Working with MDF

[chpthril]

Calling all you carpenters, woodworkers and DIY weekend worriers. I'm looking for your tips, suggestions and methods of working with 3/4" MDF. I've built a few sub boxes lately and they have not gone together how I want, and just not come out as good as I want. Once they are assembles, they are strong, durable and sealed, and a good coating of bed liner or carpet will cover all the mistakes, I just think I can do better.

What tricks and tips for cutting straight:

What size screws do you use:

Do you pre-drill and counter sing:

What do you use a wood filler:

What kind of sealer do you use o the inside:

Post your work-in-progress pics please

[jwanck11]

Calling all you carpenters, woodworkers and DIY weekend worriers. I'm looking for your tips, suggestions and methods of working with 3/4" MDF. I've built a few sub boxes lately and they have not gone together how I want, and just not come out as good as I want. Once they are assembles, they are strong, durable and sealed, and a good coating of bed liner or carpet will cover all the mistakes, I just think I can do better.

What tricks and tips for cutting straight:

What size screws do you use:

Do you pre-drill and counter sing:

What do you use a wood filler:

What kind of sealer do you use o the inside:

Post your work-in-progress pics please

1. Make a fence!!! Either use a decent table saw with a fence or make one out of a metal level and several clamps. Make sure you have a perfect 90 on at least one corner to work off of.

2. Depends. You are using SS I presume? no more than 2" is necessary. Can prolly use 1 5/8. Pre-drill and countersink (YES!) Use a drill to take screw(s) almost all the way in and finish with a screwdriver... No exceptions even if your drill has a clutch!

3. Glued Dowel and finish with stain pencil(s) or better yet, paint.

4. I always use butter (caulk). A polymer adhesive is good to use... Check out Geocel. Never use straight silicone or latex.

I love working with MDF.

[Timmy!]

I agree with #1, you need a nice panel cutter for your table saw (that you can make). When I was building 2-3 boxes a week I made a panel cutter. Basically it has a guide that runs in the track of the table saw and a stop on the top so you can get the board lined up flush and get a straight cut every time. The other tool that I used was a counter sinker/drill bit thing that has the drill bit and counter sink bit all on one piece. I used 1 1/2" drywall screws and then always glued together with elmers wood glue and then caulked from the inside after the hole was cut out.

If you are doing custom stuff and need the holes filled, you can use Bondo (or higher end polymer body filler) to cover the holes and then sand smooth.

[TRD]

1) I agree w/ both comments. I do like dodo's. The gluing surfaces w/ some Gorilla glue works assume. I am a big fan of glue and nail guns (lazy I guess)

2) Yes you do need to drill/countersink w/ MDF. You can use helicoils that are glue or epoxied in place for strength. I have done this. Works great. Threads are stronger this way.

I will post where this comes from when I find the magazine I read it in. I have NOT tried this yet. But it stated that drill the hole slightly larger then the screw size, fill the hole w/ epoxy and then screw in the screw. It also mentioned to use heat to allow the epoxy to spread into the MDF for strength. What I need to check on is when do you put the screw in, if the epoxy is not solid I don't understand how that would help. I will add to this when I find my magazine, it my be at work.

CHP, if you have any questions give me a call. I have a full work shop up here if you need some tools. I need to build a sub box anyways.

[Bad05]

If you don't have all the above mentioned tools or access to them, a T-Square can be used to ensure 90 degree corners and a straight edge or level with clamps can be used as a guide. You can use a jig saw or skill saw with these other tools and create nice square edges with straight lines. I've made many custom boxes including the one in my Avalanche and wood glues and caulks make a hue difference in sealing the boxes. One thing I like to use after finishing the box and filling all edges/holes is Rhino Liner. This creates a nice finished look and rugged shell that won't dent/scratch or absorb moisture. Just my 2 cents!

[Jason B]

I avoid MDF if at all possible. Get it wet and it's toast. Sealing helps--of course-- but there is no "foolproof" method for using MDF in any sort of wet environment. I've had some stuff last 10 years and other projects last 6 months before deteriorating. If you can afford it use 1/2"-3/4" acrylic. Yes, it's more money, but it's easier to seal and will last long after your children's children's children are gone.
MDF and water are akin to children and sharp objects... keep them apart if you can. (unless you don't like your children)

[Dan and Christy]

I avoid MDF if at all possible. Get it wet and it's toast. Sealing helps--of course-- but there is no "foolproof" method for using MDF in any sort of wet environment. I've had some stuff last 10 years and other projects last 6 months before deteriorating. If you can afford it use 1/2"-3/4" acrylic. Yes, it's more money, but it's easier to seal and will last long after your children's children's children are gone.
MDF and water are akin to children and sharp objects... keep them apart if you can. (unless you don't like your children)

Where can you get acrylic of that thickness?

[jwanck11]

I avoid MDF if at all possible. Get it wet and it's toast. Sealing helps--of course-- but there is no "foolproof" method for using MDF in any sort of wet environment. I've had some stuff last 10 years and other projects last 6 months before deteriorating. If you can afford it use 1/2"-3/4" acrylic. Yes, it's more money, but it's easier to seal and will last long after your children's children's children are gone.
MDF and water are akin to children and sharp objects... keep them apart if you can. (unless you don't like your children)

That is where paint comes in handy.

[Jason B]

Where can you get acrylic of that thickness?

I have always found the best prices BY FAR are on ebay. The retailer in my area is crazy high with his prices. I order all mine off ebay.

That is where paint comes in handy.

Sometimes paint works well, other times.... not so much.

[chpthril]

Thanks for the tips, here are some things I've learned from the past few builds:

Dont put screws too close to the ends, the MDF will split, stop about 2" from.

Prime the box before the bedliner coating. The cut ends like to soak up the bedliner and tend to look weak (thin coated) when dried. The primer prevents most of the liner from soaking in, then when dry, the cut edge looks as good as the flat sides. The spray-on spray can liner works better then paint/roll on.

Because the boxes are coated, I use wood screw, if the box gets wet, it will fall apart long before the screws rust. I will try sheetrock screws o the next one as MDF is easy to strip out, the sheetrock's will add a little extra bite.

[Timmy!]

Wood screws would be the proper thing to use but I'm cheap

[jwanck11]

Actually deck screws are the proper thing to use.

I have used MDF in pantrys and it holds up very wekk if properly primed and painted.

I went next store to a very high-end home theather center and found that quite a few top end speakers are constructed of MDF - although many are multi-lined sometimes with other materials... FWIW

[chpthril]

Regardless of type of wood used for construction, I think it should be sealed for the boat environment i.e bed-liner, polyurethane, 2 part epoxy, etc

[philwsailz]

Actually deck screws are the proper thing to use.

I have used MDF in pantrys and it holds up very wekk if properly primed and painted.

I went next store to a very high-end home theather center and found that quite a few top end speakers are constructed of MDF - although many are multi-lined sometimes with other materials... FWIW

Top end speakers are built from MDF becasue it is a very easy material to machine in a manufacturing environment, and in terms of damping, it is about the most acoustically inert material that is still easily milled and machined in a mass production envorinment. Its acoustic properties are due to is makeup, as it is a mix of very fine sawdust, and adhesives. Acoustically, it is desirable for home audio, as it is hard to excite to resonance by midrange and high-frequency drivers.

Additionally, the density of MDF is very precisely controlled at manufacturing, and it has a uniform resonance from sheet to sheet, from speaker to speaker, making it easy to design in features which will prevent unwanted resonances. Plywood, and hardwoods on the other hand have naturally varying densities, making them resonate differently from sheet to sheet, and speaker to speaker.

These things are relevant to FULL range speakers only. Subwoofers resonate, heck yeah, and there is nothing you can do to prevent it, but it is not the type of resonance that makes for bad sound coloration. Thing is, the frequencies we are reproducing in a subwoofer have wavelengths that are longer than can be made to create a standing wave within any single enclosure panel, (unless you are building enclosures that are like, uh 400 cubic feet or something).

For low frequencies that we are talking about, much of the acoustic benefits of using MDF are unrealized.

Regardless of type of wood used for construction, I think it should be sealed for the boat environment i.e bed-liner, polyurethane, 2 part epoxy, etc

Agreed completely!