Tenon Depth. What's your rule of thumb

[Eric Roberge]

I’ve looked online and found several different answers to this question.
What is your “rule-of-thumb” when it comes to the depth of the tenon? Specifically a floating tenon.
One of my recent threads asked about what bit size for the intended stock, but how deep should one plunge into the work piece? Is it 2/3rds the width of the stock? So for a ¾ piece of stock I should plunge ½ in? Is this right?

[Rod Sheridan]

Hi Eric, I don't use loose tenons, however for regular tenons I make them 6 to 8mm shorter than the depth of the piece go into.

Having said that, I don't make them longer than the width of the stock.

ie if I have a piece 50mm wide, even if it was going into a piece that was 100mm wide, I'd make the tenon 50mm long.

Regards, Rod.

[John Thompson]

For me.. it depends on the stock widths.. thickness ect. and the strenght I feel necessary for the intended piece. So... anywhere from 1/3 to 2/3 just depending on other factors so I have no set rule of thumb.

Sarge..

[Chris Friesen]

I like these rules of thumb:

http://blog.woodworking-magazine.com/blog/Tenons+Rule+So+Here+Are+The+Rules+On+Tenons.aspx

According to the above, the length of a tenon should be 5x the thickness. Of course, if you physically can't do it then you just go as deep as you can.

[Eric Roberge]

So is that the overall length of the entire tenon? ex: If it's 1 1/2" that means 3/4" into each piece?

Forgive me, I'm trying to wrap my mind around this. :rolleyes:

[Frank Drew]

Eric,

If you're joining two pieces of wood at right angles to each other with a loose tenon (spline), the part of the tenon that goes into the piece parallel to its length can in principle be shorter because with a snug fit the glue joint will be stronger (long grain to long grain); conversely, the tenon goes crossgrain into the other part (i.e. giving a less ideal glue joint), so the tenon depth should be deeper to give you more glue line plus greater mechanical advantage. If your bits are long enough, I can't think of any reason not to make that latter tenon 3/4+ the width of the piece it's mortised into, within reason.

[glenn bradley]

So is that the overall length of the entire tenon? ex: If it's 1 1/2" that means 3/4" into each piece?

Forgive me, I'm trying to wrap my mind around this. :rolleyes:

I can only describe what I did;

3/4" x 3" aprons = 1/4"x2" fixed tenons 1-1/8" deep.

3/4" x 2" leg stretcher = 1/4"x1" flaoting tenons 1" deep into each piece (2" long tenon).

[Eric Roberge]

I believe that I have it figured out.;)
I appreciate all your help guys!

[Cliff Rohrabacher]

Honestly I just look at it, and if I like it then, it's good.

[Peter Quinn]

ADAP...As Deep As Possible, but leaving at least 1/4" on the receiving end of the cross grain. Same rules for me, loose or integral tennons. I have made 2 3/4" tennons with a plunge router using long Onsrud bits, not much fun but possible. Using a slot mortiser now and depth is not a problem at all.

[Eric Roberge]

I just got done playing with my new mortise pal and realized that my bit is to short. It has a 1" cutter, but you lose 1/2" due to the height of the MP.
Time to order another bit:(

[J. Greg Jones]

I just got done playing with my new mortise pal and realized that my bit is to short. It has a 1" cutter, but you lose 1/2" due to the height of the MP.
Time to order another bit:(

The limiting factor on the depth of the mortise will be the overall length of the bit, not the cutting length. For a 3" long bit with 1" cutting length, I can easily, and safely, plunge the bit 1 1/2" which would give a 1" deep mortise. If needed, I can go deeper still as the bit does not need a cutter length as deep as the mortise to make the plunge cuts, but the final finish rout would need to be made in two passes. The first finish pass is made at a depth up to 1" and the last pass at the full mortise depth.

[Eric Roberge]

Do you extend your bits beyond the little safety line when in the chuck? I could pull it out further then tighten to get more depth, but it’s only a 1/4" shank. Probably safer to buy a longer overall bit.

[J. Greg Jones]

No, I would not pull it out so far that it is not safely and securely held in the collet. If that's what you are up against, then yes a longer bit would be best. You'll still be fine with a 1" cutter length though. If your router will take a 1/2" collet, you'll have more depth capacity from the available bits, at least that's the case with bits from Whiteside. 1/4" shank spiral up cut bits are harder to find in overall lengths longer than 2 1/2" while 1/2" shank up cut bits are pretty common at 3+ inches.

[Mark Valsi]

as big as my "thumb" :)

[Cliff Rohrabacher]

I just got done playing with my new mortise pal and realized that my bit is to short. It has a 1" cutter, but you lose 1/2" due to the height of the MP.
Time to order another bit:(

Got to Whiteside and order a 3/8" staggertooth bit they are plenty long.
Either that or get some half inch shank slot mortising bits.

[Jesse Cloud]

Longer is better as long as you can keep the cut smooth and true.

However, all machines have some runout, and few setups are perfectly square, so a little nit won't matter in a 1 inch tenon, but will totally screw up a 3 incher.

Other than leaving 1/4 inch or so left in the workpiece, I cut as deep as the method I am using will do accurately (and funny, as I grow older its not as deep as it used to be, maybe the nit is in the operator.:o)