Powermatic HPS67 Free Cut Blade to Sliding Table, Symptoms of positive free cut

Free Cut (Blade to Sliding Table)

The sliding table does not run exactly parallel to the saw blade. It runs away from the back teeth by a fraction of a millimeter. This is called "free cut."

A very slight amount of free cut is desirable to avoid the problems of back cutting due to saw blade flutter. All saw blades vibrate to some extent. They flutter less at the front, where the cutting teeth are held stable by the material, than at the back.

If the table were set absolutely parallel to the saw blade, the back teeth could contact the material and spoil the clean cut achieved by the front teeth. As the back teeth are ascending, they could cause chip out on the top surface of laminated boards.

The free cut required is less than .05 mm over one meter of travel.

A dial indicator is not required. You can use your ears to compare the noise of the front teeth with that of the back teeth. To do this will require a workpiece shorter than the distance between front and back teeth. The saw blade should be raised to its maximum height to achieve the most contrast.

1.Lay the workpiece against the crosscut fence and make a cut.

2.Hold the workpiece firmly after the front teeth have cut and push it on past the back teeth. As you pass the back teeth you should feel rather than hear a slight tingling or whisper. If there is no sound from the back teeth, you probably have too much ("positive") free cut. If the noise from the back teeth is similar to that of the front teeth, there is too little ("negative") free cut and the table is running in towards the back of the blade.

3.Having passed the back teeth, stop level with the riving knife and cut backwards. The back teeth will make a noise as they are now cutting the material.

The workpiece must be held down firmly when making this backward cut.

4.As you continue past the front teeth, the noise from the front teeth should be equal to or slightly less than the noise from the back teeth. Slight back cutting on the backstroke equals slight free cut on the forward stroke.

5.If the front teeth make more noise than the back, the free cut is positive; if they make no noise, the free cut is negative. If the noise relationship front teeth to back teeth on the

forward stroke is the same as the noise relationship back teeth to front teeth on the back stroke (on a scale of 100, 100/30 in each case), the sliding table is running exactly parallel to the blade (zero free cut).

To correct the free cut, one end of the sliding table must be moved outward or inward. It doesn't matter whether you move the left or the right end. The only consideration is that there is enough clearance between the sliding table and the fixed cast iron table at the end you are moving.

1.At the end you have decided to move, loosen the hex nut (A, Figure 38) holding the sliding table to the frame.

Figure 38

2.Loosen the other two hex nuts in the middle of the sliding table so that the table will pivot at the remaining fixed end.

3.Move the table end in or out as needed then retighten the table mounting nuts.

4.Check again to confirm the free cut is satisfactory. Repeat the process if needed.

NOTE: The sliding table should be approximately 0.3 mm higher than the fixed cast iron table (thickness of a piece of paper). This is pre-set at the factory, but if adjustment should ever be needed, use the four height adjustment bolts (Figure 38) on each end of the table.

Trouble-shooting Free Cut (Blade to Sliding Table):

Symptoms of positive free cut:

Back cutting on rip fence side. Workpiece on cast iron table pulled into back of sawblade.

Chip out on top.

Machine cutting out of square. Workpiece moves slightly on sliding table due to pressure of saw blade, without operator noticing.

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