Replies

1. 
   TomFerreira | Jun 10, 2003 04:46am | #1

   BG,

   I would use 3/8" stub tenons that fit in the groove for the panel.

   Wish this rain would stop!

   TDF

1. 
   BG | Jun 10, 2003 03:03pm | #3

   Tom,

   I'll need to get an upspiral cutter which is limited to 1 1/4" in depth....I think I'll put some dowel pins in to keep it strong.  Thanks

2. 
   fredsmart48 | Jun 10, 2003 06:29am | #2

   I like m&t 1/2 the thickness of material and as long as I can get them with out making them into a through mortise.

1. 
   BG | Jun 10, 2003 03:07pm | #4

   Fredsmart,

   I'm concerned that with a 1/2" mortice in this stock, that would give me only an 1/8" about on the walls....and given there size and weight I'm a little worried it would hold up.  Am I being to anal?....lol

1. 
   MarkRoderick | Jun 10, 2003 06:10pm | #5

   Personally I think a 1/4" mortise and tenon would hold up fine. Same glue area as the thicker choices, and in this application I think glue area is really all you are about. They're not going to be subject to significant stresses. And 1 1/4 deep mortises should also be fine. That's actually a lot of glue surface. I know that the traditional method involves through-mortises, but that seems like overkill to me.

2. 
   fredsmart48 | Jun 10, 2003 09:47pm | #7

   I said 1/2 the thickness .  as a rule of thumb

   1/2 ÷ 2 = 1/4

   3/4 ÷ 2 = 3/8

   6/4 ÷ 2 = 3/4

   8/4 ÷2 = 1 inch

1. 
   Elcoholic | Jun 10, 2003 10:01pm | #8

   I've read and follow the 1/3 to 3/5 rule of thumb.  For .8" thats a range of .26 to .48 so 1/4 to 1/2" would be the range.  Since you've already determined to use 3/8" BB Ply panels you might as well go with 3/8" and plow the grooves in the stiles for stub tenons.  The plywood panels can be glued in which will yield a door of such strength that the mortise question is moot.John O'Connell - JKO Handcrafted Woodworking

   Life is tough.  It's tougher if you're stupid - John Wayne

1. 
   BG | Jun 11, 2003 02:28am | #10

   all,

   I was out all day and did not get a chance to read everyones comments before stopping at Woodcraft on the way home.  Ouch! $52 bucks for a 3/8" upspiral cutter.....

   By the way, what is a 'stub tenon'?  Thanks for all the comments and good rules of thumb.

2. 
   BG | Jun 11, 2003 02:23am | #9

   Fred,

   Thanks, that is a handy rule of thumb.  Sorry for misinterpreting your earlier comment.

1. 
   SgianDubh | Jun 11, 2003 04:07am | #11

   I had some trouble following fred's rule of thumb too, BG. I came to the conclusion that what he was saying is that in an idealised joint equal amounts would be removed from each member-- for example in a corner halving joint of a frame (aka a corner lap joint) where the parts are of equal thickness and width, then you would remove the same amount from each thus retaining the maximum material in both parts. I'm sure fred will come back in and correct me if I've misread him, ha, ha.

   Anyway, in a full mortise and tenon, where again the parts are equal in width and thickness, the rule has to be modified. In this joint the mass of the tenon on the end of one part retains its strength due to it being all one piece, but it is generally the weaker part because a greater proportion of the wood is cut away. The mortice that receives the tenon has to hold the faces of the tenon firmly via support from the cheeks either side. 

   If you retain half of the original mass of wood for the tenon in a part 3/4" thick you would make it 3/8" thick. But this means you also have to excavate a 3/8"+ mortise leaving cheeks only 3/16"- thick, which is generally considerd too weak.

   So, the rule of thumb most often used in M&T's is to divide the available thickness by 3, and step up to the next size chisel to form the mortice. Therefore in our 3/4" thick part, 1/4" is a 1/3rd.,  and you'd use the next wider chisel, i.e., 5/16". This leaves mortice cheeks 7/32" thick each. You retain 5/16" of the thickness for the tenoned member, and a total of 7/16" of the original thickness for the mortised part, a difference of 1/8".

   These sorts of dimensions are generally considered the best available compromise. The typical order of work is to form the mortise first, and size the tenon to fit-- this order matters in hand chopping mortices or in using a hollow chisel mortiser for example where mortice chisels come in set widths, and are best suited to cutting only that width.

   There are other guidelines for different situations. Say a 1" thick rail is being mortised into the middle of a 2" square leg. Obviously the leg has much greater mass tostart with, so the tenon on the end of the rail could be the full thickness of the rail. Most workers will put at least an 1/8" shoulder on the outside face to create a clean line, hide any sloppiness in cutting the mortice, and to provide a definite stopping point for the rail during assembly and glue up. 

   It's generally difficult excavate the mortise to a precise depth so that the end of the rail can bottom out on it, so the shoulder is used prevent the end of the tenon bottoming out--- and it also leaves a wee space for excess glue to squeeze into, preventing such things as liquid hydraulic physics coming into play that might prevent the tenon hitting the bottom of the mortice anyway.

   I'm not even going to get into discussing appropriate tenon widths, and mortise lengths in different situations. I've drivelled on long enough already, and it's way past my supper time, ha, ha.

   A stub tenon is a description for a short tenon. You see them in rail and stile construction where matched cutters are used. Another example is a horizontal drawer divider into a typical cabinet side which is often about 3/4" or 7/8" thick. In this latter example, there is often a double or twin stub tenon to maximise glue surfaces. Slainte.Website                                            The poster formerly known as Sgian Dubh

2. 
   BG | Jun 11, 2003 07:03pm | #12

   Richard J,

   Thanks, now I can take back this $52 dollar bit of twisted steel ...and get a coupla chisels and either bore out with the drill press several 5/16" holes and pare the sides...or by a long 1/4" router bit and cut twice to make 5/16" thickness. I'm sure the quality of the upspiral bit is worth the price to a heavy user...but I don't fit that catagorie

3. 
   MarkRoderick | Jun 11, 2003 07:25pm | #13

   Sounds as if you might have purchased a solid carbide upcut bit. It would surprise me if the regular carbide-tipped bits were anywhere near that amount. But I've been surprised before.

4. 
   BG | Jun 11, 2003 08:16pm | #14

   mark,

   Correct...I may have good use for a 1/4" or 1/2" but I don't think I need every size...especially when I don't even have a complete set of popular chisel sizes yet.

   I've been starring at the woodcraft special this week for machinists squares (3 sizes) made in India for $31 bucks.  I've been resisting because this is becoming a $100 a week hobby...all absolute necessities..but still, I need to spend more time doing and less time shopping.

5. 
   MarkRoderick | Jun 11, 2003 08:21pm | #15

   That's always the dilemma for all of us.

6. 
   AlanTurner | Jun 12, 2003 12:56am | #16

   I use the MLCS solid carbide upcuts, at a far less price.  http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_solid.html#Anchor%201  Free shipping also.  They have worked fine for me.

   Alan

7. 
   TomFerreira | Jun 12, 2003 03:16am | #17

   BG,

   Are you sure you didn't get a downcut spiral bit? I pay about $20 for an upcut spiral bit in solid carbide at woodworkers warehouse. I can believe $50 for a downcut.

   Anyway, you should keep a 1/4" upcut in your inventory. 1/4" mortices are prettty common in 3/4" stock.

   TDF

8. 
   BG | Jun 12, 2003 04:20am | #18

   Tom,

   Yes, it was an upcut..Whiteside (I think) you can see it on Woodcraft web site.  I should have gone over to WW warehouse but I had to pick a saw I had sharpened there...so...live and learn.  

3. 
   JeffKurtz | Jun 10, 2003 07:35pm | #6

   I believe the traditional thinking on this is to have the mortise about 1/3 the thickness of the stock, in this case 1/4", which would mean needing to remove 1/8" around the edges (back?) of the panels.  (I think that's preferable to a rabbet on the backside.)

   I think you made a good choice on the 1 1/2" tenons.  I could never see how a stub tenon could provide much stability, and have noticed that the doors of most commercially produced cabinetry, which usually uses stub tenons, will warp in a rather short period of time.