I built a speaker enclosure out of MDF attaching the sides with PVA glue and brads using butt joints and spraying the surface with automotive primer-surfacer to get a smooth surface. The result was very good, but there was a SLIGHT hint of the butt joint seam. I think there is a slight difference between the porosity of the end vs. the surface or something between the two pieces. I let the two pieces dry for about a week before sanding the edge flat.
I have been experimenting with different methods to hide the seam for future projects. I have tried:
A washcoat of PVA glue covering the edge and the overlap area (first effort not a spectacular success)
Using drywall joint compound to fill the inperfections (was not impressed with the result)
A coating of superglue spread over the area (this seems to hold promise)
Has any one tried an approach to stabilize the edge fibers of the cut edge? It would appear that might hold the most promise from the superglue result so far.
Any other thoughts?
Replies
"Any other thoughts?"
Miter the corners.
Hi Eric,
Use auto body filler (Bondo). Then a heavily pigmented ( high solids) undercoater. This has worked for me in the past.
Paul
I have been very successful with shellac. I used Zisner BIN which is basically shellac with white pigment. A couple coats, a bit of sanding, a couple more coats and its hard to tell which is original finished surface and which is 'end grain'
I have been over to Parts Express speaker building forum. They have some people that are really into this subject. One of them referred me to this forum:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=100520
Quite a bunch of experimenters and quite an interesting discussion!!
By the way, I have tried to find 1/8 inch MDF of the type David Marks uses with little success, but it would be nice to have 1/16 inch MDF to cover the surface that has the butt joint in cases where you were only going to paint the MDF.
Anybody know of an MDF type of material that could be a substitute for veneer where you were only going to paint the surface? A very thin sheet of MDF veneer (or other engineered veneer-like material) would be easier to work with than real wood veneer that has flattening issues. It would have to be very thin (yet thick enough to mask joint movement of the MDF) in order not to have edge joint issues itself.
What about rabbeting the edge so you only have 1/16 or so of edge showing to begin with. Glue it together well to hold the lap on. I do that a lot w/ plywood edges w/ solid wood edging.
You know...that is a very interesting idea. That would solve several issues:
the edge problem we are discussing
aligning and holding the assembly together
reducing the amount of material that has to be removed on the edge to flush it up.
....should have occured to me. I say that too often!!!
You could cut the piece with the edge 1/32" - 1/16" short and fill it with Bondo, then sand it flat and square. Assuming the corners will NEVER be nicked, it will work. Are you rounding the corners over at all?
If you insist on painting them, you can seal the edge with whatever will penetrate, then sand it smooth. Depending on what kind of pain you use, you may be able to give it a couple of coats, sand it smooth and re-coat. That should make it pretty invisible. You could also assemble the cabinets, glue and nail a cleat in the corners, remove the corners and glue in a strip of largely non-porous hardwood, like poplar or maple. You'll still be looking at an edge of some kind, regardless of how you do it with a butt joint, but mitering the corners can be tricky and if the joint opens at all while it's drying, you'll have a gap to fill.
Why not veneer them and paint that? Many of the speaker manufacturers use veneered MDF using an overhead V groover, glue the corners, band clamp them and use the veneer as a hinge. Then, they paint their cabinets black, or just about any other color.
I am a trim carpenter and am often asked to re-create the Taj-Mahal using MDF and finger joint pine. I have found that a rabbet works very well. I leave 5/16" for the rabbet, enough for a slight head brad to hold it long enough for the gobs of glue to dry. I then finish it with a 5/16" roundover bit that terminates at the seam, making an imperceptable line at the joint. Hope this is a help.
Regards, Sean
Eric,
I used to frequent the PE and Madisound boards....now I reside over here and lurk.
The best solution I've found to date is the Target Coatings water based sanding sealer. It's easy to sand and doesn't clog sandpaper.
Now a word on technique.
Sand Very, Very, VERY gently. It's far easier to cut into the face of the MDF and not the end grain which soaks up the sealer like crazy.
I usually sand down to 320 grit using just the weight of the sanding block to even things out. Takes patience but the results are very rewarding.
Scott
Is this their shellac based sealer?
http://www.targetcoatings.com/sealer_ox_shellac.html
I have tried shellac at a 2# cut. It worked fair for me. I was going to try a higher cut and forgot. I think I will try that and see how that works. Would you characterize the Target Coatings sealer as more than a shellac based sealer, or would you say that shellac would produce the same result?
By the way. I had the BEST result with Satellite City cyanoacrylate (super glue) medium thickness squeezed on the surface at the joint. I even put it in the bathroom (in the shower) and only the area around the periphery of the glue area swelled. The joint remained flat. I was impressed.
Whoops..called out the wrong stuff. High solids pore filler...
http://www.targetcoatings.com/sealer_HSF5100.htmlThat's the stuff. I swear.It's unlike anything I've used...but then I've never used any other pore fillers.It's great for sealing the end grain up...
Wow! This looks like unusual stuff!!! It has NMethyl pyrrolidone in it. I remember that to be one hell of a solvent. Where did you get it? Homestead Finishing (Jeff Jewett) is supposed to be a supplier of their products, but he does not list this.
I bought it directly from them.The other finishes in their line work well too!
Hmm - assuming everything is square; I think I'd intentionaly make the sides a little proud then simply run a flush trimming bit along the seam. Admittedly, the number of times I've used DMF I can count on one hand have most of my calculators left over.
Good luck
That works very well to make the end flush to the side of the enclosure, box, carcass...etc. But MDF as a butt joint has a way of telegraphing through paint, paperbacked veneer, non paperbacked veneer, everything, that is truly special. And annoying. And ugly.I've had some success with miters in small boxes...I guess I should have mentioned that too...but I think someone did earlier. Larger enclosures get a little unwieldy to manage the miter joints at glue up.
This forum post is now archived. Commenting has been disabled