Kapex Mitre or Cope

[Rick Christopherson]

Ken, I understand that this is a passionate topic for you. However, I am not trying convince you or anyone else whether or not they should cope a joint. I'm simply pointing out that the reasons for coping a joint are not the reasons that are most frequently cited. Knowing and understanding the true reasons for what we do is what empowers the woodworker to properly gauge for themselves when one method should be used over another.

The concept isn't unique to the topic of coping. There are a lot of woodworking "rules" that are frequently repeated long after the "reason" for the rule is forgotten. Once that happens, we end up with these Cardinal Rules that can never be broken, until you once again think critically about the reasons behind them and rediscover when they should and should not apply. Knowledge is the sharpest tool we have in the workshop.

 

[Gary Katz]

Most of the wood we use for trim these days isn't edge grain, it's flat sawn...just to keep the terminology simple. And most of the trim we use today for paint grade applications is soft wood. Flat sawn soft wood will move 1% for every 4% change in moisture content--again, this is taken from Hoadley's book, but you can read the same chart everywhere (http://www.thisiscarpentry.com/2010/09/03/moisture-content-wood-movement/).

So, if you install 4 1/2" crown at 12% MC it will eventually dry down to about 8% MC and shrink about 1/16". The two pieces of wood, installed at a spring angle, no longer measure 4 1/2 but now 4 7/16"  Between two pieces of crown, mitered at an snide corner, that's 1/8". But if the corner is coped, it remains tight.

So wood movement is also a good reason to cope inside corners.
Gary

 

[jmbfestool]

Coping is quicker easier and and much better job in the end!

1. If you mitre a joint for an internal corner for baseboard then you have to pieces of timber which shrink towards the wall like Dean said so opening up the joint on internal mitres.  With Coping its only one piece shrinking away from the coped piece as the coped piece doesn't shrink in its length like Rick mentioned.  So your going to get less of a gap when the wood shrinks.

2. With an internal mitre not only do you have to be the exact length also need to make sure your angle is exact your piece of base board is is already fitted is dead plumb unless you want to start doing compound cuts on internal corners.  Also like mentioned like most walls your skirting can kick back so opening the joint at the bottom

but this also makes it hard to close the joint up so you end up needing to put packers behind the skirting at the bottom or build it out so it pushes your skirting joint up at the bottom.   Like mentioned also if you cant apply pressure your glue joint wont hold and will fail.

3. If your skirting has a slight cup in it this will affect your joint massively with an internal mitre as well as if der is a slight variation in thickness in timber it will show up in the joint.

4. Fixing will make your joint worse as your all happy you got your joint looking good! You then screw some screws into the skirting which then ends up opening your joint open as with external mitres its the opposite it pulls your joint up.

Coping is the best way  you will get a better joint and its far more likely to stay looking good later on!    Their is no good reason AT ALL to do an internal mitre  the only reason you would do internal if the client insisted on it but your would have to charge more for doing it and let him/her know it aint the best way to do it.

JMB

 

[Eli]

One more reason to cope inside joints......

I was hired to trim out a six unit apartment building. The new owner had decided to divide the largest bedroom into two, and they had framed and drywalled right over the old base on both sides of the new wall.  [big grin]

 

[Alan m]

One more reason to cope inside joints......

I was hired to trim out a six unit apartment building. The new owner had decided to divide the largest bedroom into two, and they had framed and drywalled right over the old base on both sides of the new wall.  [big grin]

in a few years someone is going to want to replace that  baseboard and wont know whats going on. they will leave a few choice words about you [wink]

 

[ApgarConstruction]

This debate again...........

COPE!!!!

  the only inside miters I do on crown, are when it's pre-finished for a kitchen and we can pre-assembly the pieces with glue/clamps and 23 ga pins.

 

[builderbob]

This debate again...........

COPE!!!!

  the only inside miters I do on crown, are when it's pre-finished for a kitchen and we can pre-assembly the pieces with glue/clamps and 23 ga pins.

+1 on everything Apgar said!  I always cope everything with the exception of prefinished cab crown...which, as long as I have the appropriate marker, I mark the unfinished cut edges, then glue and pin. I see a lot of prefinished moldings come slightly off in milling  and there isn't much you can do to change that, but the marker helps with any inconsistencies!

Bob

 

[Eli]

One more reason to cope inside joints......

I was hired to trim out a six unit apartment building. The new owner had decided to divide the largest bedroom into two, and they had framed and drywalled right over the old base on both sides of the new wall.  [big grin]

in a few years someone is going to want to replace that  baseboard and wont know whats going on. they will leave a few choice words about you [wink]

Ah, but what if the next owner wants to go from two bedrooms back to one? Then the choice words might be complimentary.

The past is history, the future mystery, right now, where we are, is a gift. That is why it is called the present.

There's no way to count a win when you're coping a piece of MDF base into original hardwood. I'd rather leave the hardwood alone, even if it runs through the new wall.

 

[jmbfestool]

Just a quick sketch up to help people like Rick Christopherson to understand which way wood shrinks in the UK as Dean Social tried to explain but he was clearly miss understood

I have put arrows showing direction of shrinkage which affect the joints

As you can see just like Dean was saying you have two shrinkage from both skirting boards (baseboards)   but with the cope the joint is only affected by one baseboard shrinkage as the shrinkage in length is minimal

With the Mitre both baseboards shrinking affects the joint creating a much larger gap and like Dean said this tightens up on an external mitre but with and internal mitre it opens up the front of the joint.   As wood will always shrink towards the side which its fixed too think about it Rick Christopherson or are you going to tell me it will shrink away from the wall so pulling its self away from the glue/fixings I very much doubt that.

[attachimg=#]

JMB

 

[Ken Nagrod]

JMB,

Why are you referring to Dean as miss understood. I don't know his last name, but you could reference him as mr. Social. And stop pickin' on Rick.  [tongue]

 

[Deansocial]

JMB,

Why are you referring to Dean as miss understood. I don't know his last name, but you could reference him as mr. Social. And stop pickin' on Rick.  [tongue]

I'm always misunderstood

 

[jmbfestool]

JMB,

Why are you referring to Dean as miss understood. I don't know his last name, but you could reference him as mr. Social. And stop pickin' on Rick.  [tongue]

I'm always misunderstood

Very True! Sad man!

 

[Rick Christopherson]

JMB, what your discussion is overlooking is the magnitude of the change (see my previous discussion). The expansion/contraction rate across the thickness of the board going from 12% to 8% MC, is on the order of 0.005" That's approximately the thickness of a sheet of paper, and applicable only when you install improperly dried materials for the environment. The seasonal change is even smaller, and down on the order of 0.001"

 

[Deansocial]

JMB, what your discussion is overlooking is the magnitude of the change (see my previous discussion). The expansion/contraction rate across the thickness of the board going from 12% to 8% MC, is on the order of 0.005" That's approximately the thickness of a sheet of paper, and applicable only when you install improperly dried materials for the environment. The seasonal change is even smaller, and down on the order of 0.001"

i glad for you that you live in an ideal world were every thing is fitted at the correct MC.

 

[Ken Nagrod]

I'm going back to my environmentally controlled bubble. Call me when it's snack time.

 

[jmbfestool]

I'm going back to my environmentally controlled bubble. Call me when it's snack time.

lol!  Haahaaa!  Stop pickin' on Rick Ken!

 

[jmbfestool]

JMB, what your discussion is overlooking is the magnitude of the change (see my previous discussion). The expansion/contraction rate across the thickness of the board going from 12% to 8% MC, is on the order of 0.005" That's approximately the thickness of a sheet of paper, and applicable only when you install improperly dried materials for the environment. The seasonal change is even smaller, and down on the order of 0.001"

Yes I Read your discussion   but like many people mention thats in perfect conditions.   Any way so with my Cope ill have what you say a paper thickness gap due to the 0.005 shrinkage but you will have 2 paper thickness gap with a mitre joint which is enough to break the glue joint aswell as being a bigger gap than my cope gap a gap is a gap and my cope gap is smaller than your mitre gap  [tongue] [tongue] [tongue] 

 

[Rick Christopherson]

Yes I Read your discussion   but like many people mention thats in perfect conditions.  

So you consider a 4% drop in moisture content to be "ideal"? You might want to stop buying your materials off the back of Guido's pickup truck in those dark alleys.  [tongue]

But that's not really the point. You and others have claimed that seasonal change is going to significantly impact the thickness of the material, when in reality it only results in 0.001" change, or worst-case (wet to dry) of only 0.005".

 

[Alan m]

come on guys (not you ashley) stop nit picking. at the end of the day we are all certain that for one reason or another a mitered internal corner shows a larger gap than a coped one.
i personally think that it is a combination of a lot of things causing it
structure moving
wood drying out
structure drying out
not secured to the wall strong enough
gaps behind the skirting (base board)
warping wood
wood grown too fast

 

[Ken Nagrod]

Alan,

You left out termites that like to attack corners also known as mitermites. Most people just caulk them which leaves them in suspended animation.