Tear out on table saw

[ErikY]

I am cutting 45 degree miter cuts on my table saw and I am getting pretty bad tear out, but only on the bottom and back end of the wood, not the top or front end.

I have a delta contractors saw, and a band new combo blade with 50 teeth.

I am using the blade insert that came with the saw.

Can anyone tell me how I can get a nice clean cut?

My questions are:

1) Should I try a zero clearence insert?
2) should I get a cross cut blade rather than a combo blade?
3) Can the speed of my feed rate affect this? I try to go pretty slow, but not rediculously slow.

Any help would be greatly appreciated.

[Lou_williams]

The problem could be a lot of things. Your blade might not be a good one, and a cross cut will do a better job. A zero clearence plate will help. But I think the most likely issue is the alignment between the blade and your miter slot. if you saw is not aligned right then as the blade exits the cut it will be on a different plane than the one it was on when it enters the cut and will cause tearout.

A slow Feed rate will cause you to have a burning issue and heat the blade causing runout and can also tearout. A steady feed rate that does not log down the motor or burn the wood is the right speed.

[ErikY]

Lou,

thanks for the response. Based on your reply, I may not have accurately describec my problem, maybe tearout is not the right term.

I am getting minor chipping on the bottom of the cut.

I am not sure what you mean by the alignment being off, I have checked all measurements and my blade is 90degrees to the table, and the miter slot is perfectly parralel to the blade.

Can you give me an idea of what you mean by alignment being off?

Thanks, Erik

[Lou_williams]

It is the blade angle to the slot I was talking about. It should be parallel to within about 0.003 of an inch. They kind a wood, also may have an impact.

If you still have it with a zero clearance plate and you have aligned the saw then it is the blade quality.

[TDHofstetter]

To coin a pun, I might chip in here...

There are two states in which you've gotta check the alignment of the blade. They're related to each other, but they are NOT the same.

State #1 is with the blade standing proud at 90 degrees to the table. Straight up in the air. In this state, it's fairly easy to check parallelism between the blade & the miter slots and between the blade and the fence. There are just whole slews of different and good ways to get it done.

State #2 is with the blade tilted, leaning over to something like 45 degrees. The fact that the blade is parallel to the miter slots at 90 degrees is nothing like a guarantee that it will be parallel at 45 degrees - it can swing all sorts of funny ways when it's tilted. This state makes it much harder to check parallelism, but it can be done with a little block of steel accurately mitered to 45 degrees and used as a buffer against the blade's body.

Note that the adjustments for the two checks are different, and may possibly effect each other - you may go round in diminishing circles for a while before it's completely right.

Also look at your blade's quality, tooth count, and tooth geometry. A blade with strong positive rake will tend to tear out more than a tooth with zero or negative rake.

Zero-clearance inserts help, if you've got one you're willing to slot at 45 degrees. Sleds also help a lot in that they serve as backers for both the bottom and the rear of the cut.

-- Tim --

You can always take one more step against the wind.

[Chagrin]

The quick, temporary answer is to set a piece of scrap underneath the piece you're cutting (so the scrap chips and your wanted piece doesn't. The better answer is to use a zero-clearance insert, and of course a good quality blade never hurts either.

[KJGLitz]

Is it a miter cut when the blade is perpendicular to the table top and the wood is angled 45 degrees going into the cut? Whereas a bevel cut has the wood going in 'straight' but the blade is tlted to an angle other than 90??

Not quite sure which one is being done here.

Ken

[eriky]

It is a miter cut when the blade is at 90 degrees, but the miter gauge is set for 45 degrees

[TDHofstetter]

Good call KEN! :) This changes my viewing angle considerably.

Now the problem looks like... what kind of wood are you cutting?
... you would probably be well served by using a zero-clearance insert, a good-quality crosscut blade with zero or negative rake, and a miter sled. ...or as close to that as you can get.

-- Tim --

You can always take one more step against the wind.

[ErikY]

I am cutting Red Oak, and using an Incra 1000 miter gauge