Machining Dadoes into Door Jambs

      Ideas for high-volume production methods for cutting dadoes in door side jambs to receive the header jamb. April 30, 2006

We have to machine dados in a large quantity of door jambs. We have production grade moulders to produce the S4S blanks and rabbet. What are your ideas for making the dado that receives the jamb header?

Forum Responses
(Solid Wood Machining Forum)
From contributor R:
I have done thousands of these in a production mode. There must be many ways of doing these. Here is the way we used to do them. Radial arm saw with dado blade set up and a stop set to the correct sizes. I'm sure others will have some alternative ideas.

From contributor D:
Using the radial arm saw is fine, but when we had a similar setup, we had problems with bowed or thin jambs being of inconsistent dado depth since the R A saw references off the back.

First solution was to make a stop above the saw table with a foot activated air clamp below that enabled the dado to reference off the face of the jamb and hold consistent sizing. We also used a larger diameter blade on the right side of the dado stack to do the cut-off. Second solution was to use a single end tenoner with the jambs face down. The fastest way would be a feed-through double end tenoner.

From contributor F:
Face down on the table saw with a miter gauge?

From the original questioner:
Thanks for these ideas. We had thought of the dado blade in the radial arm saw or table saw, but... how do you get rid of the score marks? We have hundreds of these to do and they must all be consistent, clean and flush with the rabbet. The tenon cutter seems like it would work. Any other suggestions?

From contributor R:
Router table set up with fence. But if you have a tenoner, that would most likely be the best the solution.

From contributor F:
With the exception of the tenoner method which I haven't personally done, I can only tell you how I have done it with a dado blade when the stop is rabbeted into 5/4 stock. I rabbet the head jamb to a width of the side jamb stock minus the depth of the stop. I make the rabbet deep enough - 3/8" deep - so that the casing will cover the horizontal portion of the joint. Then, I rabbet the stop sections of both side jambs at their tops to a width of the rabbet depth in the head jamb plus the depth/thickness of the stop. The way I keep from scoring the side section(s) is to refrain from rabbeting the stops to their full depths. I leave just enough wood remaining so that the dado blade cannot mar that area. To finish up, I pare the small amount of wood remaining using a chisel and cutting with the grain. I know this is not production. I believe contributor D from above post does production and I am curious what he does about the problem of cutting the dados without cutting into the hinge surface that will show after assembly.

From contributor J:
Like contributor D, we started with a radial arm dado setup and that sucks for all the reasons he lists. Plus the labor of trying to clean up a dado cut. We are now doing it face down on the shaper using the sliding table and a high quality rebate head. We just started running the legs and heads on a moulder and this has presented another problem at the end cut with right and left legs. We have to add another chip breaker when the rebated edge is at the end of the cut. This is a little awkward. Next batch I am going to try turning the cutter over and reversing the sliding table feed direction for half the batch. Before we started using the moulder the end cut was done first so this was never an issue. We are getting good results with no hand work required to clean up but it is not a high production method.

I agree that the double end would be the production way and I am sure most large door companies do it that way. Also I wonder if anyone uses a CNC router or a 2 head coping machine like the Stegherr KF2 to do this task.

From contributor J:
Another idea is to use a European adjustable groover in a sliding table saw. This might be more of a problem for the left and right than on the shaper, though. The tool would be cutting like the bottom head on a single end tenoner and I don't know if this is better than the shaper cut from the side.

From the original questioner:
These are great ideas. Please keep them coming - especially the production oriented suggestions. So far, it looks like the double end tenoner is the best solution, albeit the most costly upfront investment. The end product will be bundled and sold as "off the shelf" items in retail outlets. They have to look professional; i.e., smooth, clean and fit well.

From contributor D:
Jambs and how they are made/machined are a highly regional/decentralized item, like many things in our industry. Around here (Midwest) we make interior jambs at about 3/4", with either square or beveled edges, and an applied stop, nailed only in place, mitered at the head. A 5/16" dado on the sides and the head butts into the dado and stapled. I assumed the questioner was talking interior.

Exterior jambs are 1-1/8" square edge with a 1/2" deep x whatever door rabbet. These are also rabbeted 1/2" deep for a head, and the head is stapled in place. An aluminum sill is tacked on the bottom.

In our shop, we have changed the interior jambs to a mitered, glued and cross screwed joint at the heads. Easier to cut to length in our (somewhat limited) production, and accurate to assemble, and far more durable in shipping, handling, and install. We just endure the alleged carpenters telling us "yer doin' it all wrong."

We also glue and lag bolt our exterior jambs at the head and sill, and use a canted sill. The cross grain rabbetts are done in a variety of ways, personal choice. Mostly they are machined very close, and cleaned up with a rabbett plane. We are a bit labor intensive, but many of our exterior jambs are with transoms, arches, and/or sidelites, etc, so they take a lot of hand fitting.

High production would follow the single end tenoner, then the double end tenoner or similar end-matching equip. Contributor J's mention of a counter rotating pair of rabbet heads is a good point and will enable feed through with no tearout. Counter rotating heads are available on some single ends and some double ends. Even some of the higher production cabinet door equipment - Unique and Jenkins are two - have counter rotating heads and a solid feed system.

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