Double Mortise/Tenon--Long

[Bill]

I have been contemplating the "best way" to cut a double-tenon on the end of a 4by4, the tenon should be 3.5" long 3" wide .

A "dado blade" would appear to work well, perhaps even best, for everything except the space between the tenons--and it is this space which I am concerned about and which motivated me to make this post. Options appear to be:

1. Drilling and routing it out (from both sides, before cutting any other part of the tenon).

1. Cut as much of it as possible with a TS and chisel the rest of it away.

3, Relying on BS and (which doesn't seem as precise as #1, or even #2)

1. Other???

2. Compromise and shorten the tenon in order to cut it on a 10" TS (which can make a 3" cut at 90 degrees)?

This is one of those details that, to the untrained eye, is easy to take for granted at first, and then it sort of sneaks up on you! My eye is still learning....

This problem made me wonder whether the original designer (Garrett Hack) might have used a TS bigger than 10" to make easier work of this?

Bill

[StephenM]

I would do it all on the TS and then get the last 1/2" with the BS. Any inherent sloppiness of the BS will be minimised.

It should be easy to set a up the cut in the BS as you can just align it using the TS kerf. I would also make a couple of extra stopped BS cuts between the tennons to make it easier to chisel out the remaining center accurately (follow the depth of the kerfs).

BTW I agree that making 3.5" thorugh tennons is deceiving. The geometery is straightforward but making those cuts with the desired accuracy is non-trivial. Make no assumptions about the squareness of your stock, jigs and fences. Check and tripplecheck.

I helped a neighbor with a similar project (Red Oak headboard w/ 3" through tennons). Bless him; he thought the ends of his S4S oak came from the supplier square. He was in way over his head.

Regards,

Steve

[Leon]

The simplest and probably easiest approach would be to simply put double mortises in both pieces and use 2 floating tennons.

[Swingman]

Bow saw and chisel; band saw and chisel; hand saw and chisel; all previous with coping saw to remove most of waste between tenons and chisel to clean up.

These are not all that hard to do and tubafours are cheap. Spend more time wasting a few by practicing, and less time posting, and you'll be an expert in no time. ;)

Are you familiar with using a guide of some type with a hand saw to help make a square cut?

If not, DAGS ...

[Joe]

I don't think you mentioned how long the 4x4 is, which affects the answer.

However, I think this is a prime opportunity to get in touch with your inner Neander, grab the handsaw and go for it.

jc

[SonomaProducts.com]

Here is the methodI would use.

1. First draw sharp lines, even use a knife to define all cuts both shoulder and cheek etc so you end up with a shoulder line around 4 sides of the piece, cheek lines on two opossing faces and lines across the end grain showing locations of the end of the tennons.
2. On my router table I would install the smallest straight bit I have. Then using a fence I would adjust for maybe 1/4" deep cuts aligned to the correct faces of the cut lines setting up a stop block so all cuts stop at 3 1/2 exactly at the shoulder mark. Do slots on two opposing faces along the edges of the tennons.
3. With slots now cut on two faces defining the edges of the tennons, use a bandsaw (if you are good with a bandsaw and can trust your setup), or use a hand saw (I would do this) and saw along the correct face of the slots to the shoulder. Take your time and think about Noah.
4. Hand cut the shoulder cuts on the two outside pieces. You could router these first on the table if the 4x4 isn't two long or use a an edge guide and free hand it. Use a backer to avoid blowout at the exiting edge.
5. Drill out, with a single appropriatly sized drill or fostner bit, the inside drop pieces drilling about 1/8" bach from the shoulder line. Go slow and with light pressure to avoid drift. Then clean up those two interior shoulders with a chisel.

[SonomaProducts.com]

Sorry, single interior shoulder, I was thinking triple tenon I guess.

[Bill]

Swingman, I do try to do my "homework" between posts. You saw me list 4 different options. I didn't ask, "How do I cut a tenon?", I asked "How should I cut the space between two 3.5" long tenons?" My questions are getting better, no? : ) You have given me a lot of help. I appreciate everything on-topic which people post to the newsgroup which furthers my thinking and I thought there were some very fine and useful responses to my post. There are lots of ways to "skin a cat-fish". I think it's awesome that we can discuss them here. I'm probably in a bit "over my head" like StephanM's friend, but I'm learning! I'm glad I asked for a Starrett combination square for Christmas, it appears I'm going to need it! :) I still need a TS and a DP... Will do what I can with a BS and router in the meantime... Thanks!

Bill

[Bill]

Nice idea! It seem one doesn't usually talk about stopped BS cuts (because of issues in backing up). Is this permissible here becuase these are straight-line cuts?

I was already wondering whether the "hardboard" mortissing jig I saw in a book is stuitably accurate for cutting the mortise... It basically consisted of two onebytwos, or so, placed one on each side of the (4by4) workpiece spanned by a piece of hardboard to which the router is afixed. As you mention, the desired accuracy is non-trivial!

No doubt, I am in over my head too... Wait until I get to planing the benchtop.... :) This project represents a "curriculum of study" to me. Maybe that gives me an advantage over your neighbor, maybe not.

I take it one of your first steps would be to put the 4by4s through a bench planer (which I do have)? BTW they are less than 30" long.

Bill

[Steve]

I might be able to help with the table saw -- got one that needs a good home. AND I'm somplace near the crossroads of America.

[Bill]

Now, there's an attention getting post!!

Steve, Please send me further details. I just put my email address on my web site:

[Larry Jaques]

On Thu, 6 May 2010 15:27:20 -0400, "Bill" wrote the following:

In that case, Bill, the answer is a resounding "Carefully and precisely!", of course.

-- All national institutions of churches, whether Jewish, Christian, or Turkish, appear to me no other than human inventions, set up to terrify and enslave mankind, and monopolize power and profit. --Thomas Paine

[Bill]

You may as well have said, "You're just talking about the space-- you don't need to cut the space, you need to cut the wood!" : )

[Bill]

I have used a mitre box before. I can imagine a custom version, clamped to my workpiece, which could possibly work similarly (if all of the clamps held). DAGS failed me. Would you please provide another clue to the idea to which you were referring?

Bill

[StephenM]

Frankly i did not know that it was a "rule". I drive in reverse regularly (but with care).

make the first two cuts diagonally to remove the bulk of the waste and then subsequent cust will be much more shallow.

I think the place where you are likely to have trouble is not the jig but non-square stock.

"Never assume that wood is straight/flat/square. Only beleive that it is, when *you* made it that way"

No. Jointer First. Not just for flatness, but establishing the first

90-degree edge.

In lieu of a jointer. just make sure you plane first with any bow facing up. When the bow is gone, flip and get the other side. This will mitigate the bow. OTOH, you could knock off the high spots with a a hand place.

Establish your 90 angles at the TS after planing.

One more asside. It sounds like you are making this with dimmensional lumber. If I were doing it, I would (re)design my final dimmensions to something a little smaller (1/8" or 1/4") than the supplied stock to that I could mill to flat/square.

Cheers,

Steve

[Swingman]

Trust your imagination ... a picture being worth a couple of words, here is one that comes quickly to mind, if I understand what you are trying to do:

[Bill]

picture was worth more than 1000 words! Thanks!

[Bill]

Thank you for the numerous suggestions! It was my error for assuming a carefully selected 4by4 would be properly dimensioned. A good woodworker never blames the wood, no? I am sending your post to the printer and will be thinking about your outline as I work through this!

Bill

[Bill]

I think I finally "get it" (great lesson)!

If I understand your instructions, the first of the sides at the TS is to be cut using a *miter guage* (probably wise to use some sort of "sled" to help support the stock, huh). Then the other side can be cut using the TS fence. Finally the ends can be trimmed square. Then it's time to take a break and admire the square stock...! : )

Bill

[dpb]

...

Unless it is quite thick stock or your planer has very little down force (in which case it probably doesn't feed well), the planer will have a tendency to simply flatten the piece leaving you w/ two parallel (but still cupped) surfaces.

The point of the jointer in the operation first is that it doesn't have that mechanical force on the opposite side that does the "mashing down" so will, indeed, only hit the high spots.

If going to do this w/ a planer unless the stock is so thick as to not bow under pressure, you need to shim the cup places to prevent the flattening that otherwise will occur. This generally entails a planer sled.

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