Crown Molding Coping Cuts Problem

Old 11-12-17, 02:23 PM
Thread Starter
Join Date: Jan 2013
Location: US
Posts: 135
Received 1 Like on 1 Post
Angry Crown Molding Coping Cuts Problem

My digital angle finder measures 89.3 to 89.7 for all my inside corners, and 89.6 to 89.9 degrees from walls to the ceilings. So I cut 45 degree and coped it. But it creates big gap at the bottom of the inside corner. I also cut 42 degree (lowest for the left side of my 12" sliding compound miter saw) and coped it, but still has big gap at the bottom.

I watched several videos instruction on youtube, and measured several times and flipping it upside down when cutting, but I can never get it fit properly. What am I missing??? Appreciate some guidance.

I'm wondering, I've been going from left to right, coping the left side of the molding. Should I move from right to left, coping the the right side? Seems it's easier to cope the right side.

Also, having same issue with outside corners. The angles are pretty close, 89.3 degree or so, but the top side has big gap.

Last edited by itchibahn; 11-12-17 at 03:37 PM.
Old 11-12-17, 05:15 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Posts: 29,631
Received 1,642 Likes on 1,470 Posts
Number one, are you cutting the crown flat, or in position? (meaning upside down and backward). Many newbies forget to turn it upside down when they cut. Then when they go to install, the miter is open on bottom.

I find that cutting it in position is easiest... the miter saw table is like the ceiling, and the fence is like the wall. Thus you just need to remember to cut all your pieces upside down and backward. Narrow edge of the crown is facing upward, against the fence. Holding it at the correct spring angle when you cut each piece is also critical.

The reason all your angles are less than 90 is the tape in the corner. Everything can usually be cut to a 90. If you are measuring your rise (bottom edge of the crown) based on a measurement from the inside corner (the hump in the tape) you will be off, and the crown will all need to go higher than what you think. Generally it's good to mock up an inside corner and an outside corner, nail them together... and use them as your gauge to mark where the the bottom edge of the crown should be. If you have nailed the crown too far down on the wall, your miters (or copes) will be opened up on bottom. The opposite happens when it's too high.
Old 11-12-17, 06:19 PM
Handyone's Avatar
Join Date: Aug 2000
Location: U.S.
Posts: 5,449
Likes: 0
Received 0 Likes on 0 Posts
I rarely cope crown. It takes a severe back cut. I only cope crown when I can use painters caulk, not on a finished product.

For the gaps in the outside joints, I hold the crown (upside down and backwards) firmly against the fence and then "tilt" it a little.
I keep in my mind, shave a little off the bottom, which is the top, or the opposite. There is no need for any fancy jigs if you learn to let the crown relax and then hold it and make your cut.

Hope that makes any sense at all It takes some practice.
Old 11-12-17, 07:30 PM
czizzi's Avatar
Join Date: Jul 2007
Location: USA
Posts: 7,388
Received 15 Likes on 13 Posts
Yep, upside down and backwards. The junction between the surface of the saw and the backstop mimmicks the joint of the ceiling. When you put the stock on the saw, have to make sure that the profile on the back of the saw is both flat on the saw and flat on the backstop. When I hang it, also make sure that the stock is positioned appropriately on the wall so that the back profile is flush and then push it up in position. When you back cope the end miters, have to do it with the stock sitting up in position so as you sight down your miter you are looking at it from the perspective of the stock it will marry up against. Carve out enough to clear the profile.
Old 11-12-17, 08:54 PM
Thread Starter
Join Date: Jan 2013
Location: US
Posts: 135
Received 1 Like on 1 Post
Yes I'm cutting upside down and backward, in position to crown molding jig that came with the saw. I'm doing everything that's shown on all the videos.

After playing with two small sample cuts, I found out I wasn't positioning the molding against the ceiling and the wall properly. My 1st piece is 16' long and started out correctly, but at the end it was positioned 45 degree from ceiling to wall causing subsequent two pieces to cause gaps. It was difficult to notice the error due to the corner diagonal cabinet being on the way.

I'm going to fill the two gaps trying to make it least noticeable, and then I'll adjust little by little on subsequent pieces to eventually position properly.

Old 11-12-17, 11:07 PM
Marq1's Avatar
Join Date: Sep 2016
Location: USA MI
Posts: 9,941
Received 1,052 Likes on 954 Posts
I have a set of inside and outside "samples" that are labeled LH and RH that I use to set up the saw and check fit.

Have had them for 30 years and they have saved many a board foot of expensive molding, and frustration.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: