Hi there!
I am currently in the process of starting a limited production run of speakers for which I will be using CNC machining to cut the panels and provide driver flush mounting. The cabinet is 16" wide, 46" tall and triangular in shape. All three panels are identical.
The current design uses 9x19 mm grooves in a 18mm panel, running the entire panel width - the 19mm brace slides in place, then glued to fit. This is making the panel very weak - it can't even take its own weight and tends to cave. I has suggested mortise and tenon joints, but it turns out it cannot be done because the brace cannot be turned vertically (it's a 2-D machine, not 3-D) and it is impossible to cut a rectangular slot using a CNC machine. I see what my machinist is saying, because of the diameter of the cutting bit. I suppose it is possible to get a mortise done with rounded edges, I can't get my head around a tenon and how the bit might cut it (gapless fit is desired).
Now I know as much about CNC as I do about nuclear physics, which is zero. Surely there must be a way to attach the braces without significantly impacting the panel strength? Or do I have use a Gepetto with a chisel?
I am currently in the process of starting a limited production run of speakers for which I will be using CNC machining to cut the panels and provide driver flush mounting. The cabinet is 16" wide, 46" tall and triangular in shape. All three panels are identical.
The current design uses 9x19 mm grooves in a 18mm panel, running the entire panel width - the 19mm brace slides in place, then glued to fit. This is making the panel very weak - it can't even take its own weight and tends to cave. I has suggested mortise and tenon joints, but it turns out it cannot be done because the brace cannot be turned vertically (it's a 2-D machine, not 3-D) and it is impossible to cut a rectangular slot using a CNC machine. I see what my machinist is saying, because of the diameter of the cutting bit. I suppose it is possible to get a mortise done with rounded edges, I can't get my head around a tenon and how the bit might cut it (gapless fit is desired).
Now I know as much about CNC as I do about nuclear physics, which is zero. Surely there must be a way to attach the braces without significantly impacting the panel strength? Or do I have use a Gepetto with a chisel?
Dowels fitted into holes. Even if they couldn't be CNCd, you can make (or buy) a jig and do that part by hand.
I guess dovetails and 3D CNC are a best match, what isn't always the case for good looking speaker building.
Post your results if you can, for your ideas and final results.
CNC Panel Joinery Notebook | MAKE
Box Joint on CNC 4x4 Hybrid Joes - First Try - YouTube
Post your results if you can, for your ideas and final results.
CNC Panel Joinery Notebook | MAKE
Box Joint on CNC 4x4 Hybrid Joes - First Try - YouTube
You want to add to each corner what is called a "dog bone", which allows the cutter to go slightly outside the line of the mortise (in black) that allows the tenon (in red) to fit inside. This allows for the diameter of the cutter not being able to cut tightly in the corners.
The light blue depicts (in this case a 1/8 inch diameter) cutter path.
The light blue depicts (in this case a 1/8 inch diameter) cutter path.
Attachments
Wow, that's really helpful. Thanks so much for the replies. I will get my machinist to take a look, the dog bone idea seems really interesting. I also thought a bit about it and Google threw up a hint about flipping the brace piece over and trying to mimic the varying depth of the cut, to create a rounded 'shoulder' on both sides of the tenon.
tomlang, how would I cut a tenon on this kind of a router (where the workpiece is flat and the cutter operates vertically)? Would it also not have rounded ends? I heard of a process called 'sparking' where they burn off the edges after cutting to create a sharp edge. Would anyone have some insight on that?
richie00boy, we're trying to eliminate any hand-produced work, though I suppose if it comes down to it, that is what we will do.
tomlang, how would I cut a tenon on this kind of a router (where the workpiece is flat and the cutter operates vertically)? Would it also not have rounded ends? I heard of a process called 'sparking' where they burn off the edges after cutting to create a sharp edge. Would anyone have some insight on that?
richie00boy, we're trying to eliminate any hand-produced work, though I suppose if it comes down to it, that is what we will do.
I would probably just make the routed grooves (dadoes) shallower to keep the main panels strong and flat. The grooves are mostly to locate the braces, if properly glued the joints should still be plenty strong enough to do their jobs. I generally don't cut dadoes for braces, they just get butt joined to the sides.
Dovetails are for solid wood, not ply.
Bill
Dovetails are for solid wood, not ply.
Bill
If you are not making ten thousand of these, you could simply round the corners of tenons by hand with coarse sandpaper or a knife or chisel. Or use a chisel to square the corners of a mortise where the CNC rotary cutter leaves the corners rounded. That's standard woodworking in the old school. However the "dog bone" trick is very useful, you just need to figure this out graphically, determine the shape that the rotary cutter will remove, and make room for square corners to fit into a mortise.
I'd suggest vertical slats with an internal horizontal cross brace that supports only the slats. A shallower groove cut say 6mm deep cut the length x2 per board minus baffle and the horizontal braces cut so they slide into place. Easy todo with a two axis. Would pass the rap test while maintaining greater strength and integrity. Could butt the magnet up against the horizontal braces to reduce vibration further.
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Thanks for the helpful replies 🙂
@lousymusician: I've used dovetails to corner-join box style furniture (ply) and speaker boxes (MDF). Results in the former were excellent and the latter pathetic as the boxes literally opened up with moisture changes 😀 Lots and lots of tiny bass ports. It was a vent - you can't get a 90 degree inner cut with a machine costing thousands of dollars?
@thomasjefferson: The manual process seems the only way out. The other option we were discussing is to let the dimensions match and then fill the gaps with glue and sawdust, sand the faces and apply veneer. The dog bone cut seems to be the best bet as of now, or the rounded corner on dados with a mismatched tenon.
@Greebster: The cabinet is triangular in shape and about 50" tall, and using four horizontal braces to hold it all together. Vertical slats are a question mark, not enough width and too much height. As of now the sliding horizontal braces are exactly what is used, and though making the groove shallower will work better than what it currently is, we were hoping to not weaken the main panels. At the same time, this is a commercial proposal so I can't use the techniques that I normally would if I was following DIY discipline. Butting the magnet up against the brace is a great idea, will see how we can implement it!
@lousymusician: I've used dovetails to corner-join box style furniture (ply) and speaker boxes (MDF). Results in the former were excellent and the latter pathetic as the boxes literally opened up with moisture changes 😀 Lots and lots of tiny bass ports. It was a vent - you can't get a 90 degree inner cut with a machine costing thousands of dollars?
@thomasjefferson: The manual process seems the only way out. The other option we were discussing is to let the dimensions match and then fill the gaps with glue and sawdust, sand the faces and apply veneer. The dog bone cut seems to be the best bet as of now, or the rounded corner on dados with a mismatched tenon.
@Greebster: The cabinet is triangular in shape and about 50" tall, and using four horizontal braces to hold it all together. Vertical slats are a question mark, not enough width and too much height. As of now the sliding horizontal braces are exactly what is used, and though making the groove shallower will work better than what it currently is, we were hoping to not weaken the main panels. At the same time, this is a commercial proposal so I can't use the techniques that I normally would if I was following DIY discipline. Butting the magnet up against the brace is a great idea, will see how we can implement it!
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