[Jon.N.CNC]

Hi there, looking for people's views on the size of vacuum pump required for an 8x4ft bed. M3/min kW etc. Links? Most appreciated.

[ger21]

It depends on a lot of things.
Mainly how deep and fast you're cutting. Also, smaller diameter tools can get away with less vacuum.
Some people use as little as 3 vacuum cleaner motors, while other might need a 20HP pump.

[gfacer]

I'm hoping to use two 220v car wash vacuums on a 4x8, cant recall the exact specs. But, that is for plastic and other non porous materials, max bit 1/4" diameter, and probably the pressure wil be a little low (5-6hg). I use a 15hp regen blower on my 5x10, which is mostly cutting 4x8's....that works well, generates 10-11 inches of mercury(hg).

Ideally, more money on a higher pressure pump (20hg say) with decent flow (3-400cfm say) would probably be the best solution, but on a budget you usually need to pick cfm or pressure as priority and buy with that in mind. Pressure in general is when you leave the cheap options behind.

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[gfacer2]

The vacuum power is only part of the story. The vacuum performance is the other. I have a 7.5hp regen. blower on a 4x5 bed and it should be fine for power but due to the performance curve I have trouble keeping the level above 5 HG a lot of the time. Basically I have high flow but low peak vacuum. Once it goes below 5hg (and often before) anything smaller will start to move. Big pieces are of course better as they have more surface area.

[Jon.N.CNC]

Thanks for your replies. Okay it sounds as suspected looking for 7.5kw plus. Cutting mainly ply, 1/4" contours 10-25 parts per sheet.

Now looking at an 11hp one £2000 gb. Think this will be upto the job in hand?

Also don't suppose anyone is interested in buying my soul to pay for it?

Or do you think a motor less single stage would be my best option for flexibility.

[gfacer2]

Sounds like it will be ok but look at the performance curve if you can (get the model number and then try and find it on the internet - usually easy enough if it is a regenerative blower).

[Jon.N.CNC]

Sorry to digress, I was under the impression that rotary vanes do not produce enough airflow to maintain vacuum for use with cnc beds but found this one which has a fair air flow. what do you think? Vacuum pump DSN100 - Vacuum Tables UKVacuum Tables UK Cheers

[gfacer2]

Oh they can but they get big and expensive. Those are chinese I am guessing? I've heard they can get very hot but at any rate I did not see a performance curve. I think you have enough to go on as far as the level of vacuum you need and basically you want enough flow to ensure you get that vacuum at the end of your cuts when the flow is high. Hard to tell exactly what your flow will be which is why more is better in the vacuum hold down world.

[wizard]

You know when I read the start of this thread I was thinking you where looking for a vacuum too pull dwarf off the machine. It never occurred to me that you was looking for a pump for vacuum hold down.

Thanks for your replies. Okay it sounds as suspected looking for 7.5kw plus. Cutting mainly ply, 1/4" contours 10-25 parts per sheet.

The big problem with vacuum systems is leakage. A lot of pump capacity can be wasted on leakage. Then you have the area where you cut through the sheet goods.

Now looking at an 11hp one £2000 gb. Think this will be upto the job in hand?

Well like I said it is leakage that kills these sorts of solutions. If you have a highly repetitive product it might help to seal off the areas you cut through. Also you can minimize pump size with well sealed off zones, this technique is sometimes use on milling machine fixtures. In other words you completely shut off vacuum to one work area as you finish the machining tasks there. Any cut through so then can't leak air. Again how well this works depends upon what you are doing, but if a lot of York work fits into quarter sheets then you can get by with four zones.

Also don't suppose anyone is interested in buying my soul to pay for it?

Or do you think a motor less single stage would be my best option for flexibility.

Most of my vacuum pump experience is high vacuum at work where we work in the millitorr range. I can assure you that you don't want to buy one of those pumps. The "oil" we use is extraordinarily expensive, like a good percentage of the cost of some of these routers seen here.

We do have a number of different pumps used for end effector tooling and other lower volume needs (degassification). Most of these pumps are probably too small to consider. From the maintenance standpoint it is better in my opinion to have a separate motor and pump assembly. The pump can be C-faced mounted and be fine. The problem is the units with unitized motor which are basically disposables.

None of these are in a performance class you will likely need. So I can't offer much help here. I do have one word of advice though, some of these pumps are very loud, like ear muff loud.

We do run some Roots style blowers pulling a good vacuum. These are extremely loud even with a big muffler on the exhaust these are used for material transfer, I don't know off the top of my head how far down they will pull, the motors on these are someplace in the 7-10 hp range ( I forget, getting old). These might be worth considering. Maybe one pump assembly for a quarter of the sheet size.

In any event to come back to my main point leaks kill vacuum systems and greatly impact the ability of the system to do its job. The problem is you have two sources of leaks. The unintended ones through the table frame and the intentional one created when you cut through. The intentional ones are highly variable for many users. This makes sizing a crap shoot really.

One other thing that is hard on vacuum systems is sizing of the vacuum lines going to a table/device. Do not undersized these. In fact one idea that came to mind is to buy OEM vacuum cleaner heads and mount four under your table completely getting rid of hoses. That is build the vacuum generator right into the table using four to create a zoned table. You get rid of a need to buy and maintain hoses and valves this way. The only concern is will one unit pull enough vacuum. Well that and getting to the assemblies once the motors give out.

[gfacer2]

Yes, if you are doing repetitive parts, sealing the table is the way to go and then you can get by with a lot smaller system. When you are cutting a large variety of sizes, like we do as a job shop in plastics, then bigger is better. There are always ways to deal with low vacuum issues but they mainly mean either not cutting though (onion skin) and trim later or using tabs (cut through but effectively increase the part size by linking them with tabs). In both cases it means more labour to finish the part.

And yes they are loud, much louder than just the spindle (depending on what it is cutting).

[Jon.N.CNC]

You know when I read the start of this thread I was thinking you where looking for a vacuum too pull dwarf off the machine. It never occurred to me that you was looking for a pump for vacuum hold down.


The big problem with vacuum systems is leakage. A lot of pump capacity can be wasted on leakage. Then you have the area where you cut through the sheet goods.

Well like I said it is leakage that kills these sorts of solutions. If you have a highly repetitive product it might help to seal off the areas you cut through. Also you can minimize pump size with well sealed off zones, this technique is sometimes use on milling machine fixtures. In other words you completely shut off vacuum to one work area as you finish the machining tasks there. Any cut through so then can't leak air. Again how well this works depends upon what you are doing, but if a lot of York work fits into quarter sheets then you can get by with four zones.


Most of my vacuum pump experience is high vacuum at work where we work in the millitorr range. I can assure you that you don't want to buy one of those pumps. The "oil" we use is extraordinarily expensive, like a good percentage of the cost of some of these routers seen here.

We do have a number of different pumps used for end effector tooling and other lower volume needs (degassification). Most of these pumps are probably too small to consider. From the maintenance standpoint it is better in my opinion to have a separate motor and pump assembly. The pump can be C-faced mounted and be fine. The problem is the units with unitized motor which are basically disposables.

None of these are in a performance class you will likely need. So I can't offer much help here. I do have one word of advice though, some of these pumps are very loud, like ear muff loud.

We do run some Roots style blowers pulling a good vacuum. These are extremely loud even with a big muffler on the exhaust these are used for material transfer, I don't know off the top of my head how far down they will pull, the motors on these are someplace in the 7-10 hp range ( I forget, getting old). These might be worth considering. Maybe one pump assembly for a quarter of the sheet size.

In any event to come back to my main point leaks kill vacuum systems and greatly impact the ability of the system to do its job. The problem is you have two sources of leaks. The unintended ones through the table frame and the intentional one created when you cut through. The intentional ones are highly variable for many users. This makes sizing a crap shoot really.

One other thing that is hard on vacuum systems is sizing of the vacuum lines going to a table/device. Do not undersized these. In fact one idea that came to mind is to buy OEM vacuum cleaner heads and mount four under your table completely getting rid of hoses. That is build the vacuum generator right into the table using four to create a zoned table. You get rid of a need to buy and maintain hoses and valves this way. The only concern is will one unit pull enough vacuum. Well that and getting to the assemblies once the motors give out.

Wow thanks lots of info, thanks. Using oem vacuum cleaner motors for each zone is appealing. My bed has 8 zones in its 8x4 size and I know a 1500w vac will do a single zone. I wonder how loud 8 vacs would sound in comparison to a side channel blower :s and there's the 12000 watts burning providing I can run 8 X 13a single phase vacs at once from the ring. :s or could it be a case that it would be fine as long as the bed is covered and the air flow is minimal so drawing less amps. leaving running and removing the material/vacuum could well overload the circuit board I would imagine.

But either way sounds like an external sound proofed outhouse for the pump or vacs could be an idea?

[Eddard_Stark]

If you are doing 10-25 parts per 4 x 8 sheet then vacuum cleaner motors should do fine. I have four ~2000w motors I use to secure a 4 x 8 area for cabinet parts. Anything less than 1 square foot is onion skinned and then cut through on a final pass after all parts have been routed. I haven't had a part move. This is cutting plywood/melamine for cabinet parts. The small parts are generally drawer parts. I have a light weight mdf sacrificial spoil board that the vacuum draws through. You should use something similar. I use a .25" cutter and cut <400ipm. I paid 160.00 per motor plus ~100 dollars in other bits to make the system.

link to motors

[ger21]

Sorry to digress, I was under the impression that rotary vanes do not produce enough airflow to maintain vacuum for use with cnc beds

Actually. rotary vane pumps are the preferred pumps to use on industrial routers.
We have two 10HP Beckers like these on our 5x12.
Oil-free Vacuum Pumps, Industrial Vacuum Pumps | Becker

[wizard]

Wow thanks lots of info, thanks. Using oem vacuum cleaner motors for each zone is appealing. My bed has 8 zones in its 8x4 size and I know a 1500w vac will do a single zone.

8 zones is a lot. I would try to get a handle on how many zones that one vacuum can handle as you may not need 8 vacuums. At tome point it would become more cost effective to simply buy a much larger blower even if you have to invest in zone valves.

I wonder how loud 8 vacs would sound in comparison to a side channel blower :s and there's the 12000 watts burning providing I can run 8 X 13a single phase vacs at once from the ring.

That is a lot of power which is why you might want to look at this again. First do you need 13 amp vacuums and second how much area can one realistically handle.

:s or could it be a case that it would be fine as long as the bed is covered and the air flow is minimal so drawing less amps. leaving running and removing the material/vacuum could well overload the circuit board I would imagine.

You won't overload anything if you properly engineer the electrical system for the new loads. This isn't trivial as you would have to run a large feeder to the machine and probably install a local panel box to contain all the controls. You could easily exceed the cost of the vacuum motors simply by installing a suitable electrical system. The cost of the vacuum motors becomes small in comparison to the whole project. Don't for get the need to modify your vacuum table.

But either way sounds like an external sound proofed outhouse for the pump or vacs could be an idea?

If you want to live with yourself. Some of these pumps put out a lot of energy in the form of sound waves. You can actually feel it and frankly that can be fatiguing. The place I work now isolate the Roots blowers in a room not normally housing people. These are small blowers. Many many moons ago I worked at a place that had the Roots blower out doors, these where much bigger, even then they had to cover them with engineered sound proofing enclosures.

So yeah an outhouse is in order. In this case you would want to insulate it to reduce sound transfer. You do have one trick that you need to perform and that is finding a way to remove heat without letting the sound out. The other problem is that long pipes aren't the best thing for a vacuum system.

I really urge you to look into which solution you go with. My gut feeling is that if you need more than about four vacuum motor assemblies then you will be far better off going with another solution. Someplace online I say an example where a guy used three vacuum assemblies mounted on a manifold box to generate vacuum for his router table hold down system. I don't have a link at the moment but that might be a good and less involved solution

[gfacer]

And, spending that much you'll be able to probably buy bigger and better suction too. Vac pumps are at the low end for pressure... So 8 would be overkill for flow, weak on suction

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[Jon.N.CNC]

Thanks again for your replies. The vac motors such as the ones in Edwards link, thanks for that btw Seems there are some more powerful vac motors at lower wattage than I was aware of, may do the job in multiples.

So the only way I'm going to find out is to buy one at £100 or so and like mentioned trial it on how many zones its capable of. But run the risk of it not being up to it so the selection of supplier will have to have a no quibble returns policy or I've thrown my money away if the entire bed would need more than say 3 vac motors due to anymore potentially adding costs by upgrading mains supplies etc as kindly mentioned.

Or it's £2000 on a 13kw side channel or £2500 for a used 10hp rotary vane.

So the difference between the two is that rotary vane requires maintenance, creates a strong vacuum but requires a slightly more efficient less lossy table due to lower air flow, where as the side channel blower doesn't require maintenance but doesn't create as strong a vacuum however will prove to be better in on an less efficient table.

Ahhhhhhh kinda feel like I need to just write all 3 options in a circle and spin a bottle

[ger21]

So the difference between the two is that rotary vane requires maintenance

From my 18 years using Becker rotary vane pumps, they require almost zero maintenance. Clean the filters, and grease the bearings every few months. Depending on how much you use them, replace the vanes in maybe 10 years?

You can never have too much vacuum.

What are the specs on the pumps your looking at?
in Hg and CFM?

The real question is how do you plan to use them?

More CFM helps to maintain vacuum when it's bleeding through the spoilboard, but the tradeoff is that you're starting with a lot less vacuum. If you're cutting full sheets, and the sheets are the size of the spoilboard, than leakage shouldn't be that much of an issue.
Regardless of what you choose, you'll wish you had more, and you'll learn to tailor your workflow around what you have. Unless you want to spend more money, for more vacuum.

[wizard]

Jon

Here is a link for one of the commercial vac manufactures: Homepage.

As Ger21 has pointed out it is hard to have too much capacity. Especially in the context of a vacuum table where leaks are intentionally introduced. On the flip side too much capacity is wasteful from the standpoint of economics.

A couple of things to keep in mind, leaks have a significant impact on vacuum systems. Everyone has pointed that out but the other side or the equation here is that you only have atmospheric pressure to work with to do anything. The vacuum isn't what is clamping your sheets in place it is the air pressure on top of the sheet that is holding it in place. That 14.7 pounds per square inch at sea level. That isn't much on small objects which is why sometimes other clamping arrangements must be made for small pieces. On the other hand on a full sheet 14.7 PSI is a massive amount of clamping force, if you can get a complete pump down. Since you can seldom achieve no air at all the actual clamping force will always be less that 14.7 PSI. This is where leaks really cause significant problems as you can loose a lot of performance with leakage.

From personal experience with material transfer systems even a small leak causes significant problems. Finding those leaks is always a bear. Vacuum leaks don't show themselves like leaks in a water pipe. Obviously with a vacuum table most of your leaks will be obvious, put there by the machining actions of the router. However don't discount any other possible leakage.

Also this vacuum motors are often using brushed motors. The problem there is that brushes are just another maintenance item. If you expect to be using the vacuum table regularly, I'd stay away from any system using brushed motors. In the end systems using discrete AC induction motors and free standing pumps are far easier to maintain.

[Jon.N.CNC]

Jon

Here is a link for one of the commercial vac manufactures: Homepage.

As Ger21 has pointed out it is hard to have too much capacity. Especially in the context of a vacuum table where leaks are intentionally introduced. On the flip side too much capacity is wasteful from the standpoint of economics.

A couple of things to keep in mind, leaks have a significant impact on vacuum systems. Everyone has pointed that out but the other side or the equation here is that you only have atmospheric pressure to work with to do anything. The vacuum isn't what is clamping your sheets in place it is the air pressure on top of the sheet that is holding it in place. That 14.7 pounds per square inch at sea level. That isn't much on small objects which is why sometimes other clamping arrangements must be made for small pieces. On the other hand on a full sheet 14.7 PSI is a massive amount of clamping force, if you can get a complete pump down. Since you can seldom achieve no air at all the actual clamping force will always be less that 14.7 PSI. This is where leaks really cause significant problems as you can loose a lot of performance with leakage.

From personal experience with material transfer systems even a small leak causes significant problems. Finding those leaks is always a bear. Vacuum leaks don't show themselves like leaks in a water pipe. Obviously with a vacuum table most of your leaks will be obvious, put there by the machining actions of the router. However don't discount any other possible leakage.

Also this vacuum motors are often using brushed motors. The problem there is that brushes are just another maintenance item. If you expect to be using the vacuum table regularly, I'd stay away from any system using brushed motors. In the end systems using discrete AC induction motors and free standing pumps are far easier to maintain.

Thanks wizard and ger for all your good advice, I will look over the pumps again tonight and post up some specs.

I agree with the brushed motor issue, and having multiple motors running also means if one drops out its not going to be as obvious as a single pump.

Fortunately I am literally a stones throw from an sea estuary which puts me about 10m off of sea level but I'm thinking rotary vane is definitely the way to go.

Leaks are definitely a concern. I would initially be making a pad type bed from 25mm ply sealed at sides and undersides with a bitumen type paint, but it's not going to be majorly efficient.

Will be looking to swap out for something like Presspahn f2 (Tufnol equivalent) who do it in 8x4 sheets when I have grand just laying around for it.

Thanks again.

[Jon.N.CNC]

Spoke to the electrician that handles the estate today.. Rubbish news, a 3phase supply is going to cost £8000 so looks like single phase is the only option which is another issue. The single phase supply ring is one of two here both on a single 100a fuse, each ring running on 50a fuses. Each ring has 7 or 8 or so units running of it. One ring is running at close to 50a as its tripped quite often, so I have negotiated my supply be moved to the other ring which is currently running at around 20a. 50a potential. Realistically this gives me just 20 available amps. With Weston power refusing to add any larger fuse than the 100a to the estate.

A 7.5kw pump runs at around 32a. So that rules that out. It would be cheaper for me to move than install 3phase but something I'm desperately trying to avoid.

Single phase I think I'm pretty much limited to 4kw 3phase 13a side channel lateral blower off a vfd 420m3/min -200hpa. That's going on the basis that the blower and vfd consume 13a. Anyone know if it works this way or will the vfd consume additional amps? Also do you think the 4kw blower spec is enough for the 8x4 bed?

Cheers