I'd like input on a zero clearance insert

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Forum topic by Tenfingers58 posted 07-28-2012 12:52 AM 1849 views 0 times favorited 15 replies Add to Favorites Watch
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96 posts in 2675 days

07-28-2012 12:52 AM

I’d like to make several zci’s for my tablesaw. For my saw they need to be 17/32 thick. Instead of leveling screws, I plan to make them the thickness of a playing card thinner and glue rare earth magnets into holes drilled into the bottom with the magnets protrudeing the thickness of a playing card bringing them flush with the table.

Any reason not to use magnets to hold the zci in place? Seems most saws just use gravity / maybe some friction to hold them in place.

What material would be best for them? It’s muggy now ‘till the end of summer and I don’t want them to shrink this winter to be able to move around in the recess of the tabletop.

Can UHMW plastic be sanded to thickness in a drum sander?

If I take the Melimine off one side in the thicknessing operation will it warp?
Could I seal the bare side with shellac or poly?

Is there a better material that I haven’t considered?

15 replies so far

View cabmaker's profile


1730 posts in 2806 days

#1 posted 07-28-2012 12:55 AM

solid surface coutertop material (ie: corian)works well. Easy on cutting tools and stays constant.

View MrUnix's profile


6709 posts in 2196 days

#2 posted 07-28-2012 01:19 AM

I make them out of plastic cutting boards (polyethylene or HDPE) found at wallyworld or the dollar store for way cheap, particularly if you find them on sale.. you can usually find them just the right thickness and one board will make several inserts.


-- Brad in FL - In Dog I trust... everything else is questionable

View cutworm's profile


1075 posts in 2791 days

#3 posted 07-28-2012 01:30 AM

I use 1/2” MDF. I fasten mine down. Don’t know if it’s necessary.. I usually make 10 or so at a time while I have everything out. Stash them in the cabinet.

-- Steve - "Never Give Up"

View gfadvm's profile


14940 posts in 2687 days

#4 posted 07-28-2012 01:31 AM

Most inserts have some sort of tab or pin on the edge furthest from the front which keeps it from lifting and becoming airborne if the back edge of the blade catches it. I think this is an important safety feature that I incorporated in all of my ZCIs.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View Sawkerf's profile


1730 posts in 3066 days

#5 posted 07-28-2012 01:37 AM

I use scraps of 1/2”, prefinished, baltic birch. I cut them to shape and do a bit of sanding to get a good fit (not too tight and not too loose). I don’t bother with leveling screws – if one is a little “off” some sanding or a bit of duct tape brings it to where it needs to be.

After I make the first cut (raising the blade), I bore a largish hole at the back of the kerf. This seems to help get more DC airflow at the rising blade gullets. Not perfect, but it seems to keep some sawdust off of the table.

-- Adversity doesn't build reveals it.

View Tenfingers58's profile


96 posts in 2675 days

#6 posted 07-28-2012 01:40 PM

So, it seems like most any man made material would work well for a zci.

I seems to me that the magnets would hold the zci down, unless you were intentionally trying to dislodge it.

I saw on stumpys website he has holes alongside the blade. I thought of putting a baffel to divert the incoming air (suction from the dust collector) through the gullets between the teeth to help keep the sawdust from blowing back in your face. Maybe in addition to Sawkerfs idea of a hole in the back of the slot?

Thank you all for your ideas.

View CueballRosendaul's profile


484 posts in 2137 days

#7 posted 07-30-2012 03:29 AM

Don’t use plexiglass. It gets brittle when thin and chips if you drop it. Looks cool when it’s new, but gets scratched up fast. My next batches will be MDF with laminate countertop material. I like the thought of magnets, but mine is thin and uses screws. Post them when youre done. I’d like to see how they turn out.

-- Matt CueBall Rosendaul. I don't think I've ever had a cup of coffee that didn't have cat hair or sawdust in it.

View Tenfingers58's profile


96 posts in 2675 days

#8 posted 07-30-2012 08:02 AM

I went to Woodcraft yesterday to get magnets. I arbitrarily decided that 3/8ths would be about right. Of course they were out. So i bought 1/4 and 1/2 inch, 3/8 was a guess anyhow. I won’t get any shop time ‘till wednesday or thursday, so I’ll let you know then how it turns out.

Do your inserts warp with laminate on just one side? Or dosen’t MDF expand that much with humidity?

I’m hoping to find a plastic that power sands well. So I can run it through the drum sander to flush it with the table.

View Charlie's profile


1100 posts in 2284 days

#9 posted 07-30-2012 09:54 AM

My table saw has the magnets mounted in the recess for the ZCI. So my inserts are held in with magnets. I put t-nuts into the bottom of my ZCI and use little allen set screws to adjust height. The t-nuts are centered on the magnets and even if I raise the ZCI off the magnet a little using one of the leveling screws, it has never moved.

Despite cleaning out the recess whenever I remove a ZCI, every once in a while I need to tweak a leveling screw.

View lumberjoe's profile


2899 posts in 2246 days

#10 posted 07-30-2012 10:46 AM

My local woodcraft started carrying phenolic coated plywood. I picked up a half sheet of 1/4” that I am going to use to make a lot of ZCI’s. The first batch will be for different dado sizes. The next set will be for different blades. I will need to cut for the riving knife, which will be tricky.

Can you use a ZCI for angled cuts? I use my standard Insert but get more tear out that I would like on miters


View Tenfingers58's profile


96 posts in 2675 days

#11 posted 07-31-2012 03:56 AM

I assume you mean by angeled cuts that the sawblade is tilted. You can use a ZCI in this application but you need to cut the slot at the angle of bevel that you want. That is part of the reason that I want magnets to hold the ZCI in place. To make it easy to change. The insert that came with my saw fits so tight you need to get under it an tap it up and out with a hammer.

I like the idea of the phenolic ply except I plan to sand to table height after mounting the magnets. I wonder if I could find emery paper that would fit on my thickness sander to sand the magnets instead of the top surface. I don’t much like the idea of magnetic dust in the sander though.

Did they have the phenolic ply in 1/2” then I could glue the magnets 1/32nd proud to be flat with the table.

View harvey4804's profile


120 posts in 2679 days

#12 posted 07-31-2012 05:23 AM

I’ve got some scrap 1/2” Glass Epoxy Laminate “G10” sitting in my office at work that I’m gonna WJ cut into ZCI’s.

-- Ryan, FRMR HMM165 - HMX1 01-10

View GarageWoodworks's profile


531 posts in 2154 days

#13 posted 07-31-2012 05:36 AM

Use a screw at one end and dial in a nice friction fit. Forget the magnets.

-- Subscribe on YouTube:

View knotscott's profile


8013 posts in 3373 days

#14 posted 07-31-2012 05:36 AM

UHMW is too prone to warping and it flexes, making it a poor choice for something as large as a TS insert. Phenolic and birch ply are both better materials IMHO.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View lumberjoe's profile


2899 posts in 2246 days

#15 posted 07-31-2012 11:28 AM

Tenfingers58, That is what I meant. The phenolic plywood is really nice. You can get it in any nominal plywood thickness. My saw actually has leveling screws that I can adjust. I need to figure out a way to put a tab on the back as gfadvm suggests.

My saw also has a magnet in the front already, so I am just going to inset and epoxy a washer in the bottom to make contact with the magnet.


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