Dust extraction rethink - help please

[knappers]

My small workshop consists of a Kity 419 TS that has been modified to extract from the bottom of the cabinet via a 4" outlet, an EB bandsaw again with 4" from cabinet, a small Axminster benchtop PT with 4" outlet and a number of power tools - domino, router etc..
I have actually been disappointed with how well my RSDE2 collects from the under-cabinet outlet of the TS, and have found that using my dust deputy cyclone, my old Earlex vac gives oustanding results from power tools, I am thinking about changing out my RSDE2 for a HVLP extractor for use with the TS, BS and PT.
What do people think? Will this be better? Would it cope with fine dust from TS? Also, if I go this way, if anybody has a HVLP unit for sale let me know.

Thanks

Si.

 

[Chems]

The RSDE2 is awful on the 4 inch pipe so I'm not surprised your not getting good extraction. Switching to a HVLP would be much much better but then you have the other downside in that a standard HVLP won't contain the finer dust that is created by the TS and BS. A cartridge filter will help some but you really want a 1 micron one not a 5 micron one and they are v.expensive.

If I was going around again, and when I do go around again I'll start by getting a cyclone for the HVLP system to easy that problem and hopefully that combined with a decent filter should catch a lot. I'd just buy a big sheet of 3mm plexi and make a Bill Pentz design.

 

[ondablade]

A quick look at one suppliers published spec for the RSDE2 says it has 1kW and does 60L/sec airflow - which if converted to cubic feet per minute is about 125cfm.

Those numbers are more typical of a basic shop vacuum. There was no suction number listed for the unit, but typically they seem to pull more suction than a low pressure/high volume system but don't shift much air - which is why they work well on closely hooded power tools and the like but not on full size floor machines.

It isn't enough to shift chips reliably in a 4in duct, and certainly not uphill - the industry rule of thumb for effective transportation is around 3,800 feet/min airspeed which converts to a volume flow of about 330cfm in a 4in dia duct. Unsurprisingly this isn't far short of the roughly 400cfm minimum specified by OSHA in the US for what amounts to bare minimum chip and dust collection.

Just as importantly it's not (unless the cutter is much tightly and effectively hooded than is normal on floor machines) going to be pulling enough air in at the machine (creating a large enough low pressure area) to stop dust getting thrown out into the workshop.

A basic say 1KW blower and low pressure bag filter dust system will just about shift enough cfm to give decent chip collection - provided the hose is kept short (collector on wheels beside the machine), and provided the filter isn't dirty or restrictive. The very open weave fabric used on most of these bags reportedly doesn't stop particles much below 30 microns (it may improve a bit for a short while after a long 'seasoning' run - by which time it's semi blinded/blocked) which unfortunately does little if anything to stop recirculation and dispersion of the reportedly dangerous fine particles below say 3microns back into the shop air.

The hard fact (and we're all struggling to keep the show on the road financially) seems to be that most of the commonly sold lower cost DIY low pressure systems fall into this territory. A properly functional LP dust system (as matters stand) reportedly needs to shift more or less double the air, and needs to filter down to particles much much smaller than the average bag - which requires a cyclone or similar to prevent blinding the cartridge filter. All of which unfortunately ups the cost considerably, even DIY. This page sets of the basics and background to this scenario: http://www.billpentz.com/woodworking/cy ... Basics.cfm

 

[Eric The Viking]

Wot eee said, definitely.

A few thoughts:

1. The bandsaw extraction on a 4" pipe will inevitably be rubbish.

I'm lucky with my SIP 12" - OPJ had it before me and modded it very effectively to collect from just under the table, using a shop vac (he documented what he did, but I can't find it right now). The mod is extremely good and the bottom wheel case is practically devoid of dust almost all the time. With these standardised smaller Chinese bandsaws, not only is the 4" outlet almost always in the wrong place, there isn't anything like enough air coming IN to the machine to stop the velocity dropping (a 4" pipe has an area of roughly 12.6 square inches!).

You could improve this with brute force, I suppose (bigger, more powerful extractor), but it still won't alter the fact that the dust is not 'collected' before it's spread around the machine (and elsewhere). A better solution is to do what Olly did, and arrange the extraction to come from a more appropriate place.

2. I too have a 419 table saw. There is a similar issue there: if you close up the casing, you need to ensure the airflow is good, and going in the right way over the right bits of the machine. It's not enough to just prevent dust escaping.

I haven't got a favourite solution yet, but I'm giving it thought. 4" duct should do it for the Kity, and I'm convinced it can be made effective. The cunning plan will almost inevitably involve leaving the back mostly open and adding or modifying the baffles within.

3. Planer/thicknessers are tricky for three reasons:

Firstly the chippings themselves are denser than the dust from saws. This is because they're physically bigger, and the mass-to-area ratio is higher. They need higher velocity air to move them successfully.

Secondly, it's hard to duct air through a p/t effectively because of its layout. There's a bit of a Catch #22 here: I've noticed some smaller industrial machines (Sedgewick, I think) have a perforated extractor hood. This is a good idea as it increases the air velocity - necessary to move the denser chips, but the problem is you need to direct the incoming air so that the biggest draught affects the chips, not travels past them from cleaner parts of the machine (or outside). Restricting the airflow is counter-productive, as you need velocity to prevent blockages.

Finally, the volume of chippings is much greater. I suspect brute force (or a teenage sweeper-upper) is the only answer to this one, BUT the consolation is that p/ts ought to produce less of the dangerous, fine dust than other machines (you ain't gonna be machining MDF with one, or at least you shouldn't be!).

So I think the first two are realistically fixable in a small workshop, a cyclone will probably help, and the p/t will always need a broom and someone keen to augment their pocket money

Cheers,

E.

 

[woodbloke]

I too have a 419 table saw. There is a similar issue there: if you close up the casing, you need to ensure the airflow is good, and going in the right way over the right bits of the machine. It's not enough to just prevent dust escaping.

I haven't got a favourite solution yet, but I'm giving it thought. 4" duct should do it for the Kity, and I'm convinced it can be made effective. The cunning plan will almost inevitably involve leaving the back mostly open and adding or modifying the baffles within.


E.

The extraction on a standard K419 is appalling, so the way I got round it was to take off all the internal gubbins shielding the blade and block off the big 'ole at the back (and all subsequent holes thereof...hardboard and hot melt glue) I then made a large hopper wot was bolted to the underside of the saw and a 63mm pipe was then glued to the inverted apex. The extraction was improved 90%...not perfect, but a lot more got sucked up - Rob

 

[knappers]

Exactly the same as me, but I used 100mm pipe and am struggling to get enough suck.

Si.

 

[ondablade]

To be the devils advocate and pitch plan B Eric - radical DIY to get both a high performing system, and keep the cost down. (you're familiar with most of this by now I'm sure - sorry to keep on repeating the mantra, it's for others too)

It's true as you say that if we could invent much improved machine hoods that the job can be done with much less air, but given the state of the hooding and ports on most floor machines, and the basic problems some present it's not easy. Another option is to decide 'to hell with that' and 'go for the cubes' as our US friends say.

So far as I can tell these are the essential elements for a DIY 850cfm LP system. (LP won't deliver enough suction to replace a vacuum on power tools) Add a bit of ingenuity and care in choosing parts and sorting out an effective layout and it should deliver a flyer.

While the Pentz cyclone is tall (unfortunately this may also be why its said by many to perform better on fine dusts than the other comparable units on the market) I think a mobile unit may even be feasible if the fan is relocated off the top of the cyclone, and a lower chip drum is used.

1. It takes about a 3hp (mobile version of the Pentz system = short hose?) to 5hp (double garage sized ducted shop system = longer ducts) blower with the correct impeller. A 15 or 16in dia impeller for the larger size motor is available from Clear Vue in the US for about $250 plus shipping: http://www.clearvuecyclones.com/index.p ... &cPath=2_8 , and the rest of the fan is DIY from MDF from Bill Pentz's drawings: http://www.billpentz.com/woodworking/cyclone/Blower.cfm. It may be possible to dig up an impeller to suit a say 3hp or thereabouts unit as a spare part from Axminster or the like for use on one of their mobile cyclone units.

Or with some digging you may find a used single phase fan and motor giving a similar pressure/cfm curve to that listed on the Clear Vue site.

Either way read Bill's notes on matching impellers to motors - there can be pitfalls. Keep the ducting on the short side of what Bill recommends too as the 2,850rpm/50Hz motors we get here tail off a bit on performance at higher pressure drops (= longer duct runs, over say 9in WG) compared to the US 3,450rpm /60Hz motors he tested with. Over 4hp doesn't seem to be normally available over here on single phase either - with I suspect the current draw on start up being the limitation given our much lower 60 - 80A supplies.

2. It takes 6in dia ducting and hoses to flow the required 850cfm or so, but this is widely available. The cost of a short hose for use on a mobile unit placement beside the machine will be minimal. Spiral ducting from a manufacturing HVAC supplies outfit seems to be the cheapest for a ducted system. (stay away from the guys re-selling/selling branded stuff) Machine hoods usually need opening up to suit too - see Bill Pentz's page on this topic again.

Don't use this size duct with an undersized fan - it probably won't move the air fast enough (over 3,800 feet/min) to prevent blocking.

3. HEPA 15 cartridge filters are needed to capture the fine dust - 2x dia 13in x 26in long minimum. There's several UK cost effective sources for these been listed recently here, and there's lots of info on suitable cartridge types the Wynn's (US) web page linked from the Clear Vue site.

4. The final major cost is a cyclone that drops out very fine dust, as without one the filters will blind up too quickly to be economical, and may be damaged by chips. Mine cost a bit over €220 to get fabricated locally in zinc plated steel, but they are easily DIY. There's drawings (with size adjustments for differing HP levels) on Bill Pentz's pages.

Google Clear Vue forums to access lots of information and photos on many people's experience of building and installing the Pentz/Clear Vue system. I've been asked to post photos etc of my install - I'll do so in a few weeks when I get started on fitting the ductwork and can pitch it in some sort of order.

 

[Eric The Viking]

Ian,

Many many thanks for that.

There's much to digest, and I intend to. I'm also looking forward to your system description and pics.

Cheers,

E.

 

[miles_hot]

have a look for the Thien separator links on here recently for an alternative to the home cyclone build. If I hadn't just got one of the "not quite Onieda cyclones" I'd be looking to have a go at one of these as they look very much easier to build than a cyclone...
Miles

 

[ondablade]

This only my passing on hearsay Miles, and pardon my coming in like this - it may come across wrongly. My apologies in advance.

According to Bill Pentz the so called 'trash can separators' he tested had quite a lot of internal turbulence, and as a result didn't work well on fines. He says he problem became so pronounced at the higher cfms he advocates that they 'scoured out'. i.e. Almost all the solids got blown through.

It's very possible that the Thien model does things differently and so avoids problems like these, but it's also possible it's typically used at lower airflows (i.e. around 350 - 400cfm) and with less emphasis on the use of very fine cartridge filters and the separation of fines. i.e. It might be safer to ask some specific questions above separation efficiencies on fine dust at high (750cfm+) airflows before committing...

 

[miles_hot]

Ondablade
Yes I'd agree with the normal separators - I can completely see how the nomal trash can ones will do that - and even the more elaborate ones consisting of a box with baffles which were briefly the craze on here last year (work very well with high pressure, low volume but not with high volumes). However the new one seems to have the scouring thing sorted out which looks very good.
I'd still have a damn good filter on the end of what ever system put in place!
Miles