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Discussion Starter · #1 · (Edited)
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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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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Discussion Starter · #3 ·
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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" 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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Discussion Starter · #5 ·
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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they should if made accurately...
 

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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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"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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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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Discussion Starter · #11 · (Edited)
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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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:
Wood Plywood


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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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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Discussion Starter · #15 ·
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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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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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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Discussion Starter · #18 ·
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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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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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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