How long to make a tenon?

[dg152]

I am in the process of making a table using walnut planks which will be about 1-3/4" or a little thicker when planed down. I'm going to edge glue the 4 center boards going lengthwise but attaching the 2 end boards (breadboards) with mortise and tenons since their grain will be perpendicular to the center boards. How long should the tenons be for boards this thick?

[JGrout]

1/2 to 2/3 the width of the breadboard for the tenons the intermediate stubs I make 1/2" and stop them about 1/2" in for the ends

Joe

[Edwin Hackleman]

From Fine Woodworking:
"The breadboard end is cut in two separate operations and the joinery appears similar to a tongue-and-groove joint. However, unlike the tongue-and-groove joint, the grain on both pieces runs parallel. On the breadboard strip -- which typically measures 2 in. to 3 in. wide, depending on the overall thickness, width and length of the panel -- a groove is cut along the grain. The end of the panel, which receives the breadboard end, has a tongue cut into the end grain. The parts are joined with mechanical fasteners, usually screws, in slotted holes so that the parts stay joined and are able to move with seasonal expansion.

Generally, the proportions of the joint are determined by the thickness of the material. A good rule is to cut the tongue 1/3 as thick as the material. The length of the tongue should be equal to the thickness of the material. For example, on a 3/4-in.-thick blanket box lid, the tongue should measure 1/4 in. thick by 3/4 in. long. This is not a difficult joint to execute, but the parts should be fitted painstakingly to provide both strength and a good appearance."

[JGrout]

Edwin Hackleman said:

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From Fine Woodworking:
"The breadboard end is cut in two separate operations and the joinery appears similar to a tongue-and-groove joint. However, unlike the tongue-and-groove joint, the grain on both pieces runs parallel. On the breadboard strip -- which typically measures 2 in. to 3 in. wide, depending on the overall thickness, width and length of the panel -- a groove is cut along the grain. The end of the panel, which receives the breadboard end, has a tongue cut into the end grain. The parts are joined with mechanical fasteners, usually screws, in slotted holes so that the parts stay joined and are able to move with seasonal expansion.

Generally, the proportions of the joint are determined by the thickness of the material. A good rule is to cut the tongue 1/3 as thick as the material. The length of the tongue should be equal to the thickness of the material. For example, on a 3/4-in.-thick blanket box lid, the tongue should measure 1/4 in. thick by 3/4 in. long. This is not a difficult joint to execute, but the parts should be fitted painstakingly to provide both strength and a good appearance."

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having build several large table tops over the yrs and having been asked to fix others that were built as the above states has led me to the formula I gave above
1 3/4 is too short unless the bread boards are around 3 1/2 - 4" which is too out of proportion to a large slab top

JME

[dg152]

Edwin Hackleman said:

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From Fine Woodworking:
"The breadboard end is cut in two separate operations and the joinery appears similar to a tongue-and-groove joint. However, unlike the tongue-and-groove joint, the grain on both pieces runs parallel. On the breadboard strip -- which typically measures 2 in. to 3 in. wide, depending on the overall thickness, width and length of the panel -- a groove is cut along the grain. The end of the panel, which receives the breadboard end, has a tongue cut into the end grain. The parts are joined with mechanical fasteners, usually screws, in slotted holes so that the parts stay joined and are able to move with seasonal expansion.

Generally, the proportions of the joint are determined by the thickness of the material. A good rule is to cut the tongue 1/3 as thick as the material. The length of the tongue should be equal to the thickness of the material. For example, on a 3/4-in.-thick blanket box lid, the tongue should measure 1/4 in. thick by 3/4 in. long. This is not a difficult joint to execute, but the parts should be fitted painstakingly to provide both strength and a good appearance."

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If I understand correctly, the tenon should be a little over 5/8" thick (the boards will end up about 1-3/4" thick) and about 1-3/4" long. Because of potential grain movement, the breadboard won't be glued to the center boards. Rather, I plan to connect the breadboards to the center boards using 3/4" wooden dowels. The holes in the tenons will be slightly elongated to allow for expansion/contraction of the breadboards.

[BigD]

How long to make a tenon?

It depends on how fast you work!

Sorry, just could not resist.

[dg152]

BigD said:

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How long to make a tenon?

It depends on how fast you work!

Sorry, just could not resist.

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Funny guy! That sounds like a joke I'd make. Actually, I'll probably take all the time I need to make sure this is right.

[Edwin Hackleman]

The best table tops, cabinet tops, desk tops, and chest tops that I have made using edge glued hardwood planks have held together for years and never checked up. Proper finishing has much to do with that. I am, therefore, not sure why you elected to use breadboard construction for this table top. I believe you could get by very well without it. Just MHO.

[dg152]

Edwin Hackleman said:

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The best table tops, cabinet tops, desk tops, and chest tops that I have made using edge glued hardwood planks have held together for years and never checked up. Proper finishing has much to do with that. I am, therefore, not sure why you elected to use breadboard construction for this table top. I believe you could get by very well without it. Just MHO.

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The lady I am building the table for asked for the breadboard ends. I agree that it would be easier to complete without the breadboard, but if I can pull this off well, it should look very nice.

Once I've completed the table, I'll post pictures.

Thanks for all your suggestions Edwin. I wish you were close by for some some hands-on advice!

[Edwin Hackleman]

You are going to be working with some really thick and heavy stock for a table top--massive as they say. I generally limit table tops to 5/4 stock or perhaps just a hair thicker, using planed down rough cut 6/4. There are some good plans for table tops at the WoodNet site.

Very few plans for wide table tops call for bread board construction. There are at least two major reasons why. First, breadboard ends on a table have to allow for wood movement across the width of the panel. Since the panel on a dining room table is wide, it's not unreasonable to see movements as large as 3/16" to 1/4" between seasons. That's the difference between the end board length and the width of the glued up planks. Second, the end caps are also subjected to stress from people leaning on their elbows, and wide end caps will also show a seasonal shrinking, creating a loose joint between the end cap and the panel.

You may wish to explain this to the lady requesting the breadboard ends on her dining room table. I doubt that she realizes this.