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Mods 20

Bob Gamble's Spline Cutting Jig

Bob has made a superb box from spalted beech and used splines on the mitred corners. He has sent us some shots of his simple jig to hold the box in order to machine the spline slots.

finished Here is the finished box in all its splendour!
The splines are the contrasting inserts in each corner. They are normally just glued in and then planed flush with the box sides before finishing.

The splines are 4mm wide, the box measures 255mm long, 140mm wide and 82mm high.

Bob made up the jig from planed softwood. The backboard could be plywood and can be as long as will fit in the clamps. The wood battens are just screwed on as can be seen in the photo.
Remember to keeps screws well clear of the cutting area and set the router to the correct plunge depth!
Jig  I guess that the battens must be less depth than the box sides so that the top fixing board will securely hold the box. Just pass the correct diameter router bit through the corner of the box. It appears that Bob is using a standard WoodRat bit but I think a spiral bit would be best if you have one. He doesn't say what system he used but I suspect he rotated the box and cut each corner before moving the router to the next spline position just to ensure each corner matches.
I used a large G-cramp to hold the box against the battens on my jig.
The splines all glued in. When the glue has dried then they are cut off and planed flush with the sides. They always look best when in a contrasting wood. Splines
Close_up The finished joint. They look good don't they!?
Here is a joint I made using a very similar jig on the 'Rat.
Its a fun joint because people scratch their heads on how it is done.         A double dovetail?
Simple when you know how! Use a dovetail bit to cut the spline slot then cut a double tapered matching spline to pass through the joint. Glue and trim to get the opposite result. Easy peasy!

To make the spline, form it on the edge (for the long grain) of a board as if you were making a sliding dovetail for a shelf etc. Cut the dovetail strip off the edge of the board to leave you with a tapered spline to match the slot.
Fine dovetails can look really good but require more care.

Thanks for sharing with us Bob.

Feedback from Bob:-

"I used a good quality solid carbide bit to cut the slots (to minimise tearout.) The jig was indeed slightly lower than the height of the box to allow the two screws to pinch the box. Unfortunately I don't think a box of larger dimensions would fit this jig. If you look at the second photo you will see that the jig is offset to allow the length of the box to pass under the fixed jaw which means the box must be turned over to cut the other two corners - careful marking out is therefore critical with a "large" box."

Now folks this is such a quick and simple jig to make I would really like to see some photos of your spline joints. Just make up four sides and apply your version of a spline and email it to me here. Please place "spline" or "WoodRat" in the subject line to pull it out of the spam traps

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