Hi,

Getting ready to aquire the materials to start putting this thing together.

I looked at Home Depot today, and they have both 1/2" and 3/4" MDF.

I've noticed that every PLOG I've read that is using MDF is going with 3/4". Is there a reason for this? I think I'd rather go with the 1/2" since it would make for a lighter box, and easier cutting.


I'm a newbie when it comes to wood working (despite all of the tools I have), so any help would be appreciated.

Forgive me if this has been covered but I got back nothing when I used search.

1/2" is flimsier and more prone to split if you're not careful. It most certainly can be used if you're very careful and do a good job of pre-drilling all the holes for your screws.

I went with 3/4 because I wanted the extra thickness so I could use longer screws for screwing stuff to the box. My box is very heavy though, and if I were to build another projector, I would probably use 1/2" MDF for as least some of it, if not all.

I think ½" is fine also. Might wanna glue some small pieces of scrap around some of the joints for extra stability.

1/2 MDF will drive you nuts if you have never worked with it before.....as a warning (and you dont have to believe this, lol) i bet you will split 75% of the screws you put into it! (seriously).


3/4 is much easier to work with, but still very prone to splitting (practice on some scrap pieces first....it is not at all like wood, if you use a drill to set your screws and over torque, it will break it like paper).

You can get very nice 9 or 11 ply plywood for about the same price of 3/4 MDF....it definately wont be as straight, but you can square it up yourself if you have a saw and a couple of clamps and take your time screwing it together....... and approx 30% lighter.

I agree with everyone else here. More thickness makes building the box easier. Pre-drill all of the holes and countersink them to hide the screw heads with wood filler.

I went with 3/4" for this reason and am happy with the way my box is looking.

Food for thought.

Thanks guys.

I used 1/2 inch MDF on mine. If I were to do it again, I'd use real wood, not because the 1/2 was hard to work with, but because wood is so much easier than either size MDF IMHO.

I used 5/8 on mine, seemed to be a nice compromise. Go easy with the screws, and predrill every hole. Also, dont put a screw anywhere within 1" of the edge of the board.

The size of the wood really depends on your design. If you are going to route lines into the wood, I would use 3/4", if not, 1/2 will be lighter, but still useable if you predrill all holes. It is difficult to drill into the side of 1/2", let alone 3/4". I would avoid MDF or plywood all together due to their tendency to split, and the overall look. I am using aspen which I bought at menards (shrinkwrapped) that was 24" by 76" for $28. Looks nice and cuts easier in all ways than MDF or plywood. Another nice looking and useable wood is edge glued pine. Look at Haas Man's PLOG. He used that, and it stainded nicely, and comes in 3/4" if you buy the stuff that comes shrink wrapped. Good luck!

I have not worked with MDF but I am having absolutely no problems working with 1/2 " birch plywood. It is strong, solid and cuts easily.

It also looks good. It is furniture grade plywood. Got it from Menards.

I'm building mine with 1\4" Baltic birch ply, it's flat and square with no voids.
And light.
Don't need no stinking screws! Gorilla Glue only.
You will need a lot of clamps though.
Pictures soon.

If you pre-drill your holes, you will never split any wood you work with.

What Agent said is correct. I pre-drill all of my screw holes. But I would do this regardless of the wood thickness. It just provides a cleaner and more precise connection.

Druid,

I would not wory so much about the strength of 1/4 inch plywood as would about using only glue as the fastener. It may work, but it seems to me you are risking a lot of expensive equipment for brevity. As the glue heats up and ages, if it weakens even just a little you may get a cascading weakening effect that allows the bottom to drop out of the box. Good buy lcd and ballast. I would consider that possibility in your overall design, and maybe even supplement the glue with brackets or such.

With good joinery (ie: not just but-end joints) the glue is stronger than the wood that it holds.

It is in the interest of brevity that I forgo making proper wood joints in favor of screws.

I second that. If you properly glue a plywood box together. It AINT coming apart!
With a shotty glue job, maybe. If you do a good job using good carpenters glue and clamps, that aint gonna happen. An 800 pound gorilla couldn't rip it apart.

My computer desk, I made from 5/8 birch plywood 10 years ago. It is in 3 sections. Each section is 100% glued together. Zero screws. Of course each section is screwed together.

The wood would tear apart if you tried to pry any of the joins apart.

Glue is MILES stronger than any screws when properly done.

I forgot to mention, I did use dowel rods on my desk too.

Attention to detail is everything.
A glue joint is always stronger than mechanical fasteners when the right glue is applied correctly (a tight joint doesn't hurt either ).
MDF (Medium Density Fiberboard) is more stable to temp/humidity than wood stock, but it is pressed paper basically and must be predrilled. Avoid screws in the ends and add stiffener blocks if you are unable to make tight enough joints. Common sense stuff.
I've used Gorilla glue and literally gallons of Tite-Bond II to make commercial MDF cabinets and highly recommend either.
The downside, of course, is that you have to wait for the glue to cure before handling the parts, whereas a screwed part is ready now.
If you are confident in your wood skills go 1/2, if you are lacking either tools or experience, 3/4 is fine too, only heavier.

Can't argue with anyone about what is stronger since I have never successfully used glue. Gotta take your word for it if ya'll say glue is "Da Bomb". However, I still don't get that warm and fuzzy feeling glueing all of my parts together.

Thanks fellow glue users.

I've used Gorilla for years and have not had it fail yet,or tite-bond II for that matter.

Tight joinery, good jigging and good clamping.makes for a strong glue-up.

Your right on with your advice V&J.

My box is not really a box, but is two trunacated pyramids base to base. 1\4" Baltic birch is plenty strong for this applacation.

And... Here's an observation...

Thos of you using laminated pine... Or even plywood. What do you think is holding hte individual pieces of wood together? (Hint, it's NOT screws!)

While I've seen laminated pine panels split from being overdry, it's always been the wood that splits, not hte glue joint. Occasionally there may be a defect in the lamination process that leaves a defect in the panel, but you tend to find out about those things ahead of time...

Simple reason: That's what Brain called for in the guide.

I do pretty good with just glue, biscuits, and scrap glued to the inside of the joints. The only time I use screws is when I want something temporary. With MDF definitely predrill when using screws and use glue also. I don't trust MDF structurally. If you've never worked with MDF before I'd suggest using plywood instead, especially for such a small project. The advantages far outweigh the cost compared to MDF. Even then I still use glue. It's the wonder fastener of the world! Another way to look at it is. Would you feel safe if every weld in your car was replaced with pop rivets? I'd much rather have something bonded than point fastened. You can always find something else to work on your projector while the bond cures.

While you may be right about the glue, I don't think you can accurately compare a welded joint to a glued joint. Maybe a better comparison is, would you feel safe if all of the welded joints in your car was replaced by superglued joints?

I think we all know the answer to that one. But then again, a PJ is not a car.

One good analogy that supports the use of glue is that new civilian spacecraft that made orbit recently. It is all glue and fiberglass.

Well the lotus elise chassis is glued together so my answer to that question is yes. From my limited experience of using glue with MDF, I would say you need to be careful. The no more nails glue I use is incredibly strong, but with MDF basically being loads of bits of paper glued together, all your gluing to is the top layer of paper (unless gluing the side obviously), that can come away easily.

I thought my analogy was correct in a comparison of point fastening and molecular bonds. Point fastening is only strong linearily in a given point while molecular bonding is strong linearily and radially throughout as long as it's truly a molecular bond in which super glueing metals isn't. Choosing the right bonding agent is of the utmost importance, else the bond is worthless. I've used the liquid nails type of adhesives with woodworking with great success. I've yet to find a good one for acrylic though.

Just wanted to put in my two cents (canadian - so only one cent american). I agree with jcrack - you still need to exercise caution with 3/4 mdf - even if predrilled. I recently finished my last project (glued+screwed 3/4 mdf) and had a couple cracks from overtorqing the screws.

Sorry for the off-topic pic. I can't wait to get started on something that really takes some ingenuity. Very impressed with all the projectors I have seen on the forums. Kudos to all.

If you built that speaker box, then I'm sure your PJ will look equally good. Looks very nice.

As far as the glue vs screws debate, I used to build custom enclosures for competition audio as well as customer boxes like the one pictured in Pinky's post. We use Liquid Nails and screws every 3" or so on all the boxes. The wood we used was always 3/4" MDF. One time me and my partner glued and screwed the wrong pieces together. We realized this about 20 minutes after gluing it and quickly unscrewed the screws and tried to take the box apart. Lets just say that it didnt happen. We eventually resorted to a sledge hammer and a piece of 2x4. The box ended up breaking before our joint did. I highly recommend Liquid Nails for something you dont want to ever come apart. I would liquid nails my car together WAY before supergluing it (as in the previous example). The reason liquid nails is so strong is that it stays soft and will absorb impact unlike superglue and other brittle wood glues.

Yellow wood glue is stronger than wood, the wood will always fail before the joint unless the glue was not applied properly. I sometimes use screws instead of clamps so I can keep working on the project while the glue cures.