Bits for Mortises - Router Forums
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post #1 of 10 (permalink) Old 05-23-2018, 08:46 PM Thread Starter
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What I think I understand about using a mortise jig is to use an upcut spiral cutter the actual width of the needed mortise. But then I run across these mortise cutters from Infinity. What is the better/safer method recommended? I know this is subjective but as someone starting out with mortises what would you use? Buys cutters/bits I'm also guessing you would want those that can go the needed depth. For through mortises I guess you can cut from both sides if say going through a 4" square piece of wood but when not cutting through is there a calculation to use for what is an appropriate depth? I know, lots of questions......
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post #2 of 10 (permalink) Old 05-23-2018, 09:10 PM
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hog out your mortise w/ a flat bottom drill bit like a fostner
don't use a spade bit.. the guide point tends to set up a ''fault line'' leading to a crack in your material...
after that it's what bit that suits your fancy to clean up the mortise...

note..
up spirals can leave burrs on the mortise rim...

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

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post #3 of 10 (permalink) Old 05-23-2018, 10:05 PM
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If I'm cutting mortise/tenon in table legs and aprons, I generally use 3/4" material. I've cut mortises on a router table with an upcut 1/4" spiral bit. Depth is 1/4" to 1/2".

Some folks call me Vince - other folks call me...........
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post #4 of 10 (permalink) Old 05-23-2018, 10:34 PM
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The main issue is clearing the chips out of the cut. Up cut spirals do a good job of that but are usually limited to 1.5 to 2 inches in length. Usually that’s enough except for windows and doors which are subjected to more extreme racking forces. Drill bits obviously do a great job of getting rid of chips and one method is to use a bit slightly smaller than your router bit to hog out waste and then you can use a straight bit to finish with. Most woodworkers cut tenons with shoulders that hide any imperfections in the mortise with the exceptions of through tenons in which case which have to be perfect on the side that shows.
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Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #5 of 10 (permalink) Old 05-24-2018, 02:01 AM
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I'd go with a forstner bit and ultra sharp chisels. If I were doing a lot of them, I'd likely invest in a mortising machine with mortising chisel and bit. I don't think I'd use a spiral bit, and think the forstner in a drill press is the most logical choice.

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post #6 of 10 (permalink) Old 05-24-2018, 08:20 AM
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I have the mortising attachment for my drill press. A drill press is a good investment to start with and the mortising attachment makes it even better. They’ll cut at least 3” deep, maybe a bit more. You have to be careful setting it up to get the chisel square to the fence or you get a stepped edge and they aren’t good for through mortises unless you are sure you can flip the piece over and line the two sides up accurately. Luckily there are a number of ways to make them so there are options.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #7 of 10 (permalink) Old 05-24-2018, 08:30 AM
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Check this video out on how to make a mortise and tenon joint on a router table.

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Don in Murfreesboro,Tn.

Measure once cut twice and it's still to short.
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post #8 of 10 (permalink) Old 05-24-2018, 04:47 PM
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There are many ways to cut mortises and tenons, and I think I've tried them all. I now use a router with an up cut spiral bit. I found that this produces the fastest and cleanest way of making mortises (a clean cut, but frequently chips everywhere). It works best to plunge cut the bulk of the mortise out and then move the router back and forth to clean out and smooth the side walls of the mortise whenever using a router to cut mortises. It reduces the side pull of the bit so you get better accuracy of the mortise dimensions. I never bother to square my mortises, unless they will be through mortises and the ends will be seen. I just leave the mortises and tenons with round ends and they are just as strong If making floating tenons i leave the mortise with round ends and make the tenon fit the length of the flat sides of the mortise and leave the ends square. The half round gap in each end of the mortise leaves a place for the excess glue. It's the fit of the flat sides of the mortise and the tenon that gives the joint the strength, so rounding the ends of the tenon doesn't gain anything.

For mortising accuracy I now use a Leigh FMT Pro because of it's accuracy and the fact that it lets me cut both the mortise and the matching tenon using the same setup, router, and bit. A template is used to guide the router. You follow the outside of the template to make the tenon and the inside of the template to make the matching mortise. Only the part clamping needs to change and there is a centering cross hair for getting the first piece located. Then all additional pieces can have the same mortise or tenon cut without needing alignment. I can fit the first tenon to the 23rd mortise and it will fit just as perfectly as the first. No hand tuning of each tenon to mortise is ever needed. I just cut them and then assemble them.

The jig has an adjustment for how loose or tight that you want the tenon to fit into the matching mortise. This feature doesn't seem to exist on any other M & T jig. I can also use the jig to make precise floating tenon joints with it too, by cutting matching mortises in both adjoining pieces, then using floating tenon stock made with my table saw and planer.

There is a vacuum port on the FMT that works quite well, except when cutting the front side of tenons. I Velcro attach a piece of clear Lexan to hang down the lower front of my FMT, which prevents these chips from hitting me directly. It also helps get some of the chips from the front side cutting of the tenon to be collected by the rear vacuum port, but most of them just fall to the floor. At least the Lexan keeps them from hitting me.

I like my mortise and tenon joints to "POP" when I dry fit them and then pull them apart. It's easy to get them to fit this accurately when making them with an FMT jig. Add glue and they are "forever" without all of the hand fitting that's usually involved when making them other ways.

Charley

Central North Carolina

Last edited by CharleyL; 05-24-2018 at 04:53 PM.
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post #9 of 10 (permalink) Old 05-24-2018, 04:51 PM
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that FMT sure is sweet...
I did the same for a chip delector...

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #10 of 10 (permalink) Old 05-25-2018, 09:03 AM
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Delector? Maybe a typo for deflector? Yes, it makes a good deflector.

I bought my FMT when I was facing a project that required just over 1,650 mortise and tenon joints. I would likely still be cutting and re-cutting them if I hadn't bought it. My FMT paid for itself on that job and has been saving me several times a year since then. Before I bought it I had tried making M & T joints about every other way possible, and the hand fitting of each pair took forever. The FMT completely eliminates this step and makes these joints easy to get perfect on the first part and every one made after that one with no custom hand fitting It's quite amazing to be able to make a mortise and tenon joint that fits so well that the dry fit "pops" when you pull it apart because it's such a perfect fit. Only someone who has chopped mortises with chisels or mortising bits and then cut tenons with hand saws and then trimmed them to fit the mortises with rabbet planes and chisels can appreciate this level of fit without the need for any hand fitting. I love my FMT Pro jig.

Charley
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