ZCI Chipping on Unisaw

[Jeff Ramsey]

I've a 10" Unisaw with a relatively new Freud 10" combination blade. I inserted a new ZCI and I'm getting chips. Might this be from blade wobble, and if so what can be done about it? The initial kerf I created was smooth and clean

Pictures are included. 316754

[Charles Lent]

That looks like blade wobble to me too. Is it a standard 1/8" kerf blade? I've seen this when using the narrow kerf blades. A pair of blade stabilizer washers will stiffen up the blade, but they will change the position of the kerf so a new zero clearance insert will be necessary. They will also hit the insert when you try to raise the blade too far, so the saw's depth of cut will be reduced by about 1/2 of what it can do without the stabilizers. I have a different zero clearance insert for each blade that I use as each has a slightly different character. I write the blade information on the bottom of the insert so I can select the right one when I change blades. Eventually, all zero clearance inserts wear and need replacement. I usually make a dozen or so blanks every time I run low on them.

Charley

[glenn bradley]

The blade is deviating from true as is shown by the cuts in the ZCI. There are many things that could cause this so let's talk it through a bit:



This happened after cutting some material and not just by running the saw without cutting anything.

That is, something is causing the blade to deviate besides a bent or wobbly blade.


The arbor is in good working order.

This can be quickly checked by going through the blade to miter slot alignment steps that include checking the arbor, arbor washer and blade.


No spoil has been captured between the washers and the blade during blade changes.

This can foul a cut more than you might think.


The material being cut has been jointed true on one face and one edge.

Tablesaws are made to cut straight, material that is not straight running over the table and fence reference surfaces will be forced out of plane causing burning, tooth marks, blade deviation and motion resistance.

This can also be caused by lively wood that releases tension during the operation. That is, it started out milled but did the hokey-pokey once internal tension was release during the cut.




Just to help others respond better, check these things and let us know. Also the model of the blade would possibly help. If you cut a lot of rough stock on the tablesaw (something I don't recommend unless your framing a house), stabilizing washers can help the blade resist being pushed out of square by the poor mating of the tablesaws reference surfaces and the un-milled material. If you are doing much of this though, the ZCI is pretty much moot ;-)

[Jeff Ramsey]

Freud LU84-R011 11757289 10/12. 1/8" kerf.

No debris anywhere between washer and arbor flat.

I'll check the arbor and alignment.

I don't cut rough lumber on my Unisaw. I've a cutoff station and RAS for that.

With the blade off, lying flat on my Unisaw table (which is flat, but I don't know how flat), the blade fails the tap test when tapping on the shoulders of the teeth (it rattles on the table at two opposing points). If I rotate the blade 90 degrees and retap, the rattle moves with the offending edges. I'm suspecting the blade is warped (either it always was, or it happened during certain cuts).

[Bill Orbine]

The question is how does the cuts look on your materials? And does your saw "shudder" on shut-down?

[bill tindall]

It is not uncommon for a blade to wobble during start up or coast down. If your cuts look good don't worry about it. All my inserts look like your picture.

[John Schweikert]

With any angle cuts, an insert can look like that. Mine does for my Sawstop.

[Jeff Ramsey]

The cuts look fine and I ran a "feel" vibration test with the blade on then off. I don't notice any shutter with the blade on; I notice little difference with the blade on or off.

[Alan Bienlein]

A zci isn't meant to produce chip free cuts. It's main purpose is to close the gap between the insert and the blade preventing thin pieces from getting caught and possibly kicking back.

For a zci to produce a chip free cut the piece your cutting needs to remain in constant contact with the zci to support the back side where tear out is likely to occur. Why do you think sliding table saws come with scoring blades. You have a better chance getting a chip free cut by using the proper blade that is sharp.

[M Toupin]

A zci isn't meant to produce chip free cuts. It's main purpose is to close the gap between the insert and the blade preventing thin pieces from getting caught and possibly kicking back.

A ZCI certainly does significantly reduce chip out, especially when crosscutting thin veneers or laminates. And I suspect that's the main reason it was "invented" though the safety issue with small off cuts is a nice side benefit. Not that a ZCI is a magic bullet by itself, it needs to be coupled with the proper blade for the job. For crosscutting, especially thin veneers or laminates, a Hi-ATB works wonders and even more so when when coupled with a fresh ZCI.

And it's not just my opinion; Not that I agree or even believe everything I read on the internet, there's just too many at least half legit sources all touting a ZCI to reduce tear out.

From Highland Woodworking - "A zero clearance insert is a necessity for reducing chipout and cutting very thin strips."

From Wood Magazine "we discovered that some sets will make clean, chip-free, cross-grain cuts in veneered materials only if you use them with a zero-clearance insert in your tablesaw. " (http://www.woodmagazine.com/woodworking-plans/tablesaw/zero-clearance-insert/)

From LeeCraft "Offers superior rigidity, flatness, durability, and low friction; reduces chip-out and splintering"

From Woodcraft - "minimizes tear out"

Mike

[Alan Bienlein]

A ZCI certainly does significantly reduce chip out, especially when crosscutting thin veneers or laminates. And I suspect that's the main reason it was "invented" though the safety issue with small off cuts is a nice side benefit. Not that a ZCI is a magic bullet by itself, it needs to be coupled with the proper blade for the job. For crosscutting, especially thin veneers or laminates, a Hi-ATB works wonders and even more so when when coupled with a fresh ZCI.

And it's not just my opinion; Not that I agree or even believe everything I read on the internet, there's just too many at least half legit sources all touting a ZCI to reduce tear out.

From Highland Woodworking - "A zero clearance insert is a necessity for reducing chipout and cutting very thin strips."

From Wood Magazine "we discovered that some sets will make clean, chip-free, cross-grain cuts in veneered materials only if you use them with a zero-clearance insert in your tablesaw. " (http://www.woodmagazine.com/woodworking-plans/tablesaw/zero-clearance-insert/)

From LeeCraft "Offers superior rigidity, flatness, durability, and low friction; reduces chip-out and splintering"

From Woodcraft - "minimizes tear out"

Mike

They have to sell them some how. Personally I don't see a difference between using my regular insert and a zci when cross cutting plywood. All the cabinet shops I've worked in since 1982 never relied on a zci for chip free cuts. They were only used for ripping thin strips. Using the proper sharp blade was the only reliable way of chip free cuts on the table saw or it was cut on the sliders that had a scoring blade.

[glenn bradley]

Freud LU84-R011 11757289 10/12. 1/8" kerf.

No debris anywhere between washer and arbor flat.

I'll check the arbor and alignment.

I don't cut rough lumber on my Unisaw. I've a cutoff station and RAS for that.

With the blade off, lying flat on my Unisaw table (which is flat, but I don't know how flat), the blade fails the tap test when tapping on the shoulders of the teeth (it rattles on the table at two opposing points). If I rotate the blade 90 degrees and retap, the rattle moves with the offending edges. I'm suspecting the blade is warped (either it always was, or it happened during certain cuts).

I would go ahead and check the arbor since you've come this far but, it sounds like the blade is tweaked. A sharpening shop can true the plate for you. Even a wobbly blade will make a cut that appears fine in general if the feed rate is slow enough to allow the full width of the wobble to cut all material. At tablesaw speeds "slow" is a relative term ;-) Lay a square to the perpendicular faces and see how they look.

There is obviously some difference of opinion about ZCI's and what they do. While the safety factor is primary, the reduced tearout is a reality in my shop and worn ZCI's are repaired by filling the slot with epoxy and re-cutting or eventual replacement.

I agree that larger plywood panels do not benefit from the tearout reduction of a ZCI. The irregularity of the material is such that it often does not remain in contact with the table at the throat. For milled material the ZCI keeps things "fuzz free". I have ZCI's in all my crosscut sleds for just this reason. We all do different things differently so broad general statements on some tools or techniques can sometimes conflict.

[mark kosse]

It is not uncommon for a blade to wobble during start up or coast down. If your cuts look good don't worry about it. All my inserts look like your picture.

I agree. For me its mostly on coast down.

[Brian W Smith]

Check your washers for flatness. Hopefully they're machined flat, but you never know?