# Spline vs miter lock bit



## Joshh (Sep 16, 2016)

Is there any significant advantage of one against the other:









vs


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## joey502 (Mar 30, 2014)

The splined joint is simple and can add visual appeal. The lock miter bits are frustrating to set up correctly. They will both give you a solid miter joint.


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## pintodeluxe (Sep 12, 2010)

The locking miter offers more surface area for glue. It also locks together quite well, even before the glue is applied. I think it is a better mechanical joint than a spline, so I use it for making hollow legs.

On smaller projects such as a decorative box it probably won't matter much.

One tip if you decide to go the locking miter route… mill both edges of each board the same way. In other words mill the left and right edges of board "A" identically (say milled with the board flat on the router table). Then mill both edges of board "B" referencing the router fence. This way you will only need clamping pressure in one direction during assembly.

I have never had any issues setting up a locking miter bit. A couple test joints and they will look perfect. Once you have it right, make a pair of setup blocks for next time.

Here is a router bit review that may give some additional information…
http://lumberjocks.com/reviews/3503


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## ScottM (Jul 10, 2012)

> The splined joint is simple and can add visual appeal. The lock miter bits are frustrating to set up correctly. They will both give you a solid miter joint.
> 
> - joey502


Ditto. Have never used one of those router bits but everyone I heard from talks about the setup frustrations.


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## Joshh (Sep 16, 2016)

> The locking miter offers more surface area for glue. It also locks together quite well, even before the glue is applied. I think it is a better mechanical joint than a spline, so I use it for making hollow legs.
> 
> - pintodeluxe


It might be two edge sword. The spline is cut across the grain as pictured above so it is very strong . The miter lock for hollow legs is cut along the grain, If you do not glue it well it can just snap off along the length. Would be interesting to if someone tried an experiment breaking the joints.


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## bondogaposis (Dec 18, 2011)

Correctly done w/ a cross grain spline. The splined miter joint is going to be very strong. I really doubt there is much difference in strength between either joint. Perhaps some one will make a test. I do believe the splined miter is easier to set up and can be done on the table saw.


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## Cooler (Feb 3, 2016)

I have a miter lock bit. For just four corners it is a hassle. It seems to take forever to get the depth and fence adjusted for a tight fit.

Its faster to use a dovetail jig if you have one.

I don't make splines either. I just throw in a couple biscuits. But if it needs to be strong, then it is a dovetail.

I have an old router that I leave setup for the dovetail and never use it for anything else. So the dovetail is quick and easy.


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## splintergroup (Jan 20, 2015)

The miter lock has an additional advantage that the 45 degree angle it cuts into the board ends is *perfect* (at least it should be!). This makes for a gap free corner joint. Down sides are the setup times and expense of the bit.

Splines are quick and simple. If the grain is oriented correctly (as with Jose's top photo), the joint is quite secure.


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## Joshh (Sep 16, 2016)

> The miter lock has an additional advantage that the 45 degree angle it cuts into the board ends is *perfect* (at least it should be!). This makes for a gap free corner joint. Down sides are the setup times and expense of the bit.
> 
> Splines are quick and simple. If the grain is oriented correctly (as with Jose s top photo), the joint is quite secure.
> 
> - splintergroup


One has to be very deliberate to get a gap on a 3/4" stock because of imprecise angle. For example 0.2 degree discrepancy (which is sloppy) on one side is equal to 0.0035" gap while ideal gap for Titebond glue is 0.006" to 0.009".


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## splintergroup (Jan 20, 2015)

> One has to be very deliberate to get a gap on a 3/4" stock because of imprecise angle. For example 0.2 degree discrepancy (which is sloppy) on one side is equal to 0.0035" gap while ideal gap for Titebond glue is 0.006" to 0.009".
> 
> - JoséMário


True, but many other things limit miter angle accuracy beyond the resolution of the miter gauge, or even the accuracy of any device used to set a 45 degree blade angle. That 0.2 degree accuracy isn't always a given.

Of course for myself I will tweak the settings after trying on scrap first 8^)

Your lower photo (the lock-miter) shows how some bits leave a small gap on the fingers, presumably for glue squeeze out. As with a splined miter, this may or may not be acceptable depending on ones tolerance for any glue gap lines showing up on the finished part.

This can be seen on a hollow leg I made for a table. The joint is hidden so it's ok, but it would not be acceptable if visible.


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## ChefHDAN (Aug 7, 2010)

> One tip if you decide to go the locking miter route… mill both edges of each board the same way. In other words mill the left and right edges of board "A" identically (say milled with the board flat on the router table). Then mill both edges of board "B" referencing the router fence. This way you will only need clamping pressure in one direction during assembly.
> - pintodeluxe


Pinto is on the money with this tip, my first project with the lock mitre bit was this set of candle stands and i put a different profile on each side which made it near impossible to clamp up.

I've yet to use the bit again though because I need to build a tall vertical sled to clamp narrow boards to to be able to run the standing profile. When looking at the bit in the catalogs it seemed like it would be a magic bullet for miters but the small stock use does require some jigging


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