Zero Clearance and Dust

[steve-norrell]

I am reluctant to use a zero clearance throat plate because it would notably increase the amount of dust blown into the air. It seems to me that the ZC throat plate would block significant amounts of dust from being drawn downward and into the rear dust collector.

Why would one want to use a ZC throat plate if it significantly increases the amount of dust thrown into the air? Would it be necessary to install "the Shark" (after saving up for the $100+++ cost), especially when working with MDF?

Comments welcome.

[gjbivin]

Some people drill a hole at the back end of the saw slot, where the blade edge is coming up out of the table. This doesn't affect the advantages of the zero-clearance slot since the cutting and tear-out takes place at the front of the blade (going into the table). I've drilled a couple of extra holes for dust collection in "blank" parts of my insert; don't know if these really help, but they don't hurt, either.

[LarryG]

You're right that a ZCTP increases the amount of dust that escapes upwards. A few folks have fashioned "Swiss cheese" ZCTPs to help get the dust drawn down into the collection shroud, below the table.

The primary reason for using a ZCTP is to reduce splintering on the bottom side of the workpiece -- veneered plywoods are especially prone to splintering unless a shallow scoring cut is made first, and sometimes even then.

A secondary reason for using a ZCTP is to keep narrow offcuts from falling into the saw, and/or being grabbed by the blade as they fall in and possibly turned into dangerous projectiles. Although safety is always paramount, this is not really that big a problem unless you routinely work with very narrow pieces.

Since MDF is a monolithic material not subject to splintering, you could use the regular factory throat plate when cutting it. I sometimes take the time to install it when sawing up MDF, but usually don't.

[RodKirby]

Having used a ZCTP for the last 12 years - and been cutting MDF for the same length of time:

• IMHO dust is only marginally increased - not notably. Consider the path of the saw blade - it's into and down thru the workpiece. You could argue that dust that would be thrown up at the back is reduced by the ZCTP (?)
• The safety aspect of a ZCTP for small/thin workpieces -AND- the reduction of tearout, outweigh "additional" dust considerations - IMHO
• A ZCTP and Sharkguard don't HAVE to go together. The Sharkguard's HUGE advantage is it's ability to be taken on/off with ease. IMHO the Shark's overhead DC is just a "nice to have".

[mschrank]

I've not noticed much more (if any) additional dust since switching to a ZCTP. Like the others mentioned, the sawdust is primarily directed down into the slot by the blade, so ZCTP or not, it's heading in the right direction.

I HAVE noticed super clean cuts with no tear-out/chipping, especially when "crosscutting" plywood.

[davidtu]

Newbie here, can someone explain in a little more detail why the ZCTP reduces splintering or tear-out? Is it just that it supports more of the underside of the workpiece near the blade?

[thestinker]

Is it just that it supports more of the underside of the workpiece near the blade?

Pretty much.

[Tom Miller]

Where you'll really notice the problem (ZCTP and dust collection) is when you're cutting less than a kerf's width (i.e. just trimming the edge of the board). You're generating a lot of dust that leaves the blade gullets before getting pulled under the table.

Sadly, this is where the dust collection efficiency of a blade guard (equipped with a DC port) is at it's lowest, since there's a lot of open area to lose air flow.

Regards,
Tom

[vaking]

In my opinion - ZCTP does increase amount of dust. By how much depends on type of cut but if you start using ZCTP all the time - it becomes noticeable. Because of this I would make this suggestion - if you have a shark guard you can use ZCTP as much as you want - shark will compensate for that. If you don't have a shark - then make a ZCTP but use it sparingly, only for cuts that benefit from it significantly.

[LCHIEN]

Newbie here, can someone explain in a little more detail why the ZCTP reduces splintering or tear-out? Is it just that it supports more of the underside of the workpiece near the blade?

yep. Right up to the edge of the cut.


But Liek Rod Kirby, I feel compelled to spell out some additional benefits of the ZCTP and the SharkGuard individually or in tandem.

The ZCTP not only helps reduce tearout, but also keep those small cutoffs from falling into the saw. They either rattle around in the blade shroud waiting to get picked up and thrown or end up banging around the inpellor in your DC.

The SG best feature is the ability to remove and replace it very rapidly (for non-thru cuts and other operations).

I have yet to plumb my DC to the SG so I don't know about dust collection efficiency. I have two DC hoses on the BT TS, one on the bottom and one to the dust port/shroud in the back. I capture virtually all the dust in the inside of the saw, some dust routinely escapes when I make a trimming rip cut of 1/8" to 1/16th inch - the dust goes out the side of the saw.
I suspect maybe it would be better to have regular TP instead of ZCTP on this operation but I do know either way it throws a lot of dust to the side above the table.

[Bruce Cohen]

I've been using both a ZCTP and a Shark Guard since just after I got my 3100.

I'm using a 16 Gal. shop vac and the Sears controller switch that turns the vac on when the saw is turned on. I have the vac hookde up to both the saw outlet and the shark by way of a "T" fitting for the hoses. The dust problem is practically eliminated, although there is still smoe saw dust floating around.


Only Rod Kirby works in a dust-free shop, or does he have a second shop for photography only.

Bruce

[MilDoc]

Only Rod Kirby works in a dust-free shop, or does he have a second shop for photography only.

Bruce

Nah. He has a maid. Or spends hours cleaning up before he takes pics!

[davidtu]

I have two DC hoses on the BT TS, one on the bottom and one to the dust port/shroud in the back.

What do you mean by "one on the bottom"? How is that connected? All I know about on the BT is the connector to the back (and am vaguely aware of the SG, which I can explore elsewhere).

((And in the next year or so, I am going to get to tear down my garage (1/2 "shop") and rebuild a shop from scratch (as well as garage and workout space). THEN we'll talk about Dust Collection... hope to learn it all so I can design everything in up front! ))

[JimD]

I tried a test once to see if I could semi-quantitatively investigate my belief that the stock throat plate helped dust removal. I cut a piece of scrap with the blade exposed on the left - I removed a little less than 1/8 inch with the top of the saw vacumned off. I then took a digital picture of the top of the saw after the cut and then cleaned it for another test. The results were not real clear-cut, no unambiguous differences between stock throat plate and a zero clearance plate. I then tried opening up the slot of the zctp on the back half of the slot. My theory is that the front half of the blade does the cutting and throws the dust into the housing. The back half of the blade can carry the dust back up and out of the housing if you do not move some vacumn air past the blade. Opening up the slot allows more suction past the back half of the blade. I tried openings of varying width up to about 3/4 inch. The biggest worked the best but I was uncomfortable with a 3/4 slot even for just half the slot. I ended up deciding that about a 3/8 slot on the back half with the right side no wider than normal but the extra 1/4 inch on the left worked well and was OK safety wise. The right side of the sawblade had the motor and arbor structure to guide dust to the dust port but there is nothing on the left to perform this guiding function (at least to the same degree).

I do not think I proved much with my somewhat data driven study (how the dust looks is not a great way to measure how much there is) but it did convince me that the difference between stock and zero clearnance was less than I initially thought. I essentially always use a wooden zero clearance plate of some sort.

Preventing off-cuts falling into the housing also has another potential drawback. I lost my belts when an offcut fell into them. The blade was at a bit of an angle but I think it may be possible even with the blade straight up. That's a pretty major drawback of the stock throat plate IMHO.

Jim

[kmk]

I've been using both a ZCTP and a Shark Guard since just after I got my 3100.

I'm using a 16 Gal. shop vac and the Sears controller switch that turns the vac on when the saw is turned on. I have the vac hookde up to both the saw outlet and the shark by way of a "T" fitting for the hoses. The dust problem is practically eliminated, although there is still smoe saw dust floating around.


Only Rod Kirby works in a dust-free shop, or does he have a second shop for photography only.

Bruce

What is the HP rating on your shop-vac? I've 4.5 HP (peak) shop vac and not happy at all.