Hi,
I am replacing our existing door jambs which are soft wood w/ walnut. My question is that the existing jambs on the back of them have material removed similar to the bottom of oak flooring. Do I need to do this to my new jambs? The new ones are 4.5 inches wide and 5/8 inches thick. If so, what function do they provide, how do they work?
thanks,
Les Otte
Replies
You'd probably get more knowledgable replies on Breaktime, but I believe that relief on the back is space for adhesive to be, as well as assuring that the edges sit flush with the wall, even if the material cups slightly. You probably don't need to reproduce it, but as an industrial production item it has its raison d'etre.
DR
I was once told by someone in my millwork shop that it helps to improve stability.
Pete
Les,
The reason commercially prepared jambs are backcut is to relieve stress in the wood and to account for any unevenness in 2x4 rough openings. Some companies prepare all jambstock that way irregardless of species(most of the time it's veneered fingerjointed anyway). Walnut is a pretty stable wood and will work well for your application without backcutting. The most important consideration is to bring the walnut into the house for a week or two and let it equalize before milling. Use the straightest boards for jambs and the more active stuff you my want to make into trim. Dado the side jambs at the top to accept the head jamb and screw and glue them together before installing with hinges already mortised in place. I forgot one important fact, for jambs you can get by with sapwood on the backside and you'll never seeit.
I trimmed about a dozen doors in walnut 25 years ago and the are still perfectly straight. You'll love how the patina changes over time. My cherry doors and jambs have mellow to about the same color as the walnut doors and jambs.
If this is all redundant I'm sorry, as a teacher I never assume anything.
Terry
Edited 11/23/2006 9:30 am ET by terrylee86
Edited 11/23/2006 9:33 am ET by terrylee86
The back reliefs are to prevent cupping of the jamb. Your jambs sound narrow enough that this step is unnecessary. If you would like to add reliefs a couple passes throught he table saw with the blade set at 1/16" or 1/8" will be fine. For wide jambs (6" +) I use a roundnose bit in a router table or with an edge guide to cut a few reliefs for my own peace of mind.
Rabbeting the head into the legs is a nice detail but a screwed butt joint works well also. Tack the jamb legs in postion even with the ends of the head then predrill and countersink the screws and wax them with your choice of product before driving. I make most of my own jambs to acount for compound build up and poor framing. Most prehung doors also use a veneered particle board for stain grade jambs which I feel is not sturdy enough for solid core doors of any width , size, or species.
Pull a series of measurements around the jamb and rip stock to the widest dimension. Commercial door manufactures make jambs for 3 1/2" stud walls with 1/2" drywall at 4 9/16" but mine usually end up aroung 4 5/8". For walls with 5/8" drywall my jambs are usually 4 13/16". For old plaster walls they can be anything.
The casing at the narrower sections is either shot tight to the wall and rocked back a bit or shimmed out slightly and either caulked on paint grade or floated with compound on stain.
Good luck,
Justin
Those are relief cuts which help reduce cupping. They also help if you're attaching the relieved boards to something that isn't flat. Relieved boards have less contact area.
For door jambs, contact area isn't that important since you'll probably be shimming them. Relieving the jambs to reduce potential cupping would probably be a good idea.
Walnut door jambs!!?? What kind of doors are you using?
kywood, terry lee has it right. By the way, if the space allows, add wood blocking to the jamb areas behind the hinges (use three butts) The 5/8" material, in my opinion, is not thick enough to hold wood screws securely. ) Blocking in the lock/locks area is important too. Steinmetz.
Edited 11/23/2006 1:58 pm ET by Steinmetz
Thanks for all your excellent information, it will definately make this project turn out better! I will include your recommendations. The doors are going to be six-panel walnut. I am planning on making the stile that has the door handle a solid piece of walnut. The other stile and rails will be a glue up of two pieces.
The other part of the project is installing five inch baseboards and two and 5/8 trim once the door jams are installed. So far I have the materials all milled except for the door parts.
I am finishing the walnut by applying the following:1) water based tint mixture; 2) sealing w/ shellac; 3) sanding; 4) gel stain); 5) sanding; and 6) varnish finish coat.
Thanks again for all your exellent knowledge!
Les Otte
Well, I didn't respond to your question initially since I wanted to see what kind of answers you got. All very similar to what I have heard or repeated for the last 35 years.
I resisted the urge to respond with "to account for the Earth's rotation" as my standard smart a** response for things said but not understood.
So I will ask: How does a backout/backcut/relief/recessed thingy prevent cupping? Hocus pocus? Does the wood know this? Or is this just crusty old guy info that is passed on and repeated for no reason other than what has been said for generations?
As one who has made miles of jamb stock and other moldings (12 million l/f), and hung thousands of doors, I have no idea how backouts makes any sense at all. Backouts and relief cuts all have that air of mystery that no one I have asked has been able to give an answer beyond "Don't know, always that way."
It is not easy being a sceptic, but someone has to do it.
Dave S http://www.acornwoodworks.com
The cuts you are referring to are actually called relief cuts. They give relief to the stress that can happen to a board when only one side of it is painted or sealed.
If the surface of the back side gains moisture and has little relief slots cut in it, the slots squeeze tighter together rather than the surface of the entire width expanding which, if the front is stable results in a cupped board.
They are not there for gluing as someone suggested.
This way, the back surface will not have as much tendency to swell and cup the face side of the jamb. It is the same reason that flooring has relief cuts.
Relief cuts also work well in making mouldings in that the relief (or back) cut balances out the board after it was moulded, and a lot of material was cut off of the opposite face. The difference in mouldings is that the relief cut (back cut) is generally one wide cut.
If you have really made all of the molding you claimed to have made, and installed very much of it without a backcut, you would have noticed that a lot of it was not exactly the same shape as your molding knives. It was cupped.
Hal
http://www.rivercitywoodworks.com
We always made backcuts, backouts, relief cuts and recessed thingies in all our molded products, chiefly because we copied what had gone on before. In fact, I developed extensive guidelines as to where and how wide and deep and how many such cuts should be made. Many of these guidelines have spread from that shop and are now used by other shops, somewhat religiously. I'm aware of the backout easing install of door and window casing, and even flooring. And I'm aware of the early type molders (and some recent) that first cut a series of grooves to aid straight feeding of the material through the subsequent heads. I also know which direction the Earth rotates and our distance from the Equator.
You are right, I didn't install all that molding I claimed to have made. I only got complaints about cupping of jambs or wide stock when I subsequently found moisture problems on site. Once we had a bad kiln run of Poplar that caused quite a few problems before we caught it.
What I am talking about here is the physics relating to wood movement and equilibrium moisture content. The paint or stain does not prevent moisture absorption or gain, but only slows it down a bit. If things are at risk of cupping, then the wood was not properly dried, or stored improperly somewhere between the kiln and the end use, or both. Wood moves in response to changes in M/C, period. The logic does not pan out. Read Hoadley.
If the relative humidity increases, it will increase uniformly - it is in the air, not just on one side of the jamb. If one is truly concerned about cupping (unsaid "as a result of moisture gain/loss") then one would finish both sides of the jamb equally.
Don't take personal offense at my remarks, I'm just pointing out the difference between science and superstition. Rarely done today, perhaps a major reason why so many things are just plain illogical.
Dave S
It's very logical. Until moisture equilibrium is attained, the rate of moisture absorbtion (or drying) is different for the unfinished side versus the finished side, ergo cupping!
Art
No offense taken. I hope you feel the same. After I wrote all of that I started thinking that I was a little harsh. Sorry!
Just to give you a bit of my background, I built houses in Oregon for many years beginning in 1973, and after that was a finish carpenter working in high end homes here for a long time. I should have said "curious finish carpenter," as I was always trying to figure out the best way to do everything. Not the fastest, the best.
The problem we have in Oregon is that although we grow the best framing lumber in the world, and dry it before we send it elsewhere, our houses are mainly built of green lumber. Some say "pond dried." There is some kiln dried available these days, but it is stored outside in the rain.
So we have a moisture issue on the back side of the unfinished jamb right from the start. It is in the framing.
I would also guess, based on my experience, that most houses have an excess of moisture in the framing lumber even if it was kiln dried. Framing lumber is not dried to 6 - 8% like we try to do with our moldings and millwork, then on top of that, a ton of moisture is introduced into the house during construction, especially the drywall phase and painting phase. Add a bit more if there is a concrete slab. It also rains here inside the house until the roof is installed. The framing lumber sucks it up.
I do think that the back cut in moldings is to keep the molding flat, plus make it actually touch only at the edges when it is nailed.
Thanks for the input!
Hal
http://www.rivercitywoodworks.com
Those back relief cuts are handy,when nailing slightly twisted boards Also on moulding to 'cheat' when nailing to 'wavy' sheet rock walls. Steinmetz
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