"Swiss Cheese" ZCTP

[steve-norrell]

I am looking to improve dust collection with a ZCTP and a Shark blade guard. At present I have the ZCTP cut so that its is very slightly wider than the blade (about 1/16 inch total or 1/32 each side of the blade). Dust collection is good, but I will be working with MDF and cedar in a couple of months and I do have some allergy issues. (I do wear a respirator when in the shop.)

My plan is to drill holes in the front half of the plate, in rows that are parallel to the saw blade kerf. Pending advice, I am thinking of 3/8" diameter holes, centered at 3/8" from the kerf. I want to start with one row of holes on both sides of the kerf, but before starting I would like some input on:

a) how close to the kerf can I safely bore the holes, and,

b) what diameter hole.

Thanks again for your help.

[Pappy]

This was tried a couple of years ago but I don't remember the results or who did it. The best collection is your Shark with a hose on the saw port and another on the guard.

[Veramacor]

I am in a similar boat,

I too am looking at a ZCTP with the swiss cheese holes. I ordered a 'no frills shark guard' from Lee a month ago and asked him not to put the dust port on top of the guard. I'm looking to get dust collection from the bottom exclusively.

Hey steve if you have a ZCTP already cut for a BT3100 (or anyone else for that matter) I can take it off your hands. I'd be interested in the hole pattern you come up with and if it works out for you I'll steal your design

[Stytooner]

I imagine that any pattern will work okay. You may want to stagger smaller holes, say 1/2" from front to back. I wouldn't put any holes on the fence side.
If you are collecting dust from the shark port while cleaning up some edges, you can actually clip a piece of thin ply or cardboard to the left side of the shark to help with collection.

If you are collecting from above and below and not cleaning up an edge, I don't think the swiss cheese will help.

I don't recall who did the previous testing or the results either.
Let us know how it goes. Thanks.

[whitecobra]

All the "swissing" in the world won't help since the dust is trapped DIRECTLY in front and behind of the blade as the sheet is passed over it

You need to make small "triangular" cuts in front and to the rear of the blade slot to allow the dust to "drop" into the vacuum area being created by the rear DC hose

Of course as was pointed out the dust that is created ON TOP of the sheet must be collected by the Shark so ordering one without the dust port will defeat this function

Look at the geometry of the dust being created. The dust is coming off the MDF and is being forced UNDER the sheet as it passes over the ZCTP since the plate has no room adjacent to it to allow all the dirt to fall into the box then it stays trapped UNDER the sheet; but not under the sheet 2" away from its origin until it builds up it does so RIGHT adjacent to the plate

You need to cut significant areas in front and behind the blade to allow the dirt to fall before it builds up and moves to the adjacent "side areas" of the table

Putting in holes any more then 1/2" away will help but it will need to "build up" to get there you need to catch as much as possible at the source because once it builds up there is no predictable way to determine where it will move to as it is building.

In front is where it is created in the rear is where what gets past will go the sides is only for "build up stuff"

The other issue is this depends on vacuum pressure to work. Your DC must be able to produce enough vacuum to overcome the blades ability to carry the dust back UP onto the table and under the MDF. This will take some doing in most set ups. The blade has a good ability to overcome most vacuum pressures from most DC or shopvac systems

Dr D

[Tom Miller]

I tried the Swiss Cheese design, and found that it is not very effective. Here's why:

The dust collection under the BT3x00 is not really sucking just under the throat plate, so when you drill a few extra holes in the ZCTP, you're not getting the huge sucking effect you desire.

The as-designed under-saw DC (with a DC attached to the port) works as well as it does because there's a fair amount of air flow coming through other gaps of the saw cabinet, and picking up the dust. Only after the dust is under the saw top does it have a fair chance of getting collected.

As someone else pointed out, the Swiss Cheese design, even if it did work well, would only work when the piece being cut is not covering these holes (like when you're trimming less than a saw kerf off an end). Sadly, this is where my Shark Guard doesn't do so well either, because there's a huge gap between the guard and saw top. I think you can get a Shark now with a 4" DC port, which would solve this problem. Otherwise, I've considered adding a swiveling side plate to my guard -- maybe Lee has considered this too(?).

Regards,
Tom

[steve-norrell]

Thanks for all the input.

It is beginning to sound as if the "swiss cheesing" may not be worth the effort. I will think about it for a while longer.

I am using the ZCTPs that were sold by Jeff (T-Nuts) for a while. They are cut a little wider than the blade -- with the blade at full height. It also is cut to accommodate the Shark's riving knife. The Shark itself is hooked up to a collection system, as is the dust port on the back of the saw. I am using a 6.5hp ShopVac but don't have room for a dust collector. There is room for some air movement on both sides of the blade as well as at the front and back.

Based on the advice received so far, it looks like I may be getting the best dust collection I can, short of going to a dedicated DC system.

I need to look into the swivelling side plate as suggested by Tom and Stytooner. -- Hey, wouldn't that be a neat add-on!

[Lance]

This was tried a couple of years ago but I don't remember the results or who did it. The best collection is your Shark with a hose on the saw port and another on the guard.

Pappy,

I think this was the thread on the DC collection for throat plates that you were thinking of. I think there might have been a related thread as well.

http://www.bt3central.com/showthread.php?t=8515&highlight=zctp

-Lance

[Tom Miller]

...I've considered adding a swiveling side plate to my guard -- maybe Lee has considered this too(?).

Uhhh, yeah, I guess he considered it just a couple posts above:

If you are collecting dust from the shark port while cleaning up some edges, you can actually clip a piece of thin ply or cardboard to the left side of the shark to help with collection.

In this case, most of the excess dust is going to be shooting forward; hopefully by closing up the sides, you will gain enough flow to reverse the forward motion of this dust. Otherwise, maybe you could add a little baffle in front, too.

Regards,
Tom

[JimD]

If you want to do this, I recommend an opening about 3/16 to 1/4 inch wider than the saw kerf on the left side (only) of the slot on the back part (only) of the kerf - this is illustrated in my previous post on this subject noted above.

My theory is that the dust on the top is the result of dust carried into the saw housing by the downward motion of the sawblade that does not exit out the chute to the dust port on the back. Instead it follows the blade up and out on the top of the saw (or into the air). Increasing the suction inside the saw cabinet in general and at the part of the blade where it is carried up onto the surface helps, I think. I still get dust on top, however, and have accepted that as long as I do not get a shark guard or something else where I can suck off the top of the blade.

The reason not to do holes is the increase airflow is not exactly where you want it to capture the dust. The reason not to increase the slot on the right is there is not much room for airflow on the right side of the blade and you are increasing the chance an off-cut will fall into the belts. The reason not to increase the front part of the slot is that is what controls chipout and not what controls dust on the top (the dust is traveling inside at that point, not onto the top).


Jim

[steve-norrell]

Update and Solution

Thanks for all the suggestions. Based on those suggestions, expecially from Tom, Dr. D and Jim, I cut a ZCTP with the dimensions given below. A picture is attached. (I apologize for the poor contrast between the black UHMW and the blade, but most of the features can still be seen.)

1. The opening on the right of the blade is true zero clearance.

2. The opening on the left of the blade is wider, about two kerfs wide.

3. The opening for the riving knife and the back half of the blade is wider on both sides, about three kerfs on the left and two kerfs on the right.

4. The hole at the very front of the blade opening opening is 1/2 in dia., although it could probably have been 3/8 in. I am not sure that it helps in capturing any dust. And, since any pieces that would need zero clearance would be thin enough so that the blade would almost never be high enough to reach up to that hole.

Thanks again for all the help.