I have never cut a coped joint that fit accurately up against a scrap piece .
I can make an accurate cut to the line generated by the power miter saw, and I back cut the joint severly. I use a coping saw.
I hold the stock against stops on the miter saw fence to insure the tilt angle is correct.
I think the problem is that the line I am cutting to is not the correct line. This is caused by two things:
I have never used a miter saw that cut a true surface That is ,one that lies in a plane. They all look good until you hold them up to a light with a straight edge.I have used Delta, Milwaukee, DeWalt, Bosch.
The blade pressire bows the stock. Will appreciate comments. Jim
This is a function of both the blade, the saw, and technique.
A thicker blade is less likely to deflect in the cut--my miter blade is
0.134" thick. Also, make sure the blade is sharp.
Most sliding miter saws have more slop than most non-sliders.
For technique, on an angled cut the blade will tend to pull the workpiece into the blade. If you're compound cutting with the moulding flat on the table, it might help if you use a clamp to hold the workpiece in place. Then smoothly make the cut with moderate speed.
Make sure the blade is sharp. If you're cutting at the spring angle, make some supports to keep the crown in place and reduce bowing. There are commercial ones available
formatting link
but you can make something similar using plywood or just hot-gluing some wood strips directly to the saw.
I've taught a lot of guys to cope crown over the years and the biggest problem they seem to have is that although they think they are under cutting enough, usually they are not. When coping base you barely need any back-cut but with crown you have to back-cut way past 45 degrees. If I was guessing (which I am) I'd guess that your coped piece is hitting in the back before it ever gets tight in the front. In one's mind you think that the cope should fit if it's a hair over a
45 degree back-cut. It won't. You need much more back-cut.
When your coping, lay the coping saw over until you think there's no way in hell I need to lean that blade that far. Then lean it just a little more and make your cope. My guess is that it will fit. I know you think I'm nuts...I've seen that look before...but try it on a nice soft piece of pine crown and see if it works for you.
How are you placing the crown on the saw? Are you cutting the crown upside down on the saw?
Any of the above saws with a decent blade will make a good enough cut that you should be able to follow the line for a decent cope. We use Dewalt chop saws on the job and I'm sure I've made a few cuts well past time for a sharp blade. I don't think it's the saw(s). If the line is not correct it's more likely to be because the piece was not positioned correctly on the saw.
It's also possible that the pieces are not positioned correctly when installing them...or at least not positioned the same as they were positioned on the saw when they were cut. If you are cutting the crown upside down and (for example) the bottom edge of the crown comes up 3" on the fence, the bottom edge of the crown will also have to be positioned 3" down from the ceiling, during installation, for the coped angle to fit.
Yes, I cut upside down in the miter saw. I do'nt think you are nuts as I know the back cut has to be severe. I am talking of a fit to a scrap piece on the bench, let alone its mate on the wall. Thanks, Jim.
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