As for the "glue is glue" quote , my gut response after over 23 yrs working for a commercial woodworking company would be politely translated to "NFW"
That's a tradesman's term for " actually, no" -try and find a tradesmsn who can complete an over 5 word sentence without at least two being biological or scatalogical references - or is that just my personal experience?
Our standards are Dural or Franklin TypeI - IINM both cross linked yellow PVAs - not the same as white glue - period.
That's a tradesman's term for " actually, no" -try and find a tradesmsn who can complete an over 5 word sentence without at least two being biological or scatalogical references - or is that just my personal experience?
Our standards are Dural or Franklin TypeI - IINM both cross linked yellow PVAs - not the same as white glue - period.
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PVA white is usually a sheer strength of 2800 lbs per square inch, yellow 3200 lbs, brown cabinet makers 4200 lbs, cabinet makers has the best gap filling qualities as it is of a thicker body, PL Premium is 650 lbs"ish" for dry wood & 450"ish" lbs for where it is filling gaps, Epoxy 1900"ish" lbs, fibreglass resin as memory serves me 1000 lbs & foam (Gorilla) 500 lbs. Pre-drill for low root wood screws is great. It seems to me that your glue needs to be able to soak into the wood you are using, which isn't much of a problem when taking of MDF but close grained hardwoods or oily ones become much more difficult & need to be roughed up with 80 grit to give your glue a surface to get into. Feel free to correct any of the PSI quotes I have made if they are way out 
Know[n] many in my time [been one too] and only one didn't fit the 'mold'. He always had an expensive haircut, wore a bowtie with his painter's white long sleeve shirt and overalls and never swore, etc. and very erudite; so one day in a conversation that was well outside a then typical tradesman's 'wheelhouse' I asked what his 'deal' was and turned out he was a licensed, etc., labor lawyer that by the time he'd graduated after many years of being a tradesman to fund his education, young family only to find out that he would be starting out at near minimum wage, he made the smart decision to have dual careers and only represent his fellow workers, becoming one of many that 'spearheaded' the 'runaway' labor costs/problems of the mid '60s forward, very comfortably retiring in his 40s to teach the trades at his leisure.
GM
I have seen on videos, some people working with air nail gun on MDF. does anybody recommend it? I think that the trick should be using very thin nail gauge, but many of them for strength (one every few inches), so the mdf does not split. I have been thinking that 1-3/4" should be fine for 3/4 mdf enclosures. What would be the correct gauge size for this? I am not familiar with air gun nail gauges.
No experience, but Google returned a lot of interesting info: https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=air nail 3/4" mdf
GM
GM
18 ga & 2" remember to angle them slightly alternating direction as you go so they hold like a dovetail joint about 6-8" apart. Clamp it tight together 1st or the nails will bridge & keep your joint open, clamping can just be body weight by pushing down or a scrap piece of wood (with a straight edge) as a stop block, screwed/clamped it to your work surface as a stop at the opposite end of the board/joint you are wanting to join. Layout placement of the stop block of wood so the working end of things is at front edge of your working surface/bench, that way nothing will impede the placement of your gun. Push two opposing piece together against the stop block this way you are working on the horizontal & not trying to balance everything on edge, if your work surface is smooth that your pieces are resting on then they will self aligns & you just need to focus on the ends of the joint....just be careful if you are not familiar with working with air nailers as you don't want to end up with an ex-ray of your hand with a power actuated fastener in it!
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I would still use screws and glue myself from a practical point of view - depends on what tools and setup you have to work with.
When lining up the two pieces at a corner join, a pilot hole can be made accurately with the edges perfectly aligned at the point of the pilot hole. Then the pilot hole will guide the screw to exactly the same place and will be holding the two pieces firmly together, still perfectly aligned. You'll be able to rotate the pieces around this screw hole but as long as it's aligned at the screw hole, the straight edges will line up all along the edge.
I'm a little inexperienced with large clamps and find them unwieldy and awkward, and they're expensive and you need lots of them if you want to glue everything together at once (rather than glueing each join separately and waiting 24hours for it to dry before moving on to the next, if you only have two clamps).
Glue alone does mean you can re-position the join for a while but it can also mean that the join moves whilst you're tightening the clamps without you noticing, or whilst rotating the clamped piece etc etc.
So essentially for me, screws help align the peices and also act as clamps pulling them together (as long as you don't over tighten the screws). You could use brads/nails for the same reason but if you make a mistake then pulling the peices apart again risks ruining the surfaces whereas with a screw you can just take it out and pilot a more accurate hole further along.
Long term - having destroyed a few pairs of already damaged speakers in my time, it's rust from the screws that causes them to expand and the boxes/MDF to fall appart - but if there's moisture getting to the screws through the MDF then that MDF isn't going to last long anyway. Don't get that with plywood - rusty screws yes, but not the blown wood part.
When lining up the two pieces at a corner join, a pilot hole can be made accurately with the edges perfectly aligned at the point of the pilot hole. Then the pilot hole will guide the screw to exactly the same place and will be holding the two pieces firmly together, still perfectly aligned. You'll be able to rotate the pieces around this screw hole but as long as it's aligned at the screw hole, the straight edges will line up all along the edge.
I'm a little inexperienced with large clamps and find them unwieldy and awkward, and they're expensive and you need lots of them if you want to glue everything together at once (rather than glueing each join separately and waiting 24hours for it to dry before moving on to the next, if you only have two clamps).
Glue alone does mean you can re-position the join for a while but it can also mean that the join moves whilst you're tightening the clamps without you noticing, or whilst rotating the clamped piece etc etc.
So essentially for me, screws help align the peices and also act as clamps pulling them together (as long as you don't over tighten the screws). You could use brads/nails for the same reason but if you make a mistake then pulling the peices apart again risks ruining the surfaces whereas with a screw you can just take it out and pilot a more accurate hole further along.
Long term - having destroyed a few pairs of already damaged speakers in my time, it's rust from the screws that causes them to expand and the boxes/MDF to fall appart - but if there's moisture getting to the screws through the MDF then that MDF isn't going to last long anyway. Don't get that with plywood - rusty screws yes, but not the blown wood part.
Good tips. I'll remember the first one. I'm already aware of the second with a work coleague having told me how he once fired a long brad through a joint so that he could no longer move it.. Might have been his wrist - was very lucky not to hit a vein.
Hey thanks for all that data. I made some wood angles L, so I can glue the boards and clamping them hard before nailing, so everything is straight when and after nailing.
Do you know whats the diameter size of the #18 gauge? I was thinking a 2mm nail should be nice, so there will be about 8mm of fibers on every side of the nail (on 3/4" mdf). I think that definitely screws sucks and do not give any holding power to final piece, that's why I am interesting in trying thin nails, surely that's the ticket for a proper mdf joint.
I think that its common sense to think that if mdf splits very easy, no matter what technique you use with your screws to avoid immediate splitting, even if it looks good and did not split, that thing is not really holding hard anything, but not only that, that coarse screw there can cause in the future a split if the structure is stressed, being in this case more recommendable to simple use glue instead. Hope to get a gun soon, so I can make some tries.
Pilot drilling to the full depth of the fastener used is essential with all sheet goods - both to avoid splitting, but also bugling of top face - and even an air driven brad nail can split the material if too close to an end. The tapered pilot drill bits are actually worth the extra dollars, but are a bit fragile
Robertson brand Lo-root and Maxx are examples of screws specifically designed to reduce splitting on sheet goods and softwoods.
Sorry to disabuse the notion, but with appropriate preparation, a good screw has much better holding power and durability than a brad nail
Robertson brand Lo-root and Maxx are examples of screws specifically designed to reduce splitting on sheet goods and softwoods.
Sorry to disabuse the notion, but with appropriate preparation, a good screw has much better holding power and durability than a brad nail
How are we supposed to get a good holding power on mdf, if we are screwing just into its weakest point? because of that I think screws are not doing big thing there even if the board did not split while screwing. I think that a thin brad nail in angle would be much better, since it takes just a minimum fraction of the fibers.
I would go with 5/16 hardwood dowels instead of screws, it makes more sense when talking about properly joining mdf boards, because there's no force involved when we put them in, and the glue will practically weld the 3 elements.
I was answering a question about power nailing, 18ga= .04", 1.2mm, but I would personally rather dry assemble the joint with a clamp on either end with assistance from a flat surface, pre drill straight in with a tapered countersinking bit, disassemble sweep away the dust, apply PVA glue & then put the low root wood screws to her baby!....cleanup the squeeze out with a soft warm damp (not sopping wet) cloth quickly as not to swell the wood fibres.
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Brads alone would certainly not pass any type of millwork association field inspection. Not that the spec relates at all to speaker enclosures, but for premium grade certification, the rules for cabinets are clearly designed to not rely on just the glue. I've bored folks in the past with the spec that requires 2" (or longer ) wood screws on 100mm (4") spacing on the rear panels of both wall mount and base cabinets that will sit in kick bases. Some cases will even require Confirmat screws- which require a much larger pilot hole in 3/4" core panels than a #8 lo-root. As a matter of interest, the site inspection of an AWMAC guaranteed installation gives the inspector authority to randomly select any base or upper cabinet for the full monty exam - such as - are the wall mounted upper attached with appropriate number, spacing and type of screws . Those need to have a very large fillister type head, and should really be countersunk enough to have a precision fit cover cap in matching material to the panels.
Rarely do the project specs call for thicker than 3/4" core material -it can vary from particle board core melamines, to MDF laminated panels, to pre finished veneer core plywoods - and they all get screwed together. We build and install thousands in lineal feet of cabinets in a year, and unless an assembler does something really stupid - such as too close to an edge of panel or not pilot drilling , these won't split.
Dowels / lamello biscuits / Festool dominos are all fine - they just take a bit more time, cost more for tools than you might want to invest. Festool is a German company who make great power tools - if you have to ask the price, shop at Home Depot for Ryobi or Rigid.
How does any of that relate to most types of speaker projects? Not much at all, really. I will definitely use screws for large sub enclosures, or something subject to a lot of moving/ potential for abuse, such as a small PA syste, but for small speakers, dadoes and a few brad nails to hold things in place while I set the clamps has proven more than sufficient.
As for wet wiping down any squeeze out - I just let it dry and scrape it off with, what's that thing called - a glue scraper?
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In DIY speaker building, the plywood, board, metal angle or the popular 'window'/'holey' bracing holds it all together. All these can be glued/screwed in one way or another in larger cabs and far stronger than brads, nails. If it's a small cab, then just a motor brace is ideally required with a few clamps to hold it together long enough for the joints, cleats, or glue/screw blocks dry.
If you want miter joints, then use dowels, hardwood flooring nails or similar to 'pin' them: http://www.lansingheritage.org/images/altec/plans/1974-enc-design/page18.jpg
The main thing with MDF IME is not having any irregularities such as filled screw holes on visible surfaces if painting or using thin veneers, wallpapers, etc., as they always came back to haunt me sooner or later if not in a well controlled environment [rare down here in the Deep South], so I intentionally have seams as a visual accent 'breakpoint', using a pizza cutter to 'crease'/bevel/inset the veneer a bit as required.
GM
Can't quite let that one go - dowels are fine for alignment, but will not have the strength of a properly piloted coarse thread wood screw. MDF, particle board or even Baltic Birch plywood is only weak on the edges in the absence of proper pilot holes, or when the fastener is too close to the end of a panel.
Practically "weld"? - well wouldn't that require the temporary melting, then solidifying of the 3 components? Today's wood glues are pretty good, but they don't exactly do that.
I've worked in the commercial millwork / cabinet trade for 23yrs, and whenever structural integrity / load bearing is required, we always use threaded mechanical fasteners such as the aforementioned Lo-Root or Confirmat screws. The installed cabinets would fail inspection by the millwork inspection authorities, for whose services and insurance of an installed project we pay a flat fee of $1500, plus a graduated percentage of the total contract amount. We'd be happy to avoid that expense, but on a several hundred thousand dollar project, when those are the architect's specs ...
So, I guess when the inspection stamp is on the guarantee certificate, you could say the cabinets are glued, screwed, and tattooed.
Sorry, couldn't resist.
An externally hosted image should be here but it was not working when we last tested it.
Polyurethene glues
Are there any steps preparing MDF prior to gluing with a polyurethane glue?
I'm using 3M 5200 marine adhesive and the spec sheets recommends "abrading the surfaces with a 180 grit to 220 grit abrasive to enhance the bond strength", but doesn't mention MDF as one of it's substrate examples.
Should I do the same with my MDF board (i.e. on the MDF face, not the edge).
Are there any steps preparing MDF prior to gluing with a polyurethane glue?
I'm using 3M 5200 marine adhesive and the spec sheets recommends "abrading the surfaces with a 180 grit to 220 grit abrasive to enhance the bond strength", but doesn't mention MDF as one of it's substrate examples.
Should I do the same with my MDF board (i.e. on the MDF face, not the edge).
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