Saw top guard layout?

[Ryan Brucks]

one other point I haven't seen mentioned yet regarding sliders. this might not be true for felder/hammer, but minimax sliders are set to angle the blade away from the sliding action by around 4 thousanths across the diameter of the blade. that is supposedly to keep the slider from binding against the blade to allow for some slight wobble to develop on the blade during heating/cooling cycles.

What I interpret this to mean is that sliders will ALWAYS have a more challenging above table dust collection problem. You aren't passing the blade perfectly though a 100% aligned kerf and fence, you are always scraping the sides by a few thou on the upcut on the backside. of course this could just be MM but I would be curious to hear if the hamers or felders are the same. What made me think of this is someone way back with a regular tablesaw who drastically reduced above table dust by aligning his blade/fence/miterslot all within a few thou. Makes sense to me.

[ian maybury]

Hi Ryan, good to see you post both as another slider user, and as a builder of a large format guard. My K3 has a scoring blade as well, although I've not used it yet and don't know how big a deal it's likely to be as a dust producer. (it should presumably always be covered by the workpiece, on the Hammer the dust chute is below it too)

I don't think you mentioned what dust system you are running, but judging by the duct sizes it's something like a Clear Vue or a big Oneida. What we all seem to be finding is that while having lots of CFM helps a lot with dust collection, the layout of the guard and the lower chute still matter.

It also seems to be the case that simply going big or small on the top guard isn't of itself the whole answer either - it's more a case that there are crunch points that matter. We've all mentioned the physical interception of high speed dust as an essential, and that the throwing of dust forward under the guard as a common problem. i.e. there doesn't seem to be much option but to run the guard tight down on the work, and to consider the possibility of some sort of deflector to the front.

There's also as you said places where it pays to keep the air speed high - as in the perimeter/under guard to work gap you mentioned. The other variable is total CFM being moved - plenty seems advisable for ambient dust collection and air cleaning. Trouble is we have to keep all the balls in the air at once.

David K has said before that top guards are very tough to get so they work well in all situations. When all possible cutting scenarios are factored in it probably becomes a bit of a tall order. I don't mind a few coarse chips escaping, but being sensitive to dust am very keen to catch the fines.

Right now the challenge seems to be to properly understand/develop a list what these balls/success factors all are - then designing a guard becomes a little less a matter of hoping for the best.

The K3 specifies the same toe out relative to the slider - that's .002 - .004in over the diameter of a 12in blade, and about the same for the rip fence - but that ends up going in the opposite direction. i.e. the slider travel and the rip fence end up out of parallel by the combined amount of the two toe outs.

Mine is set around the lower number in both cases. For sure having the up coming edge of the blade significantly contact the side of the cut can greatly increase the amounts of dust thrown forward - I had a late 90s Robland combo with a fairly crude adjustment arrangements and bare minimum 1HP dust collection. Having once or twice managed to accidentally set it that way I can confirm that it really makes a difference.

I've never tried setting it up at zero toe out, but there's presumably no reason why not other than what out come you prefer in the trade off between dust production, marking of the cut face, and of course the risk of kick back. i.e. it's probably not much different to a traditional table saw.

I'm quite tempted to try a Format 4 -like layout guard of the sort liked above, but mounted on a ceiling mounted articulated arm so that it can be easily raised/lowered/tilted and on occasion (when using jigs etc) easily swung out of the way. Trouble is i've a lot of other shop set up stuff on, so it may be a while until i get to it. One question is whether or not there's a low cost commercial (e.g. camera/tool mounting/anglepoise lamp like) arm available with conveniently locking joints.

DIY is an option, but the most immediate problem is perhaps to find a convenient way to lock three joints in the arm every time a position adjustment is required....

ian

[Ryan Brucks]

Lots of good points in there.

My DC is a CV 1800 body with the 16" impeller.

Re: scoring blade dust:
you wouldn't think the scoring blade would be a big dust producer, but it was more of one than I expected both above and below the table. A very visible "puff" of dust gets emitted above the table at the start and end of each cut (when the blade isn't surrounded), and after cutting a few sheets of melamine using the old stock cu300 guard I had way more dust above the table than when not using the scoring blade. I have only lightly tried the scoring blade a few times with my new guard so I can't definitively say how much it helped other than its better but still not perfect.

My scoring blade actually makes the inside cabinet much dustier too. The problem is its on the far end of the under cabinet blade shroud, and there are some restrictive components nearby which encourage most of the air to be drawn in before the scoring blade part. it's right above the lift/tilt threaded bolts and hardware and has the annoying habbit of gumming up these threads with fine dust after a while. I think the CU300 saw shroud might have too many air openings, so very little air is being drawn near the scoring blade. Going to see in the future if there's anything I can do to improve that, short of running maybe another 2.5" or 3" line to under the scoring blade inside the cabinet (some view windows would make this possible).


I asked Sam Blasco (minimax rep) about the blade toe-out thing. He mentioned the only reason slider manufactures do that is because when a workpiece is clamped to the slider, if the blade were to develop wobble and toe IN to the slider, the clamped workpiece could shove into the side of the blade binding it... which is slightly more likely than on a regular TS because there the workpiece wouldn't be clamped in place.


One other danger I'd like to point out with the large guards (has been alluded to), is the possibility that a thin offcut piece gets lifted up by the airflow/suction, and this piece is just the right width to contact the edge on the side of the guard. The piece would rotate at this point, possibly striking the blade. In this scenario I imagine some crazy kind of kickback where the piece may get jammed between the blade and the guard. I am glad I am using a slider if and when this happens, since I am standing on the other side of the blade and somewhat shielded by the guard itself... but that might not help if the thing self destructs on you.

I have done some test cuts using really small slices because I wanted to be prepared and see what would happen. I only took slices that were just thinner than the gap between the blade and guard side (around 3/4" for me). I think I know what will happen if the piece is just slightly larger (not good). Offcut piece instantly gets sucked up against the top of the gaurd if I have the guard set low (1/8 to 1/4" offset). Then you have to turn off the saw to pull these pieces out. If I set the guard 0.5" above it can't pick up any workpieces, even small ones.

From this I have learned that its probably best to have the guide a little on the high side when cutting small pieces, just to be safe, unless of course you use bristle brushes around the whole thing (love that idea, but of course you trade off some visibility, if that matters to you).


One other minor thing: you mentioned needing to secure 3 points for the ceiling mounted guard. Not sure which design you are commenting on, but my guard only requires tightening two hand knobs to fix the height position. A third knob allows left/right adjustment but is rarely used unless doing tennoning. I made a really simple plywood jig to hang the guard from the ceiling. Only took me a little over one night to get it built and mounted.



The hand knob you see in the plywood support above is the only thing supporting the guard's weight. This 1/4" bolt goes through the 1 1/4" steel tubing. I used a 1x1" scrap of cherry that fit inside that steel tubing and tapped some 1/4-20 holes in it which lined up with the steel tubing holes. That's how the hand knob tightens to seceure the left/right position. There is also kind of plywood "key" screwed to the back of the steel (using the same cherry strip tapped inside), and that pieces rides inside the plywood and keeps the steel tubing at 90 degrees when you are adjusting the position (and helps strengthen it a bit). This means I can slide it aside for tenoning easily. Notice the ceiling cabinet screws are in routed slots as well giving a few inches of adjustment on the other axes too... so its fully adjustable on all 3 axes.

I am glad I found this thread because now I know those are the Format-4 guards. Saw a picture of one a while ago and really liked the design but couldn't figure out what it was. The wheel on the front and back leads me to believe these ride up the workpiece, is that right? I like how thin they are and how massive, they look like they could move a ton of air, all at incredible velocity. I am curious how large the actual ducting port is though. It would be pretty trivial for me to design a new blade guard and mount it up to my existing ceiling mount system I think. I might try it eventually depending on what the long term results of my current guard are.

[ian maybury]

Thanks Ryan. You have the same fan as myself. They really do shift some air, and develop a lot of suction at the same time.

Sounds like top guards and bottom chutes need to seriously cover the needs of the scoring blade - so thanks for the tip off.

The Felder K700S ( top model) also uses one of those semi circular guards. The stock/narrow/vertical use guard has an opening of 21 x 1 1/2 in. I've just found out via FOG that rather than tilting it they offer a wide guard for angle cuts. Tilting would need a fancier mounting.

I was toying with the possibility of an articulated mounting - a hinge bracket at the ceiling, an angled link, one at mid point (like an elbow to the rip side), an angled link and one at the guard. The hinge pivots would run front to rear. The aim would be to allow the guard to be adjusted for height, tilt and side to side as needed. Not sure if it can be done in a way that's convenient to use though - it wouldn't do to have get out step ladder every time to make an adjustment. Something fabricated in steel would be a lot neater too - but whatever it would need a means of locking the joints/hinges.

How do you get on with the issue of access to your high level ceiling bracket for adjustment?

ian

[Ryan Brucks]

(uhh. oops I screwed my post somehow)

(having really bad forum day. twice lost really long post... will post again later tonight with picture instead).

[Ryan Brucks]

Comedy of errors lead my post yesterday to melt down, and didn’t get time to fix.


You basically guessed it, I just use a step ladder to reach the top knob to move the guard. But I don’t do tenoning on the TS too often so its no big deal for me. If you would need to move it a lot a big articulating arm does sound pretty awesome. But I feel you on getting buried in shop projects. It’s hard to make any progress when everything is a potential project Especially when you get caught up making everything just right.

Interesting to know the dimensions of the felder guard being 21 x 1.5” . That’s actually almost exactly the dimensions of my guard when I first built it.

When I was planning the dimensions for the acrylic part of my guard, I thought about making it a semicircle like the format4 one. The only reason I didn’t was I couldn’t figure out why it would be that much better. For one, unless you jack the blade so it is projecting way above the workpiece, the saw blade will barely protrude into the guard in actual use. So why does the semicircle matter at all, aside from looking sweet? The only advantage I can think of is that the air stays at really high velocity all the way up the guard (not just the bottom area). But then you have to put the dust port on the side near the top. Even with a 4” port, going sideways into a 1.5” wide space is definitely going to restrict more airflow than the sloping design I have. Unless of course a custom transition is used that maintains the area of a 4” port. At 1.5” wide, it would have to be around 8.3” x 1.5” , kinda funny looking. I don’t think the format-4 has that transition area from the look of it. Being wide at the top and sloping in at the bottom is a less restrictive transition, but I also trade a small amount of air velocity as the guard widens… is it enough to be important? Hard to say IMO so I didn’t dwell too long on it.


I did make a minor change to my guard the other day that improved the dust collection as well as safety factor pretty significantly.

I added a kind of baffle inside the guard that surrounds the riving knife. It’s just two pieces of acrylic with a ¼”space between them. This reduced the volume of the guard around 25% and noticeably increased airspeed around the parts of the guard closer to the blade(s).





The area at the bottom of my guard is now around 15 x 1.5”.

It was tempting to just build the guard smaller like this to start with (cutting a kerf in the back for the riving knife), but that presented some challenges. First, with a kerf in the back the guard would have no strength and could eventually sag, closing the kerf on the riving knife (bad). Second, the mounting point that supports the weight of the guard would be way off center. It’s heavy enough to matter. This way the guard is centered from its mounting point.

It also has the safety benefit of guaranteeing that if the guard is bumped really hard, the riving knife will get hit first and not part of the blade. With any ceiling mounted guard you need to be mindful of the potential for some really nasty kickback experiences should the guard ever come into contact with the blade…or a small piece of wood get lodged between.

[ian maybury]

Interesting that reducing the internal cross section improved dust collection Ryan. It's not always discussed a lot, but there definitely are places where it really matters to maintain lots of airspeed even though it might reduce the CFM a little. e.g. as in getting the guard down close to the work.

The difference with the articulated arm is that ideally all three joints need to move for each position adjustment - which would mean the step ladder every time and not just occasionally as with your system.

Maybe one advantage of a fairly tall semi-circular guard is that it's pretty narrow for quite some height - meaning that it's probably good at getting down beside e.g. a tall rip fence. The circular profile should also gather the flow fairly smoothly to the outlet duct. It takes a fairly wide section of flat duct to deliver enough open area to match say a 4in hose as used on a high flow system - and it's not too hard to mount such an arrangement off the relatively large circle/perimeter of these guards.

I'm relatively new to high flow top guards, but last night when cross cutting to square the ends of some roughly 1in x 3in pieces it instantly sucked the 1/8 thick offcuts up through the guard and off to the cyclone. So it's definitely not short of puff - even though it still needs the top guard well positioned to catch the dust effectively.

You made the point to the effect that (presuming correct blade alignment) most of what the top guard has to deal with is what the bottom chute fails to 'empty' from the blade. This i think is 100% true - to the point where i'm cautious about putting too much work into the top guard before the bottom is optimised.

I'm going to start a parallel thread asking for input on this topic - do people find that with a very well optimised bottom chute that it's possible to leave the top guard with minimal work to do?

ian