Sizing CNC Vacuum Pumps
Advice on sizing the vacuum pump to the CNC and its usual tasks. November 24, 2008
Question
So what's the deal with vacuum pumps? There are pros and cons for vacuum systems. Some guy's say a regen blower is sufficient. Some guy's say no way you need to spend 6g's plus on a liquid ring or vane pump to hold material down. We will be cutting mostly 4X8 melamine and pre-finished plywood. I would imagine the smallest parts we would be cutting would be 12" X 3 1/2". I just would like some feedback.
Forum Responses
(CNC Forum)
From contributor Z:
No matter what type of pump you go with you will end up having to do two pass (onion skin) cuts. We cut a lot of melamine cabinet parts and for drawer and spanners we do onion skin second pass. This is with a good pump and a Flexicam router.
From contributor K:
It sort of depends on several things. What kind of router you have, how big is the table, what HP spindle, how fast do you want to cut, how many vacuum zones, etc.It would be a waste to buy a 40HP vacuum pump and you only have a 3HP spindle. Or you buy a 10HP regen blower and you have a 6 x 12 table with 1 zone.
From the original questioner:
The routers I am looking at are 3hp, 4X8 table, with 6 vacuum zones. Secondly we will be using a 5mm strait bit to do all the cutting (in two passes, 3/8 at a time) and boring. I’m thinking 10 hp regen blower would be adequate.
From contributor G:
The manufacturing/cutting thought process has changed over the last 10-15 years. Back then, a 10 hp would be great because a lot of parts were cut on dedicated spoilboards and some with gasketing. Today, the process is to cut your parts through a bleeder board, finish the job and resurface for the next job. For this, you will need more than 10 hp for your process to run smoothly and without the anticipation of parts being pushed around your table. The dedicated spoilboard process works well (I know because I still use it) but you will find yourself with a warehouse full of spoilboard fixtures. If your product is proprietary, then no big deal. If your products are custom, go with 40+hp.
From contributor K:
I also have 3HP spindle and a 4x8 table, but I have a 15HP regen blower on 5 zones. Forget cutting parts 12 x 3.5, they will move around unless you tab them. But for the most part 15HP is fine. I cut cabinet parts and with the table surfaced right it works pretty good.
From contributor F:
The regen blower is a high flow low pressure pump. The advantage is it’s cheap. Disadvantages are noise and they don't hold down smaller parts because of the low pressure they run at.
A vacuum pump that operates with oil in the air stream (liquid ring) provides higher pressure but is inefficient due the oil in the airstream thus requires higher HP 25-40 to overcome it. Notice most people that have liquid ring pumps are this size.
A dry vane pump in the 20 HP range is a economical choice that works well but you will get one for six grand. Rotary screw pumps are also a good choice but they are more expensive than the vane pumps. If you want 15 HP worth of vacuum you are stuck with a blower and its limitations.
From contributor O:
I have 12.5hp rotary vane pump on a 5' x 10' table although it is zoned down to 4' x 9' almost all the time. Airflow is 245cfm. It's not enough; I really need at least a 25hp pump I have found.
From contributor F:
This is the classic case of CNC routers being bundled with a specific vacuum pump in order to sell the "package" at a specific price point. Each application requires attention to the size and type of vacuum pump being used. To make a bad situation worse some offer two smaller vacuum pumps (10-12 HP) with the claim of redundancy. Imagine buying a car and having to purchase a second engine just in case the first one isn't powerful enough. Plus, twice as much to maintain as a single pump that is correct for the application. It is a good way for the OEM to maintain a discount with the vendor though.
From contributor M:
Contributor F is right, it's better to have one large pump that can handle your needs instead of having to maintain two smaller pumps. Many machines come with a small pump to fit the correct pricing, although many need to add additional pumps. There are a lot of variables to determine the proper size pump, but it's better to have one that's too strong than to have one that's not quite strong enough and allows your parts to slide because of the lack of hold down strength.
