Getting rolling - dadoes, mortises and tenons

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Chris Hall
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Re: Getting rolling - dadoes, mortises and tenons

Fri Feb 17, 2012 5:41 pm

T-t-t-t-time for tenons!

First I used the bandsaw to kerf the waste:
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You could of course use a handsaw for the same thing.

Then I removed most of the waste, also using a bandsaw (you could use a coping saw or chisel):
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From here it is a matter of using a paring guide and a sharp chisel to trim the end grain clean, however I elected to use a router and cut the end grain directly using a bottom bearing bit. The result:
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Here I've placed the tenoned end board atop the mortised side board. The mortises have not been trimmed clean yet, nor have the tenons been trimmed to a precise height nor have they been diminished by 1/16" each face to target thickness of 0.375" Things are at an intermediate stage.
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I will do that tenon width dimensioning work on the router table sometime next week.

Note: if you are doing all these steps by hand, it may make more sense to follow a different sequence - for you to diminish the board end by 1/16" each side (using a filister rebate plane or similar), before laying out and cutting the tenons.

I also moved the handle a little further along today, kerfing the backside on a tablesaw:
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You can see that the tongue portion is defined by the cuts, the tongue left about 1/32" fat on each side at this stage. I will complete the sizing of the handle's tongue portion next week on the router table. I have my reasons for doing it this way. If you are cutting these tongue out using, say, saws and corner cutting/shoulder planes, you would proceed a bit differently.
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Chris Hall
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Re: Getting rolling - dadoes, mortises and tenons

Tue Feb 21, 2012 5:56 pm

Next up was to shape the mortises on the long side boards for the wedged tenons. The boards are 0.5" thick, and the wedge will be 0.0625" (1/16", about 1mm) thick, one on each side of the tenon.

So, the flare is 1/16" over a distance of 1/2"

There are sixteen 16ths to an inch, so if I multiply the 1/16" by 16, and the 1/2" by 16, I will end up with a slope of 1:8

I then lay that slope out with the sashigane, 1 on the short arm and 8 on the long arm, on a piece of clean and flat scrap material (the transfer board):
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If you are using a metric sashigane, I would suggest doubling those numbers, 2 on the short arm and 16 on the long arm.

I mark along the short arm of the square:
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Then I set a sliding bevel gauge to the line just drawn on the transfer board:
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I then used the bevel gauge to set the blade angle on the tablesaw, and then ripped a board cross-grain. I'll be setting up a paring jig, and I prefer the jig be durable so it is best to make the paring surface the end grain of the board rather than the side grain. If you lack a tablesaw, then plane the edge of the board until it is at the desired angle. When done, check to make sure you have the exact angle with your bevel gauge:
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Once the paring jig is ready, I clamp the long side boards down and position and clamp the jig to the board. Be very careful to make sure that you have the outside face of the board up. You really don't want to cut the flared mortises the wrong direction!!

I go just a hair towards the inside of my marked line, making the mortise just a fraction tight. Our come the (freshly sharpened) chisels, and I process the cuts:
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Remember that you will not be paring the mortises for the handle, as they are not flared mortises.

When all the chisel work is done, the flared mortises are complete, save for a final paring at fitment:
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It's a good idea to mark your paring jig '1:8' so you know what angle it is for any future use that might occur. It's easy to forget later on what the jig was specifically used for.
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charlie
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Re: Getting rolling - dadoes, mortises and tenons

Tue Feb 21, 2012 8:43 pm

Looks like your sashigane is set at 1:4.
Can you show in the model how the flared mortices work? and the wedges?
Maybe a cross section through one?
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Chris Hall
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Re: Getting rolling - dadoes, mortises and tenons

Tue Feb 21, 2012 9:00 pm

Charlie,

look at the sashigane again - when setting a slope, the measures are taken along the outside edge of the square, not the inside:
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I could have chosen a better camera angle. The line at '8' on the long arm of the square, to the left, meets the edge of the mdf.

As for pictures of a wedged tenon, ask and ye shall receive. I modified the drawing to show one wedged tenon, so it can be compared with an un-wedged one below:
道具箱 wedged tenon 2.jpg
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All 5 tenons will be wedged, however I am only illustrating one tenon as wedged at this point.

The mortises compared:
道具箱 wedged tenon 3.jpg
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Assembled:
道具箱 wedged tenon.jpg
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With wedging, the mortise and tenon finishes out as a square in appearance, 0.5" x 0.5", on the face of the long board. These wedged tenons will be trimmed flush once the assembly is done.

Did that make things clearer?
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charlie
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Re: Getting rolling - dadoes, mortises and tenons

Tue Feb 21, 2012 9:58 pm

Thanks. Now the sashigane looks like 1/2:4 on the inside. Thanks for clarifying.
And the wedging is clear as well. The tenons seem to be wedged on their long faces, rather than their short faces, as I had assumed.
Granted, the small ones finish as squares.
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Chris Hall
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Re: Getting rolling - dadoes, mortises and tenons

Tue Feb 21, 2012 10:42 pm

The tenons seem to be wedged on their long faces, rather than their short faces, as I had assumed.
The problem with doing it that way is two-fold:

- the pressure of the tenons being wedged outward would tend to crush the side grain in the long board mortises. This may result in a joint that is not especially tight, especially after a few seasonal moisture cycles

- the pressure of the tenons being wedged outward could possibly induce a split in the long board mortises

So, we wedge the tenons so that they press against the end grain inside the mortises. In joinery design, a general rule is to try an bear against end grain where possible with pegs and wedges, and even in certain types of connections such a scarf joints and those joints in trusses.
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Re: Getting rolling - dadoes, mortises and tenons

Thu Feb 23, 2012 4:48 pm

Next step in the work was to deal with the dadoes in the floor and long side walls of the box which receive the main partitions, shown in red in the following sketch:
道具箱 floor dadoes.jpg
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The dado in the floor panel is quite shallow at only 0.0625" deep, (about 1mm) while the dado in the long side panels is 0.125" deep (about 3mm).

First I'll show some pictures of how I went about the cutout, and then I'll give some suggestions for alternative approaches.

I did the dado processing with a router and a shop-made guide jig because I think it gives the most accurate result with the least fussing about.

First, I bought a 2'x4' piece of MDF for about $9.00, which I then sliced into a couple of pieces for this jig:
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The skinny piece will become a fence for the jig. A used the table saw to slice the main piece so that the edges were parallel to one another and were clean surfaces. I don't trust the factory to make the edges clean and parallel.

The important thing about these dadoes is that they be exactly the same spacing apart from one another on all three boards. If the pair of dadoes is offset to one end of the box or another some slight amount, it is less critical. If just one dado on one board is spaced differently apart than the others, you will have a spoiled fit, and troublesome indeed is the repair.

So I made a jig which would allow me to automatically form the dadoes the same spacing apart on all three boards.

Then I used my mid-size router with an edge guide and 0.5" spiral shank carbide bit to mill a slot on each end of the board, taking a couple of passes to penetrate all the way through:
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You can also see that cross-wise to the slots, I cut a dado across the board for the fence.

Here's the assembled jig, ready to go:
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Here's the bottom bearing router bit I will use for the cutting of the dado in the floor panel:
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For this cut out, I use my small Festool router. A trim router would also be fine.

I clamp the jig to the floorboard, making sure that the floorboard, which is longer then the jig is wide, protrudes an even amount at each end, and then I execute the 1/16" deep pass to make the dado:
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The completed floor panel dadoes:
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A check to confirm that I hit the target depth:
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I'm not planning to plane the interior side of the floor panel, so I went to target depth.

Then I reapply the same jig to the side boards. First though, I reset my router for the target depth of 0.125":
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For the side boards, placed them together and made sure their ends were flush to one another and then cut the stopped dadoes on each board.

When the routing was done, I used a couple of chisels to clean up the ends of the dado:
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The completed dadoes in the side boards:
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If you are not going to process the cuts with a router, then I can make a few suggestions:

-eliminate the dado in the floor panel
-cut the floor panel dadoes using a carefully set-up dado stack in a table saw. Then transfer the spacing of the dadoes over to the side boards. Those side panel dadoes are a bit deeper, so they could be readily cut using chisels, knife, router plane, goose-neck chisels, azebiki saw, etc. since these are full-width housing for the partitions, it is important to cut the sidewalls really cleanly.

The floor dadoes could be cut using a fillister plane of the appropriate width, one with a nicker blade. A wooden fence could be made to guide the plane back and forth. I don;'t own such a plane myself, but even if i did, I would choose to template-guide rout this cut out. A trim router is not an expensive tool and would suffice for the job.
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Dan McC
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Re: Getting rolling - dadoes, mortises and tenons

Thu Feb 23, 2012 6:36 pm

Chris,

I'd like to verify the way I'd figured out some dimensions before I start cutting.

For example, I am pretty much ready to glue up the two pieces that will make up the bottom, and before I do I want to cut them close to their final dimension to get the best grain pattern. I thought I would take the dimensions off your drawings and adjust from them for my different box size to figure out what it should be, but I couldn’t seem to find what I needed to do that, so I decided to figure it out directly, as follows.

To find the width of the bottom for my box, I figure the following calculation will give me what I need:
width of bottom = length of end piece - 2 * width of side pieces – 2 * length of tenon protrusion that will be trimmed off after wedging + 2 * depth of slot for bottom

In my case, the ends are 13 ½” long, and my sides are .475” thick, the tenons will protrude 1/8" and the slot is 1/2" deep, so the calculation will be:
width of bottom = 13.5 – 2*0.475 – 2*0.125 + 2*0.25 = 12.80”. Before assembling the bottom into the box I will trim it down a bit to allow some room for wood movement. My bottom is quartersawn cedar so I would not expect too much movement.

Finding the length of the bottom piece is similar:
length of bottom = length of side piece – 2 * thickness of handles – 2 * thickness of end piece + 2 * depth of slot for bottom

In my case the side piece is 23 ¾” long, so the calculation will be:
length of bottom = 23¾ - 2 * 1 -2 * 0.475 + 2 * 0.25 = 21.05

Hope my thinking is correct here. Sorry to subject you to so much math!

Dan
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Chris Hall
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Re: Getting rolling - dadoes, mortises and tenons

Thu Feb 23, 2012 7:11 pm

Dan,

I would suggest leaving the boards slightly long, gluing them up for best grain match, and then trimming the panel to final dimension afterwards.

As for the panel dimensions, your method seems perhaps more complex than it needs to be. But if it makes sense for you (and I read through your post and it does make sense!), then all is good.

I work from the inside dimensions of the box, since the box is all about what it stores. Let's say the inside dimensions of the box are 14" x 26". The floor panel needs to be that size plus an amount for the portion of the floor which fits into the dado on the box sides. On my box, the dadoes are a little deeper on the side panels, at 1/4", than they are on the end panels, where I made them 3/16". Since the end grain of the floor board panel inserts into the end boards with their 3/16" dadoes, I can anticipate that the seasonal movement will be minor in that direction (along the grain) and make the floor board insert almost all the way into the dado- holding them just 1/32" shy. That means the floor board needs to be 5/32" longer than the inside long dimension of the box, at each end. That means 2 x 5/32", which of course is 5/16". If the inside measure of my box was 26", then I need to make the floor panel 26.3125" (26 and 5/16") long.

For the dadoes in the long side of the box carcase, I can anticipate a bit more seasonal movement in the floor panel due to the cross-grain orientation. So, I make the dadoes in the side panels 1/4" deep, and I have the floor board panel insert 3/16" into that dado on each side. That allows 1/16" each side, or a total of 1/8" for seasonal movement. So, 3/16" added on two sides of the floor panel adds 3/8"; the inside dimension of the box is 14" in this example, so we add 3/8" to that to give 14.375" for the width of the floor panel.

The final dimensions of the floor panel then would be 14.375" x 26.3125". You can see, if you followed the numbers I gave all the through the example, that you can simply take the internal dimensions of your box, whatever they may be, and add 5/16" to the panel's length and 3/8" to the panel's width, and you will obtain the required total floor panel dimensions. Does that make good sense?

And by the way, if anyone was not following my explanation too well and wants some pictures for clarification, I'm happy to oblige.
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Dan McC
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Re: Getting rolling - dadoes, mortises and tenons

Fri Feb 24, 2012 1:58 am

Chris,

Thank you for your feedback! I will keep the bottom piece as long as possible and trim at the end as you suggest.

I see the difference in our approaches now, and I understand it arises because I found some nice wood I wanted to use and I cut from it the sides to the biggest size I could get from it, which was shorter than your sides, then cut the ends so my box will roughly match your box's proportions. So my box's interior dimensions will be what they will be. Whereas you started with the interior dimensions you have determined for the specific tools you want to store.

Anyways, as I read here elsewhere there is more than one way to swing a cat, and hopefully I will avoid any grievous mistakes with my approach and wind up with a box at the end!

Dan

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