Saw top guard layout?

[ian maybury]

I've been doing some cutting on the Hammer K3 using the Pentz/Clear Vue dust system - with a 4in top connection via a DIY transition to a modified Hammer top guard (see below), and 5in to the cabinet.

It's working very well, and is streets ahead of anything I've ever had before. Not a speck of dust escapes, but with one proviso - the top guard needs to be adjusted down so that it's fairly close to the top surface of the material being sawn. The air flow is pretty strong - it'll hold a say 2 1/2 x 1 1/2 in piece of 1 in ply to the roughly 3/4in wide x 12in long entry slot in the top guard against gravity.

It's equally the case though that once the blade is raised an inch or two above the saw blade (e.g. to clear the cross cut fence) that (a) dust from the top of the blade can be thrown forward and clear (it's not caught by the guard), and (b) the velocity of air movement around the blade falls pretty dramatically.

None of this is news, but it underlines what is always said on the topic - there's inevitably going to be specific situations/set-ups where it's tough to intercept all the dust. Trouble is I don't do so well when this happens, as I'm pretty sensitive to the stuff.

I guess I'm wondering whether it's worth trying some further mods (David K and i have already tossed some thoughts around), and wondering what's been the experience of some of you guys running high CFM dust systems with wide e.g. Shark type top guards?

The riving knife mounted top guard at present (see photo) is still fairly restrictive compared to the 4in duct (the open area at the entry to the DIY transition is about 40% of that of the duct), and further mods are possible but:

1. A very bulky guard that can't anyway be used so close to the work, the rip fence, and on angled cuts might not be any improvement overall.

2. The reduced (local) entry velocity into a wide guard might disimprove dust collection - but might improve it too by pulling moving more air from the surrounding volume.

3. A much freer flowing top guard would reduce suction at the cabinet - which itself is a little restrictive since despite having upgraded to a 5in duct inside the connection to the dust chute is a not easily modified 4in entry. i.e. the dust system can in theory easily deliver the CFM, but the restrictive chute (which could if necessary be modified) may hamper this.

As ever this stuff is a lot about the sort of work you do. The aim here is to come up with something that's going to be a very effective all rounder.

It's very likely that I'm just being a bit too picky, and need to work on evolving set ups for certain cuts. It'd be a pity though to not avail of easily available further improvement if it's available.

Thoughts/experience appreciated....

ian

236502

[Thomas Hotchkin]

[QUOTE=ian maybury;1953853]I've been doing some cutting on the Hammer K3 using the Pentz/Clear Vue dust system - with a 4in top connection via a DIY transition to a modified Hammer top guard (see below), and 5in to the cabinet.]

Ian
Are you losing air flow at the blade guard to your dust collector by routing dust collection from blade guard to your cabinet first? I find that I have better dust collection at my DIY blade guard with its own 3" duct to collector. I also keep guard about 1/4" above stock surface for better air flow and dust pickup.Tom

[ian maybury]

Hi Thomas. Both connections branch above the saw from a 160mm (6 3/8in) duct.

My sense is that the cabinet is not taking more than it's share of air - basically because regardless of the duct sizes (which anyway are a fairly good match for the 160mm main duct) there is a pretty good balance between the restriction in the chute and the top guard. Which is why I'm as a above a little cautious as above about opening up the top guard on it's own and unbalancing the two.

There's no doubt but that the dust system can move (probably a fair bit) more air (CFM) than at present, but it seems likely that it would require modification to free up the flow through both the top guard and the under table chute.

Doing so would beg a question I don't have a good answer to. Both the top guard and the chute part enclose the blade. The blade projects through a slit in each case - a fairly narrow gap that ensures high inward air speed. There's a picture of the bottom chute here - the hose connects and pulls from the bottom: http://tiny.cc/d5p8gw

Opening up the clearance in both cases would reduce the resistance and so increase the CFM/air volume while reducing the velocity - but it's not clear relatively speaking how important the velocity through these gaps is versus volume.

It could be that lots of speed is in both cases important to clearing the dust out of the tooth gullets for example, while volume is more important to pulling in floating/ambient/escaped dust in the broader area around the blade.

Going to a wide top guard like the Shark would definitely reduce the speed of entry of air into it versus my present guard, but it would move more CFM. But could also pirate more than it's fair share of air versus the chute below if it relatively speaking was too free flowing....

It seems likely that the chute and the top guard are designed to flow much less sir than my system is already moving - the stock top hose is for example only 2 1/2in dia, and a Pentz dust system pulls a lot more suction than most dust systems these saws will be run on. Which suggests if their designs are remotely optimised there probably is scope to open up the above slits/gaps...

ian

[Michael W. Clark]

Hi Ian,
Is your cabinet connection restricted by a smaller diameter hose that connects to the blade chute/hood? If so, it may be causing too much air at the upper blade guard.

Could you damper back the upper blade guard? If so, its possible that you may encounter a situation where you drop the flow too much to convey the dust that is captured in the top guard. Another option might be to have an adjustable opening(s) in the duct or on the top guard so you can adjust the amount of air being pulled through the guard but still maintain your conveying velocity. When the guard is moved farther away from the work, you may want to close off the bleed. This is becoming a common practice on conveyor hoods where too much air pulls in good material, but if you damper it back, material falls out in the ductwork. We accomplish the bleed with a register collar or moveable openings on the hood.

I'm going to convert my Grizzly saw to a 5" cabinet connection (no close-capture on the blade with the model I have) and a 3" shark guard. The 5" and 3" will go into a 6".

Mike

[ian maybury]

Hi Michael. The cabinet connection on the K3 is misleading. It's got a 5in connection, but when you look more closely you find it immediately steps down to a 4in hose inside connected to a similar cross section square outlet/connection at the bottom of the dust chute.

Knowing that I had plenty of CFM available with the Clear Vue/Pentz system I replaced the hose with a 5in, but had to put in a 5 to 4in reducer just before the entry to the dust chute - doing otherwise would have required cutting metal to modify the chute connection so it seemed best to try it first.

It's no problem to fit a 4in gate in the top guard's hose to provide the ability to adjust the flow there if needed - I actually bought one, but thought I'd try without it first since per the original post the top guard by at one point reducing the open area to about 40% of that of the 4in flex hose is already quite restrictive.

Right now picking up work is not an issue - I mentioned that it can do so only to illustrate that despite the restrictions top and bottom the flow is pretty strong. The fan is a 16in Clear Vue CV Max, and due to its quite a high pressure capability it still shifts a lot of air.

The present set up actually works well, but the fairly narrow inlet top guard (which is convenient because its not bulky/obstructive) loses effectiveness quickly if it's not dropped down well over the blade to sit just above the top surface of the work. It's as simple as needing to keep the lip at the infeed end of the slot in the guard placed low enough (say 1/2in or less over the work piece) so that dust flung tangentially out of the blade teeth (and forward into the operator's face :)) hits it and can be sucked away before it gets out of the guard. Raising the guard more than say an inch means this high speed dust is left free to fly clear, and ends up in the shop air. This is clearly a well known effect - the guard is shown dropped right down in all the drawings in the Hammer manual.

The dust system is for sure capable of moving a lot more air if needed/wanted, but this would require reducing the restrictions in the top and bottom connections. The proviso is probably that both would need sorting together to maintain a decent split between the flows.

I should perhaps have been a bit more specific in framing the questions/requests for input - it's surprising how many aspects there are to this situation when it's thought through in detail.

(1) The first thought was whether or not fitting a wider and more free flowing top guard like a Shark might reduce the need to drop the present guard very low over the work to get decent collection.

There's pros and cons - the very large inlet area on the Shark would greatly reduce the inlet air speed and possibly the ability to capture dust thrown from the teeth, and being very wide it might not be possible in many situations (e.g. tilted cuts) to position the guard down close to the work. Yet it seems likely given its lower air speed that getting this guard into a position where it intercepts flying dust is necessary for good collection. It's also likely that plenty of CFM is best for this type of guard.

It seems likely that there's a trade offs involved. High inlet air speeds may better capture flying dust off the blade, but higher CFM will do a better job of pulling in air around the work area for cleaning. Large size may help intercept flying dust, but may make it impossible to get the guard into the most effective position.

Which leads to the questions: how have people got on with these wider guards? Do they work well, do they need to be dropped down tight on to the work, do they need high CFM to work properly, how much of an obstruction is their size? Are there other strengths/weaknesses/problems?

(2) A second thought quickly follows. Would fitting a free flowing guard like the Shark disrupt dust collection below the blade?

The reason for wondering about this is that unlike in the case of some of the fancier Felder models the lower chute on the K3 does not fully enclose the blade - the blade exits through the slot in the back of it. (see the photo linked above) It relies on maintaining a high speed inwards airflow through this slot and over the blade to prevent the escape of dust.

The concern is that a free flowing guard up top might reduce the air speed through this slot enough to matter.

A second thought quickly follows. This slot is a source of resistance, and if widened would allow the dust system to flow more air - but would reduce the airspeed over the blade.

Which leads to the second question: do people have experience of these through slot type dust collection set ups, even on other saws? How sensitive are they to maintaining the right flow of air through them? (possibly not all that much, in that many dust systems used on these saws will flow much less air than a Clear Vue)

Pardon the complexities, it's likely that most won't have direct experiece...

ian

[Alan Schaffter]

Realistically you have two, completely separate but related problem environments- cabinet and above blade. As long as you have a sufficient source of make-up air that can enter the cabinet, just about any level of CFM will work in the cabinet. Dust thrown off the blade inside the cabinet will stay in the cabinet and generally be collected. The source(s) of make-up air can't too large or the DC too weak that they allow dust to waft out. The blade slot, especially if using a ZCI, is too narrow and mostly covered by the stock to be considered much of a source of take-up air.

The second problem - collecting dust over the table is a different. Little dust just escapes from the blade slot- as mentioned it is too narrow to allow much air to pass in either direction, despite the best dust collection. Instead, the dust generated by the blade it is captured in the blade gullets, and a significant amount of it is carried above the table and hurled at the user at over 100 MPH. Unlike below the table, there is no cabinet to restrain the dust. You need a decent, over-blade shroud that must do two things- prevent the dust from being hurled outward kinetically and restrain it until its velocity decreases so it can be collected. Air flow alone is not sufficient to stop dust from flying out- typical DC duct air velocity = 4000 FPM; dust velocity generated by a 10" blade turning at 4200 RPM = 10,995 FPM!! Also, you can verify this yourself, but DC suction isn't much good when even low velocity dust gets just a few inches away from the DC inlet. Make-up air is needed above the table as well. That is one reason I use a soft "bristle" shroud- it stops kinetic dust yet allows make-up air to enter. The biggest issues with above the table collection are that close shrouding works against make-up air and the size and shape of stock limit good shrouding. It is often impossible to shroud the blade when using tenoning or other jigs.

[ian maybury]

That's about the way I see it too Alan. Especially that if high speed dust isn't physically intercepted that there's no realistic dust system or shrouding that can hope to pull it back. Although it's probably advisable to have lots of air speed through the interception/collection area too to help mop up what's been intercepted.

It's got to be a good idea for the system to move large volumes of air, in that it helps remove ambient dust/clean the air in the area - but that's a separate function.

What is a soft bristle shroud? Is it a DIY option? It could be that something fairly minimal in the infeed end of the blade slot in the top guard could help a lot.

I'd not even thought about tenoning jigs and the like, but it seems like the thrust of what you/we are saying is that there are going to be situations where especially a large and bulky guard become a problem. There's also the problem with a big guard of needing to move enough air through it to get good collection of what's been intercepted.

Another problem scenario is cutting with the top of the blade just showing to minimise splintering. Chances are in that case that it's not going to be possible to get the top guard to do much to intercept dust - although it may not be so bad since the blade is mostly submerged.

I've not yet looked closely at what's happening under the table, and at where it's taking air in down there (but there's a decent gap between the table and the cabinet) - but it does seem to be working OK as it's staying pretty clean.

ian

[Alan Schaffter]

What is a soft bristle shroud? Is it a DIY option? It could be that something fairly minimal in the infeed end of the blade slot in the top guard could help a lot.

ian

Here is my soft bristle above blade shroud. I works fantastically when cutting sheet goods. It performance starts to decline as the stock gets narrower and thicker. As already mentioned it can't be used with a tenoning jig and the like. Obviously, it is not a blade guard!

http://www.ncwoodworker.net/pp/data/1403/medium/PB050012.JPG

http://www.ncwoodworker.net/pp/data/1403/medium/PB050010.JPG

http://www.ncwoodworker.net/pp/data/1403/medium/PB050013.JPG

[ian maybury]

Now i remember it Alan - that's definitely a 1960s 'big hair' style top guard. More seriously it's got to do a good job of allowing it to get very close to the work to intercept flying dust. I wonder if it does equal duty all around? The worst of the dust seems to get thrown forward off the top of these blades.

Since the last I've been looking at European industrial saws which presumably are sold into regulated low dust environments. They too seem to be going for a full half circle enclosure in a narrow guard - much like the Felder Format 4 examples here: http://www.format-4usa.com/us-us/products/table-saws.html

The bit i can't quite figure is how they handle angle cuts - but perhaps they are fairly rare on a panel saw. If the blade only ever projects slightly through the material being cut then it may not need to tip out of the vertical, only to move laterally a bit? Not sure either why the duct/mounting is angled so that the guard moves back and up as it's lifted. Maybe it's for better visibility?

I'm thinking that it mightn't be too hard to organise a DIY version of this type of guard. A hinge (front to rear) would allow it to be tipped for angled cuts, while a knee joint of some sort at high level would allow it to be adjusted side to side. Maybe something a bit like an anglepoise lamp mounted upside down at ceiling level...

Has anybody ever worked with a guard like that on the Format 4 saws? Felder interestingly enough don't seem to regard dust collection as a marketing priority, it's not discussed that I've seen in their material...

ian

[Michael W. Clark]

Hi Ian,
I would also agree that the cabinet and top collection are two different "hoods". When the board goes over the blade, the two hoods are basically separated. The cabinet collection point is going to get air from any gaps or openings in the cabinet, I would suspect very little is going to come throught the throat plate, but I'm not familiar with your saw.

Regarding the top hood, it is doubtful that you can pull those chips back into the hood and duct once they are thrown toward you. The best bet is to physically knock them down as Alan says, then have enough DC to carry the chips away once they are knocked down. I'm wondering could you put a set of bristles only on the front of the guard? The wheel on the front of the stock guards seems like it would also create a barrier.

Mike

[ian maybury]

Bristles to the front could well do a decent job Michael, and wouldn't be too hard to try. Maybe even mounted horizontally from the front edge of the opening, and pointing back to the blade.

Wonder if even a piece of something like thin 1/8in ply mounted that way with a slit to reach past the teeth each side of the blade (a bit like a low clearance throat plate, but with maybe a 1/4in gap to avoid issues and reaching back and inch or so) would work and/or be safe? It'd intercept more flying dust, but at the expense of reducing the air flow into that part of the guard opening.

The positioning of the guard is (regardless of the type) still going to be an issue, in that if the blade is only slightly projecting above the top of the workpiece it's not going to project up inside the guard. Meaning that it'll be hard to intercept flying dust coming forward out of the teeth.

Another way of looking at it says that the Format 4 type wheeled half circle guard more or less achieves this effect - and copes with this issue too. By being dropped down close to the top surface of the work/forming with the workpiece a near enclosure of the blade. (it can't seal fully, as enough air has got to be drawn in through the gap to transport dust back up the duct)

It's still not going to be perfect in that its going to struggle with e.g. the top of the blade projecting out of the side of a workpiece during an angled cut - but maybe that's where Alan's bristles come in, or even something like an adaptation of one of those adjustable plastic profile gauges used in tiling.

I started this discussion wondering if my guard could be made less sensitive to needing to be positioned right down on top of the workpiece. It starts to look like that's rather than a problem actually a given requirement with any guard given the dynamics of flying dust, and the sort of airflows we have available. (even on high CFM systems)

It'd need experience to get to the bottom of it, but by this measure it may be that a very wide guard of the sort now popular may have disadvantages in this regard. Moving lots of air has to be a good thing, but their bulk may create limits in many situations as to how closely they can be placed above the work.

The other conclusion i seem to be drawn towards is that a properly (conveniently adjustable for tilt and position) ceiling/roof mounted guard has got to be way ahead of the riving knife mounted item on the K3. Another advantage of this combined with the Format 4 type guard would be that (a) the riving knife becomes independent of the guard, and (b) the guard can be moved right up out of the way (support arm permitting) for awkward work like using a tenoning jig.

ian

[Alan Schaffter]

There is one more option that might negate most of the need for above-blade dust collection.

Assuming the the blade is actually cutting on the downstroke (backside of the blade rides in the kerf)- dust that is thrown from the top is carried in the gullets in the cabinet for one half or more of the blade rotation. The problem then becomes removing the dust from the gullets before it is carried back above the table. How about (1) really good cabinet CFM, especially in the area of the blade with the source of make-up air ported directly over the blade disk and down towards the DC port, (2) a curved, compressed air manifold mounted on one side of the blade, starting just below the top of the saw, that directs compressed air at a right angle so it can blow the dust from the gullets? The manifold would need to articulate just like the blade- up/down and tilt- so the nozzles stay aimed at the gullets. It might be a bit noisy but there is a good chance it would work. Compressor requirements (PSI and CFM) might be pretty high, however, but the velocity and strength of the air streams should be able to dislodge the dust.

So who wants to mock it up and test it?

[Jamie Buxton]

There is one more option that might negate most of the need for above-blade dust collection.

Assuming the the blade is actually cutting on the downstroke (backside of the blade rides in the kerf)- dust that is thrown from the top is carried in the gullets in the cabinet for one half or more of the blade rotation. The problem then becomes removing the dust from the gullets before it is carried back above the table. How about (1) really good cabinet CFM, especially in the area of the blade with the source of make-up air ported directly over the blade disk and down towards the DC port, (2) a curved, compressed air manifold mounted on one side of the blade, starting just below the top of the saw, that directs compressed air at a right angle so it can blow the dust from the gullets? The manifold would need to articulate just like the blade- up/down and tilt- so the nozzles stay aimed at the gullets. It might be a bit noisy but there is a good chance it would work. Compressor requirements (PSI and CFM) might be pretty high, however, but the velocity and strength of the air streams should be able to dislodge the dust.

So who wants to mock it up and test it?

I remember somebody posting here about that approach several years ago. He said that it was very very loud. A high-speed stream of air blowing sideways across the moving blade turned out to be a siren.

[ian maybury]

We talked that one before. Noise as you say is one issue, ditto that it might require a decent sized compressor. It'd be possible to arrange a port, but given the low level of suction in the dust system the flow would probably be too low.

The blade on the K3 is actually in open air once it clears the slot at the rear of the dust chute. Yet it seems to stay fairly clean inside the cabinet. Either it's hard for the dust to get out of the gullets, or else there is more dust production going on at the back/upwards moving side of the blade than we would like to think. Whoever at Felder designed it seems to have figured that they could capture most of the dust from the downwards moving section of the blade.

It's one that needs trying all right, although my compressor is only mouse power and not big enough. I wonder is there any way to sidestep the need for a compressor by generating enough turbulence in the airflow through the chute???

ian

[Ryan Brucks]

hey guys. looks like this conversation has already been well hashed out. Figured I would post a pic of my guard and give my thoughts anyways.

http://worstkind.com/shop/cv/7-6/07.jpg

http://worstkind.com/shop/cv/7-6/06.jpg


I made my guard from the wood central plans. I made my guard 19" long so that it could go over the riving knife and scoring blade on my minimax saw. Since I was almost doubling the length, I made the shape slope inwards to maintain the surface area at the opening to keep velocity up. Full 4" port.

Now Michael correctly mentioned in a different thread that it's not the 2d area of the guard that will determine air velocity, rather the height gap offset times the parimeter. He is right about that in most cases. The one case where the 2d area of the guard matters is when making a non-thru cut, like where the blade is taking a slice less than keft thickness on the edge. In this case one side of the blade is open to air, so the parimeter isn't the only factor anymore, and the smaller 2d area of my guard (from the sloping sides) helps to maintain some of that velocity.

, and with my 4" port and guad set between 1/8 and 1/4" above the workpiece, I get really good dust collection, but still some chips escape out of the small gap in the front.

I notice however that for me it is only larger chips that end up on the table afterwards, there is no fine dust. I think the reason here being that my guard extends a good 6 or 7 inches in FRONT of the sawblade, in the direction of the spin. So the fine dust that gets thrown off doens't have enough inertia to escape the high velocity air, but the larger chips do. I noticed that melamine and veneer ply left alot more large chips behind.... baltic birch ply left almost nothing behind.

I am considering adding the bristle brush to the front of the guard as well, but I thought it was interesting that I get only larger chips and not fine dust. I think its due to how long my guard is extending in front of the blade.

[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.
http://worstkind.com/shop/dc/blade_guard_02.jpg


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).

http://worstkind.com/shop/dc/blade_guard_03.jpg

http://worstkind.com/shop/dc/blade_guard_04.jpg

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