do splines help prevent mitres from opening up over time?

[thetyreman]

question:

do splines help prevent mitres from opening up over time?

I've just made a picture frame and wondering if it's worth adding splines, I like the way it looks without splines but wonder about movement longterm, nobody seems to be able to answer the question of whether splines actually help prevent movement, but there is an obvious strength benefit.

regards,

Tyreman

 

[Cabinetman]

Hi, i’ve done a few picture frames over the years, never really had a problem, the only one that ever moved was much wider than normal, and thinking about the way wood moves more across the grain than along it, you can see why a frame made from wide stock would open up in the outside corners.
So if the frame is only a couple of inches wide don’t worry, if it’s wider, would a spline be able to stop the movement? Something has to give somewhere and I suspect that a wide spline well fitted might cause the frame to split. It’s an interesting question. I look forward to everybody else’s years of experience Ian

 

[sunnybob]

Essentially, a spline is a cross brace. It greatly increases the glue area. Two or three splines would more than double the joint face.
The wood grain of the spline is across the grain of the frame, so I dont see how it can not be a strengthener.
Plus, it can make a plain joint look interesting. Win win.
Unless.... the frame needs to be plain to stop the eye being attracted away from the content. But even then you could use the same wood and almost lose it in the finishing.

 

[Doug B]

If you were to cut a mitre & incorporate a dowel or biscuit in the joint it would definitely be considered to strengthen the joint & by the same token help reduce movement.
A spline is doing a similar job to the dowel or biscuit so has to be adding strength, that said no type of joint can completely eradicate the chance of movement in the wood that’s more to do with the law of sod.

 

[Eshmiel]

The splines in a mitre can be hidden or not. They can be for decoration as well as strength. The hidden ones are obviously for strength. Mind, so are the show-splines.

Smaller mitre joints in a stable environment (where only small changes occur in humidity / moisture content of the wood) won't open up of their own accord. Larger ones in a less stable environment will. Even a small mitre will open in wildly varying humidity. A well-oriented spline may prevent the mitre joint opening but the stress of the wood's change in dimensions with a significant change in moisture content will have to exhibit somehow, as another poster mentioned. It might just twist the frame a bit and stay closed i' the mitres; or it might crack elsewhere in the frame. I once saw a pine-framed picture in a holiday lodge gone damp over winter end up looking like the pic had been framed in large square spaghetti!

Even a small crack in an un-splined mitre joint held only with glue can significantly weaken the whole frame. Gravity might eventually amplify that crack if the frame hangs on a wall. Crash! (Usually in the middle of the night). Best to put splines in, hidden or otherwise. Other solutions are possible in the back of the frame, out of sight - plywood plates across the mitred corners; those right angle push-in picture framing "nails" across the mitre faces (a sort of metal spline).

Eshmiel

 

[custard]

question:

do splines help prevent mitres from opening up over time?

Yes, they do.

I try very hard to incorporate splines, or something similar, in all my mitre joints. On picture frames/mirrors, nothing looks worse than the hairline gap that can open up over time, it generally gets filled with household grime, normal dusting/wiping will pack any dust into the gap making it look even worse. Even a flawless mitre is subject to the joint differentially swelling and shrinking with seasonal movements.

Biscuits work particularly well for mitres, the rugby ball shape gets support right out to the edges of the joint where it's needed most, but any spline will be a big help.

Another trick is to pre coat the mating faces of a mitre with PVA that's been diluted with 10% water. This acts as a "size" and gives a far better end grain bond for the final gluing, I also know makers who use Pu glue for this specific job as apparently it delivers a particularly good end grain bond.

 

[marcros]

Another trick is to pre coat the mating faces of a mitre with PVA that's been diluted with 10% water. This acts as a "size" and gives a far better end grain bond for the final gluing, I also know makers who use Pu glue for this specific job as apparently it delivers a particularly good end grain bond.

My wife told me that size doesn't matter.

Then the mitre joint failed.

 

[thetyreman]

thanks, that definitely answers the question, splines it is then.

 

[Argus]

This is the way they did it before biscuits came in.



Done properly, it's rock solid. This is done on an ordinary 45 deg mitre, but it is easy to adapt the technique to picture frames and you don't see any splines on the outside.

 

[TheTiddles]

As said, yes.
Splines at the outside corner can look nice too, a loose tongue can add hugely to the strength but needs to be planned in better. Biscuits are great because they don’t go right through the joint and rebate.
Wood movement is why I prefer to veneer picture frames and use solid edges

Aidan

 

[thetyreman]

here's the joint in case anyone was wondering, also posted in the show us what you made forum: