Which router bit for hidden spline mortises

Hello, I am in the process of making a mitred corner box with hidden splines, my first attempt with this design.

The lid will be cut off, and the ends of the splines will then be visible on each joint, so the spline needs to be a very neat fit in the mortises to be cut along the length of each side in each of the joints.

Can anybody please advise on which router bit gives a nice clean mortice with a flat square bottom finish and nice clean edges? i.e., a sharp straight bit, spiral upcut or downcut bit? The splines will be either 4mm or 6mm in thickness.

Hi Dengue.

I would suggest a spiral upcut for the job. Very clean face across the "top" of the mortise. CMT have a good range.

Regards,
Rob

What about cutting the slot on your table saw with a ripping blade? The ripping blade leaves a square bottomed slot. Tilt the blade to 45 degrees and cut the slot in the box side, bevel down, using the mitre guide to hold and secure the wood square to the blade.


Paul

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Originally Posted by homesy135

What about cutting the slot on your table saw with a ripping blade?

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thanks for this reply, Paul. The sawblade approach is great for through mortices or slots, but I want to make hidden splines, so you don't see them when the box lid is closed

Quote:

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Originally Posted by Dengue

thanks for this reply, Paul. The sawblade approach is great for through mortices or slots, but I want to make hidden splines, so you don't see them when the box lid is closed

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A fancy box, eh? Fair enough. I was just trying to save you some $$ using the tools you already have. I guess you'll have to make a jig to offer the box side to the router at 45 degrees? Is that what you had in mind?

Quote:

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Originally Posted by homesy135

A fancy box, eh? Fair enough. I was just trying to save you some $$ using the tools you already have. I guess you'll have to make a jig to offer the box side to the router at 45 degrees? Is that what you had in mind?

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Alternatively, cut through mortices for the splines assemble the box and inlay a 1/4 circle of burl or other fancy timber over the exposed spline on the box lid.

Yes Paul, made the jig last weekend, still to post pics, aiming for next week. In the meantime need to order a spiral upcut bit as recommended by LGS above