Vacuum Motor

[donclifton]

When selecting a vacuum motor which is more important CFM or lift (vacuum). Which one works the best.
Thanks
Don Clifton

[tkovacs]

Don,
It really depends on a whole variety of factors.
Have you looked at the open source vacuum discussions? They are quite extensive. Here is a link to the latest:
http://www.talkshopbot.com/forum/mes...tml?1220015539

Terry

[Gary Campbell]

Donald...
To hold parts down on a CNC you need a combination of both. I feel that you should be able to hold 5 inHg at 50 CFM (per zone) to have reliable holdown. Look at the following chart, most reliable mfgrs publish them, and I will explain how to get the info on the motor that you need to make a decision.

38137.jpg

This is a chart from the Ametek 117123 240V motors that I use. (vac converted to inHG from inH2O by dividing by 13.6) The columns that are of use to us are the Vac and Flow, more importantly the relationship between them. You will notice that as Vac goes up, flow goes down, and visa versa.

Notice the red arrow. It shows that between 44 and 57 CFM the Vacuum developed is between 4.85 and 5.99 inHg. When thru cutting parts this is a general area where our systems run. According to our gauges when cutting, this is very close to our gauge readings. Any less and the parts move. Of course we have higher readings prior to cutting. To compare motors, look in the area of 50CFM and see what vacuum can be developed. Th higher the vac at 50cfm the better your hold down.

To take this a step further, I will explain all the columns. Take the line above the red arrow; working from right to left, you will see that you are flowing 57.8 CFM, developing 4.85 inHg ov vacuum, the motor rpm is 20,440 and it is drawing 6.8 amps. I have left the orifice for last. That is HOW they test these motors. This means that all the above are actual test data when the air flow is restricted to a 3/4" hole.(orifice) I have tested these and other motors and found that the test data is very close to real world. Plenty close enough for our use.

We can also use the chart to supply us with flow when we know vacuum. For example: we have 3.5 inHg with an open spoilboard. This tells us that: (using the line with 3.71 inHg) that we flow around 69 CFM and this would be the equivalent of a sealed system with a 7/8" hole in the pipe. Another condition is with a full sheet of plywood on the table: we show just under 9 inHg. THis means that we are moving only 8.8 CFM or the equivalent flow of a 1/4" hole. This also tels us that we are LEAKING 8.8 CFM.(same as a 1/4" hole drilled in the pipe) These leaks are in the edges, between the parts and spoilboard, and are virtually unavoidable.

You could also determine that 8 sq. ft.of open spoilboard on a zone (2 by 4) has resistance to flow equal to a 7/8" hole in a sealed system.

Hope this helps, Gary

[donclifton]

Thanks this was real helpful. How large of table will one of this handle.
Thanks
Don

[Gary Campbell]

Don...
I have 1 of these motors on each of my zones (4 total) but do cut some things that could use 2 per zone.

Depending on what, and how aggressively you cut determines how much vacuum you need. Many out there are using a single Fein vacuum over a 4 by 8 table. The motor specs above are close to 50% higher than a Fein.

An alternative solution that myself & David Buchsbaum have been working on is a manifold that allows 2 or more to be used and branches that go to each zone.
Gary

[layertone]

nOOb alert here - confused about specs

how does this compare to the 9-15 setup?

http://www.grainger.com/Grainger/items/6JD22

Regenerative Blower, Inlet/Outlet 1 1/2 Inches, Power Rating 3 HP, Voltage @ 50/60 hz 230/460 Volts, Phase Three, Full Load Current 10.2/5.1 Amps, Minimum Air Flow 30 CFM, Open Flow Positive Pressure 120 CFM, Overall Length 14 1/16 Inches, Overall Height 14 3/4 Inches, Overall Width 14 1/16 Inches, Flow @ 10 Inches of Water Vacuum 112 SCFM, Flow @ 100 Inches of Water Vacuum 29 SCFM, Flow @ 112 Inches of Water Pressure 48 SCFM, Fuji Current VFD4

Thanks

[Gary Campbell]

Tony...
Here are the comparisons. The 9-15 specs are around 8 to 10% less than the 240V version listed above. (they are both sold by lighthouse ent.) I will compare the Fugi specs to the above numbers.

Minimum flow and max vacuum: FUGI is 29 cfm and 7.4 inHg Ametek is 30.6 cfm and 6.99 inHg (PRETTY CLOSE)

Minumum Vac and max flow: FUGI is 112 cfm and .74 inHg Ametek is 90.5 cfm and .72 inHg (also PRETTY CLOSE)

In our use, and the general drift of the 9-15 thread, shows that using multiples of these less expensive motors works well. A single doesnt fare so well over a 4 by 8 area unless a seal is maintained.

Price... our 4 motors ($138 ea shipped) cost $550, to get the same performance out of the Fugi you will also need 4 @ $1585... not so close!
Gary

[layertone]

Thanks Gery for the very prompt response! Time to build one!

[bill_lumley]

Gary , a few more questions


- The motors you are using are they these http://www.centralvacuummotor.com/Ametek/117123-00.htm The reason I ask is it says they are rated at 7 A. and your musings piece indicated you run 4 of them on a single 20A circuit .

- Also in your musings piece you mention using a thin plexiglass zone mask . Is this your plenum or are you referring to something else .

- what are the specs for your plenum grid assuming it is a grid . I have seen mention of using a round bit to cut the channels . Is this an enhancement ?
- Any updates on sound deading ?

Thanks Bill

[Gary Campbell]

Bill...
I am using the Ametek 117123 motors and they do draw 7 amps. We operate 4 of these on a 30A circuit. However, when I wrote the column I was using the Ametek 116 196 motors that draw 4.9A and they were on a 20A circuit.

I use 1/16 thick plexi cut into various sizes to cover the spoilboard where the parts are not. This keeps vacuum to the max. In some cases, we slide them tight to the part to resist sliding.

Here are the spec for our current plenum: http://www.talkshopbot.com/forum/messages/28/35559.html

Not working on sound. The same as the Navy is not working on sound on a carrier deck. Ask the guys at our camp. When all 4 motors are running along with the dust collector... same noise!
I will save my noise reduction energy for a large regen, when we change to that.
Gary