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Making a .001 clearance insert

June 28th, 2009
Padouk Insert

Padouk Insert

Tired of closing my eyes as I trim boards, fearful of the offcut falling between the blade and the stock insert and being launch back at me,  I decided to make one of these high-falootin gizmos called a zero clearance insert. These inserts are a panacea… they protect you from the aforementioned offcut falling between insert and blade and also improve cut quality by backing the material, reducing tear-out. Beyond that, they are known to get rid of warts and make you more virile. Ehhh maybe not all of that, but we live in age of over-hype and unsubstantiation so I’ll ask you kindly to not question my claims.

I have a bit of a history with zero-clearance inserts or ZCI’s as we call them in the biz ( the “as we call them in the biz” is there simply to annoy). You see,  I’ve previously mauled an HDPE,  which is High Density Polyethylene aka “space plastic”, version. Ideally you’re able to just stick a blank insert in throat, clamp a sacrificial board over it, and raise the blade to cut the kerf. No such luck with my Craftsman 22124 (Steel City clone) as the blade sits to high and prevents the insert from sitting flush for the operation. So I aligned my fence with the throat and pushed the blank insert over the blade to create the kerf in the right spot. It seemed to work but when I installed the new ZCI it just bound up my blade and made the belt whine like a Guantanamo detainee (What?? Too soon? I don’t condone torture, I just make fun of it so we can all heal… and by “all” I mean those of us that weren’t tortured of course… I’m guessing those guys are scarred for life). I tried to make the insert work but I ended up just making a mess of things… so I just declared “mission accomplished” and walked away.

Recently I got the nerve to try it again. Pretty much forgetting my first experience, I went ahead and repeated most of my mistakes… and yes, I interrogated the hell out of that blade and belt again. This time I made the insert out of some padouk, a rather dense and stable hardwood. The stable part is the important word there… a zero clearance insert needs to not move… especially if it wants to expand and become a negative clearance insert, or NCI as we call it here in the biz. Actually, I would think “zero” clearance insert is a bit of a misnomer as well, as it would imply that that the entire insert is always in contact with the blade.

We should probably be calling these things .001 clearance inserts or something, as presumably one tooth is going to be set fractionally further out than all other teeth and/or slight variations in blade path as the arbor is raised enlarge the kerf, etc. This strikes me as potentially being on the anal side of things so I will not mount a substantial campaign to do so. Anyways, back to my incompetence. First off I half-assed the making of the insert after bandsawing it to shape… no, wait… I half-assed it well before that by jointing only the top surface since set screws are the mating surface on the bottom to the machine (since it’s hardwood, everything should probably be uniform to ensure that there’s no impetus for that sucker to move).

After bandsawing I doubled-down on my half-assedness (achieving overall full-assedness) and brought it to finally shape with a spindle sander instead of using a router with a bearing to follow the exact shape of the stock insert. I guess I just wanted to see how well I could do it freehand and frankly I just like playing with the spindle sander as it’s just one of those tools you can get into a zone on…. especially with that woooo-waaaa, woooo-waaa sound that I find so soothing (yes, I just dropped some onomatopoeia on ya… and how come that sounds dirty?). I’m half tempted to replace my white noise machine in my bedroom with this sander.

This is where I cut the kerf in exactly the same way as I did previously. They say it’s a sign of intelligence to repeat things that don’t work with the expectation of a different outcome (still waiting for my invite Mensa… hint, hint). My table saw was kind of enough to make sure I got the message this time by tossing the insert back at me… I think I even heard it say “No soup for you!” at the same moment. I didn’t get the reference but was still offended. I finally grew a brain cell and carpet taped the new insert to the top of stock insert, clamped a board on top and proceeded to raise and lower the blade 418 times. The insert no longer grabs the blade.

Lastly I replaced the stock safety guard/splitter with a slightly more compact home made version.


For the short-term I’m going to use it. Shortly after making that decision, however, I found myself engaged in further debate of the idea. The conversation (with myself) went something like this: You know that you are still a relative newbie to this woodworking thing don’t you? Well, duh, your point being? Do you really want to always have the question in the back of your mind “is this insert going to blow up because I didn’t know what the hell I was doing” every time you use this inherently dangerous tool? No, no… you make a good point… and um… nice pants, by the way. Thanks! I didn’t think you noticed any more. [end scene] So with that I ordered a phenolic insert.

When I started writing this I was concerned that there wasn’t much to say about it and thus removed my tangent muzzle…. begs the question, overcompensate much??? Wait, are you talking to me again? Seriously?? You’re going to take a shot at me after I complimented you on your pants, wtf? [And with that I’ll take this conversation offline as it’s about to get heated up in here]

On a separate note, I think it’s time that I start educating my viewers with short educational videos covering the more complex and nuanced aspects of woodworking.  First up, how to properly chuck a bit:

How to chuck a drill bit. on Vimeo – Watch more Videos at Vodpod.

I will certainly endeavor to continue sharing my woodworking knowledge. Please be patient as I’m sure you can understand that these videos take considerable time to storyboard, shoot and produce. I mean getting the gaffer(me), key grip(me) and best boy(me) on the same page is a nightmare.

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  1. megan
    June 30th, 2009 at 16:27 | #1

    The video caused an unplanned effluvia of Diet Coke from my nose. Nice.

  2. megan
    June 30th, 2009 at 18:36 | #2

    Well my dictionary defines it as “an unpleasant or harmful odor, secretion or discharge.” My nose is still burning from the discharge. I think you’re covered.

  3. July 6th, 2009 at 14:19 | #3

    What is the purpose of bit chucking?? Good luck?

  4. Rob Young
    July 7th, 2009 at 16:08 | #4

    re: ZCI slot starting

    1) Change blade to a smaller diameter before starting the cut. Just be sure it has the same nominal width at the blade you intend to use. And 8″ or 6″ outer blade from a stack dado set is good for full-width, a 7-1/4″ circular saw blade is good for narrow. Raise just enough to start exposing the teeth through the top. Drop that blade back down, turn off, unplug and switch back to your “real” blade and finish the cut.

    2) Go back to your router table (or do it by hand with a plane or even chisels) and cut a rabbet on the bottom side of the ZCI to clear the tips of the 10″ blade so it can start cutting. You can cut a through rabbet or a stopped rabbet. The stopped rabbet has the advantage of leaving more material behind, you only need to remove enough to clear the top three or four teeth of the 10″ blade anyway.

  5. July 7th, 2009 at 16:55 | #5

    First, great avatar. Thanks for your comments. I thought about a smaller blade, but my my circ saw is the small 5″ skill saw. Didn’t even think about using the dado blade. Removing some material from the bottom of the insert would have been another good option. My brain really wasn’t earning it’s keep when I did this, although the carpet tape idea finally worked like a charm.

    Recently received Leecraft phenolic insert and their instructions added another decent idea of using the leveling screws to lift the insert above the blade. It seems that anyway of doing this besides what I originally attempted should work. I think I’ll cut the beginning kerf on this new insert using your dado blade idea if the thicknesses are close, otherwise carpet-tape again probably. Or maybe I should actually follow manufacturer instructions for the first time in my life… just for the novelty of it.

    Thanks man!

  6. July 9th, 2009 at 12:32 | #6

    Charles, a few things:

    1) You’re a nut. And I mean that in a very good way. I was going to say that I love nuts, but that sounds naughty.
    2) I will never utter the word “onomatopoeia” again without thinking about something naughty.
    3) Phenolic and plywood are better choices than hardwood for inserts, because they’re not knotty.

  7. WoodMangler
    July 17th, 2009 at 13:24 | #7

    The easiest, safest, and most accurate way to make the ZCI is to start by carpet-taping the rough blank to the stock insert, rout it using a patter bit and the stock insert as a guide, and then (and this is the important part) without removing it from the stock insert, place it back into the table saw and raise the blade through it. Only then do you remove it from the stock insert. You get an exact copy of your stock insert, a perfectly placed kerf, and your hands are safe the entire time.

    When making mine, I then used my router table fence and a 1/4″ spiral bit to cut the slot for the splitter attachment. ZCI or not, I feel better when that’s in there.

  8. WoodMangler
    July 17th, 2009 at 13:26 | #8

    ha. “Pattern” bit is what I was looking for. Not patter. That would get annoying.

  9. July 17th, 2009 at 13:47 | #9

    Thanks WoodMangler. After reading around, the way you mentioned is the best way to make a ZCI in my opinion too. Makes a perfect copy in the safest way.

    I have the patter bit and you are right, it definitely gets annoying after a while. When that happens I just switch it out with the matching pitter bit. heh.

    Thanks for concisely stating a great and safe way to make a ZCI!

  10. August 24th, 2009 at 23:29 | #10

    That’s some mighty fine comedy writing there, I must say… and the post about the groundhog? Pure gold! And the bit chucking? Did NOT see that coming… I’m on to you now though, fool me twice, won’t get fooled again…

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