Mitered Versus Cope and Stick Door Joinery

A customer's red herring about "strength" of mitered versus square door joinery leads to a discussion of the pros and cons of different door construction joints from the cabinetmaker's point of view.June 7, 2011

I have a customer who is moving here from the west coast and building a new home. A salesman in CA told him mitered doors were superior to stile and rail. He is an engineer and is certain this is true. I have always assumed mitered doors were not as strong. Am I wrong? Anybody know of any documentation I could point him towards?

Forum Responses
(Cabinetmaking Forum)
From contributor J:
Since we are getting technical here, both doors have stiles and rails. I think what you are asking is which is stronger, a cope and stick door or a mitered one. So this salesman "engineer" is an engineer because he knows how to use CAD software, or because he holds the mechanical engineering degree? I would say him being an engineer is irrelevant.

The strength of a door in general has a lot to do with how well it was made and not necessarily which type of joinery style was used. If someone uses an inadequate amount of glue or creates joints that are too loose, I think the results are obvious. But if you built two very good doors, mitered and C&S, both the same type of wood, I would tend to think it would depend on the type of wood used for the spline/biscuit in the mitered door.

I prefer C&S doors any day over mitered doors. Mitered doors aren't as authentic and are indicative of cheaper euro tomato box cabinetry. They have no place in higher end beaded inset cabinetry. But that's my opinion. In terms of mechanics I bet they are pretty close in strength, but like I said I think it has a lot to do with species of wood and the quality of construction.

From the original questioner:
Let me clarify. The customer is the engineer, not the salesman. I mention it more as a stereotypical reference in that it will be difficult to change his mind without some evidence or documentation. He is making the design decisions with minimal input from his wife. Initially he wanted arch top doors on both base and uppers which I explained could not be done if he wanted the "superior" mitered door. I also told him I would only stain mitered doors, no paint or opaque finishes. So for comparison sake, the debate would not be between two different species but between two different construction styles. The latest round of drawings, he has changed the door style in several rooms from cope and stick to mitered. I am concerned that he is sacrificing what he would really prefer design wise based on some faulty information. My source for mitered doors is also more expensive than my source for cope and stick.

From contributor A:

A salesman from Unique told me that mitered doors with finger joint construction make for a stronger door (as opposed to cope and stick). He had no reason to suggest one over the other, as they make machines for both.

From contributor L:
I imagine in a strength test they would be about the same. But a miter door can be made more ornate without requiring moulding be nailed on. We typically charge more for miter frame doors than a 9 piece door.

From contributor C:
Ask your door manufacturer for info. How are the mitered doors put together? With a floating tenon 90 degrees to the joint/true tenon at 45 degrees to joint? Does the C&S have a mortise/tenon? What kind/how thick/wide?

I think miters tend to have a chance to open slightly over time. I am not a wood tech specialist, but I prefer the C&S. Especially for opaque finishes.

From contributor M:
The strength is irrelevant. As mentioned, if they are properly made, both will last. It comes down to design. I have a lot of clients that prefer the look of a mitered door. Cleaner lines, no endgrain, and they look nicer on European style frameless cabinets. For the more traditional ornate doors, we use C&S, and for arched top doors, I would really not want to do mitered (although it would be just as easy to do either way). I offer both and I do not even bother to explain to the client the difference. They simply tend to prefer the more contemporary styling of the mitered doors.

From contributor D:
The strength of a joint is relative to the area of contact surface in the joint, the orientation of the grain in the joint, the species and the size of the components. Contact area is by far the most important factor, hence the use of a true mortise and tenon joint for strength. Miter doors do not allow such joinery, for the most part. A cope and stick mortised joint will also survive seasonal humidity cycling much better than a miter joint. Beyond that, is the falling apart of cabinet doors some national problem I am unaware of? I have never had a door fail or fall apart.

From contributor M:
Mitered gives you many more styles to work with. I love mitered doors because I love the look of a heavily profiled 3" wide mitered door frame. You can only get so creative with C&S styles without adding expensive applied molding, which you can still do to a mitered door, but usually you can incorporate it into the profile. I feel most people that don't like mitered doors think of cheap doors with biscuits or even senclamps or such holding them from the backside - they open up, aren't aligned properly, look cheap, and are exactly that. I've dissected a mitered door from my supplier and it was a true solid tenon through the whole profile, I'm guessing cut by one of those CNC miter router whatever-you-call-it machines that mortises one side and tenons the other through the entire size of the profile that allows it. The profiles are always lined up perfectly and joints closed completely. It's all in the quality of the build.

From contributor O:
I have to agree with contributor J. Miter doors just look cheap. From a mechanical standpoint, when I worked as a fine cabinet maker, I was taught that a glue joint's strength is all in the surface area of the finished joint. PVA glues will not bond end grain, so only the face and edge grain will hold the joint, hence why mortises are so strong. If you use a common C&S, then only the small tenon is holding the joint. If the miter is using a tongue and groove, it will be significantly stronger than a miter with a butt joint. In my opinion, it gets down to the design of the joint, and the face/edge area glued. From an aesthetics point of view, miters look cheap.

From contributor L:
Aesthetics is in the eye of the beholder. Wood movement will be slightly more of an issue with miters because the miter is longer than the cope joint. Well made, either is perfectly strong enough for the application. The machines that make the integral tenon and mortise are expensive and not often seen in the small shop. By comparison, shapers are cheap. Does that affect cabinetmaker's preferences?

From contributor I:
Contributor L hit the nail on the head. Another point, specifically addressing the comment that they have no place in beaded inset cabinetry... If a customer wants a raised panel door with beaded molding on the outside and inside of the frame - is a 13 piece cope and stick door higher quality than a 5 piece mitered door (with integral tenon) that matches the profile exactly? I would say no - applied molding is more delicate and there are way more seams to show over time if they ever go, and the cope and stick would cost twice as much if not more.

I think the fact that most lack the ability to produce a high quality mitered door in the same timeframe they can a cope and stick, or even at all, has a lot to do with many anti-miter opinions.

I used to think cheap when I heard mitered door, but since I've been in business the last few years, cope and stick has been my standard, low cost door. Mitered and applied molding tend to be higher end; most end up being mitered simply for the look they can't get with cope and stick and the cost of applied molding doors making them an attractive alternative.

The more detailed doors are harder on the finisher too... And regardless if they hold up over time, if not built well and the profiles don't line up or detail is lost in heavy sanding, this could lead to the feeling of a cheaper or inferior product.

From contributor T:
I totally agree that failing doors must be some kind of national emergency we haven't heard about. Since he's an engineer, ask him if a suspension bridge is superior over other designs in any circumstance. He'll likely say any known bridge design will do the job - it's all a matter of cost and what the end product looks like. If strength of the joints is such a big deal to him, I'd say the weak link is probably going to be the type and brand of hinge used. Now let's argue over that one for a while!

From contributor E:

I have two customers who have had issues with miter doors. Mostly occurs on small doors, and it is due to an abnormally high swing in humidity, but somehow it's still my fault. Joints open up about 1/8" at the outside edge. Never had a problem with a cope and stick door.

From contributor S:
I have copies of a few different tests performed by an independent party. It breaks down most of the joinery methods used in doors, drawers, frames and boxes. It does show that a cope and stick is among the weakest of door joinery methods.

From contributor N:
If a miter door looks cheap to you, you have been looking at cheap mitered doors. They do span the full range from cheap metal insert to butt joint, all the way up to a full mortise/tenon from a Balestrini machine.

A well built S&C door and a well built miter door will both have suitable strength for the application. Under fluctuating humidity, the miter will be more noticeable as the miter opens up, whereas the S&C will make a little step at the top and bottom of the door where the rail and stile meet, being much less noticeable when viewing the door face-on. Generally a good miter door needs a few more construction steps, and is therefore more expensive than a comparable S&C door.

From contributor I:
Why is strength an issue? Are you making it an issue because you want to use C&S doors? If the customer wants mitered doors, I say give him mitered doors. The issue of whether one is stronger over the other is really irrelevant. As contractors we have a duty to express our opinions and advise the customer, but after doing so, the decision making is ultimately theirs.

From the original questioner:
Mitred doors were not his original choice. He changed his mind based on information he received that may or may not be true or relevant. Strength is an issue for this customer. My point is that he is using strength of door construction as criteria for deciding what door style he wants. A criteria that I believe is irrelevant. It is my job to point out to a customer that he is making a design decision based on irrelevant criteria. I don't care what door style he uses as long as doesn't want me to paint the mitred doors. The mitred doors are more expensive - he will be paying more for doors that he perceives to be stronger. That may not be true. I have an obligation to educate that customer. I will present him with the facts as I understand them. That is, there is no appreciable difference in strength between the two door styles - the likelihood of either door failing is minimal. So make your choice based on design and cost, not strength of door construction.

From contributor I:
I misunderstood who was making strength an issue - my apologies. I see where you're coming from. I've had many customers use third party information and it can be quite a headache for the contractor, especially when they don't know you or haven't seen your work.

As a cabinetmaker of 30+ years, one who orders doors from a custom door manufacturer here in LA, I can safely say that I never had an issue with breakage from a mitered joint. This is not to say I haven't seen any. I've seen plenty from poorly manufactured doors with inadequate joints, joints that are destined to fail. When you see enough mitered doors falling apart, word gets around and many will assume that all mitered door joints are bad. Not true.

The issue of strength really comes down to what type of joint is used at the miter and how well that joint is assembled. I like both C&S and mitered. They each have their own application. The cabinets I've made for myself (sparing no expense) I used mitered doors, mainly because I like a lot of detail in my doors, whereas with C&S you're limited in this department.