still while I used my router to cut the mortises. The mortises are 1 1/2" long x 1/4" x 1" 1 1/4" deep. I did 2 doors worth of mortises and tenons with no problems....well nothing major. I started on the next set of doors. Up my second cut in the oak rail I snapped my bosch spiral upcut $20 router bit. It was no deeper than any of the other first cuts but it didn't go much more than an inch before it snapped in half. I am using a rigid 2 1/4" hp plunge router. I am using the spiral upcut bit because I broke my 1/4" slot bit and this was recommended to be a better bit to use. I went out and bought another bit and finished that cut and the remaining 3 rails without issue. Those 2 frames are in the clamps drying. If you have any helpful hints or suggestions on how to keep from breaking these $20 bits I would appreciate it. I have another 18 doors to do......

On a related note, for mortise and tenon joints do I need to do anything beside glue them securely together????


Bryan

[Nancy Laird]

Hi Bryan.

If the bit that you are using is a solid carbide bit I am suprised that you got that many mortises done. I had a similiar problem with them and finally decided that using a high speed steel bit was the better option.

I broke several bits and then found out that since carbide is so brittle that any flexing of the bit just broke them immediately. I switched to high speed steel and have cut over 50 mortises with one bit and it is still going strong.

I use only 1/2" shank bits and get them from Woodworker's Supply.

Hope you have better luck getting those mortises done.

Dave

[Bryan Rocker]

The very first standard slot bit, carbide tipped broke before I finished the first mortise. The second one which cut 8 slots did not have any carbide. It appears to be high speed steel. I will have to check out their supply of router bits.

Thanks

Bryan

[Tyler Purcell]

Were you making full depth passes? I usually make multiple passes when cutting deep mortises to avoid any stress on the bit or motor. I've never had a problem with bits breaking.

[David Dundas]

Like Tyler, I always make multiple passes when routing mortices with spiral bits. You should not attempt to remove more than 1/4" of waste in each pass. If you stick to that limit, you should have no problem with broken bits. By the way, if you want to build a precision router mortising jig, you can download free plans for one from my blog (http://rockerswoodwork.blogspot.com/).

David Dundas

[Cliff Rohrabacher]

mortises are 1 1/2" long x 1/4" x 1" 1 1/4" deep.

I am confused it appears there is one more dimension in that than there ought to be.
The mortise is
1 & 1/2" long
1/4" thickness of the Tenon?
1 & 1/4" is the depth of the mortise

Then there is that 1" dimension that I don't know how to place. or is that a typo?

Anyway 1.250" is awfully deep for a 0.250" wide tenon.
I don't know the ratio calculation but, there are limits on how deep a tenon can be before it begins to return zero structural pay back. I rather suspect that a 0.250" thick mortise only needs to be maybe half an inch deep max. Beyond that, I am unsure that there is any structural return.

I could be wrong. It wouldn't be the first time.

[pat warner]

Morticing with a router, tips & method. (http://patwarner.com/router_morticing.html)

[Bryan Rocker]

The extra 1/4" was to make sure the tenon seated all the way. I could probably reduce that to 1" with no issues. As to the depth of the tenon, it is a 1" tenon going into 2" wide oak. It is 3/4" thick oak, with 1/4" thick tenons that leaves 1/4" on each side. The door frames seem extremely sturdy.

As to the passes I was making between 6-12 passes per mortise. I never did a full cut, the one that broke was probably around 1/4" deep maybe a little deeper but not by much.

As to the structural side I will have to go find that wood magazine that did the article on mortises vs biscuits vs dowels to find out that answer.......

[Jason Beam]

For the record: The only solid-carbide spiral bit that i HAVEN'T had break on me was bigger than 1/4". I'm left with the impression that 1/4" on these spiral bits is just too small for any major cutting. I've even tried taking my passes in 1/8" increments and eventually that little 1/4" cutter snaps.

If I need 1/4" mortises now, I use a 1/4" straight bit and that seems to have solved my problem. I've burned through far too many spiral bits to bother with them at less than 3/8".