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Old 01-31-2009, 03:13 PM   #1
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Lap Joint


When installing chair rail and you have a long wall how do you cut the lap joint on a chopsaw? If you hold both pieces together, how can you be sure they are square when you begin the cut. In other words due to the curves on the chair rail the front piece can turn just enough to ruin the cut.

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Last edited by joe3534; 01-31-2009 at 03:16 PM.
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Old 01-31-2009, 03:28 PM   #2
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Lay the moulding flat on the saw and bevel it 45 degrees-a scarf joint. I really don't understand the second part of question about cutting both pieces together.

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Last edited by jerryh3; 01-31-2009 at 03:30 PM.
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Old 02-01-2009, 02:28 PM   #3
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Thanks, I guess it's wrong to hold the chair rail with the back against the fence and set the angle. You suggest the chair rail flat with the edge against the fence and adjust the bevel.
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Old 02-01-2009, 03:16 PM   #4
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If you have the clearance with the saw you can put the back against the fence. Either way will work.
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Old 02-01-2009, 05:24 PM   #5
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I can understand how you may think that you would be holding the two pieces of molding together. But this scarf cut (that’s what it’s called) is not made that way. You will cut each piece independently.

Here’s how:
· Leave your bevel setting on zero. You will not be using the tilt feature for these two cuts.

Decide if you want a right-hand overlap or a left-hand overlap. This will depend upon from which direction you will be viewing the joint most of the time. The joint will look best if you are seeing it from the side with the piece of molding on top. You want your eyes to slide over the back of the joint, not look into the cut.

Do this. Place your right hand over your left hand, just in front of your chest, elbows up, and fingers pointing at the opposite elbows. Now look at your hands from behind your right wrist. Switch, and look at them again, this time from behind your left wrist. See how the overlap is much more distinguishable from the left side? The overlap on molding joints is much the same.

So this is how you will determine whether to turn the angle of your saw to the right or to the left.

· Turn your saw angle either right or left to 45 degrees. This will be up to you, according to which side you want to overlap.
· Lock it off firmly. Do not touch it again. You will cut both pieces from only this setting.
· Place one piece of the molding, top-side-up, on the left side of your saw with the back of the molding firmly and flatly up against the rear fence of your saw.
· Slide a few inches of the molding to the right, under the saw blade... enough to get a clean, clear cut.
· Cut it.
· Now, place the other piece of the molding, top-side-up, on the right side of your saw with the back of the molding firmly and flatly up against the rear fence of your saw.
· Slide a few inches of the molding to the left, under the saw blade... enough to get a clean, clear cut.
· Cut it.

You are done cutting the scarf joint.

They make a glue called 2P-10, I think it's called. This stuff sets up in 30 seconds. Basically super glue for wood. It will help make a great joint when it comes time to put those two pieces together. But most any glue will get the job done... eventually.

Try to arrange this joint so it will fall directly over one of the wall studs, so you will have something to nail into to hold the joint together.

Place the UNDER-lapping piece of molding on the wall first. Then fit the other (top or OVER-lapping piece) to it.

Nail and glue your joint firmly before going on down the wall. This will ensure that the joint will remain perfect while you futz with the rest of the piece.
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Last edited by Willie T; 02-02-2009 at 12:36 PM.
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Old 07-10-2011, 05:37 PM   #6
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Willie!!!!!!

thanks for the great instructions about scarf joints. don't know how I missed them.


Thought I was doing scarf joints. For the cuts below, I was just cutting each piece on a 45 degree bevel. Not sure if that's called anything. I am trying to decide if I pull them down and do them the way you described.

my best joint


not as good***I am embarrassed to show this piece. I had to remove it at some point and I messed it up a bit when I was removing the nail. If I can find another place I can cut up this piece and use it, I will. At this point, I really need to minimize waste (23$ for an 8ft piece...AZEK) and if I can learn from my mistake and maybe clean up the hammer marks (a nail gun would be nice for this work!) I am going to have to.
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Old 07-10-2011, 06:30 PM   #7
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One more comment.

Some people set their saw to a 30 degree angle. But I feel that the longer glue surface of the 45 degree joint is best.

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