*update* tips for consistent repeatable double bridle joint

[mound]

Hi all -

Does anybody have a good foolproof way to make these double-bridle joint corners? I need to make two of these "frames" and they both need to be identical.  Just did some trial runs with my delta tenon jig and table-saw on scraps, results were just OK and were based on lines I marked with a gauge and lots of sneaking up on things. But it seems like there should be a consistent order of operations to take the marking and guesswork out of it to yield identical results, but I'm having trouble wrapping my head around it. The final parts are 1-7/8" square Wenge, and I can't mess up my actual stock 'cause of limited supply. 

   


edit: wondering if maybe ganging the parts together and mounting them on my cross-cut sled with essentially a box-joint type jig might work? Or is that asking for trouble?

   

Thanks!

[barryvabeach]

I have done a single bridle joint , and while there is a bit of head scratching, it is very repeatable, and should work with a double bridle as well, though twice as much head scratching. 

 First, you need to make a shim that is wide as your stock  and as tall  as you jig, with a thickness that is exactly the width of the kerf.  By exactly ,  I mean exactly, though if it is a few thousands thin, you can add some tape till you get it right.   One you think you have it,  set up the jig to take a shoulder cut on a piece of scrap, then put the shim up against the jig, and run another piece of scrap.  Cut off the part from the second piece and test the fit of the two pieces as a lap joint.  If it is not perfect, then you need to make another piece of shim and use a plane , or tape , to get it so that when you do the two cuts, one with the shim and one without, the shim moves the second piece exactly the thickness of the kerf.

To cut your joints,  label a face side off all the pieces, then label each of the ones that will have a shoulder cut as A and the opposing as B.   Put the shim in place, then take each of the A pieces,   face side to the jig, and run both ends through the saw.  Without changing anything, take out the shim and run the same cut on all the B sides.   For the next run,  add a spacer ( the thickness of each finger ) and the shim and run all the B pieces through, the take out the shim, but not the spacer, and run all the A pieces.    Repeat the process by adding additional spacers for the thickness of the fingers, and you are done.
I don't use spacers, since I am using using a bridle joint for strength, not appearance, such as a stretcher for a canvas, so I don't use a spacer, I just move the fence that my jig runs against.

The shim, in effect, is allowing to cut a line that has 0 thickness, so the only hard part for me is trying to remember which pieces need the shim, and which don't.  BTW,  the suggestions above are based on looking at your diagram,  for all I know I have it backwards,  so think it through before you start cutting, and you may want to make a few test cuts as well to make sure you have it right.  Once you do, each joint will fit exactly the same way,  it is just a matter of remembering which ones you add the shim and which ones you don't.

[GeeDub]

Tenon jig or bandsaw using spacers as opposed to using jig or fence adjustments.  FWW members can watch Brian Boggs show you how.

[DaveR1]

A box joint type jig might work for that but if your pieces aren't all exactly the right size, you'll end up with cumulative error that would be problematic.

I can think of a shop-made tenon jig designed by a Brit that would make this job easy although I'm guessing you wouldn't be wanting to build a tenon jig for your table saw.

If you're going to gang cut them, I would be them one behind the next instead of side by side.

If I were doing this in my shop I would do it on the Router Boss with pairs of parts clamped up. Easy to make the cuts and increment the router position. I understand you probably don't have a Router Boss. Just sayin'.

[Phil Thien]

I've watched Mathias @ Woodgears.ca make them with his geae-driven table saw sled. I think the precision required for consistency is "up there."

[mound]

Thanks all. Yah I don't have any crazy jigs though I could see their utility.

I suppose a simple approach with spacers and shims matched to the size of the finger and saw kerf accordingly should do the trick either with a tenon jig on the tablesaw or on the bandsaw.

[DaveR1]

I sent you a PM with a link to that tenon jig I referred to. I expect you'd get good mileage out of it you had it.

[mound]

I sent you a PM with a link to that tenon jig I referred to. I expect you'd get good mileage out of it you had it.

Thanks Dave!


A lot of these style tablesaw jigs require a bessy style fence to ride squarely on.
That's one thing I don't like about my Unifence, you can't make jigs and such that ride on it like that.

[DaveR1]

Thanks Dave!


A lot of these style tablesaw jigs require a bessy style fence to ride squarely on.
That's one thing I don't like about my Unifence, you can't make jigs and such that ride on it like that.

There are ways to manage that, though. I have a TS-III on my tablesaw. With the T-square arrangement you can't make a thing to complete encase the fence but it's still easy enough to make jigs that can slide along on it.

[mound]

Thanks all for the tips! The "shim exactly as wide as your kerf" was the "Aha!" moment for me when I tried it out.

With the shim and another spacer 3/8" for the fingers and my tenon jig on the TS, I was able to batch everything out rather quickly (I still marked layout lines everywhere just so as to not get confused).

The key was the shim exactly a kerf width.. After cutting everything, some 80 grit sandpaper glued to a piece of 1/4" ply, 20-30 seconds of sanding each tenon face and they slide together perfectly. 

I like it when things work!