77 - Sliding Door Shop Cabinet, страница 14

THE SHOP

3. Checking for Runout

There are a number of things that play into how smooth a table saw runs. But if the arbor, flange, and blade exhibit any "wobble," or runout, due to misalignment or looseness, all the tuning in the world won't make a lot of difference.

You can do a "rough" check of the arbor by pulling up and down on the shaft, and then moving it in and out You shouldn't feel any play. And rotating the shaft by hand should be smooth and quiet.

For a more accurate check of the arbor, you can use a dial indicator and a shop-made holder, like you see in the upper photo at right The holder is nothing more than a couple pieces of hardwood held together with a carriage bolt and knob. A hole and bolt at the end of the assembly

allow you to position the dial indicator exactly where you need it

With the indicator resting on the arbor, rotate the shaft (upper photo). Any runout will show up as movement on the indicator. In a similar manner, you can position the indicator to check the flange (lower photo).

So whafs too much runout? Since any runout here will translate into even more at the blade, it can affect the quality of the cut So I don't like to see anything over 0.001" on the arbor or 0.003" on the flange. Anything more could be a sign of a bent arbor or bad bearings — something you can't take care of with a simple tune-up.

If you want to minimize any blade runout you do have, be sure to check out a couple of the after-market accessories shown on page 17.

A Read the Runout. A dial indicator is an accurate method for checking the runout of the table saw arbor (top) or flange (bottom).

2 4. Blade & Miter Slot Alignment

No matter how well your saw checks out for runout, it still won't make a smooth cut if the saw blade isn't aligned parallel to the miter gauge slots.

To check this, start by marking an *X' on the saw blade. Next position the dial indicator so the tip of the spring-loaded shaft contacts the blade on the %' as in the photo above.

After "zeroing out" the dial indicator, rotate the saw blade and slide

the gauge back so the plunger contacts the blade at the "X' once again. Note: Rotating the blade ensures that any small runout in the saw won't affect the reading.

If the reading remains the same, the blade is aligned. If it doesn't you'll need to align the saw blade. For most saws, this means adjusting the trunnions. (Cabinet saws are adjusted by shifting the table.)

Adjust Trunnions - The front and rear trunnions are bolted to the underside of the table and support the carriage and arbor assembly. Adjusting them is simply a matter of loosening the bolts that hold them in place and shifting them to bring the saw blade into alignment

But first, it helps to remove the belt and motor. Besides reducing the excess weight, this also makes it easier to reach the trunnion bolts.

Now you're ready to adjust the trunnions. The trick here is to just loosen the bolts. And I find it best to leave one of the front bolts slightly snug. This way, it acts as a pivot point and keeps things from moving too

much. The bolts should be just loose enough so you can tap the rear trunnion into alignment with a piece of scrap and a mallet (photo below).

But the trunnion can move as you retighten the bolts. So it's always a good idea to recheck the blade alignment as you did before to make sure the adjustment is correct

Sometimes, no matter how hard you try to shift things into alignment it just doesn't work. If thafs the case, you might want to check out the trunnion alignment kit on page 17.

f A Little Tap. To align the blade with the miter slot, loosen the trunnion bolts and tap the trunnion into alignment.

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ShopNotes No. 77