Compount miter angles a little off...

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Forum topic by Robert Newport posted 06-19-2011 02:48 AM 2465 views 0 times favorited 10 replies Add to Favorites Watch
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Robert Newport

21 posts in 2564 days

06-19-2011 02:48 AM

Hi, Lumberjocks…
I’m dialing in my miter saw for cutting crown with the back on the table and the bottom or top against the fence. When I set up for 45º crown and a 90º angle, I get a perfect fit with a 30º bevel and a 35.3º miter angle. However, when I try to cut a 135º corner, I have to add +.7º to my bevel (16.4º instead of 15.7º) and +.8º to my miter angle (17.1º instead of 16.3º). Basically, I’m setting up to cut a 133º corner in order to get a 135º. I’ve checked all my other adjustments: fence is square to the blade, the blade is at 90º to the table, and the bevel is accurate at 45º.
What am I missing? It doesn’t make sense that I could be dead on for a 90º corner and be off by 2º when I move to a 135º.
Thanks in advance for any suggestions!
Robert Newport

10 replies so far

View MrRon's profile


4793 posts in 3265 days

#1 posted 06-19-2011 03:16 AM

You will never get a miter saw to cut a perfect miter. If you do, it’s luck. An angle can be off just a few minutes of a degree for you to notice. Just a slight sidewards pressure on the saw handle can put your cut off. They are not precision machines. If you were to make several 45° miter cuts, and if you could measure the angle with precision machinist tools, they would all be off. Don’t expect metal precision with wood.

View devann's profile


2246 posts in 2714 days

#2 posted 06-19-2011 04:48 AM

You might try going back to your owners manual for the miter saw. Look for a page that looks like graph paper with some radius lines on it representing a four sided box,six sided box,and an eight sided box. The eight sided box is the setting I believe you’re looking for. It sounds like you’re doing crown on walls with round corner bead?

I find the same chart handy for making the corner cut for the fascia board when doing a hip roof with square cut tails.

-- Darrell, making more sawdust than I know what to do with

View sparks44pay's profile


24 posts in 2556 days

#3 posted 06-19-2011 05:38 AM

There are to many variables in cutting the crown molding. Your miter saw could be vary slightly off, as MrRon said a slight side pressure could effect your cut, you could position the crow slightly differently on the saw.

View Robert Newport's profile

Robert Newport

21 posts in 2564 days

#4 posted 06-19-2011 07:03 PM

Thanks, guys, for your responses. I guess I’m just expecting too much from something with too many variables.
Darrell – My owners manual doesn’t have a page like you described. I’m not sure I understand what it’s purpose is. Could you expand on it or tell me where I might be able to find a copy? I am doing crown, but not what you described – I just want to have my angles come out accurately, especially when I’m working with natural finished crown above kitchen cabinets, as opposed to painted crown on walls.
Thanks again for everyone’s input.

View Loren's profile


10476 posts in 3670 days

#5 posted 06-19-2011 07:53 PM

Really hard to get it perfect.

Learn to refine the inside of miters with a block plane, chisel
or surform. Also, you can roll the ends of an open miter with
a round screwdriver shaft and close up a disparity in the

Also, there are many back angles of crown produced, and you have to
check them carefully to know which you are working with. I
don’t remember off the top of my head, but it seems I
expected it all to be 45 degree when I was starting out and
later found out I was dealing with 52 degree and other back
angles on a fairly regular basis. Suppliers of crown are seldom
knowledgeable enough about actual craftsmanship issues that
they can tell you the back angle of the crown.

View Robert Newport's profile

Robert Newport

21 posts in 2564 days

#6 posted 06-20-2011 02:11 AM

Thanks, Loren!
I’m aware of the different spring angles of crown, so definitely “lumberjock beware”.
Good suggestion about the screwdriver shaft.
Certainly, the key is to always leave yourself some extra wood to refine the corner to get the best results.
Thanks again,

View Grandpa's profile


3259 posts in 2697 days

#7 posted 06-20-2011 04:34 AM

The screw driver will become your best friend. The problem with crown molding is it doesn’t all come off the same cutter so it will vary slightly so it has to have a little tweaking sometimes….well, most of the time. Work the back and roll the front side.

View devann's profile


2246 posts in 2714 days

#8 posted 06-20-2011 07:43 AM

Robert, A De Walt miter saw manual will have the page I’m referring too. First, are you using crown that you made or bought?
As Loren mentioned most store bought, commercially made crown is cut @ 52/38 degrees, and the proper miter saw settings for this angle of crown is 31.62 degrees miter and 33.90 degrees bevel. This is for a square (90degree) corner, cutting the back of the crown laying flat on the miter saw table and top/bottom against the fence.

When you said you had a 135 degree corner I was thinking that you were cutting an outside corner with the round corner bead on a wall.This scenario requires a small piece between the two longer pieces running down the wall to the corner, the reason for the eight sided box setting on the chart from the owners manual.

Is this corner you’re working on an outside corner or an inside corner? If it’s an inside corner I would probably use a coping saw on the second piece to get a good fit. The method is more forgiving and easier to make a good looking joint. If it is an outside corner you have probably already taken a couple short pieces of scrap by now and tried different settings on the saw until you have found a satisfactory fit.

When I start a crown job the first thing I do is cut a pocket full of small shims ( 1 1/2”- 1 3/4” long x 1 1/2” wide x 3/16”-0”). I use these for any deficiencies in the wall/ceiling to help with the joints. You applying you crown to the face of cabinets shouldn’t need any there but you may need some along the ceiling/crown connection to close up your joints.

I’m no mathematician Robert but I can tell you this. 12” run and 12” rise equals 45 degrees. 5” run and 12” rise equals 22.5 degrees. You would think that 6” run and 12” rise would be 22.5 degrees but it’s 26.5 degrees. I know that doesn’t make sense at first. And I’ve forgotten the answer why years ago but that’s why you’re scratching you head wondering why your setting are slightly off.

-- Darrell, making more sawdust than I know what to do with

View Robert Newport's profile

Robert Newport

21 posts in 2564 days

#9 posted 06-20-2011 06:04 PM

I’m just using some 45º MDF to dial in my saw. The 135º was for a cabinet job where the crown sits on top of the cabinets (not attached to the ceiling) and is attached with a railing that runs around the top of each cabinet (Costco is where my customer got the crown, along with the cabinets). One of the cabinets had an outside and inside 135 and then a 90 to return to the wall. That job turned out fine, but I realized that my fence was off, requiring a .5º adjustment + or – to get the right angle. After the job was done, I set about doing a full adjustment on the saw (only 2 months old) to make sure it’s completely square. That done, I set about re-cutting my sample pieces to see if everything was square. My 90’s are dead on, but the 135’s were coming up at 136.5, so I was concerned that something might not be completely adjusted. As we all know, nothing is 100% square, level, parallel or vertical, but it seemed odd that I would need to cut a 133º to get 135º when the 90’s are spot on. Shims are a definite, and I was even having to shim the attachment rail (with pieces of chipboard!) on the cabinets in order to get the height to all match up. Cutting long and leaving a little extra on each piece to dial everything in is my key to good looking crown. Thanks very much for your suggestions and your brain twister. I’ll check the DeWalt site to take a look at the grid you mentioned.

View Moron's profile


5032 posts in 3915 days

#10 posted 06-20-2011 06:27 PM

maybe try cutting the crown by putting the crown mould on the miter saw, upside down with one edge on the back fence and the other on the bottom. If you put a false 90 degree wood fence onto the saw you should get perfect results and its easier to “tweek” the miter

-- "Good artists borrow, great artists steal”…..Picasso

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