[WireNut]

You need to add some 403 Microfibers and 410 Microlight filler to your collection 

Got that brother 

[WireNut]

Have you ever tried sanding something with the Colloidal silica filler in it?  It'll eat up paper faster than sanding a concrete floor.

Yes I have. The Colloidal silica filler is the filler I use the most, but I didn't realize it was the hardest to sand

I hate to preach about West Systems but look at some of Vapors Audio's cabinets, They're awesome  This dude no's his shit 

[dBe]

It all depends on what your definition of hide is, and on how long of a time horizon. 

All the tricks described here, we've used ... none are guaranteed.  When we need to be 100% sure that a seam will never pop, we skin the cabinet with formica. 

We've used Medex, painted the seams with West Systems epoxy, sanded that and put 3-4 coats of lacquer sanding sealer, sanded that and used high build primer, sanded that and paint ... and STILL had the seams pop. 

Bottom line is MDF moves like crazy, even the fancy expensive stuff like Medex will move a lot.  Trust me, I've seen a Medex cabinet that was left in the shop literally almost tear itself apart from all the movement, even though it was covered inside and out with epoxy.

That is odd behavior from the Medex.  I put two pieces of material in the bed of my truck and left them for a year as a durability test.  Both were 3" x 6" - one MDF and one Medex.  The truck bed had a black sprayed in liner. Here in NM it would get very hot.  At the end of the test the MDF was split, swollen, warped and twisted.  The Medex was a flat piece of material 3" x 6".  A little dirty, but the grime just wiped off.

I wonder what the difference is?  Of course our average relative humidity here is 11%...

The WEST epoxies are the best product I have ever used, bar none.  When I laminate panels up I use 105 and 206 or 209 and vacuum bag them.  Titebond II is just a lot more convenient.

Cabosil is an awesome filler for sure, but I agree it is like sanding a rock.  A squeegee is your friend as is plastic sheeting over the repair to remove some of the labor.

The Vapor Audio products are indeed stunning in all ways

Dave

[TomS]

http://www.plywoodcompany.com/application/home/itemdetails.aspx?categoryid=41&itemid=320

Dave

Small world Dave. My brother (also Dave) works there as a sales rep. They have nice stuff

[WGH]

I did some research for a large veneered table a while back to find out what would be the best substrate to use. Although MDF would be the logical choice, after reading about the material I discovered it moved too much with humidity changes and would not work at all. When making speaker cabinets with MDF the builder has to deal with two factors: linear expansion and thickness swell. Manufacturers who ship their products world wide have to allow for temperature and humidity extremes that the average home owner never encounters, so extra ordinary measures need to be taken.

A construction technique that may work is to assemble the entire speaker cabinet with West epoxy, making sure the end grain is completely wet out first, then a thickened epoxy is used for assembly so you don't get a starved glue joint.

The document "Dimensional Stability of Particleboard and MDF for Use as Substrates for Lamination" explains why your joints are failing.

Wayne

 

[dBe]

Small world Dave. My brother (also Dave) works there as a sales rep. They have nice stuff

WE took our daughters to Disneyland about 30 years ago and I bet we rode It's a Small World 6 times.  They sang it all of the way home... a very long trip.

Does Dave live in Ft. Worth?  That is where my Medex comes from I think.  They ship to Stock Buildging Supplies here is ABQ IIRC.  The guy Sean there said it came from Ft. Worth.

Dave

[mlundy57]

Does the method of joinery, i.e. dowel or biscuit vs butt joint make any difference? Logically it would seem that dowels or biscuits would keep the joint from moving.

Mike

[Danny Richie]

I'll also add that cutting the wood with 45 degree angles and allowing the seam to be in the middle of the corner helps a lot compared to a butt joint. 

[WGH]

Dowels have very little strength, they are used for alignment only. A dowel joint used for strength is guaranteed to fail. Biscuits are great, I use them all the time but still mostly for alignment but they do add some strength. I use them to join two panels together. Neither do anything to mitigate the humidity and thermal expansion problems inherent with MDF.

This is a fun page: Graphically compare different material properties, look at the properties of MDF against other materials including bamboo plywood.
http://www.makeitfrom.com/material-data/?for=Wood
 

[dBe]

I did some research for a large veneered table a while back to find out what would be the best substrate to use. Although MDF would be the logical choice, after reading about the material I discovered it moved too much with humidity changes and would not work at all. When making speaker cabinets with MDF the builder has to deal with two factors: linear expansion and thickness swell. Manufacturers who ship their products world wide have to allow for temperature and humidity extremes that the average home owner never encounters, so extra ordinary measures need to be taken.

A construction technique that may work is to assemble the entire speaker cabinet with West epoxy, making sure the end grain is completely wet out first, then a thickened epoxy is used for assembly so you don't get a starved glue joint.

The document "Dimensional Stability of Particleboard and MDF for Use as Substrates for Lamination" explains why your joints are failing.

Wayne

 

It is the thickness swell that telegraphs through the finish IME.  linear expansion is more or less constand in dimensional panel boxes (as long as they are rectangular) but the 5% swell from MFD is a lot.

Gluing seems to be a lost art.  We have bought into the "glues anything, anytime, anywhere, anyway marketing hype and it just isn't try.  With a lot of composite materials there are certain things that have to be done to insure a good glue joint.  First, use a  glue that is not prone to creep.  Regular Titebond just doesn't cut it.  Then you have to rough up the surface of the panel that has the manufactured skin on it to easily accept the glue and penetrate somewhat.  I use 100 grit for this.  Here is the kicker: edges of the material (end grain) have to be primed with either a thinned waterbase glue or with a very thin initial coat of epoxy and allowed to soak in for a couple of minutes.  THEN hit the joint with a coat of glue and assemble.  Anything else will tend to give a starved joint.  Also, to avoid starvation do not overclamp.  Be sure to wipe of the excess on the exterior to help with sand out.

it works for me.

Dave

[WGH]

I'll also add that cutting the wood with 45 degree angles and allowing the seam to be in the middle of the corner helps a lot compared to a butt joint.

Agreed, but I would use a lock miter router bit, to make glue-ups easier.

[Hank]

Well, WGH, I've been building speakers for at least 20 years, with regular MDF and have never had a failure (warp, split, humidity swell, etc).  I use regular Elmers or Titebond and never had a joint come apart.  I've never used dowels or biscuits - they don't add strength IMO.  No screws.  No nails, except for large towers I will hold braces, fronts, backs and sides in alignment while the glue dries, using my pneumatic brad nailer.   Bookshelf size to towers to Danny's original ALPA LS cabinets monsters.  All with butt joints.  I did buy a lock miter bit for my table mounted router and tried it on MDF, but the thin strip it left broke off too easily, so I abandoned it.  There's more:  I use old-fashioned contact cement to bond 10-mil paper-backed veneer to my cabinets.  Guess I'm doing everything wrong

[WGH]

I use regular Elmers or Titebond and never had a joint come apart.

Good point there Hank. Titebond makes all types of glues, the Original, Type II, and Type III wood glues all have different properties. The Type II and III each have more water resistance, they are also more flexible which is a good thing because parts will stay together even if the wood moves due to different humidity conditions. The bad part is the glue never drys hard and it is always flexible. As the moisture in wood increases it will squeeze the joint tighter and wood/glue joint will raise up creating a raised glue line, sand it down and it will come back.

The Original Titebond dries harder so raised glue lines are less of a problem.

[TomS]

Does Dave live in Ft. Worth?  That is where my Medex comes from I think.  They ship to Stock Buildging Supplies here is ABQ IIRC.  The guy Sean there said it came from Ft. Worth.

Dave

He lives in Plano but covers Ft. Worth among other areas in the metro area.

[lacro]

Haha, well as much as we love using epoxy for everything, when it comes to hiding seams on painted epoxy it's no miracle cure.  Although when we skin with formica, we use epoxy to glue it down because I don't trust contact cement for anything!

 Have you tried softer epoxies? I find Wests epoxy the least desirable for wood strip boat building. It cures rock hard (brittle). I used a softer epoxy (flexible) on my latest speaker build, including several seal coats on all surfaces which really hardened the MDF prior to painting. There are no seams showing so far.

[mrhyfy]

I try to cover my exposed ends with  1/8 inch mdf,,then you have a very thin mdf edge exposed.

[WireNut]

Have you tried softer epoxies? I find Wests epoxy the least desirable for wood strip boat building. It cures rock hard (brittle). I used a softer epoxy (flexible) on my latest speaker build, including several seal coats on all surfaces which really hardened the MDF prior to painting. There are no seams showing so far.

West systems makes their G/flex epoxy where a flexible epoxy is needed.

[Colin Barron]

If laminating butt joints are good enough held together for pre assembly with plaster board screws, pre-drill and countersink, don't forget to predrill the material you are screwing into or it will split.  when it is all dry assembled and everything fits and square, then remove some sides and glue with Cascamite and screw back together.  When those sides are dry then glue another joint, for me this was the best way to ensure good quality.  Wear cheap disposable gloves, Cascamite is very difficult to get off hands.

[lacro]

West systems makes their G/flex epoxy where a flexible epoxy is needed.

WireNut: Thanks for the info. However, what I was trying to say is REGULAR epoxy from different manufacturers has different characteristics. Some are hard and some are  more flexible.

What I have found is that for certain applications each a has its place. In my experience the slightly more flexible epoxies are more desirable. I am not referring to G-Flex which is a special epoxy.

 In the boat building community there are proponents of both types. What I am trying to convey is that it may be worth trying a slightly more flexible epoxy on MDF (not Wests).
 
 Please don't get me wrong. I like Wests epoxy and use it and all their fillers regularly.
I just want to let you know there are other epoxy choices that may work better on MDF.
 

[WireNut]

Hi Lacro,

Yes I agree, there are many to choose from. 3M epoxy is used exclusively where I work for any Proctor and Gamble project.