I've searched around a bit and my question seems a bit more specific than my searching skills yield. Long story short I'm building a pair of fonken floorstander MKII's for a good friend. I'm wanting to streamline the build and make the finishing process much less time consuming, but not sacrifice long term durabilty.
Is it generally considered structurally acceptable to use just butt joints (no dado, dowels, biscuits, etc.), pva glue, and obviously sufficient clamping when assembling a speaker cabinet of suitable engineered materials (ply, mdf, etc.)? I'm really trying to avoid using screws, and adversely having to fill and sand holes to the tune of 50 per cab. Thoughts? Any advice/input appreciated.
Is it generally considered structurally acceptable to use just butt joints (no dado, dowels, biscuits, etc.), pva glue, and obviously sufficient clamping when assembling a speaker cabinet of suitable engineered materials (ply, mdf, etc.)? I'm really trying to avoid using screws, and adversely having to fill and sand holes to the tune of 50 per cab. Thoughts? Any advice/input appreciated.
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Apart from the first couple of boxes I built I've always just used butt joints and glue (first PVA now always Cascamite) and never had a problem. Adding a rebate makes it a lot easier to keep the panels aligned though.
I like dowels, with the right jig it makes assembly a lot easier. I aso use polyurethene glue, it will fill any gaps, so guaranteeing a good air tight seal.
But using butt joints only can be done, I find it awkward if glueing large things, which is why I ended up bying a couple of doweling jigs. Tried biscuits, but found dowels more accurate.
But using butt joints only can be done, I find it awkward if glueing large things, which is why I ended up bying a couple of doweling jigs. Tried biscuits, but found dowels more accurate.
I like throwing a few biscuits in to help with alignment during glue up. I tend to use biscuits over dowels because it does have a little wiggle room and facillitates a last minute micro adjustement.
Gluing the sides together is easy. Gluing the baffles on is another matter entirely!! you would be amazed at how much they slip around when you start to tighten the clamps!
Absolutely essential to have clamps holding them in place laterally as well as clamping them to the surface being glued...
and when Pinkmouse says "enough", double what you think is enough and you might be getting close 😉 Long time no see Al!!
Tony.
Absolutely essential to have clamps holding them in place laterally as well as clamping them to the surface being glued...
and when Pinkmouse says "enough", double what you think is enough and you might be getting close 😉 Long time no see Al!!
Tony.
Strategically placed biscuits will add significant strength, help with alignment during assembly while allowing for some lateral adjsutment and are much easier and less fussy to cut than dowel holes.
Hi Tony, yup, it's been a while. 🙂
To stop stuff sliding around on a film of glue whilst clamping, just sprinkle a tiny bit of sand on the joints, it'll cut through the glue, yet compress into the wood and not hold it apart. Oh and I'm not saying there aren't many ways of building cabs, I have dado blades for the tablesaw, biscuit and dowel cutters, as well as my favourite, the air nailer, but glue and clamps does work.
To stop stuff sliding around on a film of glue whilst clamping, just sprinkle a tiny bit of sand on the joints, it'll cut through the glue, yet compress into the wood and not hold it apart. Oh and I'm not saying there aren't many ways of building cabs, I have dado blades for the tablesaw, biscuit and dowel cutters, as well as my favourite, the air nailer, but glue and clamps does work.
I've never had a massive problem with that. Also I recommend cutting the front and back oversize to allow for some movement and imprecise cutting/measurement then trim flush with a router.
Never would have thought of that, I try for as tight a tolerance as possible so would have been horrified at something in between 😉 but makes sense that it will just compress into the wood/mdf.
richie the oversize and flush routing is also an approach I hadn't thought of 🙂
Tony.
I would be very comfortable with just gluing and clamping butt joined plywood, knowing that this makes a very strong joint as is. However, MDF is not the same situation. I would want to reinforce these joints in some way, since the face surface of MDF is not nearly as strongly attached to what's under it (the 'glue' used to bond the fibers in MDF is now very strong).
You could do any of the suggestions above, such as biscuits, dowels or nails even. Another method is to use glue blocks in the corners or cleats that get glued and screwed to the inside corners.
I'd agree for something structural or a peice of furniture, but a cab is under very little loading, so unless it's being chucked in and out of a van a butt joint is fine.
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Simply not needed. I have stood on my speaker boxes and had one roll around in the boot (trunk) of my car whilst crashing (rolling) at motorway speeds and remain intact. All butt jointed MDF with no rebates, so glued face to end. Also stood on boxes I've done rebates on.
Once the glue is cured and the parts are no longer slippery, the mechanical advantage of dowels or biscuits remains dormant until the glue joint fails (not likely) at which point, the boxes are not longer useful as speaker enclosures.
In short, they help with assembly but do not strengthen the carcasses, particularly with engineered wood products that do not experience differential expansion.
In short, they help with assembly but do not strengthen the carcasses, particularly with engineered wood products that do not experience differential expansion.
Gentlemen, I said "I" wouldn't be comfortable with just glue and butt joints for MDF - voicing an (experienced) opinion. I went on to say how I would do it. Short answer: I would always reinforce any butt joint, regardless of the material. I prefer biscuits, since I have a biscuit joiner.
You got one thing right - they do help in assembly.
Any time you increase the gluable area in a joint, you strengthen the joint. Whenever you effectively reinforce a joint you increase shear strength and breaking strength - the joint will fail later rather than sooner (if at all). This is a fundamental rule in joinery.
To illustrate, take 2 small pieces of MDF and butt glue them together to form a corner. After the glue has cured, break the joint. Note the small amount of force it takes to break the joint and how the joint fractured (it tears the face layer from the MDF, leaving the glue joint intact). Make another corner with 2 more pieces of MDF, this time reinforce the joint with biscuits. Break it and note the force needed. You will find that there is a lot more force needed to break this joint and much more than the face layer gave way.
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