45 degree joints - Woodworking Talk

TooPicky · 04-12-2009, 09:07 PM

I have been driving myself crazy for a few weeks trying to make a square part out of walnut. I want a square with edge grain on all 4 sides, so I need 4 triangles with 45 degrees on them coming to a point in the middle. I can't seem to make the angles tight. I am using a dewalt non-sliding 12" chop saw, 80 tooth crosscut blade, and a miter trimmer with a brand new blade. I keep adjusting the 45's to the point that I can't see that it's off with a square, yet, when I put the 4 together, it's not tight. I joint the blank so it has 2 parallel sides to within .005", rough cut them with the chop saw, and then take a trim off one edge with the trimmer, then set up a stop on the trimmer and cut the other side. About the only thing I can come up with at this point, is I have ordered a 45 incra square that I hope will help adjust the trimmer to a perfect 45. Parts are being clamped with a rubber band clamp using gorilla glue. Am I missing something?

**TexasTimbers** · 04-12-2009, 09:46 PM

It doesn't take being off much to show. If you're saw is off .5º then multiply that times how many corners you'll have. .5º is a lot, but a contractor grade miter saw can be off that much.

Are you flipping every other corner over when you make your cut? If you do that, the error cancels itself out. You can also bevel each miter ever so slightly so the face joint will tighten up. Just make sure if you do that, you reverse the bevel when you flip the next corner over to cut it, or else cut it from the opposite side of the blade if your saw is not dual bevel.

Getting really tight miters means working with dead flat stock, and near perfectly tuned machinery. If your blade is a little dull it can wobble in the cut also even though you cannot see it happening with the naked eye.

A quality miter box, with a good quality sharp saw, western or pull doesn't matter, can do better miters with a little practice.

johnep · 04-13-2009, 04:11 AM

Ensure your blade is dead square with one of those electronic angle gizmos.
johnep

phinds · 04-13-2009, 08:27 AM

I do this frequently and long ago gave up on that kind of precision from the saw. What I do is glue the sides in pairs then use a belt sander to make the two resulting internal edges flat, then glue them together. Gives me an absolutly perfect joint every time with no hassle. I only do it on squares up to 6" on a side though, so if you're looking for something really large, might not work.

firehawkmph · 04-13-2009, 10:05 AM

TP,
If all else fails, try making the square 1/4-1/2" larger that what you need. Glue the triangles together as close as you can. Make up a simple jig to hold the square in such a way as to run it across your table saw so you cut right through the joint from corner to corner, diagonally. Glue the two halves back together, they should fit perfectly together now. After it dries, do the same with the other diagonal seam and glue it back together. Lastly, take a light cut on all four sides to get your square back to the exact size you wanted it in the first place. By the way, what is the square supposed to be when you are done?
Mike Hawkins

TooPicky · 04-13-2009, 09:13 PM

I'm only looking to make a square 4" right now. Actually, the saw doesn't matter, since I'm using a miter trimmer, which takes off all sawn edges.
Texas timbers, what brand & model miter saw do you suggest?
Phinds, I though about this briefly, but didn't think it would work. Maybe I'll try it, though.
firehawk, interesting idea, but i'm not sure my contractor table saw is up to the challenge, maybe I'll revisit when I get a cabinet saw.

Thanks for the help! Everyone else's ideas still welcome......

phinds · 04-13-2009, 09:49 PM

I've done it maybe 200 times now, works like a charm. Mike's idea is good but mine will cause less waste, patricularly as percentage of such as small square.