Vacuum Sizing, will a 1 1/2HP and a 5HP work?

[zeke]

I just ordered a PRSstandard 96 x 48. I'm trying to get all the prep work done prior to receiving it. I have 2 vacs in my shop. Do you think this will work?

1) For Dust Collection - It's a 1 1/2HP Jet DC-1100 Dust Collector, 1100 CFM Kit with Remote and Canister
http://woodworking.jettools.com/Products.aspx?Part=708636RCK&cat=333122

2) For Vacuum Hold-down - It's a 5HP, 4944 CFM, I don't have any other specs on this.
http://www.woodmastertools.com/NS/accessdetail.cfm?PID=88

Regards,
Zeke

[Gary Campbell]

Zeke...
Dust collectors dont have anywhere near the vacuum needed to hold down parts on a CNC router table. Typically, they have between 10 and 20 in wc (H2O) this converts to less than 1 to 1 1/2 inHg (mercury) there is somewhere between 1 and 4 inHg lost due to a spoilboards resistance to flow. This would leave... nothing to hold the parts down.

There are many posts on this forum where many before you have made successful systems, some on very small budgets, some on large. I am sure that if you do your homework, you can find something that will work well for you.
Gary

[woodworx]

Gary is right on the money. Buy 2 fein turbo 3 vacs from Shopbot. They work great even if you are not setting up zones on your table.

[zeke]

How small of a square can you successfully hold with the two fein 3's? Does anyone have the link handy to the best vacuum table plans?

Zeke

[richards]

Zeke,

Contact Brady Watson. He's written THEE authoritative guide about creating a vacuum system from individual vacuum heads. (Unfortunately I'm running late or I'd try to find that tread for you.)

[beacon14]

How small of a square can you successfully hold with the two fein 3's?

Like most questions, the answer is "it depends". if you want to leave the table wide open (all zones open) and just plop a square workpiece down you'll get one answer, if you turn off all but one zone, mask off the area of the open zone that the workpiece does not cover, tape all seams, etc, you'll get a very different answer. If you are cutting full sheets and want to know how small a part you can nest on the sheet with the other parts, a third answer still.

And each of these scenarios will still rely on enough variables that the answer will be "it depends". How smooth and flat is your spoilboard? Are you at sea level or in the mountains? How well sealed are your plenum and the edges of the spoilboard? How aggressive are your cuts going to be? What type of bit are you using?

Now that I've given you the run-around, a few more practical answers. I use two Fein III's, and I can nest parts down to the size of my smallest cabinet parts (around 4" x 12") without a problem, with a reasonably clean spoilboard and proper toolpathing strategies.

For light machining on small parts I have routed pieces as small as 2" x 3" by using a single zone and masking the open areas.

Bottom line is I have been able to machine everything I've needed to using the two Fein III's, and a little ingenuity and common sense as to hold-down and toolpathing strategies.

Does anyone have the link handy to the best vacuum table plans?

There are as many opinions as to what is the "best" table design as there are people who have made tables. A search of this forum will yield a wealth of information.

[woodworx]

David is correct. With a little common sense and practice with hold down you will figure everything out. By using a downspiral bit, the material will be forced back down in the channels you are cutting. Therefore you never loose much suction power. Holding a 2" X 3" square is never a problem using this kind of technique. There is no "one solution" to hold down. You will always use a combination of techniques. I originally cut my plenum with a 1/4" bit leaving 1.5" squares. I have since ripped that plenum up and machined larger air channels (2.5") and left large 3" squares for my spoilboard to sit on. This is similar to Gary Campbell's high volume plenum. I have found the high volume plenum has worked much better, even when I don't have full sheets sitting on my table. As time progresses, and your business changes, you might find different uses and applications for your Shopbot. At that time you might feel compelled to rip it up and design something different, and that is ok.

[zeke]

Great information and I'm learning there are probably an infinite number of variables with a vacuum and table although some common and basic themes. I ran into this link, could this do as good a job or better than 2 Fein 3's? Figured I check before reaching into my wallet. What would some of the challenges be? http://www.grainger.com/Grainger/items/3WU95.

Zeke

[Brady Watson]

Well put, David.

Zeke,
Vacuum hold down encompases a pretty wide area. The needs of a cabinet shop are different than someone who runs a job shop, or someone who mostly cuts small parts. As David pointed out 'it depends' is a crappy answer, but at the very least, honest & fair. Without knowing exactly what you are trying to hold down, specifying a setup for you is difficult at best.

Personally, I use several vacuum tactics and setups depending on what I am cutting. Small plastic parts require higher Hg" and lower CFM with a gasketed jig, while sheet goods work best with lots of CFM and a decent Hg" rating (>6"Hg). There are other times when vacuum will not work at all on a part since it either has too many holes or is just too small to be held properly. In these cases I'll use clamps, carpet tape, screws or other means.

"The most challenging part of CNC routing is part hold down."

If I could tell anyone looking to 'get into vacuum' one thing, it would be to do your research, and then try some of the concepts that you have researched. Personally, when I 1st heard about people using vacuum to hold down parts I thought it was a waste & that 'it'll never work!' - Only through my own observation & actually trying things on my own did I figure out what did & didn't work for MY shop. Don't be afraid to do your own R&D, and make lots of mistakes. Try making a SMALL vacuum setup using a vacuum source that you already have in the shop, office or house.

-B

[beacon14]

The Grainger pump you linked to is a high vac, low CFM system which as Brady says will work with non-porous parts and dedicated, leak-free jigs. For sheet goods and most general cutting I think you'd be better off with the Feins or another high-CFM, low vac setup.

I recently did a training for a new owner and in the course of the training we drove to a nearby lumberyard for a sheet of 3/4" MDF, routed a grid into one face, flipped it over like a giant "BradyVac II" setup, and stuck the hose from his old and beat up shop-vac into a hole in the middle of the table. He was amazed that it worked well enough to hold the PVC sheets he will be cutting. I told him it might not suit him forever but it would get him started and save him a lot of time and 2-sided tape.

Sometimes the best method is to just get started with something simple and see how it works, then make improvements over time until you have it just the way you want it.

[zeke]

How do I compare a $400+ Fein III that produces 126CFM or two Fein III' that collectively produce 252 CFM with a $9,000+ Becker that produces 173CFM? I'm still learning about the vacuum aspect of this. The simple math says that the two Feins are superior than the Becker, however, I'm thinking there is a formula that says otherwise due to the pricing discrepancy.

Regards,
Zeke

[thewoodcrafter]

Zeke,
The biggest difference is the amount of vacuum.

A shop vac will go 7" at most.
The Becker will go 29".
So the Becker has 3 1/2 times the holding force.
They are really 2 totally different animals.

The middle of this is a Roots type blower.
A 15HP has around 300CFM at 14" and costs about $6000.

[Gary Campbell]

Zeke...
To make an accurate comparison you have to factor in the actual conditions under which you will be using the vacuum. If you are cutting thru a spoilboard, you will have leakage as you cut thru parts. This averages, if you watch your masks and toolpath options, between 15 and 60 CFM per zone, based on our average usage.

What you are looking for is a vac pump or pumps that will maintain a certain level of vacuum at that CFM. Less leakage around parts equals less CFM equals more vacuum. Vacuum and CFM are inversely proportional according to the mgfr's performance data.

The Feins are great if you need a quiet solution, especially in a residential location. The published Fein data is for the motor, not the motor in a vacuum canister with a muffler and hoses attached. They will seldom pull over 6.5 inHg except at sea level. That is the price paid for quiet. They will seldom flow over 100 cfm. (each) Here is a comparison chart:

7275

The 2 Feins will be at or below the reddish brown line of the parallel vacs. A single is at or below the blue single vac line. The Becker has awesome vacuum, but at over 140 CFM leakage... they will head south in a hurry.

You will need to do some experimenting, as most of us dont get it perfect on the first try. There are hundreds of posts that will give you some ideas, but none are likely to you your perfect answer.

If you look at the chart, and do some experimenting, you will find that you will need a system that works in the 35 to 105 CFM area. The chart will tell you, at any given flow... what you can expect for a given product. Buy the most you can afford. We can all use more vacuum.

IF you need quiet, go with the Feins, it is about the only option. The noise reduction comes at the performance price. There are many Botters out there that have done very well with them.
Hope this helps, Gary

[zeke]

Good information, great chart! Any helpful tips on purchasing a used rotary vane vacuum pump or roots type (is that a brand or type, do you have a brand name)?, eBay is not always the best place to find a great deal.

Regards,
Zeke

[dana_swift]

Zeke- the difference between these also involves cost to run.

Figure both the electric costs and the costs to rebuild the devices periodically. Nothing runs forever without breakdowns.

Also when getting into high power motors > 6hp, do you have 3 phase power? Will you have to pay power factor costs?

Just a few things not to forget about, these are not show stoppers for any direction you go, just be sure to have a repair budget appropriate for your choice.

I started out with air-conditioner type oil based vaccum pumps, and am looking to switch to a medium size Becker pump system. My work usually requires high vacuum, and sometimes high flow. I use gasketed fixtures but slightly warped wood wants CFM to get the wood into initial position for gasket make-up. After that, a very humble pump will keep the workpeice in place, it only has to remove any leakage air, there is always some.

There is no perfect solution, just pick an inexpensive direction at first until you see how well it works for you, then perhaps "improve" it with more money when you know which direction will best serve your needs.

Good luck-

D

[zeke]

What do you think would happen if I combined a Gast 10CFM 26 hg with a Fein III in the same plenum?

[waterwheelman]

In my experience, the vacuum pumps need to be closely matched in size. If they are mismatched, then the stronger vacuum will suck air back through the weaker one.

[Gary Campbell]

Zeke...
David makes a good point. There is one more. The 10 cfm Gast will not pull enough cfm to hold parts thru a plenum. It will work for a dedicated fixture. Should you still need to combine them, Brady has a post or 2 about an ingenious use of a plumbing flapper valve for an automatic connection.
Gary

[dana_swift]

Zeke- don't worry about combining the two vacuums.. do a search on the forum regarding "dog ball" check valves.. cheap and they work great. It allows you to mix very different types of vacuum sources, they will work together in the part of their range where each can contribute, when one overpowers the other the check valve closes (dog ball seats) and one system is doing nothing while the one capable of higher vacuum does its job.

I use the dog ball check valves and they are simple to make out of PVC and can handle large CFMs as well as high vacuum.

D

[zeke]

Thanks all.....

[zeke]

Does it matter which vac comes first the least or more powerful when using the dog ball configuration?

Also, I was looking at Joe Johnston's drawing and it wasn't clear what the diverter valve to manifold is?

http://www.talkshopbot.com/forum/messages/312/30335.html

[dana_swift]

It doesn't matter... if a weaker vac is switched on after a higher vacuum is established the check valve will prevent the low-vac/high-cfm from accessing the system. It helps to have a pressure gage on each supply so you can see that its just wasting electricity so you can shut it off.

The value in the dual system is when a high CFM gets a part held down so that a high-vac can hold it tight as the amount of air flow drops off substantially when everything is tight. The check valves allow the high vac/low flow system to take over when the pressure drops below the high CFM's maximum suction pressure.

If you cut through the material and the vacuum drops the high CFM will automatically override the check-valve and keep your part as secure as possible as the leakage increases.

I have found a programmable pressure switch from digi-key, I have bought one, but not put it into my system yet. What it "should" do is detect that the leakage has required the high-cfm/high-horsepower vac be turned back on to maintain suction. That way it can switch off if it is not accomplishing anything and save the electricity of just thrashing the bearings. If the vacuum drops it will come back online and keep the part held until the end of the cut. In that case I don't mind paying for the extra power.



Hope that helps-

D

[joe]

Zeke,

Run your router for a while before getting into this mind game. Without knowing what you will be routing, it's impossible to give good advice as to wheather or not you will even need one.

I've made a handsome living, over the years, without a vac. I use other kinds of hold downs which are silent and require no electricity. The point is you can do some awful neet stuff without any vac at all.

But if you must, you must. Vacuum mentality is addictive. Once your bit, it's all over.

May the router gods be with you, go forth!

Joe Crumley
www.normansignco.com (http://www.normansignco.com)

[dakers]

Joe and other router pros:
We do not have vac hold down. we are sign company with new shopbot.
We mostly rout sheets of color core. We will be doing some small cut out letters in the future. Probably cutting letters from hdu or pvc. How do you hold down small letters when you cut them and do you ever have problems holding them down.

[joe]

Dick,

With the HDU, you can use little bridges since there isn't much cutting resistance. For most letters, two are all you need.

With PVC, if you use a strait, double fluted, bit there isn't any reason to do anything. The material left behind will hold your letters very tight.

I'll be glad to send you a DXF of the attached hold downs. I've been using these for a couple of years and they do a good job of holding almost all my sheet goods. They also come in handy with 2" rough cedar and oak.


7276

[dakers]

Joe, i like that idea.
An idea occured to me that may not work. I do not know. take two 2x8ft ultralight mdf board and lay them on two pieces of 2x8ft pcs of 1/4'' alumalite. Then raise the mdf up off the alumalite about 1/4'' then seal the edges all around but have a place to hook a shop vac to them on the ends. These would be portable. We can get by on clamps for the most part and i like your bridges. I do not think i need the elaborate vac set up for what we do.