Checking a Radial Arm Saw for Squareness




About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

Radial arm saws often get a bad reputation as being inherently inaccurate.  But with proper set up and usage, this reputation is an undeserved slander.

The photo shows the usual way of aligning and checking a radial arm saw for a square crosscut using a framing square.  It is a good preliminary check.

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Step 1: Sweep Away Chips

Accurate work on a radial arm saw requires good contact between the fence and the work piece.  Sweep away any dust and chips that might lodge between the work piece and the fence.  Each time a cut is to be made, sweep away any dust or chips first.

Step 2: Make a Couple of Square Pieces

I have some thin plywood left over from another project.  Cut two squares about 12 x 12 inches.  The machine cut edge of the plywood is against the saw fence.

Step 3: Mark the Factory Edge

Before you forget, mark the factory cut edges.

Step 4: Mark the Square Corners

The square corner cut in step 2 will be the standard of reference.  Mark it on both pieces so you can identify it easily later.

Step 5: Stack the Two Pieces and Cut

With the two pieces stacked over each other, trim the edge of the two pieces with one cut.

Step 6: Flip One of the Squares Over

The upper side of one of the squares will be flipped over so the edges cut in step 2 meet one another.

Step 7: Push Squares Together and Check for a "V"

With the two squares pushed firmly against the fence or any straightedge, slide them laterally into each other.  Look for any spreading at the front or the rear that makes a slight "V" between the pieces.  A knife edge allows evaluating how much of a "V" exists.  If the "V" is at the fence, the saw arm is too far to the left.  If the "V" is at the back (near the saw operator) the saw arm is a little too far to the right.  The separation noted in the "V" is actually double the amount the arm is out of alignment with the fence.  See also my previous Instructable on a way to make small adjustments in the alignment of the arm with the fence.

The alignment on this saw is pretty good.  There may be a "V" gap of a few thousandths of an inch near the operator, but it is so small over 12 inches that glue would easily fill the gap.

This method can also be used with a table saw, especially if a sled is used in place of a miter gauge.

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    10 Discussions


    3 years ago

    Very nice job. Now, I'm ashamed on the state of my Craftsman radial caused by cutting pieces too large and have been eyeing a 10" chop saw.

    1 reply
    Phil Biceng

    Reply 3 years ago

    Thanks. You may be able to salvage the radial arm saw. But, a good chop saw is nice. I have used someone else's a little, but do not have one.


    8 years ago on Introduction

    I like that vee method you describe. When I aligned my saw I just kept on cutting on a scrap piece of sheet until it really lined up checking it with a square. It took me just about forever to get it as close as I did. It was such a pain in fact that I haven't moved it since! If I ever need to do an angle cut I put the work on an angle and cut it.

    That, and by not swinging the arm I've only one cut in my table too. When I was doing the initial aligning it was wide, but once I got it just so I puttied that all up and now just have a cut the blade wide.

    You should treat yourself to an MDF shelf for a new table for your RAS there Phil. I picked one up at the big orange box store for about $3.49 if memory serves. Then I topped mine with a piece of Masonite hardboard. You don't need to get that carried away though. But it is nice :)

    The very latest was one of them laser line deals I mounted over my RAS. Flea market buy at $4. I think it is going to take some fine tuning to zero in.

    2 replies
    Phil Bpfred2

    Reply 8 years ago on Introduction

    Shortly after doing this Instructable I did get some new MDF for the saw table and made it a bit wider than the original. It appears in some of the later RAS Instructables with an aluminum wear strip across the front.

    The little blocks under the table with the screws running through them make alignment so much easier. Once aligned, you can swing the arm and it will come back to the alignment position.

    Thank you for looking.

    pfred2Phil B

    Reply 8 years ago on Introduction

    Well you needed it. I checked out some of your other articles and I see your saw with the new table. It looks good! I'm still not crazy about cuts all over my radial arm saw table and backstop so I'm just going to keep mine in one spot for now.

    I looked at your block trick and it wouldn't work with how my saw is. But my saw has similar, sort of half C clamps on top that do about the same thing if I am understanding what is going on.

    Thanks for posting.


    8 years ago on Introduction

    Make the fence out of three boards. One is the backing and the other two are the spacers and attach thesee to the backer board and make these a 1/4 inch a part to form a groove that will be just below the table. Chips, sawdust then will go into this groove and make sure your work rides against the fence and not be put out of line with dust or chips.

    2 replies

    Reply 8 years ago on Introduction

    I'm trying to picture exactly what you are suggesting...
    Would this be similar to running a shallow dado groove in the fence itself? (So that a continuous horizontal recess is formed in the fence just above and below the top rear lip of the table where it meets the fence?) Does that groove clean out easily? Could I use 2 strips of 1/4 hardboard for this? Thanks for the cool idea!


    Reply 8 years ago on Introduction

    Exactly, chips dust easily slide into the groove and can be cleaned out easily as well.

    Phil BKnexFreek

    Reply 9 years ago on Introduction

    Thank you.  The idea is not original with me.  I may have read it years ago in Fine Woodworking.  I do not remember for certain.