Recommended glue for glueing plywood to MDF?

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#23
Hi, I am throwing in my two cents here . You have recieved perfectly good advise so far but here is a tip not everybody knows . Mdf, I have a lot of expierience with it and one very effective thing to do with it seal it with a shellack (probably just misspelled that) even when veneering. Why ? because it seals all edges strengthens,the surfaces, and allows most adhesives a better bond. The big catch is its time consuming,you must sand between all coats and on top the last one to allow adhesives to bite. Good old rubber cement sticks vinyls down great to it. This is actualy a super good method for painting mdf too ,but thats not your project. It ups the work factor ,but I have found it effective for no fastner construction glue bonds (when speakers box building) and laying veneer over them.
 
#24
KTnC said:
Hi, I am throwing in my two cents here . You have recieved perfectly good advise so far but here is a tip not everybody knows . Mdf, I have a lot of expierience with it and one very effective thing to do with it seal it with a shellack (probably just misspelled that) even when veneering. Why ? because it seals all edges strengthens,the surfaces, and allows most adhesives a better bond. The big catch is its time consuming,you must sand between all coats and on top the last one to allow adhesives to bite. Good old rubber cement sticks vinyls down great to it. This is actualy a super good method for painting mdf too ,but thats not your project. It ups the work factor ,but I have found it effective for no fastner construction glue bonds (when speakers box building) and laying veneer over them.
Click to expand...

Superb advice, thanks a lot.

I have almost finished glueing the 3.6mm plywood to the cabinets (just two sides and both baffles left) so can't take your advice this time but will in future. I can understand your advice that the adhesive will bond to the MDF consistently over all surfaces inc. end grain, really makes sense. I was going to use shellac on the plywood after staining because iv'e read it gives a quality finish.
 
#25
Do I mount the midwoofer to the MDF on baffle or the 3.6mm plywood? I have read that if the midwoofer is not screwed to the plywood, the plywood is not classed as baffle depth. Plus I think by screwing driver to plywood they could get a better 'bite'. The tweeter is getting flush mounted with help from a gasket. I am going to re-design the external crossovers when baffles are finished and measured drivers etc. and was wondering if mounting the midwoofer on the plywood won't make phase matching the x/o harder.
 
#27
I have put a lot of drivers on a lot of baffles of many builds. I believe you are asking if you should go ply vrs mdf for the baffle because of fastening a driver. There are a lot of schools of thought on what material is superior so I will keep it general. A good ply can have advantages for holding screws particularly at open edge grain. If you pre drill mdf straight on a good match of drill bit to screw size your speaker drivers will fasten up great. Ply might have some advantages if you pull drivers in and out a lot. I am very into flush mounting drivers even to the baffle, that can prevent some basket mounting ring diffraction issues. Mdf routers out smooth and clean for that, great for under a 30 percent in dept removal. Some plys have pocket voids that show up in the different layers or even have varying material layers,but that also depends on the ply you choose. Mdf is very uniform,no voids,and very dense to fight baffle resonance, but chips, more finicky, always needing careful pre drilling. I have doubled my baffles at times to increase strength,and used one layer mdf outer one layer ply at inner with good results. If you remove screws to get drivers drivers in and out a lot, you could just reverse that method. When finishing off mdf with veneer you won't have to fight with finish work. Some plys look so good you don't want to veneer them. So you can just consider which material you think you need and then adjust fastening method accordingly. I won't mention sonic superiority of one versus another because there are a lot of greatly varying ply woods,and it will open a debate much like is lamp cord ok for my 100 watt mini speakers or should I use Optimus Prime's jumper cables.
 
#28
Fantastic advice KTnC!

I will take your first advice and use Shellac (the right mix for use as a sealer) on the MDF baffle then glueing the 3.6mm plywood onto the Shellac with the same woofer hole cut out. Then screw my woofer screws into the plywood. I can always use another layer of plywood to flush mount the woofer flange and use thicker gasket on tweeter accordingly, which will have more advantages.

I see what you mean on these debates with BB vs MDF. I prefer high quality birch ply with 13 layer-ply (18mm) and will use it on next projects, MDF still ok for outer baffle layers.

BTW am sure some of you have seen the 3.6mm plywood am using. It is actually got a hardwood layer and plywood layer (no voids) and a pine layer sandwiched in between. Its really good for covering speakers and wont need to veneered, just stained and varnished or Shellac will look great. The glue seems to shrink the hardwood layer and really tighten the cabinets. 'Knuckle test' is much better than before, if you like stiff cabinets that is.
 
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#31
"you can route all edges afterwards, and mount real wood, rounding it up nicely"

Exactly what I was thinking, can get a better rounded edge on baffle and even use a maple wood instead.

Because am redesigning my external x/o's I was also thinking using a chisel around tweeter like Troels Gravesen, any thoughts?

SP44
 
#34
Stewart: late to the party re your post #31 above, but my first thought, which you've perhaps already realized, is that most hardwoods are far harder than MDF - maple certainly. I think you could count on many tedious hours to achieve similar results to the baffles on the SP44 design.
 
#35
yacuza said:
Wonder if anyone has tried a mixed-on-the-spot Polyurethane and Silicone blend? The rigidity needed can be dialed in by mixing more or less Silicone in with the Polyurethane.

Urethane/Silicone Adhesives for Bonding Flexing Metal Parts - Nasa Tech Briefs
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That stuff is designed for metal not wood. I don't see any point even trying it when there are excellent wood glues available easily and cheaply. You don't want any flexibility or silicone in your joints if you are painting them.
 
#37
My friend has cabinets with curved side walls. He wants some advice on which glue to use. He wants to use some heavy duty vacuum bags but I've read curtain glues need air to cure yet not sure which type. He was thinking of using Titebonds veneer glue (link below). What process is best for finish, he don't mind taking his time for better results, thanks great advice so far 😀

http://www.titebond.com/product.aspx?id=fdb9c5cb-15b3-49b3-b709-5794cc3ae102
 
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