Tenons

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Tenons

Postby dakotablue » Fri Jun 28, 2019 11:49 pm

I need to cut some tenons on the end of a board. I machined a slot into the spoilboard so i can insert a board vertically through the slot and clamp it in place. My board is 6 inches wide and i want to cut a single tenon on the end of the board that is 3/8" thick and 2 inches long. When I profile cut the tenon, how can i machine away the waste that is left on either end of the tenon? I hope this makes sense.
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Re: Tenons

Postby IslaWW » Sat Jun 29, 2019 12:17 am

Make a rectangle that is half a bit larger than the board end on all 4 sides. Make a vector the size of the tenon. Pocket between them. Not the most efficient, but the simplest to get you going.
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Re: Tenons

Postby dakotablue » Sat Jun 29, 2019 12:36 am

Sorry to sound so dumb but i understand what youre saying. i just dont know how to pocket between them.
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Re: Tenons

Postby TReischl » Sat Jun 29, 2019 1:01 am

Couple of things, pocketing is NOT the way to go when cutting tenons IMHO.

First off the shoulder all around the tenon should be about the same size. For instance, if you are tenoning 3/4 stock the tenon should be 1/4 thick and the shoulders should all be about 1/4 all the way around.

If you are cutting square tenons (and I do not know why you would do that since you are probably cutting the mortises on your machine too and that means you would have to chop out the corners of the mortise) the procedure I use for both round and square is the same:

Offset the tenon by the amount you want to cut, repeat that offset until you are clear of the outside of the piece. Then use those vectors with an "outside" profile cut. I like to use climb cutting, seems to result in no splintering.

When I am doing a lot of tenons I use a spiral to avoid as many retracts as possible.

One thing to remember is that you can cut quite deep because you are side cutting in end grain. It cuts really nice.

Pocketing works, but I am not crazy about using it for tenons. BTW, I did a project two years ago that required over two hundred mortise and tenons. I got really good with the tenoning jig I built for the front of the machine.

Oh yea, hopefully you are cutting the mortises first? It is easier to fit tenons than the other way around IMHO.
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Re: Tenons

Postby dakotablue » Sat Jun 29, 2019 1:58 am

thanks for the info. Thats what I am needing to do. Going from a tenoning jig on the table saw is quite a jump. Just to complicate things, is it possible to cut multiple tenons on the same board?? Im also needing to do some through wedged tenons. The wedges are dead easy, maybe not so with multiple tenons.
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Re: Tenons

Postby TReischl » Sat Jun 29, 2019 1:23 pm

dakotablue wrote:thanks for the info. Thats what I am needing to do. Going from a tenoning jig on the table saw is quite a jump. Just to complicate things, is it possible to cut multiple tenons on the same board?? Im also needing to do some through wedged tenons. The wedges are dead easy, maybe not so with multiple tenons.


Tenons are way easier on a cnc router than a tenoning jig. Once you understand how to tool path them it is easy to dial in perfect sizes.

Here is a video I did quite a while ago doing finger joints which is pretty much the same thing, it shows the cutting technique I use to prevent chipout.

https://www.youtube.com/watch?v=NhLkB1ZyOPo
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Re: Tenons

Postby 4DThinker » Sat Jun 29, 2019 3:24 pm

I frequently cut tenons and other joinery details for my students. For tenons I usually start with a climb cut profile ON the line using the perimeter of the board. This sheers the end grain fibers cleanly and leaves a clean shoulder edge. Pocketing is the easiest way to remove the end areas, followed by a conventional profile pass outside the tenon perimeter vector.

Simple tenon 4D.jpg

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Re: Tenons

Postby TReischl » Sat Jun 29, 2019 7:11 pm

4DThinker wrote:I frequently cut tenons and other joinery details for my students. For tenons I usually start with a climb cut profile ON the line using the perimeter of the board. This sheers the end grain fibers cleanly and leaves a clean shoulder edge. Pocketing is the easiest way to remove the end areas, followed by a conventional profile pass outside the tenon perimeter vector.

Simple tenon 4D.jpg

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That is a pretty strange looking tenon there 4D. Wouldn't do much to keep that board from cupping.
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Re: Tenons

Postby dakotablue » Sat Jun 29, 2019 8:09 pm

Thanks to all the members. Its amazing how easy this was once someone shows you how! Gary
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Re: Tenons

Postby 4DThinker » Sat Jun 29, 2019 11:22 pm

TReischl wrote:That is a pretty strange looking tenon there 4D. Wouldn't do much to keep that board from cupping.
I didn't design it. OP did. :D
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Re: Tenons

Postby 4DThinker » Sun Jun 30, 2019 7:44 am

When I cut tenons for students, the tenon width and length depends on how thick/wide the mating mortised piece will be. This example would be for a 6" x 3/4" stretcher joining into a 1.25" wide table leg. Three 3/8" wide tenons rather than one for the 6" length. They provide a little more glue surface, and weaken the mortised board less than a single long tenon would. Rounded corners to match the rounded corners of the mortises I'll also cut using the CNC. I'll add a small allowance (-0.003ish) for glue room when I cut the mortises. The gap between the tenons leaves a web between the 3 mortises which weaken that board less than a single long slot would.

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Re: Tenons

Postby dakotablue » Sun Jun 30, 2019 12:19 pm

Additionally, three (in this case) tenons tend to minimize problems associated with cross grain construction since the snug fit of the joint itself provides for the use of less glue much the same way a properly cut dovetail or finger joint works. When i build a bed, i under cut the headboard tenon widths slightly, glue the bottom tenon and leave the top tenon dry.
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Re: Tenons

Postby Wayne Locke » Mon Jul 01, 2019 3:50 am

The strength is determined by the weakest part and a1/4” wide tenon is not that strong. A 1/4” tenon in a 3/4” board is too weak. The tenons should be sized to half the thickness as should the mortises in the same sized board. This gives you two 3/16” mortise sides for a total of 3/8” the same as the tenon.
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Re: Tenons

Postby TReischl » Mon Jul 01, 2019 1:42 pm

Wayne Locke wrote:The strength is determined by the weakest part and a1/4” wide tenon is not that strong. A 1/4” tenon in a 3/4” board is too weak. The tenons should be sized to half the thickness as should the mortises in the same sized board. This gives you two 3/16” mortise sides for a total of 3/8” the same as the tenon.


Tenon size is one of those woodworking discussions that has lots of opinions. There is no doubt that a 3/8 tenon is stronger than a 1/4 tenon. But there are those who will say that makes the shoulder too narrow to provide support against racking. A long time ago there was an article in IIRC, FWW about this. There was no definitive answer about sizing IIRC.

I do know failed mortise/tenon joints I have seen were due to one of two things. The first being the glue up failed and the whole tenon fell out (common in cheap kitchen furniture) and the second was the cheek of the mortise split out leaving the tenon intact.
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