Zero clearance insert ATT. Particleboard


ColinF

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So in a thread PB mentioned the proper use of a zci, but never followed up with an explanation and I would like to hear what he has to say on this. I know he mentioned the front portion was the part doing the cutting but I'd like to see if he will elaborate on this topic. I've got about 100 of the stupid things to make and I'm hoping his advice will make my life easier.

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So in a thread PB mentioned the proper use of a zci, but never followed up with an explanation and I would like to hear what he has to say on this. I know he mentioned the front portion was the part doing the cutting but I'd like to see if he will elaborate on this topic. I've got about 100 of the stupid things to make and I'm hoping his advice will make my life easier.

 

Thanks for starting this thread...I too want hear all that PB has to say.

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Zero Clearance inserts are really only beneficial on a cross cut. You pretty much eliminate any tear out. It's also helpful if you are sneaking up on a cut, you don't get small cutoffs of wood flying down into the cabinet of the saw.

they are also necessary for thin rips, or small bevel pieces. I've fought that battle before and it's just not safe without a zci.
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I generally do really thin rips on the bandsaw and just run em through the drum sander.

I don't have a drum sander, but with these bevel cuts I'm making it's a 90 degree piece with a bevel on one side, think toy semi trailer fender :D it would be a pain on a bandsaw, at the very least it would cause a lot of needless sanding, and nobody wants that!
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PB's quote from the other thread is:

 

No. ZCI gets sloppy. Topic for another discussion but zero clearance is at the leading edge to prevent tear out. Most don't properly use ZCI inserts.

 

His response was to an incorrect response that I made...and I thank him for making it.

 

My question relates to his last sentence... "Most don't properly use ZCI inserts."

 

PB...please explain why "Most don't properly use ZCI inserts."

 

Thanks

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PB's quote from the other thread is:

 

No. ZCI gets sloppy. Topic for another discussion but zero clearance is at the leading edge to prevent tear out. Most don't properly use ZCI inserts.

 

His response was to an incorrect response that I made...and I thank him for making it.

 

My question relates to his last sentence... "Most don't properly use ZCI inserts."

 

PB...please explain why "Most don't properly use ZCI inserts."

 

Thanks

 

First lets look at the comment. Look at the lighter colored insert in the photo. Its phenolic or some sort of very hard plastic. Look at the kerf line, you should be able to see that the line is no longer straight due to normal wear and tear.

 

post-5350-0-91482900-1430144416_thumb.jp

 

A zero clearance insert has a primary use and some other secondary uses like plugging the big ass hole in the top of your tablesaw or preventing junk from falling between the blade. The primary use is to support the material being cut. Its no different than drilling into a backer to prevent blow out or using a backer on your router table to prevent tear out. None of those thing do any good if they don't fit right.

Below are an assortment of inserts, they can be cut to fit just about any possible cut. But really all we need to worry about is the front leading edge surrounding the carbide tip of the saw blade. Notice the arrow on the lighter colored insert. This is where the factory cut stops, the factory cut is probably 1/4" wide. It stops at about the center of the blade because we really don't care about the back half. 

 

post-5350-0-87603300-1430145345_thumb.jp

 

Before anyone asks I included that odd dado insert just to show versatility. Inserts can be made to fit any cut you may happen to need. That particular insert was modified to cut gable end grooves and rabbets on cabinet boxes. I'll stack a 10" blade with 8" dado chippers to cut a cabinet back rabbet  at the same time that the sheet of plywood is being ripped to width or stack a groover with a 10" blade to cut a back groove at the same time so two operations in one pass across the saw.

 

But no matter what in order for a ZCI to do its primary job it needs to surround the carbide tip. Unfortunately this makes them a one trick pony. They can only be used at the same blade height that they were fitted to cut. Below is a insert set to the blade height. If I lower the blade its no longer doing its job its just filling the hole.

 

post-5350-0-10448200-1430146013_thumb.jp

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But no matter what in order for a ZCI to do its primary job it needs to surround the carbide tip. Unfortunately this makes them a one trick pony. They can only be used at the same blade height that they were fitted to cut. Below is a insert set to the blade height. If I lower the blade its no longer doing its job its just filling the hole.

 

So does that mean I should only cut with my blade at one height? Which, I guess I would default to all the way up. Or do people really change out zci's for different blade heights all the time? Seems so overly complicated.

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So does that mean I should only cut with my blade at one height? Which, I guess I would default to all the way up. Or do people really change out zci's for different blade heights all the time? Seems so overly complicated.

 

I wouldn't but I also don't find the need to run a ZCI for all cuts. The factory insert gets used on my saw probably more than a ZCI. For so many cuts they are really not needed. So much just depends on what your doing. I don't mind buying them when they wear out. Ill just set one for maybe and inch above plywood stock and when it comes time to use it again Ill raise the blade until I just hear it touch the insert. Eventually its maxed out and worthless so it gets used for something else and I buy a new one. I do all my woodwoking from the inside out so the joinery is cut first when possible so that tear out is a non issue.

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When I make my zero clearance insert ("ZCI") I run the blade all the way up to full height then drop the blade to whatever the cut requires and rock on. Chip-out  tends to mostly occur as you exit the cut. That's why I use a scrap piece of wood in front of the miter slide (behind the wood being cut) to support the exit of the blade. 

 

My thought process for a ZCI is to prevent thin strips of wood from falling into the saw and getting stuck between the blade and insert, not so much the cut quality, which a good sharp blade should take take care of. 

 

-Ace- 

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I wouldn't but I also don't find the need to run a ZCI for all cuts. The factory insert gets used on my saw probably more than a ZCI. For so many cuts they are really not needed. So much just depends on what your doing. I don't mind buying them when they wear out. Ill just set one for maybe and inch above plywood stock and when it comes time to use it again Ill raise the blade until I just hear it touch the insert. Eventually its maxed out and worthless so it gets used for something else and I buy a new one. I do all my woodwoking from the inside out so the joinery is cut first when possible so that tear out is a non issue.

 

Could be I just have no idea when I *should* use ZCI and when I don't need it. Right now (haven't ran the blade through the ZCI because I want to get my Freud blade, as the ZCI was $60) the factory insert is spitting dust out the front of the slot into my face. I am not running dust collection yet though so maybe it will get better once I can hook up a hose.

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Could be I just have no idea when I *should* use ZCI and when I don't need it. Right now (haven't ran the blade through the ZCI because I want to get my Freud blade, as the ZCI was $60) the factory insert is spitting dust out the front of the slot into my face. I am not running dust collection yet though so maybe it will get better once I can hook up a hose.

 

 

Eventually you will figure out when you need one and when you don't. If you use a bunch of sheet goods they may become a regular necessary Item but as Ace stated with little cross cuts of real HW just a backer on your miter gauge is plenty. With some things you don't even need to care, the joinery will cut off the tear out if there is any. 

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Using a sharp, high ATB blade will help with most of the tearout.  And most edges receive some treatment anyway so as long as the tearout is minimal to begin with, it should be removed during sanding/pre-finishing steps.  I keep a ZCI in my saw, but it's not 100% effective for all the reasons laid out here.  I like it mostly for keeping the scraps from getting sucked into the slot.

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My ZCI only starts out that way.  I don't use a lot of sheet goods so tear out is not a huge problem.  If it is mission critical I will score my cut line with a knife first.  A sharp blade is the best defense.  But I do agree that having a ZCI for each blade height would be ideal.  Either or just leave the blade at 1.5" or whatever height will handle 90% of your cuts.  I don't buy into the thinking that there is an ideal blade height (i.e. that only one tooth should exit the top of your stock).  I think that is more about safety than cut quality.  

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PB...thanks for taking the time to respond. I have learned a lot about ZCIs.

Also, thanks to Eizzle for starting this thread.

yes PB, thank you for letting us pick your brain. My normal use of one is for cutting small parts, I have a good sharp blade that takes care of most cuts, but the first time I had a small rip get sucked into the blade I about pooped my pants! :D
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I'll stack a 10" blade with 8" dado chippers to cut a cabinet back rabbet at the same time that the sheet of plywood is being ripped to width or stack a groover with a 10" blade to cut a back groove at the same time so two operations in one pass across the saw.

Great pro tip! Keep em coming.

-Jason

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==>10" blade with 8" dado chippers to cut a cabinet back rabbet  at the same time that the sheet of plywood is being ripped to width or stack a groover with a 10" blade to cut a back groove at the same time so two operations in one pass across the saw.

 

Like stacking two FTG blades with a spacer to cut tenons in one pass... There are just so many things you can do with a tablesaw that aren't in the manual... Suppose we could start a 'tablesaw tricks' thread... But folks would have to sign a liability waver to access it... :)

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