Mitre saw not cutting square: how to calibrate it

Rule out the simple causes

Before adjusting anything, check the basics. Many out of square cuts come from the work, the blade or the way the cut is made, not from the saw's settings.

• Sawdust or a chip under the board or against the fence.
• A blunt, bent or dirty blade, or a loose blade bolt.
• A bowed board that rocks against the fence.
• Pulling a sliding saw towards you through the cut, which lets the blade deflect.
• Lowering the head too fast so the blade flexes.
• Mitre or bevel lock not fully tightened.

Check the blade against the fence and table

Unplug the saw or remove the battery. Lower the head and lock it down. Set the mitre and bevel to 0. Place an engineer's square or a reliable combination square against the fence and the flat of the blade, avoiding the teeth. Then check the blade against the table for the bevel.

Any visible gap shows which adjustment is needed. A square is a quick check; the five cut test finds much smaller errors.

The five cut test

This test multiplies a tiny mitre error so you can measure it. Use a flat piece of sheet material with four straight edges, around 300 mm square or larger.

1. 1

   Number the four edges 1 to 4.

2. 2

   Cut a thin strip off edge 1 with edge 4 against the fence.

3. 3

   Rotate the board and cut edge 2 with edge 1 against the fence.

4. 4

   Repeat for edges 3 and 4.

5. 5

   Make a fifth cut on edge 1 and keep the offcut strip.

6. 6

   Measure the width of the strip at each end; the difference divided by 4 is the error per cut, approximately.

Adjusting the mitre

If the test shows an error, adjust following your saw's manual. On many saws you loosen the screws holding the fence or the detent plate, align the blade to the fence at 0 using the square, retighten and re-test. Others have an adjustable pointer and a separate adjustment for the 0 detent. The DeWalt DCS782N listing, for example, mentions a stainless steel detent plate and cam lock.

Once 0 is right, check the 45 degree detents with a combination square or a test cut.

Adjusting the bevel

For bevel errors, set the head to 0 bevel and check against the table with a square. Most saws have a bevel stop bolt or cam that you adjust until the blade is exactly square. Then check the 45 degree stop the same way. Bevel scales may need resetting after.

Some saws, like the Metabo KGS 254 M and KGS 305 M, can tilt slightly past 0 for undercuts, so make sure you are on the correct stop.

Sliding saw checks

On sliding saws, play in the rails can make the blade drift during the cut. Clean the rails, check for loose bolts and follow the manual for adjusting bearings or rail clamps. Cut by pushing away from you at a steady pace.

When the blade is the problem

A blade with a bent plate, missing teeth or built up resin cuts unevenly and wanders. Clean it with a resin remover or replace it. A thin kerf blade can flex more on large, deep cuts. See mitre and circular saw blades explained.

Note:Always unplug the saw or remove the battery before checking or adjusting the blade, fence or stops. Keep fingers away from the teeth. If you are unsure about an adjustment or the saw has been damaged, use an authorised service agent.

If it still will not cut square

If the saw cannot be brought into square, the casting, arm or turntable may be damaged, often from a fall. Contact the maker's service agent. If you are replacing it, compare saws in our mitre saw guide and sliding mitre saw guide. Learn safe technique in how to use a mitre saw.

Frequently asked questions

How accurate should a mitre saw be? For trim and joinery, small errors add up across corners, so aim for no visible gap against a good square and a near zero result on the five cut test.

Can I use a cheap square? Check it first: draw a line along it, flip it and draw again. If the lines differ, the square is not true.

Why are my 45 degree cuts off but 0 is fine? The 45 degree detent may need adjusting, or the scale pointer is off. Check with a combination square or test cuts.

Does the laser need adjusting too? Often yes. Lasers drift with knocks. Align it after the blade is calibrated, following the manual.