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:
1. 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,
2. 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
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.
The angle does not merely need to be severe, it must be in the proper
When you have made your backcut, lay the piece on a workbench, profile
Take a square and lay it on the back (flat, non profiled side) side of
Draw lines to those parts of the profile that have angles, rather than
These are the parts that usually keep the joint from closing if they
are not hogged out correctly.
Make sure that they are backcut to a minimum of fifty degrees.
It sometimes helps to have a rasp available.
Thos.J.Watson - Cabinetmaker
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