2 extractors on table saw?

[Doug71]

I have a Metabo TKHS 315 site saw in my workshop that is just used for ripping down timber. It's has a dedicated bag over bag type extractor which seems to collect the dust from underneath okay. There is the usual extraction pipe from bottom of saw to crown guard, I know these are only a token gesture and don't really do much. Today I was cutting quite a bit of wood so connected one of my shop vacs to the crown guard and wow what a difference!

Now looking to buy a cheap shop vac to dedicate to crown guard, probably something like the 40ltr Titan one from Screwfix.

What are peoples thoughts on this set up, any opinions or better ideas?

Thanks in advance, Doug

 

[PAC1]

I have been doing this for 2 years. It is worth getting a remote switch because it gets boring having to switch the shop vac on separate to the chip extractor. I find it is a massive improvement especially with fine dust. You will next look to upgrade the crown guard to catch even more dust.

 

[MikeJhn]

I'v also been doing this for some time, I am about to make my modified overhead crown guard to see if I can improve the capture enough to only use one machine, I use the remotes from TLC : https://www.tlc-direct.co.uk/Main_Index ... index.html, they work very well.

Mike

 

[SammyQ]

Right. Time to stir..

Any dust thrown at you from a table saw is as a result of two things:

1. A poorly fitting 'zero-clearance' plate round the saw blade, letting dust through from underneath.
2. The saw is cutting AT THE REAR of the blade, as the teeth ascend toward the operator, due to mis-adjustment of riving knife, parallelism of fence to blade...

Ergo, there is NO need for a saw-blade guard mounted extraction :-"

O.K. Class? Discuss!

 

[MikeJhn]

Nothing to discuss, your talking rubbish. :wink:

Mike

 

[transatlantic]

I get dust thrown at me from the front with my saw, but it's difficult to know where its coming from. I'm not sure if it's coming from the top of the table, or one of the many gaps in the front of the base for the adjustments. I may try to record it with my camera and see, much safer than taking my eye off the cut and lopping a finger off!

It would be interesting to see this kind of thing in slow motion. I'd have thought that as the blade is spinning towards you into the cut, any debris from the cut would be trapped in the gullet between the teeth, not immediately thrown out. As the gullet then rotates under the table, the gullet would be removed of debri from the lower extraction within. Any left over debris still in the gullet as the blade rotates over the top of the table is then removed by the crown extraction.

I would guess that if dust is being thrown back out, it's because the gullets aren't being cleaned quickly enough and over filling.

 

[AJB Temple]

My table saw is a Multico. Rather elderly. Has riving knife and I replaced the metal crown guard with a perspex one adapted from another saw. It produces hardly any dust or chips above the table. Nowhere near enough to warrant separate extraction. Same with band saw (which I use far more).

 

[pcb1962]

My table saw is a Multico. Rather elderly. Has riving knife and I replaced the metal crown guard with a perspex one adapted from another saw. It produces hardly any dust or chips above the table. Nowhere near enough to warrant separate extraction. Same with band saw (which I use far more).

Same with my Kity 619, nothing worth extracting from above.

 

[graduate_owner]

OK, I'm no expert but if there should be no dust etc thrown up above the saw table, why would manufacturers put dust extractor ports on the crown guard? Just asking.

K

 

[MikeJhn]

IMO it equates to how good your extraction below the saw is, it makes a huge difference to what is still in the gullet of the blade when it arrives back above the table, that is what is thrown forward and sprays onto the top, if your extraction below the table is in the realms of overwhelming the extraction requirements the amount of debris on top of the table will be minimal.

I have seen some high speed photograph of this, I will see if I can find it and post here.

Mike

 

[Doug71]

Thanks for input guys.

As I said it's a site saw, guess it's really designed to be used outside without any extraction. It is far from having a zero clearance insert, I will try to improve on this. The extractor I am using is HVLP so more of a chip extractor really. Just trying to make the best of a bad job, can't justify spending much at the moment just want to cut down on the fine dust that it spits out at me.

Thanks for the tips and links on remote switches, great idea.

Thanks, Doug

 

[MikeJhn]

Just one other thing about dust above the table, this dust is brought around by the saw gullet and increased in quantity by the first tooth on the blade hitting the work piece, this all projects the dust forward, the question you have to ask yourself is why do manufacturers put the crown guard dust extraction at the back of the guard? Just convenient I suppose or is it "we have always done it that way" if so its never been given much thought.

Mike

Being built at the moment, will post more later:

 

[PAC1]

Mike not every manufacturer, check out the SUVA the air is funnelled to the front. You cannot see the detail on the attachment but it does http://www.scosarg.com/suva-s315-circul ... uard-27175

 

[MikeJhn]

Isn't that an aftermarket guard? I may not have been clear in my post above, but I was alluding to Table Saw Manufacturers, my point being that you have to pay extra to get better extraction, I'd loved to be proved wrong and find a manufacturer that has thought about this.

Mike

 

[SammyQ]

"it equates to how good your extraction below the saw is, it makes a huge difference to what is still in the gullet of the blade when it arrives back above the table, that is what is thrown forward"

Beg to gently differ Mike. As the blade moves down through the wood, cutting, creating chips, those chips acquire a force (centripetal/centrifugal, can't remember, sorry) that propels them OUT of the gullets and in a tangential direction DOWNWARD into the void that is the saw cabinet. Those dust fragments should not linger in the blade gullets long enough for a half rotation, until the blade again passes though the wood - at the kerf?

Any wood thrown forward toward you, from the blade, is either a filthy, sticky blade (unlikely in this forum?) OR...OR...the emerging blade re-cutting either side of the kerf? This can be seen sometimes as sequential burns on the walls of the cut.

Wood moves,and therefore pinches in sometimes after a cut; riving knives are designed to stop that. Even mild mis-alignment of fence and blade however, can induce an imperceptibly tapering cut = blade recontacts departing wood, after the blade = dust!

A GOOD no-clearance plate and a fettle of fence-to-blade minimises 'secondary cut' dust.

Sam

 

[MikeJhn]

All food for thought and a good discussion point, so differ away. :wink:

I do think that some of the chips are held in the gullet by the hook of the blade because of the centrifugal force on them, I agree that the secondary cut would add to the amount of debris thrown forward, but this seems to occur immediately the timber is introduced to the blade i.e. before the timber has reached the far end of the blade and a secondary cut is occasioned, with a properly set up riving knife there should only be a gap of approximately 10mm for a secondary cut to happen, anyone got a high speed camera and can video this, i'v seen stills, this is of course all only of academic interest, but interesting just the same.

Mike

This one defiantly extracts from the front of the blade: http://www.highlandwoodworking.com/saws ... guard.aspx

 

[PAC1]

Sam, I do not think it is correct to state the gullet clears fully on every cut. I have a 315mm Rip saw with only 14 teeth. It cuts 100mm oak like a hot knife through butter but it does not fully clear the gullet and so without crown guard extraction some dust gets thrown into the room even with my chip extractor moving 750cfm and a zero clearance insert. With my SUVA connected to a shop vac and my chip extractor underneath the air is clear.

 

[SammyQ]

Mike and PAC, points plural accepted. I think the definitive answer is indeed a high-speed camera and I am only too willing to have my hypothesis modified or disproved. That way, we can - if we wish - more EFFECTIVELY deal with dust and avoid C.O.P.D. etc.

Sam

 

[MikeJhn]

Pic of the start to a proposed crown guard I am putting together, the extract will be 50mm dia and at the front.



Mike

 

[transatlantic]

Interesting work Mike.

God I wish people would stop using photobucket and just attach the images directly though