Continuum Speakers Using my Trench Method on the MDF Seams

[davepellegrene]

Man I hope this doesn't' turn into another MDF seam argument.
I've had quite a few people asking me about it so since I've been commissioned to build a set of Continuum boxes and stands, with an automotive finish, I would post a thread on how I do it.

I've had three people contact me about building Continuum cabinets all in one week. Those kits must be flying off the shelves.

Basically to start I built a box with b u t t seams and glued them up. On all the end grain of the round overs I smear body putty as smooth and thin as possible to fill in the grain. My theory is the least amount of moisture the better.



I just did 45 degree miters on the stand posts and used duct tape to glue them up. I basically lay strips of duct tape glue side up on a flat surface, lay all the pieces side by side as tight as possible face down on the duct tape, run glue down the joints and then fold the pieces into a box. Forgot to take a pic of it.



Once glue is set up I run a flush bit around the boxes.



I used a horizontal crown molding bit to make the trench.
Mine was only $25 dollars though.
http://www.rockler.com/product.cfm?p...0&site=ROCKLER

The trenches are only 1/8" deep but the pics make them look way deeper.







Next up Smearing the body putty on.

Dave

[joeybutts]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Those pics DEFINITELY make it look like there is NO way those are 1/8th inch deep.....

I need to pick up one of those bits to try this.

Looking good.

[PWR RYD]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Great thread with great pictures and descriptions. Thanks Dave.

[devinkato]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Not familiar with the trench method, looking forward to more info!

[greywarden]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

If you look at the last picture, the right hand vertical "trench" looks to be about 1/8" of an inch, but the others have some optical illusion making them look to be about 1/2" deep haha.

[tomzarbo]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Yes, a few of those 'trenches' look super deep, but then looking at some others, they appear pretty shallow. It's the combination of dark and light sides of the trench combined with two perpendicular trenches adding to the effect.

Look at the last pic on the bottom and the right most trench at the top-- it looks shallow, then look at that same trench toward the bottom of the pic and it looks pretty deep. It's when it combines with another trench that it looks so deep. Kind of a neat effect.

I'm too lazy to do all that work, I just miter my corners lately. I should try this one time though, I just have bad luck with paint.

TomZ

[kmibb]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Question.

Do the edges on miter cuts swell with MDF? It seems like the easiest thing to do would be miter cuts and avoid all of this mess. However, if the seems swell on those too, then you're not really avoiding anything.

[davepellegrene]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

It depends who you talk to and what area they live in. Some don't have problems with b u t t joints. So they say anyway. Miters will show a line eventually in my experience. Being on the corner very hard to pick out especially on a dark color. It also helps to keep the corner sharp. I'm doing miters on the stands with a small roundover.

It's not really that hard to do the body filler if you have experience with it. If not it could be challenging. A DA sander makes it a lot easier. I just figure if you are going to spend the money on base coat clear coat take the time to hide the seams.

I'll have about two hours in the body putty so for me not a big deal. I'm sure a body guy could do it in less.
Dave

Question.

Do the edges on miter cuts swell with MDF? It seems like the easiest thing to do would be miter cuts and avoid all of this mess. However, if the seems swell on those too, then you're not really avoiding anything.

[jhollander]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Dave are you using the fiber reinforced bondo?

[bigfishe]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Dave try the Nason ful-pox epoxy primer over the MDF
Takes several coats to build up. Once you're there it has the best hide out capabilities
I've found for wood or Bondo.
I've been painting cars and speakers for 26 years!

[r-carpenter]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

Question.

Do the edges on miter cuts swell with MDF? It seems like the easiest thing to do would be miter cuts and avoid all of this mess. However, if the seems swell on those too, then you're not really avoiding anything.

I don't really want to sound negative but I don't understand why Dave is inventing the wheel here. The reason seams show up if bu.tt joints are used is the difference in the expansion/contraction of MDF within it's thickness compare to it's plane. Adding filler to the mix means adding another variable component which will not expand and contract as MDF all together. It's not like the "trench method" is a quick thing. You need to rout the "trenches", fill them, sand and so on. A proper 45miter joint may initially take some time to set up on the router table or table saw but will resolve most of the issues. I have never seen a miter cut show ghosting the same way as a bu.tt joint.
The other way to work around it would be veneering. Commercially, there's a thick phenolic paper that available for exactly such purpose. So, instead of veneer, this paper is pressed on the cabinets using rigid adhesives.

[Pete Schumacher]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

It's simpler to hide those B U T T joints with a laminate like Formica. The cheapest sheets with the smooth base color are maybe $45 for 4x8 sheet at Lowes. Epoxy the Formica to the cabinet, trim the excess with a flush trim router, sand smooth, and apply the next sheet. Scuff the laminate at the end with some nice automotive sanding discs to remove the shiny surface of the Formica, and it's ready for primer/paint.

[davepellegrene]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

It's simpler to hide those B U T T joints with a laminate like Formica. The cheapest sheets with the smooth base color are maybe $45 for 4x8 sheet at Lowes. Epoxy the Formica to the cabinet, trim the excess with a flush trim router, sand smooth, and apply the next sheet. Scuff the laminate at the end with some nice automotive sanding discs to remove the shiny surface of the Formica, and it's ready for primer/paint.

That probably would work using epoxy to install the laminate. Although this would limit you to sharp corners. My biggest problem with this method is I'm sensitized to epoxy so I have to stay away from it.

The West System you guys use I would think would work well also.

Dave

[davepellegrene]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

I don't really want to sound negative but I don't understand why Dave is inventing the wheel here. The reason seams show up if bu.tt joints are used is the difference in the expansion/contraction of MDF within it's thickness compare to it's plane. Adding filler to the mix means adding another variable component which will not expand and contract as MDF all together. It's not like the "trench method" is a quick thing. You need to rout the "trenches", fill them, sand and so on. A proper 45miter joint may initially take some time to set up on the router table or table saw but will resolve most of the issues. I have never seen a miter cut show ghosting the same way as a bu.tt joint.
The other way to work around it would be veneering. Commercially, there's a thick phenolic paper that available for exactly such purpose. So, instead of veneer, this paper is pressed on the cabinets using rigid adhesives.

As I mentioned in the post to Pete the veneer would not work for full round overs either. The phenolic paper you mention even if it is a smooth finish I doubt you could get it on flat enough for a high gloss finish. I have had a few people post pics of the expansion showing up under veneer as well. So under a high gloss finish I bet it would show as a wave. As far as the 45 degree corners I have tried them. I have also tried them with a lock miter bit. Both work ok but I've had the seams show up in about half of them. Not so noticeable on a dark paint but would stick out like a sore thumb on a light color. Obviously the miter would be quicker but the trench is the only way I have found that will stop the seams from showing if done right.

I have quite a bit of experience with body putty so it's really not a lot of work for me and as far as the trenches it takes no more time than a round over to do.

Dav

[davepellegrene]

Re: Continuum Speakers Using my Trench Method on the MDF Seams

This is my first test box I did almost three years ago.
I took these yesterday.





Dave