Woodworking Help!

Does anyone know how to cut a 45 degree angle on a piece of 1/2" MDF? I'm trying to build a box, but the guys down at Sears don't seem to know anything or want to really help. I'm looking to make the edges connect together flush. I don't want to just make a straight cut and just screw that into the other piece of the enclosure. Looks totally unprofessional. So when the two 45 degree angle sides are put together, they form a perfect 90 degree edge. I hope and pretty sure what everyone knows what I mean. Also I'm not looking to pickup some huge and expensive tool just to make a speaker box. I have a dremel and was wondering if anyone knows how to do it on that. Or on something that isn't very expensive.
Okay, I'll try to get a table saw then. My next question will be how good do the angles usually come out at? The first reply is I'll be testing my patience getting two 45 degree angles together. How come? Can't I use clamps or something? I want to make as perfect a 90 degree angle I can putting two pieces togeter. Like a cube, perfect 90 degree angles all around. Hopefully that can be done.


diyAudio Moderator Emeritus
2002-01-21 2:42 pm
near Atlanta, GA
If you have a table saw with good fence, then you can easily get perfect 45 degree corners. I have done it before with no problems. The first thing that I do with the table saw is to put a nice straight side on one sides of the boards, before starting, then put the blade at 45degrees. I measure from the fence to the point of the blade where the outside edge will be. Make sure you measure from the point of which it cuts the wood. Then make the cut. Rotate the board 90 degrees, and do it again, and you have one of your sides completed.

Mess around with some scraps on your table saw before starting your projects. It can be the most useful tool for speaker building.

Don't do that!

A 45 deg edge is not going to be very strong == the two planes of the joint will tend to slip on each other == and if the fence has any play you will drive yourself batty -- just a few degree or so on a 12" cut will leave you reaching for the jar of wood putty -- not pretty -- particuarly true with something like MDF which is heavy. <p> I have a 12" Delta Contractor Saw and a $300 fence on the thing and I rarely make cuts like this without spending 30 minutes adjusting the alignment of the blade, fence etc. Further, the tilt of the arbor must be exactly 45 degrees, etc.,etc.

For MDF and particle board, you are better off with a butt joint and then veneering the entire cabinet. For things like plywood a rabbet joint works well. To reinforce a butt or rabbet joint on the insides you can use pieces of 1 X 1 pine.

Veneering is not difficult, you can purchase veneers mail-order from a number of places, and you can knock yourself out on the number of woods to use as finishes. You can cut veneer materials with a utility knife (better still with a veneering saw which is only about $10). I am absolutely certain that if you are just starting out, using a simpler joint and then putting more effort into veneering the cabinet will yield a much better project.
Much depends on the dimensions of the pieces.

Sometimes a table saw is best, other times a radial arm saw is best. I do not believe you will succeed with a router. You really have to be good to do it with a Skil saw.

If it's a full miter box you have 12 edges to perfectly line up. Every single cut must be dead on. In addition, if you are going to use biscuits (or a spline which is preferable for a larger box) all those cuts must match up as well.

And then there is the problem of assembly.

Without the proper tools adjusted perfectly and a lot of patience, you will be at your wits end.

Butt joints with a spline or biscuits would be easier. You could then use MDF and veneer it. Veneering is a lot easier than mitering and you have a tremendous choice of woods.
Given up on biscuits

There was an article in Fine Woodworking 3 or 4 issues ago which concluded that biscuits aren't as strong as everyone had thought. They help a lot in the alignment of cabinetry, and unless you are going to stand on the speakers, are probably a good idea in this application. Again, however, a good biscuit cutter costs a couple hundred bucks.
I've got the little picture frame biscuit machine (can't remember the brand name at the moment). This machine is cool because it will work even on really small pieces of wood (where you really need the extra help holding things straight) and the joint strength is impressive, comparable to dowels.

I even use it for some general jointery when working in hard woods (doubt if there would be enough material for MDF), you just use a couple of extra biscuit if worried about strength.

My small biscuit machine cost about $70 US.


If you use a table or radial arm saw, test the blade angle on some scraps first because it is rare to get the cut right the first time.

I assume you have a carpenter's square. Cut two pieces of scrap and dry fit together (anyway you can--hot glue). Put the test joint in a carpenter's square and see how close the joint is to 90 degrees. Adjust blade angle.

I would suggest butt joints with veneer though.

not a good idea...

A 45 is a bad idea. First off it is very, very hard to do well. If this is your first project and you are not experienced working with wood I suggest that you use a butt joint. It is really easy and if you are painting or veneering the sucker it will never show, plus this type of joint is much stronger and more forgiving if you make a mistake. I am a very experienced wood worker with probably $20,000-40,000 worth of the best tools you can buy, and even I have had problems getting a 45 Perfect. It takes lots of time and unless you are using a fine wood witch you are going to stain stick with a butt joint. If you are painting it I can give you tips on how to make those seems disappear.

Good luck,
Is a 45 degree mitre stronger?

The surface area of a 45 degree mitre is about 40% greater than a butt joint, but I wonder, if you look at the way in which the force is distributed whether the strength is really proportionate to the surface area. At any rate, butt joint or mitre joint use battens made of 1 X 1 pine and you will have a very strong carcase!

Did I ever tell you about the time I built a pair of TL speakers using particle board as a form for concrete? Tamped down there were no voids, and no vibration either. They also couldn't be moved! As I feared that one of the kids would push them onto a younger sibling I broke them apart with a sledge-hammer! Too bad, very nice walnut veneer.
my thoughts

I have to agree with the numerous other posts discouraging the miter corners. Especially if what you're planning to use to cut them with is a dremel. First, you'll kill that poor machine, and secondly, you'll never get the joint perfect. (Or even really close for that matter) Since this is your first project, and you don't have a lot of woodworking resources, definately stick with the butt joint. It'll be stronger than you think! (For those who don't know/understand what a butt joint is, its simply taking one board and gluing it to the edge of a second board. Two straight cuts, very easy to do)

As for looking professional, butt joints are used all the time by professionals! If you're talking about how speakers look, what you're seeing is a veneer over the MDF put on after construction. (No, those beautiful walnut/oak/paduak speaker cabinets are not solid walnut/oak/paduak, they're veneers!!!)(

Okay, now to help the arguments about biscuits and joint strength. It has been shown that biscuits do not add much strength to the joint. They do, however, aid in aligning the joints. As to joint strength, if you're using a decent wood glue (Tightbond is a decent one) the glue is stronger than the wood!

My recommendations to the person building the boxes, go with a simple butt joint, making sure your cuts are straight, you'll have no problems whatsoever with strength of the joints.