Thread: Jig for hidden mitre joint splines needed

Hi, could you consider using a biscuit joiner set at 45? and using a series of biscuits instead. Ive done this many times and it works but clamping the corner together can be tricky.

hi Sii, I was reading here that biscuits have the structural strength of Weetbix. They are really only intended to provide help with alignment when assembling a joint.

You can stack the biscuits together to make the join stronger and use the right glue ie cross linked pva or av 515 for solid timber( where flexibility is required) or if using mdf then the yellow mdf pva. i have done this myself many times and know that it forms a strong joint but of course it depends on the application this is suitable for cabinet making but probably not for bigger pieces such as furniture.

thanks Dengy and Sii, your comments and suggestions are very much appreciated.

sii, the thickness of the box side is only 8mm, so I don't have the option for doubling up on biscuits.

I did find something in FWW # 82 that has possibilities, using a small diameter slot cutter like the one Gifkins sell - gives a 4mm slot 5mm deep. Have shown a pic of the jig below.

spline maker.JPG

In a similar vein to your frame mitre cutting jig, build a 45 degree clamp to hold the box side upside down and run a plunge router along a guide with stops at each end.

Making one for a router table would be a bit trickier unless you can make the cutter plunge upwards (I can show you how to make one like this if you have access to a welder); otherwise you would have to build a plungeing jig; doable but complicated and unless you're going to be building boxes forever probably not worth spending the time on.

I know you've jumped on the "biscuits are crap" bandwagon but this kind of joinery is what they excell at. You can always use the cutter to cut a long slot and fit the spline this way.

sorry jill, i didnt mean stack the biscuits on top of each other i meant use more of them at closer spacing ie 100mm centres for 20 size biscuits, but as you say for 8mm thick material im not sure if even a size 0 biscuit will work. You would have to set the biscuiter to zero biscuit size and do a test cut to see if the blade cuts out through the face. im wondering with such thin material if a different joint to a mitre might work better, good luck with it anyway.

I have been able to produce the mitre and insert the slot for some form of biscuit. All completed with only one process setting up the material and routing the angle then the slot all done with the change of template guide and cutters. Produced on my Super Jig Mortice on a Mitre 2.JPG

A slot cutter based unit will leave too long a radius at each end of the spline pocket if you are making a shallow box. Try with a straight cutting bit, this will leave a bit radius curve at each end that can be ignored by using a slightly short spline. I have seen a couple of jig articles/videos to do this but this is the first one that comes to hand and is generally accessible. Had seen before but found it by googling box hidden spline jig. There are a series of videos out there for making a more permanant and larger unit utilising a slot cutter if the box is deep. These are based on this FW article.

A slot cutter based unit will leave too long a radius at each end of the spline pocket

thanks for this reply, malb, I had been thinking along the same lines, so had not progressed much with a jig. Pity I don't have a horizontal router

thanks for the two links, they are definitely food for thought!!

Hi Jill,
This is the kind of spline I was talking about. And the inlay as well. The splines can be easily done on a table saw, or using a hand saw and a couple of guide blocks on each side of the mitre joint. I'll take pics tomorrow of what I mean. These splines are functional, holding the joint together as well as decorative.

Regards,

Rob

Hi again,
If anyone in Townsville has a Leigh FMT jig, they can make those spline pockets and splines in minutes. On the angle and all!

Regards,

Rob

Jill,

Not recommended for the beginner but:

I have cut the splines on boxes the way you suggest with a SCMS set at an angle of 45 degrees. Somewhere on here is a description and pictures of how it was done. Foolishly I used a paddle pop stick as the spline and the grain went the wrong way. The box has held together though- and only with PVA.

Don't try this at home.

Graham