Advice on cutting thru mortise

[Russell Stanton]

I am building a blanket chest and will do thru mortises between the legs and upper and lower rails. The legs are 1.5 inches thick so the mortise will be 1.5 inches deep. The width will be 1/4" and the length will be 2.5". I would like to do this on my router table to get a clean cut. I have a 1/4" spiral up cut solid carbide cutter, 1/4" shank, 1" cutting length and 2 1/2" overall length. If I take 1/4" deep cuts per pass would this work? Any other suggestions? I have a PM mortise machine but for this length and width I usually don't all cuts aligned and then have gaps on the visible side of the thru mortise.

[Keith Hankins]

Are you concerned about blowout on the back side? If this is the case, attach a scrap to the back side as a backer and cut into that to protect it. Something that deep, if the bit is long enough the do a jig and go to it If you want to come in half way from one side and the other half from the flip side, again build a jig with positive stops and test it on scrap and then go to it. I had to do similar work when I make 8 sided pencil post beds. Once you get the jig set up you can really go to it. Good luck.

[Bob Lang]

If you have the mortiser, use it. Much less fuss than trying to drop pieces on to the router table, and no risk of snapping the carbide spiral cutter. Cut a little more than halfway from each side, and use the same face against the fence when you cut the mortises. The mortise on the outside is the part that will be visible when you're done.

Bob Lang

[John TenEyck]

I see no structural reason to cut a 1/4" wide mortise that deep. Typically you cut a mortise three times deeper than it's width, so for a 1/4" wide mortise you cut it around 3/4" deep. I'm guessing you want to cut them that deep for decorative reasons. But in any case, I would cut the actual mortise 3/4" deep and then cut a shallow 1/4" to 3/8" deep one on the other side. Into that shallow mortise I would glue in a purely decorative tenon. It will look like a through mortise and tenon but eliminate the hassles of trying to cut one that deep.

John

[pat warner]

Forget this l, w and depth with a 1/4 cutter on a router table. If you must, do it with hand router and edge guide.
Notwithstanding, a skinny cutter in this much wood is hell itself. Would not do it without my skills. & I have but don't recommend.

[Robert Engel]

I would make the moritse 3/8" and use the mortiser with a 1/4" bit center of mortise.
Make a paring block and pare out the 1/16" by hand, coming from each side.
On the show side, sneak up on it for a tight fit.
Be sure to scribe the mortise with a knife on both sides first.

[keith micinski]

I see no structural reason to cut a 1/4" wide mortise that deep. Typically you cut a mortise three times deeper than it's width, so for a 1/4" wide mortise you cut it around 3/4" deep. I'm guessing you want to cut them that deep for decorative reasons. But in any case, I would cut the actual mortise 3/4" deep and then cut a shallow 1/4" to 3/8" deep one on the other side. Into that shallow mortise I would glue in a purely decorative tenon. It will look like a through mortise and tenon but eliminate the hassles of trying to cut one that deep.

John


This is is the way to go. I think making 1/4 tenons that long actually gives a chance of making a leverage point and breaking it off easier.

[Bill Adamsen]

One and a half inches should be no problem for the PM Mortiser ... I would think that's the way to go. The blow out issue, either use a backer or mortise while the stock is "thicker" and rip to size.

[glenn bradley]

I frequently use the router table for this. I cut from the back so that the shoulders will hide the possible anomalous opening caused by tilting the piece onto and off of the bit at longer lengths. Consider this when choosing which side to pivot from when lowering and raising. A quick dry run will confirm how to avoid botching your show side.

[Russell Stanton]

Wanted to let you know the final result. I cut all the way thru using a Freud 3/8" solid carbide bit. I made all cuts from the back side as suggested by Glenn. All came out just fine, no tear out on the cut thru and I did not use a backer board. Thanks for the helpful advice