Searching for perfect miters. 45.5 degrees a good idea?

[Drjay]

Hi Gents,

I have been having good results on cabinets of up to about 3/4 CF using 3/4" Baltic birch and a setting of 45 degrees on my old, cast iron top Craftsman contractors saw. Not perfect, but good enough to not need veneering. But, as panels get bigger the "fold ups" get trickier and good results are less assured. I use a magnetic electronic degree reader ( recommended by Tom Z. a couple of years ago) set to 45 degrees and that was a BIG step up in consistancy and accuracy. While searching the web today for an even better way to get perfect miters, I ran across a post that said that by setting the miter angle to 45.5 or 46 degrees, better joints could be obtained. I can see that doing that would result in the outside, visible portion of the joint, being "pinched" tighter but wonder if it would compromise glue line and cabinet strength. I am going to be building a 1 3/4 CF cabinet soon and would like to not have to veneer it to hide imperfect joints.
So, have any of you tried the 45.5 degree method and if so can you comment on results? Also, any additional tips or tricks to get great miters when using the "fold up" method of building cabinets would be appreciated.

Best,
Jay

[davidB]

It helps counteract swelling from humidity in composite board(mdf,particleboard,etc).
Because the veneer does not stretch when the substrate swells.

Not usually a help with plywood.

The old(analog) rule was as close to 45 as you could get, err only on the steep side. Glue should be absorbed, not intersticial.

[DeZZar]

45.1 and add a small cleat to the inside edge of the 45 on one panel. This will help with glue up by preventing the 45's from sliding against each other when you add clamping pressure, it'll also add a little strength and help keep it all square.

[DeZZar]

I can also recommend this method if you have a good router table setup. Perfect locking joint which is a lot stronger.

[a4eaudio]

Just to clarify if anyone is interested, this is a "locking miter bit"

[billfitzmaurice]

On those rare occasions when I do a miter I cut one piece from one side of the blade and the mating piece from the other side. When you join the two it always gives a 90 degree joint. More often than not one cut does both pieces.

[davidB]

Bill's angle, as usual, is both right and complementary.

[johnnyrichards]

Disclaimer: I am not a good wood-worker, but an avid consumer of woodworking videos.

From what I have seen (and experienced), if you are looking for perfect miters, you have to spend a lot of time making sure your gear is all tuned perfectly. The reviews I have seen of the digital angle finders all seem to indicate no better than 1-3% accuracy - that can work against you. A fence that is even a bit off can really mess things up by yielding a diamond shaped panel. Even a runout of 1/16" inch per foot will ensure poor miters. A common fix is to undersize the angles, but as you point out the glue-up becomes a problem. If you use epoxy instead, that might work a little better at gluing-the-gap.

Some machinists blocks can be helpful to set up the saws.

https://www.amazon.com/Anytime-Tools-30-60-90-Precision-Machinist/dp/B00RR0L898

I think you will find miter issues are actually tool setup issues.

[a4eaudio]

I think you will find miter issues are actually tool setup issues.

On a related note.... Assuming you are using a table saw and not going too large, build a crosscut sled dedicated to miter cuts and true it up using the 5 cut method.

You can still target a little greater than 45 degrees if desired or use Bill F.'s method but the sled will get you more accurate and consistent cuts every time.

[jhollander]

I'm not inclined to change my table saw's 45 degree stop. I've had no errors with the angle. All my errors are the blade pulling the board creating slightly not straight cuts. I've minimized this by making the last cut a shallow/ thin and slowing my feed rate. I have veneered boards flat then 45'ed them without much issue.

[tomzarbo]

I use an angle meter every time after I make an adjustment to the cutting angle. The dial on my saw is just to help me get things "close."

Things are usually going to be off by the smallest of "Smidges" when you work with angles. Just make sure the "Smidge" that the angle is off by doesn't make the resulting joint greater than 90 degrees and all should be good. We're talking about fractions of a "Smidge" here anyway.

The BEST thing to do is set the angle up on the saw as good as you can and make a few test cuts; then measure that angle to make sure it's good. That's what I do.

Bill's method seems straightforward, but you may not want to do that with veneered plywood for example, due to splintering. I sometimes get splintering on one side, but very little on the other.
Also, I don't know if that method works with the front and rear baffles, if you wanted to miter EVERY joint on the cabinet, for instance. I THINK you'd have to move the fence from one side to the other to keep the angle the same, and that might create more variability than just flipping the panel over and just getting the miter 'correct' in the first place. I may be wrong here, though, I'm having trouble wrapping my head around that for some reason today.

TomZ

[wogg]

This thread is doing a great job of illustrating just how poor my woodworking resources are. At least I'm pretty good at cleaning up crap cuts after the fact. Also explains why I don't veneer and instead go with solid if I want grain ;)

Great info though!

[ugly woofer]

Plastic triangles used for drafting are also good for setting tablesaw blade angles.

[Regore]

45.5 is a good number. Saves a lot on plastic wood. I use surgical tubing wrapped tightly around all four sides when gluing.
No nails, screws or clamps. Square it up, clean off the ooze, wait 8 hrs and you're done.

[PEB]

Ratcheting band clamp lines up the miter joints while adding pressure. Also works with non-90-degree angles.
3-4 of these work well.
Menard's copied this and their house brand runs $30 each.

[MacLaren816]

This week I cut 3/4" birch ply for a "what the hell, let's see how it goes" pair of Classix II cabinets. The "what the hell" factor being a 3/4" recessed baffle (7"x14.5") with the cabinet walls flaring out at 45° to the external dimensions of the cabinet. The top, bottom and sides are all 45° butt joins, rear of each of those panels is square with the rear flush inside them.

I just set the table saw (DeWalt 7845, nothing fancy) to a hard 45°, raised the Diablo 40T ply blade to max height, and made slow passes (good side up) to the three mitered edges of the outer panels. To my complete surprise, the dry fit was effing perfect. I didn't even tape the cut lines, just rolled the dice. I quickly slapped these together for fun at the end of the night and I was astonished at the join points. I'm attaching a pic but bear in mind i snapped it after I'd released the clamp tension so it doesn't tell the whole story, but it does give everyone a chance to call me a dope for trying this baffle/front edges design.

TLDR - While I can't speak to 45.1° solutions, et. al., I can say with 100% certainty that with a factory 45° setting, a decent-quality blade at the right height, and a little caution, near-perfect panels with razor-sharp join points are entirely achievable on 3/4" birch ply.

Sorry you can't see the corners with the clamps on here, and I'll repeat: these pics were shot after I'd released pressure and let things get loose, but they should convey the idea. If I remember to take any pictures as I get these assembled maybe I'll start a 'terrible baffle idea Classix II build' thread.

Hope this helps, and good luck!

MacLaren Pavemaker
Long-time audio enthusiast, hard copy Stereophile subscriber, member of the cables and power make a difference cult, and DIY |\|008 since 2020