Improved Dust Collection ZCTP

[JimD]

I use a ZCTP almost all the time. I ruined a set of belts when an off-cut fell into them plus I like not having to change the throat plate to avoid chip-out. I do not like the extra dust on the top of the saw when using a ZCTP, however. I tried extra holes in the ZCTP away from the blade but that seemed to make no difference. I had an old ZCTP in the saw until today so I tried drilling a large (35mm) hole in the back of the blade slot and that seemed to help but I noticed the trailing edge of the blade was covered by my big hole only part of the time (the blade position changes with the height of the blade). Today I came up with an improved design that passed a couple of tests.

I noticed the slot in the stock throat plate was just over 1/2 inch wide. I measured the position of the back of the blade (trailing edge I called it above) emerged from the throat plate at up to 6 1/2 inches up from the back edge of the ZCTP. With that in mind, I cut a 1/2 inch wide slot in a new ZCTP (I make them of pre-finished laminated hardwood flooring scraps that are about 3/8 of an inch thick) on my router table that is centered on the blade slot (I used an old ZCTP to position the fence of my router table) and starts 1/2 of an inch from the back edge of the ZCTP and ends 6 1/2 inches from the back edge. The front of the blade cut it's own grove in the portion of the ZCTP closest to the operator - I call it the front of the ZCTP. I now have a ZCTP with the front cutting part of the blade truly Zero Clearance but the back edge of the blade (and the splitter) in a 1/2 inch wide slot.

To test this design, I ripped a melamine covered particle board scrap using my normal LU84 blade (50 tooth, mainly ATB grind but with 10 flat topped ripping teeth). It will chip melamine pretty badly unless I use a ZCTP. Then the cut is almost chip free. With my modified design, a nice almost chip free cut. The wide slot did not hurt that function. Next I cleaned off the top of the saw and did a few rips including some MDF. Very little dust on the top of the saw - about like using the stock throat plate. Next I ripped through a short piece of 2x4 that was about 3 inches wide. These wide rips would put the most dust on the top of the saw. Again, very little dust emerged with the new ZCTP. I am very happy with this performance.

I do not know if 1/2 inches wide for the back of the slot is optimum. I was going to start small and work up and got lazy and just tried 1/2 inch. I am using a 1hp DC with two ports under the saw, one is on the normal BT3100 dust collection opening and I put another 2 1/2 inch port up under the saw so I wouldn't have to tip it up for cleaning as often. I have the back of the saw blocked off with one of Jim Frye's articulating plates and I put magnet pieces over the other large openings. I thus have pretty good airflow under the saw but was still getting significant dust on top until I put in a modifed ZCTP.

This idea is not mine, somebody else commented on the previously but I did not catch dimensions for the oversized opening. I think I thus may be providing a few specifics to refine somebody else's good idea.

Jim

[autiger1]

Great Idea...but I would think you still would have the issue of a small cut off falling down in the 1/2" portion. Any Pics?

Tom

[JimD]

Tom,

There is some possibility of an off-cut falling in but much less than with the stock throat plate. The larger opening is on the back portion of the blade where the movement of the blade tends to want to launch things towards the operator, not pull them down into the saw. That happens on the front of the blade which is the small opening. The airflow would try to pull an off-cut in but I think the blade would override that for a piece of any size (i.e. it would touch the blade and move out rather than in). With the blade stopped something could fall in so I will have to remember my belt experience and take the time to retrieve it. This concern would be a reason to try a bit smaller opening - I was going to start at 3/16 but skipped several steps and went right to 1/2.

I'll try for a picture tonight - I am not very skilled but should be able to manage.

Jim

[Tom Miller]

Sounds great! This one has been on my to-do list too long.

Concerning small cutoffs falling in: maybe rather than cutting a wide channel, you could cut a series of 3/4" - 1" diameter holes, centered on the kerf, with about 1/2" separation.

But I do agree that the likelihood of this is much less at the back of the blade.

Regards,
Tom

[LCHIEN]

I didn't look at my BT but the 6-1/2" from the back of the throat plate that's basically almost up to right over the arbor then?

Instead of cutting a 1/2" wide opening from 1/2" to 6.5" over the exsiting kerf,
whay not a series of 1/2" holes spaced on 3/4" center-to-center which would leave a series of 1/4" fingers to support and cutoffs longer than 1/2". Cutoffs shorter than 1/2" would seem to pose a much smaller danger of causing jams that would break belts and such.

[JimD]

I don't know if holes or a narrower slot would be best. With a 1/2 inch wide slot, the blade and splitter take up the center 1/8 of that opening so you have a 3/16 slot on each side of the blade/splitter. Nothing of any size can fall in but the hazard to the belts is probably these fairly long but narrow pieces. If the oversized opening was not centered such that the opening on the belt side was narrower, it would also minimize the chance of something getting into the belt but would you now still get half the carry-over dust (because that side of the blade did not have suction)? The hole idea would deal with that but I don't know how the airflow would be - the pressure drop of the opening will be a function of the perimeter measurement of the opening which would be increasing significantly for holes. If you went down to a 1/4 inch wide opening you would limit what could "fall-in" to stuff 1/16 of an inch or less wide which should be fragile enough to break before causing damage. But is a narrow slot like this provide enough airflow to largely eliminate the dust on the top of the saw?

Seems like there is still an optimization possibility there. Maybe I'll make some junk plates out of 2x4 scraps or something to try it out. I could also just use a couple of plates I already have made up but they don't have to be real durable to check the airflow and I don't have a real need at the moment for another ZCTP.

If I really wanted to do this right, I would make some new ZCTPs and document that process in pictures, then try several of these ideas and document the "dust" also by pictures. That is probably beyond what I have time for but would be interesting. I think of making ZCTPs as a very easy task but I sometimes get the feeling that there may be some people who would appreciate a brief tutorial.

Jim

[JimD]

I spent a couple hours testing this evening and succeeded only in frustrating myself. I am not sure at this point if this idea works or not. With the blade inside the "test block" - a scrap of softwood lumber about 12 inches long and 2 1/2 inches tall - there is no significant dust. This is what I did this weekend. Unfortunately, I did not test a normal ZCTP this same way and it also produces essentially no dust. To get dust, I ripped the edge off with the blade exposed on the left side. This generates lots of dust but about the same amount regardless of what I did. The least dust is with the ZCTP, a slightly widened slot 3/16 wide from the back edge to 6 1/2 inches from the back edge, and with the stock throat plate possibly for different reasons. The breeze off the blade seems similar with the bigger opening ZCTP and the stock TP. The breeze is noticable more with the ZCTP and this seems to blow the dust off the top of the saw which was what I was trying to somewhat measure as an indication of effectiveness. The total dust out the top may be less with the stock TP and the larger back opening ZCTPs but I did not generate data that would show that. I tried openings from 3/16 all the way up to 3/4 inch (testing each 1/8 inch after going from 3/16 to 1/4). My pictures of the top of the saw look very similar except for the three mentioned above.

I still think this has some benefit but I can't prove it from what I've done to date. I think I will try a 1/4 back opening to minimize off cut risk to the belts in my next new ZCTP.

If anybody is both interested and can remind me how to load pictures I will do so (I made them no more than about 125kb). I've done it but can't remember how at the moment.

Jim

[JimD]

I did some additional testing over the weekend and learned a couple things that may be of interest. First, in my initial testing I tested larger opening from about 3 inches to about 6 1/2 inches from the rear of the TP. I was thinking that concentrating the dust collection where the blade was would be better. It turns out that isn't true. Opening up the opening from the rear of the TP to 6 1/2 or 7 inches - about where the arbor is - apparently provides more airflow and less dust out the top.

Another interesting result is that opening up the zctp a little - like a 3/16 or possibly 1/4 opening - or a lot, like a 3/4 opening, results in about the same dust removal as the steel red stock throat plate. Opening it up 3/8 or 1/2 inch on the back portion does not visibly improve dust removal.

Lastly, in my last test I inadvertantly opened up the slot only on the left of the blade, not on the right. I made the slot about 1/8 or 3/16 larger on the left and still about zero clearance on the right. The dust collection was pretty good, about like the steel red stock throat plate. This is very interesting to me because the risk of an off cut getting into the belts is only if you open up the right hand side of the slot. I have not tried bigger openings yet oriented this way but I may. Having performance about like the stock throat plate with very little risk of something falling in is pretty good, however, and that is what I seem to get with this version. A picture of some of these plates is attached. You should see the red steel version, the offset 1/4 inch version, the 1/2 inch version I started with and the 3/4 version. All except the 1/2 inch give about the same dust removal performance.