Accurate Miter Cuts on Very Large Beams

A wide-ranging set of suggestions for making fine miter cuts in 6-inch deep members. July 12, 2012

I want to cut miters and accurate cross cuts on large pieces of wood which are too deep for cutting on a sliding table saw or other saw. Has anyone had luck making a sled to accurately cut miters on a band saw? If so, how best to do it?

Forum Responses
(Architectural Woodworking Forum)
From contributor L:
I think it is unlikely you can sled cut good miters on a band saw. How thick is the material? If these parts are so big a slider can't do them, handling them on a bandsaw would be a real challenge! You could cut them a little over and then use a hand plane and shooting board for near perfect miters (parts no thicker than your plane iron). Considering a slider can cut a 10' miter up to about 4" thick and that isn't big enough, I'm sure glad I'm not handling these!

From contributor A:
Use a circular saw or a plunge saw with a fence or track. If it's not a clean enough cut, rough it with a circular saw, then cut 1/8" off with a router, likewise using a fence.

From the original questioner:
The pieces I am cutting are 6" to 7" thick veneered hardwood and the deepest I can cut on my table saw is 4". Also the deepest I can cut on a 12" miter saw is about 4". There must be a way to do it accurately. The best idea I can think of is a bandsaw. I am not sure if there are blades fine enough, or if it would even work.

From contributor M:
Can you use a larger diameter blade in you panel saw? We do the same in our Altendorf. Be sure to reduce your RPM.

From contributor L:
Generally you need a blade with fewer teeth, the thicker the wood. At any rate I don't think you can get a decent miter cut on a bandsaw.

From contributor I:
Rough it out on the band saw as close to the cut line as you can and make a jig to clean it up with a router or shaper.

From contributor K:
I think I would rough it out on the bandsaw, trim as deep as possible from both sides with a router and guide, and clean out the center with a hand plane. Accurate initial milling and layout are key. You might get closer by cutting the miter from both sides on the slider with the fence or guide block reversed for the second side. I would be very skeptical of a 6-7" thick veneered solid hardwood mitered piece staying tight over time, unless the section were built up from thinner pieces closely matched in moisture content, and even then... What is it that you are making? You might consider a box section built up from MDF, veneered and mitered from both sides on the slider. I think you are going to have some handwork with a plane or sanding block no matter how you go about it.

From contributor K:
Rethinking my previous post, we did some similar pieces by building MDF box sections, joining them on the square and sanding flush, then veneering over the assembly with miters on the veneer joints. We ran the veneer through on one leg, then trimmed the veneer back with knife and chisel to the miter line and glued on the adjoining veneer with clamps and cauls.

From contributor G:
You think you could half miter the piece on your slider and clean it up with a circular saw and router? Like a 4" deep score cut then circular saw and flush trim. Does it need to be clean cut on both sides?

From contributor D:
I'd do it with your tablesaw for a one time solution. Cut as deep as you can on one side, then flip the piece over and cut heavy. Use accurate calipers to dial in your angle, measuring differences front and back. Once the heavy cut is even and the angle is dialed in, just skim it a little at a time until you are flush. Unless you like handplaning end grain. If you have a bearing guided flush cutter for the shaper, you could leave one side heavy and flush it with that, although blowout is more likely than with the tablesaw. The proper solution for doing this all the time is a carbide tipped resaw blade in your bandsaw.

From contributor P:
Rough cut it on a band saw or whatever and then clean it up with a disk sander - they are very accurate.

From contributor W:
However you cut the miter, you could veneer it afterwards to keep the joint you see clean in the veneer. I might take them to the Formica shop and use the panel saw they cut tops on, but without the veneer on yet.

From the original questioner:
Thanks a lot for all the great ideas. I guess I forgot to mention that the pieces are hollow but have a finished veneer on top. Another Idea I thought of would be making an old fashioned miter box and using a sharp, fine cut, hand saw. I am also going to look into what kind of carbide resaw blades are available for the bandsaw and see if I can make that work. I also like the Idea of cleaning it up with a disc sander.

From contributor P:
I have a 20" disk sander. I can't tell you what I use it for, but I use it every day.

From contributor E:

Contributor P is right. The disk sander is the way to go after it is roughed out on the bandsaw or something else.

From contributor Z:
You could make a little jig that clamps to the side of your board (or beam in this case) at the correct 45 degree angle. Then add a sub base to your router and float it over the surface to smooth it out. Same idea as if you have a board wider than what your jointer can handle. You obviously first need to rough cut the 45, which could be done by any number of methods with easiest being, dare I say it, a hand saw.

From contributor Y:
Many years ago I installed 6 inch oak crown molding on a ceiling. My manual Stanley miter 6 inch blade wouldn't cut through. Used my backsaw held tightly against cut to finish, which produced a good flush cut, sanded with a careful eye, coped out and installed. I would think being a laminate, this may not do.

From contributor B:
I used to mitre logs and timbers like this all the time. Lay out the mitre joint across all faces of the beam or box - use a sharp pencil and a combination square. Use a sharp knife to cut the wood fibers at the line, and then use a sharp chisel to chop down at the correct angle (by eye) along the sides and top and bottom (angling towards the center at top and bottom).

Take a chainsaw with a sharp chain and cut to within 1/16" of the chisel marks (this takes a little practice, but you could use a beam saw with a sled to do this also - needs a good carbide tipped blade). Use a hand-held grinder with a sanding disk (60-80 grit) to clean the wood back to the chisel marks and adjust the joint. This can be done fairly quickly on multiple joints at the same time; mark all your joints, knife all, chisel all, etc.

Obviously, this takes a little practice, but once you get this technique, you can cut any mitre in any size timber, and most importantly, you are taking the tool to the work, on a large piece, and not trying to take the work to the tool; an important procedural and safety concept that doesn't seem to be taught anymore.

From contributor O:
A radial arm saw with a 20 inch blade will give you 6 1/4 depth cut. I'll bet that you can find them up to 24". I would buy one with, or add, a hydraulic feed. (A blade that big on a RA saw that began to self-feed would be an arm full of nasty.)

From contributor D:
Yeah, I can see a bad scene kicking back with that big of a radial arm. I've used a couple with some green white oak. Let's just say I got lucky. Fast and furious doesn't work in some shops. Hand saws, chisels, patience, dexterity, and a good work ethic get it done. Seriously, even though he says the work is hollow, stock that thick is safer, quicker, and more accurately cut with a resaw blade in a bandsaw. Slicker than any cut made with a 128 tooth chopsaw blade, which none would handle, 'cept maybe a 15" Hitachi? Might be worth it if it is, but a resaw blade is cheaper. And yes, I agree a handsaw in a miterbox is cheapest. Do that a hundred times, though, and you'll think differently...

From contributor C:
How many pieces need to be cut definitely has a bearing on purchasing new gear to me. Also seems everyone is tossing out ideas, but the length of the part being cut, and the width of the cut, are still unknown.

So I might do the same and offer that if there were only four to twenty cuts, I would lay them out with a marking knife and cut with a sharp pull saw, 240mm size, probably using the rip side of the blade, then clean up with a sharp hand plane. Japanese planes handle end grain as good as edge or flat grain.

A little practice and you will be cutting the line instead of next to it. Lots less cleanup. So what are you making?

From contributor U:
In the old days we would just sharpen up a good handsaw and build a dedicated mitre box for the application. I completed dozens of built-up transom pediments 6 inches deep at the top and 18 inches tall. The mill shop joined up in lengths of twelve foot. Doorways 36 to 48 wide. Twenty years ago as an apprentice… not bad once you get the hang of it.

From contributor V:
The way I've done it in the past is cut narrow edge face down on table saw at correct angle, use backing-board to control tear-out. You then have kerfs both sides in correct position, if your sled was perfect 90 degrees. Then I register off these to lay out and finish the cuts, usually with jig saw, and leave enough material to trim with router to the layout lines. For the routing I use a straight edged board clamped to the piece at the layout line, then trim with a top bearing straight bit.