# Kerf Cut Splines on Butt Joints?



## ThatShaneDavis (Apr 4, 2019)

I'll attach some photos of the crescent- shaped shelf I'm doing. For all these endgrain joints at different angles, my friend suggested cutting kerfs down the backside and gluing in splines. I figure I can find a sled to do so with a table saw, but I am new to this. So does it sound / look like a good option? It makes sense in my head!

Fig. 1: top view. Not all together yet, but I only goofed up one pair of mitre cuts so far!
Fig. 2: back view of two pieces. At a 30° angle - I think. I am dusting off high school geometry skills here and my head hurts!


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## Steve Neul (Sep 2, 2011)

You could spline the joints by running the ends of the pieces through a table saw with the blade on an angle.


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## ThatShaneDavis (Apr 4, 2019)

Steve, I considered that as well. Would that give a stronger glue joint, do you think? This isn't a heavy load-bearing shelf, but I certainly want integrity.


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## FrankC (Aug 24, 2012)

Splined miters would give you your integrity, if your pieces are relatively short you can use a carrier to hold them vertically with the cut end on the table.


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## BernieL (Oct 28, 2011)

I'm not sure how strong you need this shelf but the above advise is good. I often assemble picture frames with no splines and the glue joints are strong enough if done right. It involves a 3 step process. First I mix glue and water 50/50 solution. I apply a generous amount of this watered down glue too the miter cuts without drowning the surface. Within 1 too 2 minutes, the solution become tacky (keep feeling and don't let it dry). At that moment, I apply my 100% glue (no watered down solution) and clamp the pieces.
What this does is it prepares your surfaces like sizing does to a wall before applying wallpaper or primer paint does to wood before applying a final paint. Do this and also apply glue to the contact surfaces with the shelf and you should be fine.


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## FrankC (Aug 24, 2012)

This is a fast and dirty tenoning jig, just clamp your mitered parts to it and set your blade at an angle to cut the slot for the spline. To set the blade lay the mitered part on the table and set the blade to the angle of the cut. Make the slots first and then cut the width of the spline to fit.


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## hawkeye10 (Feb 18, 2015)

ThatShaneDavis said:


> I'll attach some photos of the crescent- shaped shelf I'm doing. For all these endgrain joints at different angles, my friend suggested cutting kerfs down the backside and gluing in splines. I figure I can find a sled to do so with a table saw, but I am new to this. So does it sound / look like a good option? It makes sense in my head!
> 
> Fig. 1: top view. Not all together yet, but I only goofed up one pair of mitre cuts so far!
> Fig. 2: back view of two pieces. At a 30° angle - I think. I am dusting off high school geometry skills here and my head hurts!


Shane, I put 3/4"x3/4" MDF splines in these joints. I think that is enough for something that is going to hang on the wall.


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## hawkeye10 (Feb 18, 2015)

FrankC said:


> This is a fast and dirty tenoning jig, just clamp your mitered parts to it and set your blade at an angle to cut the slot for the spline. To set the blade lay the mitered part on the table and set the blade to the angle of the cut. Make the slots first and then cut the width of the spline to fit.
> https://youtu.be/opaHl3PBxJA


Frank, here is my version of that jig. It's double-sided so I can do more with it. I can make raised panels, tenons, splines in boxes and picture frames.


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## CharleyL (Jan 13, 2019)

If you go with splines as shown in the photo in post #2, look carefully at the grain direction of the spline. For joint strength, the spline needs it's grain running across it's width, not end to end (look closely at grain direction in the picture). If you make these splines with end to end grain, the joint won't be much stronger than if you just glued the two mitered pieces together without a spline. For strength, the grain direction in the spline needs to run across the narrow width of the spline. 

I use my tenon jig on my table saw to make these. When I set the jig up I set it so the resulting spline is the distance between the jig and the saw blade. The donor board is then stood up on end and clamped in the tenon jig as you would for cutting a tenon and then run it through the saw. I can then flip the board over and make an identical thickness spline from the other face of the board. If I need more splines, I repeat the process on the other end of the donor board. Then I go to my miter saw and set a stop to determine the width of the spline. Once set carefully (should be 2X the depth of the spline slots in the mitered joint) I then place the donor board against the stop and cut the splines free. The tenon between these two splines gets cut off and becomes waste. If I'm making additional splines I hen swap the ends of the donor board and cut the two more splines from that end. This results in 2 or 4 perfect thickness splines with their grain running across the narrow width of the splines. If the length of these splines isn't enough for the full length of the mitered spline slots, or if the cross grain spline should break, you can still use the pieces end to end to fill the joint and the joint will still be very strong if glued properly. 

Actually, biscuit joints can also be used as splines for mitered joints. With both the cross grained splines or the biscuits, I like to locate them closer to the inside of the resulting corner, rather than putting them in the center of the joint. Having more material left on the outside of the corner further reduces the chances of the corner breaking and keeps you from cutting the biscuit or spline slot too deep and coming too close to the outer surface of the corner. 

Charley


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## FrankC (Aug 24, 2012)

hawkeye10 said:


> Frank, here is my version of that jig. It's double-sided so I can do more with it. I can make raised panels, tenons, splines in boxes and picture frames.


That is the 'Deluxe" model, looks very versatile.


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