# Table Saw Zero Clearance Insert?



## Gaia (Feb 20, 2010)

I'm a little confused, my saw has a 100mm depth of cut. If I use the method of removing riving knife, then place blank insert in table, hold down with the fence. Then bring the blade all the up by 50mm through the insert. For the zci to work fully, does blade always have to be raised to 50mm, or can I lower to whatever height I would normally use it at say 18mm for plywood and I will still be getting the zci benefit? I appreciate the sides of the zci are flush with the saw plate but I'm wondering if the slot is longer does the zci still work like that? I'm sorry if I havn't expressed what I mean very clearly.

This is what I'm getting at,read it somewhere else.

" If you later lower the blade, the ZCI is no longer strictly ZC. It will be ZC at the sides, but not at the front, directly in front of the teeth. That might matter if you are cutting MFC ( Melamine Faced Chipboard ) for example."

When using saw as is with the standard large gap insert in place.As a safety thing I always adjust height of saw, so tips of teeth clear workpiece and no more. I wouldn't like to make a zci by raising blade up through blank say 50mm, then have to keep at that height to get zci effect, would lose complete effect if lowered blade down. I hope this explains my confusion more clearly.
Thanks.



Thanks.


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## Stick486 (Jan 4, 2013)

you can lower to any height you wish...
but why make a full slit if you don't have to...
I trust you will be reinstalling the slitter/riving knife..


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## Gaia (Feb 20, 2010)

Stick486 said:


> you can lower to any height you wish...
> but why make a full slit if you don't have to...
> I trust you will be reinstalling the slitter/riving knife..


" but why make a full slit if you don't have to... " The thickness of the workpiece may vary.
" I trust you will be reinstalling the slitter/riving knife.. " I didn't mention, yes of course I'll extend the slot backwards to accommodate it.
Cheers.


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## Stick486 (Jan 4, 2013)

Gaia said:


> " but why make a full slit if you don't have to... " The thickness of the workpiece may vary.


as the material gets thicker increase the slot on a need to basis...


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## Gaia (Feb 20, 2010)

I'm going to be making the zci out of 3mm acrylic, can get a 400 x 600mm sheet on Ebay UK for £13.84. This would allow me to make up several blanks, make up as required.

Could be a false economy, as might be a variety of workpiece thicknesses. I suppose I could sort of, stagger the length of the slots to accommodate different thicknesses?
So height of blade was say never more than 1/2 inch above workpiece. That would keep my safety considerations satisfied.
Though I wonder if swapping inserts in and out, when put them back in, they would go back in exactly the same position, maintaining the zc front and sides of blade?


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## DaninVan (Jan 1, 2012)

_"I'm going to be making the zci out of 3mm acrylic, can get a 400 x 600mm sheet on Ebay UK for £13.84. "_
Why acrylic? Seems like a bit of an extravagance(?)...


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## Stick486 (Jan 4, 2013)

they should if made accurately...


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## Cherryville Chuck (Sep 28, 2010)

Some saws have a very thin steel insert, around 1/8"/3mm. If that's the case then acrylic is probably one of the best choices. The Unisaw and a few others like it take one that is about 1/2" thick which makes them easy to make. I just dab a couple of drops of hot melt glue on the blank to hold the original insert to it and use a pattern bit to rout the blank. That only takes a few minutes each and I use mdf for mine. I use felt marker to mark the undersides as to which blade it's for and whether I used stabilizers with it. Having the sides tight is more important that slot length but I agree with what Stick said and keep it as short as you need it.


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## Stick486 (Jan 4, 2013)

DaninVan said:


> _"I'm going to be making the zci out of 3mm acrylic, can get a 400 x 600mm sheet on Ebay UK for £13.84. "_
> Why acrylic? Seems like a bit of an extravagance(?)...


acrylic is nick sensitive and brittle....
BB would be a better choice or polycarbonate...


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## gmercer_48083 (Jul 18, 2012)

Peter,
The advantage of a zero clearance insert is that it helps prevent tear out because the wood you are cutting has the support right next to the blade, which creates a shearing effect as the blade rotates. The length of the saw kerf in the insert itself is unimportant.


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## Gaia (Feb 20, 2010)

gmercer_48083 said:


> Peter,
> The advantage of a zero clearance insert is that it helps prevent tear out because the wood you are cutting has the support right next to the blade, which creates a shearing effect as the blade rotates. The length of the saw kerf in the insert itself is unimportant.


Ah OK, so can break the blade to full height, then use the saw at any height. Save the money on buying acrylic and remove any break out on the jointer. Then again might get better dimensioning on the table saw with a zci to start with.


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## Gaia (Feb 20, 2010)

DaninVan said:


> _"I'm going to be making the zci out of 3mm acrylic, can get a 400 x 600mm sheet on Ebay UK for £13.84. "_
> Why acrylic? Seems like a bit of an extravagance(?)...


The original aluminium insert is 3mm thick.


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## DesertRatTom (Jul 3, 2012)

If 3mm is all the depth you can use, then 3mm it is. On my old saw, it had a shallow opening for the insert, so I used half inch , then cut a rabbit on the insert the full width of the mounting shelf so there was a 3mm thick edge all around. Personally, I'd go with the BB. If the blade will chip out plastic, then it is likely to chip out the acrylic, defeating the purpose. My new saw has a depth of about half an inch so I have to raise it slightly with leveling screws:








If your insert isn't perfectly level with your table, you will find your workpiece catches on the higher edge of the insert or table. This can mess up your cut and is quite annoying. Given how thin the insert edges must be, you can use a layer or two of painter's tape to level a low insert. If it's slightly too thick, you could use a bit of sandpaper to thin the edge slightly. Be careful to clean off and remove any lubricant or pitch on that edge before applying the tape. On my older saw, I had to use the tape method or the piece would nearly always catch on the table.


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## Herb Stoops (Aug 28, 2012)

Gaia said:


> The original aluminium insert is 3mm thick.


My TS with that thin of insert,I use 1/2" thick and cut a 1/8" lip around the edge so edge is thinner. I found that the thin material flexes too much unless made from metal. The other option is to use the thinner material and glue some reinforcing ribs under the middle to keep it from flexing.

Herb


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## Gaia (Feb 20, 2010)

OK thanks everyone, thinking more about this. I think what I will do is rip the stock say 3mm wider, then clean edge up on jointer. Though if zci makes a significant difference on dust extraction I'll miss out on that.


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## gmercer_48083 (Jul 18, 2012)

Gaia said:


> Ah OK, so can break the blade to full height, then use the saw at any height. Save the money on buying acrylic and remove any break out on the jointer. Then again might get better dimensioning on the table saw with a zci to start with.


Yes, You can saw the insert to full height (which shows where the blade will cut). I also mark onto the surface, a line showing me the apex/center line, which helps me when setting (measuring) the height of the blade. Also mark the exact blade that was used for this insert on the bottom of the insert for future reference.


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## DesertRatTom (Jul 3, 2012)

Don't forget the blade you use will make a big difference. I mostly use a Freud Glue Line blade that not only cuts extremely clean and smooth, but is a full kerf, heavy duty blade and every fourth tooth has a flat top, so it makes a nice flat bottom groove. Because of the tooth configuration, I rarely get any tear out with this blade whether or not I use a zero clearance insert. It is also very stiff and doesn't deflect easily.


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## Gaia (Feb 20, 2010)

DesertRatTom said:


> Don't forget the blade you use will make a big difference. I mostly use a Freud Glue Line blade that not only cuts extremely clean and smooth, but is a full kerf, heavy duty blade and every fourth tooth has a flat top, so it makes a nice flat bottom groove. Because of the tooth configuration, I rarely get any tear out with this blade whether or not I use a zero clearance insert. It is also very stiff and doesn't deflect easily.


OK thanks.


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## sreilly (May 22, 2018)

Although you've gotten good advice on the ZCI the height of the blade should include the gullet above the wood to clean out when used keeping the blade free of sawdust and cooler running. I have no experience with using acrylic as a ZCI material but considering it can shatter under the right circumstances I'd be leery of using anything that can shatter. I c That's my take on it.ould be wrong but a consideration I'd think. Your ZCI keeps the blade kerf thickness nearer the actual cut it makes giving a cleaner cut. I don't really see the height of the blade making a difference other than clearing the gullet as I stated earlier. That's my take on it.


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## gmercer_48083 (Jul 18, 2012)

Peter, I started a thread at routerforums a while back called "Zero Clearance Table Saw Insert". You can search for it without the quotes (I don't know how to link it directly).


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## TwoSkies57 (Feb 23, 2009)

Here ya go Gary...

https://www.routerforums.com/tools-woodworking/127178-zero-clearance-table-saw-insert.html


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## sreilly (May 22, 2018)

That would be this thread I believe.

FYI, go to the url you want to link and copy it (CTRL+C) and either select a work to link it with and choose the 6th icon above(earth with chain link) and paste it (CTRL+V) into the resulting dialog box or just paste it in the message. Either should work. The (Ctrl+C is the control key (CTRL and the c key pressed together)) Highlighting and using copy or paste via the right mouse click also works.


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## comp56 (Mar 30, 2017)

I made mine with Lexan very happy with it


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## Stick486 (Jan 4, 2013)

comp56 said:


> I made mine with Lexan very happy with it


Lexan is polycarbonate...


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## Gaia (Feb 20, 2010)

OK thanks Steve, Gary.


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## Herb Stoops (Aug 28, 2012)

comp56 said:


> I made mine with Lexan very happy with it


Thats a Show Piece !

Herb


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## comp56 (Mar 30, 2017)

Herb Stoops said:


> Thats a Show Piece !
> 
> Herb


thanks Herb, here is a shot of the entire top with outfeed table


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## OPG3 (Jan 9, 2011)

This scenario is an excellent example of 4d (4th dimensional thinking)! Everyone knows about the first three dimensions (3d) of x, y and z...
The fourth dimension to be considered in this situation is TIME. On a zci (Zero Clearance Insert) the length of cut within the insert itself is NOT A FACTOR ON THE WORKPIECE! *HOWEVER*, THE LENGTH OF CUT IS A FACTOR _on dust collection_.
Think about it like this (first in 3d): The only place where the zci matters on the workpiece is in the amount of workpiece that is cantilevered between blade and last support edge. Now, adding that 4th dimension of time: after the workpiece has benefited from the minimized cantilever - nothing matters to the workpiece. 

Otis Guillebeau from Auburn, Georgia


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## Herb Stoops (Aug 28, 2012)

I usually make the first cut in the ZC insert enough for the saw blade to cut 3/4" stock. Then as I use it it will enlarge to max cuts.

Also since I am using a thicker ZC insert than was designed for my saw, (1/2" instead of 1/8"), the blade is too large to set the ZC insert down in place at first try.
To remedy this situation I install a smaller blade,i.e. 7 1/4", or 8" blade on the saw and start the cut enough to reinstall the regular 10" blade and complete the cut through the ZC insert.

Then I found that the washer on the mandrel will hit the ZC insert when I try to set the blade full height. 
To fix this, I take off the blade and install a dado blade wide enough to allow for the width of the washer and raise it up slowly while running thus cutting an indent in the bottom of the ZC insert NOT ALL THE WAY THROUGH, to allow clearance for the 2 washers on the saw to have clearance when the blade is full height.
I rarely cut anything over 2" thick on my TS anyway, but I have on occasion had to set the blade higher. I use the band saw for higher cuts, it seems safer for me.

Herb


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## Nickp (Dec 4, 2012)

Peter, you will most definitely keep the benefit of the ZCI even though you had raised the blade all the way up and have a longer slot than the height of the blade you might need. Here's why... as your project piece approaches the cutting front edge of the blade it will cover the "excess" length of the slot ahead of the blade...all the way up to the point that the piece passes the cutting edge.

If your riving knife follows the blade, you would need the extra length in the slot to accommodate the knife.

When you make your next ZCI raise the blade to make the slot to the point of your typical project piece (as has been suggested already and if you don't use your riving knife). 

You mentioned bringing the blade up just enough to cut the project piece...consider raising the blade until the gullet is at the top of the piece. This will help clearing more of the cut than if the teeth are just barely above the piece. This will help to keep the sawdust below the table rather than spitting some up at the trailing edge. This is my preferred method as I do not have a riving knife so "so your mileage may vary"...

Best...Nick


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## G00ber43 (Sep 13, 2018)

Acrylic may melt, due to friction, and transfer to blade teeth. This may cause all kinds of problems ie. Blade sticking to insert, transfering to workpiece etc.


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## baran (Dec 25, 2014)

Hello I have made several ZC adapters and once you make one duplicating them is simply a mater of tracing another one and cutting it out.
As to your question first understand the reason to have a ZC is so the boards thin cut will not get trapped to the left or right side of the blade opening.
Just make the blade height slightly higher than what your project calls for. If you go onto anther project that calls for the blade to go higher you have two options one just raise it up to the desired height or make another one and preserve the fist one.
Actually unless you are concerned about working with melamine which has an edge tear problem it does mater too much how long the ZC line is. What is important and why they call it ZC is the right and left sides of the blade are sealed off tight against the insert.
Have fun
Ben


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