Compound Miters on the Radial Arm Saw #1: The Broken fence method

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Blog entry by KTNC posted 04-27-2018 04:58 AM 4596 reads 1 time favorited 2 comments Add to Favorites Watch
no previous part Part 1 of Compound Miters on the Radial Arm Saw series Part 2: Outside and Inside Corners - Crown Moulding »


Reference: How to Master the Radial Arm Saw by Wally Kunkel (aka Mr. Sawdust) chapter 4 pages 69 to 79

I am planning a furniture project that includes a feature like a fireplace mantel. This motivated me to learn how to do compound miters on my radial arm saw. On the internet, I found plenty of information on how to do this with a miter (chop) saw but nothing on using a radial arm saw. I found information in the Mr. Sawdust book referenced above and also in a book by R.J. Cristoforo entitled “The Magic of Your Radial Arm Saw”.

I decided to use the broken fence technique described in the Mr. Sawdust book. The description in the book is pretty thorough but the illustrations are a little hard to understand. By documenting it here with photos, I hope to make it a little easeier.

Before describing the broken fence method, it might be helpful to see what the goal is. The picture below shows a frame I made from crown moulding. All the cuts were made on my radial arm saw (Craftsman model 113.29003) using this technique.

The picture below shows the radial arm saw set up for a 45 degree right miter cut. The pieces laying on the table are as follows (using the Mr. Sawdust terminology)

Broken Fence Board: That’s the big white piece on the left that covers about half the table. It’s function is to support the broken fence. It’s large so that it can touch the regular fence and still be clamped to the table.

Broken Fence: That’s the thin vertical board that’s attached to the right of the broken fence board. It’s an extra fence that is 90 degrees to the regular fence. Height should be max cut depth of the saw: about 2 1/4 inch in my case.

Spacers: The two smaller white boards that you see on the right side of the table. Their function is to place the positioner in the right place to make the desired left hand and right hand miters.

Positioner: The large white panel you see on the right side and covering almost half the table. The positioner and the two fences create two channels into which the moulding is supported during the cuts. It’s large so that it can be clamped to the table.

These pieces allow for cutting of all the left hand and right hand compound miters while keeping the arm fixed in the position shown and with the blade vertical.

In the next picture, the spacer’s have been removed. Once the postioner is clamped into place they are no longer needed. If you saved them along with a sample of the moulding, it would make it easier to duplicate these cuts for a future project.

The next picture shows the moulding sitting in the “cradle” created by the regular fence and the positioner. The spacers (not shown here but earlier) are sized so that the moulding will take on the desired angle. In this case, the moulding is crown moulding so it has two faces that are perpindiuclare to each other. One face is flat on the table and the other is flat against the fence. If we were actually cutting the piece to use for crown moulding the face against the saw table would be the face that goes against the house’s ceiling.

The next picture shows where the broken fence is to be placed. Mr Sawdust says to line it up with the place where the blade comes through the regular fence. I put it just a little to the left so that the blade wouldn’t cut off the corner of the broken fence.

In the next picture, I’ve moved the saw forward to cut a couple inches into the positioner. I put a clamp around the arm to limit travel.

In the next three pictures, the regular fence has been removed and a short fence that extends only to the left of the blade has replaced it. There is a scrap to the right that is lined up with the table clamp. This arrangement allows the backboards to be secured while creating a channel where you can place the moulding to be cut. Mr. Sawdust calls these cuts left hand miters.

In the next picture a piece of moulding is in place to do a left hand miter cut. Note that the “keeper” is the section laying on the table.

After the cut, the waste falls away behind the blade. Mr. Sawdust recommends doing all your left hand miters first which would involve pushing long pieces of stock past the back of your saw. If you don’t have room behind the saw, you can arrange your cutting so that you only have small pieces to cut away as shown.

The next two pictures show the set up for doing what Mr. Sawdust calls right hand miters. The broken fence is removed, the regular fence is put back in place and the positioner stays in place. Note the keeper piece is the short piece to the right of the blade in the picture.

To see if I was creating perfect compound miters, I decided to make a picture frame. For this application, I wanted to frame an 8×10 photo. I made the inside dimensions 7 1/2” by 9 1/2”. The following picture shows all the pieces laid out on top of the broken fence board.

I could tell all the pieces were going together perfectly when I held them together with my hands. I’ve rarely (like never) assembled non-planer pieces like this before, so I did the best I could for now. I put some tape across the seams to hold the shape together. I then flipped it over, loosened one piece of tape to get some room for glue. After that, it went a little bit downhill. I had a hard time getting all the pieces back into that perfect arrangement. However, the end result was pretty good and is shown in the very first picture.

2 comments so far

View Kelster58's profile


759 posts in 1782 days

#1 posted 04-27-2018 09:15 PM

Really cool…...seems like a great way to get the job done….

-- K. Stone “Tell me and I forget, teach me and I may remember, involve me and I learn.” ― Benjamin Franklin

View NormG's profile


6511 posts in 4245 days

#2 posted 04-28-2018 05:49 PM

Pretty safe method

-- Norman - I never never make a mistake, I just change the design.

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