[mattnedgus]

Hi, Looking to tap the expert knowledge on here again! I can't seem to find specific info that applies to CNC... A lot of information I've found tends to be regarding general woodworking workshops where the chips are usually already loose.

I've been using a 1kW CamVac with a 2.5" inlet and hose but I bought this second hand through convenience at the time. It mostly works (and helps keep workshop dust down with the triple filtration) but it struggles to extract some of the deep wood chips causing a lot of recutting of chips and then heat. I'd like to be able to get at these and I'm not sure which would be best:

1. a CamVac with more power
2. a different type of system altogether

If I go up to a 2kW CamVac what difference would the hose size make - 2.5" vs 4"? Might this power easily collapse a 2.5" hose and pull the ends out of the vac/machine? I use a custom shoe with a 2.5" push-fit mounting hole and a poly-something skirt (which does need upgrading to brush for a better seal!). I would re-make a shoe to suit 4" (although odds are it would have a hole size much smaller than this at the point of suction where I've 'channelled' the air flow through pockets cut inside of the shoe - which is made from 2 pcs 18mm plywood).

I think I understand correctly from reading around that CamVac's are 'High Pressure, Low Volume systems' - are these better than 'High Volume, Low Pressure' systems such as the big bagged chip extractors for CNC'ing?

(I haven't mentioned cyclone separators because it seems these can just go in-line on vac systems for easier separation and removal of chips).

[daniellyall]

big is good, cyclone separators can make it pull more air

[ger21]

Are you talking about something like this?
CGV336-1 55L 1000W Medium Extractor, 2.5" Inlet

It has an airflow of 54 liters/second. Ideally, you want about 2000 liters/second (1000cfm).
You need a 4" port to get this much airflow.
Also, the dust shoe has a major effect on how good the system will work. You want one with brushes that completely surround the cutting area.

cyclone separators can make it pull more air

Adding a cyclone (or any other separator) to a system will actually decrease airflow, due to the friction of the spinning air.

[mattnedgus]

Thanks, yeah, it's the very same one Gerry. And wow, 2000l/s is ten times more than I'm shifting now! Is it the volume that's more important than the pressure (to pull the chips out?) at point of suction then?

I imagine the only way I'll get 2000l/s is with something like this chip extractor?: MDE-HCE/UK1 139 Litre Industrial Chip Extractor. But I am a bit concerned about finer dust escaping... Do people just run air filters for that?

My dust shoe uses a plastic skirt (which needs upgrading) but I'm concerned about the air channel I've designed being too small. It was designed to direct airflow directly away from the cutting area rather than from to the side of it to help chip removal... Would you recommend directly venting the hose to within the skirt rather than trying to do what I've done and duct it to the point of cut?

This is it:

[ger21]

If you go to a larger hose and high volume, than yes, I'd use a full skirt and draw from the hose connection point.
With what you have now, I'd leave it like you have it, but switch to a brush.
The purpose of the skirt is to contain the chips until they can get sucked up. A good skirt will keep chips and dust from being thrown outside of the skirt. As long as the dust stays inside the skirt, you should not have any fine dust in the air.

[mattnedgus]

Thanks Gerry, I think I'll aim towards high volume on a 4" duct with the optional fine filter to keep the dust down.

Just to see if I understand things correctly though: won't a 4" 2000l/s set up have greater pressure than a 2.5" 200l/s setup? I think this is where I've gotten confused (with it being called high volume low pressure).

The area of the 4" is over twice the 2.5" but with 10 times the air flow... Which suggests the pressure should be 5 times higher?

[wizard]

Thanks, yeah, it's the very same one Gerry. And wow, 2000l/s is ten times more than I'm shifting now! Is it the volume that's more important than the pressure (to pull the chips out?) at point of suction then?

Volume is very important in chip removal. You need air movement to move chips, the more the better, well up to a point.

I imagine the only way I'll get 2000l/s is with something like this chip extractor?: MDE-HCE/UK1 139 Litre Industrial Chip Extractor. But I am a bit concerned about finer dust escaping... Do people just run air filters for that?

There are all sorts of systems here but generally there is a final air filter, sometimes just a bag. Cyclones do remove a surprising amount of dust though.

My dust shoe uses a plastic skirt (which needs upgrading) but I'm concerned about the air channel I've designed being too small. It was designed to direct airflow directly away from the cutting area rather than from to the side of it to help chip removal... Would you recommend directly venting the hose to within the skirt rather than trying to do what I've done and duct it to the point of cut?

This is it:

I'm not sure I follow what you are saying above. If your process is predictable with respect to vacuum and tool orientation then the thing to do is to orient the vacuum to directly remove the material as it comes off the tool. This is often easy to do on a CNC lathe for example. It is much harder to do on a CNC router as your orientation changes constantly. Here you need a dust shoe that contains the chips but also encourages air flow all around the tool so that you have chips being sucked up no matter which direction you are going. Dust shoes can be tricky to design you need to minimize the volume of air flow lost through the sides while keeping the sides flexible enough to handle the profiles your machine might be exposed to. This is where guys doing sheet goods have an advantage as they don't have to contend with the extremes in height somebody doing 3D would might have to contend with.

Speaking of 3D type work, you could run into a situation where the dust shoe becomes ineffective or simply gets in the way. Often this means dust all over. At that point a totally enclosed machine might make sense. In other words you can't always count on the effectiveness of a dust shoe.

In a nut shell it is air flow that moves chips and high air flow is a good thing. In fact it is pretty near impossible to have too much air flow it just gets to be to expensive with diminishing returns. High vacuum actually will move nothing as there would be no air to work against the chips or whatever. I work on high vacuum systems at work almost every day and this is not the route you want to take, for one the pumps are very expensive and for two they don't pump air at very high volumes. If the concept is having trouble setting in think about outer space and then a good old fashion wind storm on terra firma. A pile of leaves can lay there for weeks until a massive wind storm comes up and volumes of air start to blow those leaves around. In outer space if you dropped a leaf outside your capsule it would just float around until captured by the gravity of the planet. Your goal is to create a lot of wind around the chip generation area to lift up and pull those chips into the vacuum hose.

[mattnedgus]

Oh and also will a 2000l/s extractor tend to get the chips from the bottom of say a 24mm deep 8mm wide cut in your experience?

[mattnedgus]

Cheers Wizard,

I might consider cyclones later once I've got the air movement up - I'll just get a fine filter for (greater) peace of mind and change bags regularly.

At the moment I cut just sheet goods so I'm fortunate there - once I've mastered that and built the business up I might look at 3D. My vac shoe design is as open as possible for the size I made it but I think if I move to a 4" 2000l/s system I'll redesign it as Gerry's suggestion of just venting it into the brush 'zone', rather than trying to duct it to point of cut. Unless I redesign the Z computer so I can fit a larger duct in!

I appreciate your help - I think it was the 'low pressure' name applied to high volume/velocity systems that made me think they didn't have the force of high pressure systems, but after my quick calc./thought above I don't think this can be the case... High volume systems must also be high pressure but maybe it's a 'relative term'?

[wizard]

Thanks Gerry, I think I'll aim towards high volume on a 4" duct with the optional fine filter to keep the dust down.

Sounds good! As for those filters you will likely want cleanable filters as they can get expensive fast.

Just to see if I understand things correctly though: won't a 4" 2000l/s set up have greater pressure than a 2.5" 200l/s setup? I think this is where I've gotten confused (with it being called high volume low pressure).

You are being confused by questionable marketing.

A vacuum system is all about moving air to pull chips through a pipe. The blower does this by creating a pressure differential that causes air to flow in the pipe. The amount of air flow you can create is determined by the pipe diameter and the pressure differential you can create. Well up to some physical limits. In this case the only pressure you have to work with is atmospheric which is about 14.7 PSI. So your blower has to lower the air pressure below this already low pressure. Effectively there is little room to work here thus the need to chase high volume.

The area of the 4" is over twice the 2.5" but with 10 times the air flow... Which suggests the pressure should be 5 times higher?

Nope. You aren't increasing pressure on the vacuum side, you are lowering it to get the air to move. More importantly on the output side of the blower you want to keep pressure increases as low as possible thus the huge filters or sometimes simply exhausting to atmosphere.

Considering what you posted from previous advertisements I'm not too sure I'd want to do business with people that get it so wrong. Vacuum don't work by creating pressure. They work by lowering the pressure in the vacuum pipe below that of the atmosphere. The nominal for the atmosphere on this planet is 14.7 PSI, there is nothing high pressure about vacuum systems. Volume is the key here and this is why large factory installations will have vacuum pipes of huge diameters to serve multiple machines. Even with big factory budgets there is only so much feasible in the way of a pressure differential that can be achieved this due to being stuck on this planet with 14.7 PSI to work with.

I hope this helps. Sometimes it is hard to put into words what is happening in fluid systems. I like the reference to the leaves though because in a sense that is what you are trying to create a large volume of "wind" that blows the chips down the pipe.

[wizard]

Oh and also will a 2000l/s extractor tend to get the chips from the bottom of say a 24mm deep 8mm wide cut in your experience?

Sometimes you can benefit from an air blast to help lift the chips up into the vacuum stream. You still have the problem of constantly changing orientation though.

The other factor to consider is how long is this slot. If it is long enough to extend beyond the dust shoe then you will start to see a lot of air flow coming though the slot thus helping to lift the chips. The design of the dust shoe of course impacts this too.

[ger21]

Oh and also will a 2000l/s extractor tend to get the chips from the bottom of say a 24mm deep 8mm wide cut in your experience?

No, unless you use an upcut spiral bit, and take very shallow passes, maybe 3mm or less.
You'll have a lot of trouble getting chips out of the cut with diameters under 10mm, and sheets over 18mm thick.

[wizard]

Cheers Wizard,

I might consider cyclones later once I've got the air movement up - I'll just get a fine filter for (greater) peace of mind and change bags regularly.

This is easy enough to do, either home made or after market.

At the moment I cut just sheet goods so I'm fortunate there - once I've mastered that and built the business up I might look at 3D. My vac shoe design is as open as possible for the size I made it but I think if I move to a 4" 2000l/s system I'll redesign it as Gerry's suggestion of just venting it into the brush 'zone', rather than trying to duct it to point of cut. Unless I redesign the Z computer so I can fit a larger duct in!

Well you can try to keep the area constant around the cutting tool which will help some. But mostly yes just vent it in, as I mentioned the constant changing of direction makes a perfect solution near impossible.

I appreciate your help - I think it was the 'low pressure' name applied to high volume/velocity systems that made me think they didn't have the force of high pressure systems, but after my quick calc./thought above I don't think this can be the case... High volume systems must also be high pressure but maybe it's a 'relative term'?

Well the industry here doesn't help much as much of the advertising is at best misleading and at worst out right lies. The vacuum industry seems to have this idea that they can get more power out of an AC outlet then it will ever be capable of producing. For example one will never get 5HP out of a 115 VAC, 15 amp outlet in the USA! I'm not sure how they get away with that non sense. As for vacuum performance it is volume that really makes a difference in most applications. Higher velocities can sometime help and this does imply lower pressure points to produce the required pressure differential. For the most part though you need wind to move things.

The selection of cutters can have an impact on vacuum performance. Up cut spirals will do a lot to lift the swarf up into the air stream. Of course this impacts cut quality. For panel or sheet good work you can keep the dust shoe close to the work piece in a solid form, this can help keep air flowing into the work area evenly. Just don't get so close that you cut down on the air volume. Also don't get so close that you raise the panel and lock it to the dust shoe.

Back in the day I setup a bunch of CNC lathes with vacuum extraction, in this case machining a monomer. Lathes are great for vacuum extraction, in this case we got great results with what I remember was a 2" hose. The trick is the right nozzle close to the action. The big benefit of the smaller hose is that you can service more machines with a vacuum of a given size. Routers on the other hand want to defy vacuum collection, you need lots of volume to overcome the none optimal conditions.

[520052]

I installed a cyclone system on my router and the results are fantastic. Won't go into all the calculations as far as duct runs and static pressure calculations but I did a lot of reading and found the writings of Bill Pentz to be extremely helpful and saved me some costly mistakes. Dust Collection Research - Home

[lambodesigns]

I installed a cyclone system on my router and the results are fantastic. Won't go into all the calculations as far as duct runs and static pressure calculations but I did a lot of reading and found the writings of Bill Pentz to be extremely helpful and saved me some costly mistakes. Dust Collection Research - Home

Same here... adding the clearvue cyclone was a huge improvement to my dust collection. Also added 6" ducts to the big dust producers and only went down to 4" pipe when it just didn't make sense to keep the 6". Since I already had 2 collectors (2hp 1200 cfm each) I ended up running them in series which worked out great and just bought the cyclone from them. Found filters on ebay so I'm running 4 of the big hepa ones so I can go longer before having to clean them. Also what goes in must come out so a small filter will decrease in performance much faster and cfm ratings go out the window. The amount that the cyclone detracts from the airflow is more than made up for in not clogging the filters like you do in a single stage system. I tried using just a big hepa filter on the single stage and for about 15 minutes it had a lot of suck but as soon as that filter got coated good the performance dropped probably in half.

My neighbor witnessed the suck my system had and promptly went out and bought the full clearvue with motors and filters. I think they have about the same performance but mine with the dual blowers is a lot quieter than his. I'm guessing the mdf housing for the fan is creating the noise but that's just a guess. My only regret is not getting the clearvue max. My reasoning was I was a one man shop so I didn't need the max but then I got the cnc so it is like having a 2 man shop since I do a lot of work while it is running. The standard one still does fine running 2 machines but more would be better.

[520052]

Don't have a clearvue, had an older, unused 3hp Oneida cyclone of about 1500cfm I never installed in another shop I have. Installed the neutral vane in the Oneida cyclone and went with the high flow cartridge filters per Bills instructions, went with a very short 8" main duct and used 6" duct and flex hose for the router all the way to the 6" dust shoe I fabricated. All spiral pipe with long radius 45 degree elbows; I didn't go for clearvue's 15" fan or 5hp motor due to budget constraints at the time but the results of the 3hp performance more than exceeded my expectations. I took Bill's advice and installed an ammeter on the cyclone motor and amp loss due to restriction and static pressure loss is only about 1.25 amps off of the rated 14 amp full load. I figure with my calculations I am getting around 1000 cfm at the router pick up. Probably going to up size my fan and motor with clearvue's some day but don't really deem it necessary at the moment.

Attachment 325038 Attachment 325040

[daniellyall]

Thanks Ger I think I need to stop asking engineers questions and just ask you. (they cost lost money)

mine has 3 phase 4 hp twin bag pulling over 2000 liters with a 4 inch hose the hoses are tyed down other wise they move around when turned on, the shoe has a 125 mm X 10 mm brush on it full width around the shoe any lose dust get's sucked up dust down in the cut stays there, it is fine to use it with 3D cuts that are 75 mm high any higher you risk distraction.

one big problem having the big dust extractor was the machine was tripping the fuses quite a lot from the static, a few shielded wires and ferite blocks soved that.

[mattnedgus]

You wouldn't believe I did an engineering degree (albeit many years ago!) would you :-D

I did try to find some calculations to help me decide on the pressure difference between a 4" 2000l/s and a 2.5" 200l/s but it's wasted effort for the moment - I just need to up the suction!

Wizard: I think I was a little confused in my terminology too! You make complete sense though: it's just the volume shifted that's important. I am sure the volume shifted and hose diameter give rise to the numeric value of pressure (which is what I was tempted "for a moment" to try and calculate to satisfy my curiosity). It is the "low pressure" name applied to the high volume systems that confused me: for a moment making me think the pressure had to be lower than "high pressure" systems! I'm not sure I can escape the companies that use the HPLV/LPHV marketing descriptions tho... I'll probably end up buying something through Axminster or Record Power unless anyone knows of any better systems in the UK?

Gerry: Where I can I like to take fewer passes but you've just made me wonder which would be more tiring for the cutter: the heat from the chippings or a greater number of passes!

Overall I figure shifting a 10x greater volume per second, even with deep slots, has to be better than the airflow I have now! A fine filter to help cut down smog and a better (quieter) air filter that I can leave running will help (I want to be able to hear the radio while I work!).

I thank you all again!

[mattnedgus]

As for vacuum performance it is volume that really makes a difference in most applications. Higher velocities can sometime help and this does imply lower pressure points to produce the required pressure differential. For the most part though you need wind to move things.

Sometimes I wonder where my head is at! I've just realised: I assume when they say "low pressure" systems it's a relative term in that because like you've just said, as the velocity goes up to move higher volumes through, the pressure goes down! Like the faster air over the top of an airplane's wing... I can't believe it's taken me all this time to have that epiphany!

The selection of cutters can have an impact on vacuum performance. Up cut spirals will do a lot to lift the swarf up into the air stream. Of course this impacts cut quality. For panel or sheet good work you can keep the dust shoe close to the work piece in a solid form, this can help keep air flowing into the work area evenly. Just don't get so close that you cut down on the air volume. Also don't get so close that you raise the panel and lock it to the dust shoe.

I'm going to have to watch out for this, it's something I'd not considered with the increased suction - I just tend to screw panels down (looking for another solution!). I use down cuts as a matter of course though because I need a good edge on the top of the work.

I installed a cyclone system on my router and the results are fantastic.

I'm going to struggle enough with space moving from a CamVac to a chip extractor... Maybe when my business expands I should consider one - and Bill's website. I came across that the other day but it's not a short read!

My only regret is not getting the clearvue max. My reasoning was I was a one man shop so I didn't need the max

I had a look for clearvue out of curiosity but it looks like it's US-only - nearer the day I have the space I'll look for a UK equivalent or like Wizard suggests; look at making one myself.

[wizard]

You wouldn't believe I did an engineering degree (albeit many years ago!) would you :-D

I did try to find some calculations to help me decide on the pressure difference between a 4" 2000l/s and a 2.5" 200l/s but it's wasted effort for the moment - I just need to up the suction!

Wizard: I think I was a little confused in my terminology too! You make complete sense though: it's just the volume shifted that's important. I am sure the volume shifted and hose diameter give rise to the numeric value of pressure (which is what I was tempted "for a moment" to try and calculate to satisfy my curiosity). It is the "low pressure" name applied to the high volume systems that confused me: for a moment making me think the pressure had to be lower than "high pressure" systems! I'm not sure I can escape the companies that use the HPLV/LPHV marketing descriptions tho... I'll probably end up buying something through Axminster or Record Power unless anyone knows of any better systems in the UK?

Yeah once you realize that it is atmospheric air pushing through the pipe then it becomes apparent that a big pipe is important. Your blower still has to be able to move enough air to get acceptable velocities, these velocities are due to the pressure differential between atmosphere and the lower pressure in the pipe.

Interestingly you can go too big with a pipe and lower air velocity too much. Much like in the fall when a light breeze leaves the leaves on the ground and a stiff breeze blows them into the neighbors yard.

Gerry: Where I can I like to take fewer passes but you've just made me wonder which would be more tiring for the cutter: the heat from the chippings or a greater number of passes!

This is a tuff call but generally you want to use a good portion of the cutter.

Overall I figure shifting a 10x greater volume per second, even with deep slots, has to be better than the airflow I have now! A fine filter to help cut down smog and a better (quieter) air filter that I can leave running will help (I want to be able to hear the radio while I work!).

I thank you all again!

Getting chips out of a deep slot is always an issue. If you are running a milling machine, cutting a slot in work hardening steels the chips remaining in the slot can destroy an end mill. I've run into this numerous times, you can actually hear the end mill chip. In wood you have other similar problems, the chips left in the slot can plug up your endmills and cause surface finish problems.

One idea that has floated about the head of late is to have four air jets arranged to blow the chips out of those deep slots. Of course this implies an air compressor. With four jets you can only be effective with one jet at a time and then only when a movement is parallel to an axis. To cut down on air usage you might want to tap the direction signals to your step and direction drives. That would allow you to shut off two of the jets depending upon direction. On the other hand on the second pass it might pay to have both jets blowing.

Just some ideas!