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  #21  
Old 01-10-2013, 03:14 PM
Denny J Denny J is offline
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What kind of cfm range are we talking about being sufficient for a spoilboard? I just talked to a rep who looked over the specs on the sutorbilt pumps and he came up with a 5H pump coupled with a 15HP motor would generate 318 cfm of flow at 15hg of mercury. That seems to be in line with a regen blower doesn't it?
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  #22  
Old 01-10-2013, 03:17 PM
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james mcgrew james mcgrew is offline
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this does sound good !! what size pipe does it use mine is 3"
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  #23  
Old 01-10-2013, 03:20 PM
rcrawford rcrawford is offline
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Quote:
Originally Posted by Denny J View Post
What kind of cfm range are we talking about being sufficient for a spoilboard? I just talked to a rep who looked over the specs on the sutorbilt pumps and he came up with a 5H pump coupled with a 15HP motor would generate 318 cfm of flow at 15hg of mercury. That seems to be in line with a regen blower doesn't it?
I think that is great for a 4x8 spoilboard. You will be able to cut through on nested sheets. Might not be enough to pull the warp out of plywood, but there are not many set-ups that will do that (unless you are willing to go 30hp!)

I would love that set-up. Just be sure you will be getting 15" at 318cfm (not 15" max or 318cfm max - which means you will be getting 3-4" at 318cfm, or 15" at 20-30cfm!!). There should be a flow/pressure chart that shows the pressures at different cfm.
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  #24  
Old 01-10-2013, 05:03 PM
Denny J Denny J is offline
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Originally Posted by james mcgrew View Post
this does sound good !! what size pipe does it use mine is 3"

You can spec different pump sizes. I have a guy who is shutting his dairy down that is going to sell me 2 5HP vane pumps for 125 dollars each.. They run a 3 inch line but I am going to use 2 inches for my particular system.
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  #25  
Old 01-10-2013, 05:56 PM
rcrawford rcrawford is offline
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Thats awesome! Need to go and talk with my dairy farmer friends.

Two 5hp pumps is better than one 10hp because you can titre the amount of vacuum you need for the job you are doing.
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  #26  
Old 01-10-2013, 06:45 PM
Denny J Denny J is offline
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Originally Posted by rcrawford View Post
I think that is great for a 4x8 spoilboard. You will be able to cut through on nested sheets. Might not be enough to pull the warp out of plywood, but there are not many set-ups that will do that (unless you are willing to go 30hp!)

I would love that set-up. Just be sure you will be getting 15" at 318cfm (not 15" max or 318cfm max - which means you will be getting 3-4" at 318cfm, or 15" at 20-30cfm!!). There should be a flow/pressure chart that shows the pressures at different cfm.
Do you know what terminology I should use to get those numbers? I m pretty green to all of this. I think I understand the relationship of vacuum to flow, but are there types of blowers that work differently than others? From what I see there are low pressure pumps and high pressure pumps.
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  #27  
Old 01-10-2013, 10:26 PM
rcrawford rcrawford is offline
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Most manufactures show a graph. Flow is up the side (cfm) and pressure is along the bottom ("hg). There will be a curved line showing the relationship between flow and pressure. I tried to post one here, but all the ones I could find were part of large pdf files.
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  #28  
Old 01-11-2013, 09:11 PM
Denny J Denny J is offline
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Quote:
Originally Posted by rcrawford View Post
Most manufactures show a graph. Flow is up the side (cfm) and pressure is along the bottom ("hg). There will be a curved line showing the relationship between flow and pressure. I tried to post one here, but all the ones I could find were part of large pdf files.
OK

I found the info you were looking for and it looks to me like a good pump to look for is the Sutorbilt/Boumatic lobe style pumps in the 5H sizing. This is a high vacuum style and IMHO the benefit of this style pump is you can mate it to the motor size you want and you can save money by finding your own motor,either new or used, and you can change the CFM and HG by adjusting the HP of the motor and the pulley size.

Here are some numbers

HP "HG CFM
10 8 350
10 12 228
10 14 171
10 15 165
15 14 323
15 15 280
20 16 312

So you can see, with the same pump, if you are running 10HP and running at 14HG you are pulling 171CFM. If you need to increase your CFM rating, a switch to a 15HP motor will bump your CFM to 323.
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  #29  
Old 01-11-2013, 09:26 PM
rcrawford rcrawford is offline
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That looks like a nice pump. If you get it, let us know how it works! It would be interesting to see if the VFD works for this.
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  #30  
Old 01-12-2013, 01:19 PM
Eric Mims Eric Mims is offline
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When I had my 5'x8' machine, I used a Sutorbilt lobe with 5hp single phase motor driving it. Bought the lobe pump from a scrap yard for $50. Bought 5hp motor on eBay (Leeson) for maybe $400. Built my own relief valve and tuned it to open around 15"hg. I think my setup had around 160cfm at 15".

Pulling through a piece of standard MDF (both faces skimmed off), I could hold a piece of plywood 12"x24" anywhere on the table with nothing else on the table (ie. vacuum open to all zones and not having other sheets to seal up the open areas) as long as the table surface wasn't too scarred up.

4x8 sheets of anything from 1/8 sintra, dibond, etc up to 2" HDU all held, including warped plywood (within reason...you would need to plan your cuts with sh$%ty plywood... like not cut all the way through.. leave a skin). It will hold it down but as you cut through, warped plywood is much more likely to spring back and break the vacuum force, especially if the pieces are smaller/midsized.

If I were cutting full sheet of a bunch of small letters (8" or smaller) out of a big sheet of sintra, I might drape plastic over half of the sheet once that half is cut to seal the bit grooves leaking air.. or turn off zones once the cutting is done in that area.. BE CAREFUL if you do such a thing.. the key if you do not have 300-400+ CFM is to just manage your air leakage within reason.

For something like a Vcarve on a 20"x30" board face, you just turn on one zone, throw it down and go. For a 10"x10" you might turn the zone on and use scrap plywood 'bumpers' that have a greater surface area to both block air leakage in that zone, but also act as a physical edge clamp for your piece.

Life was much better with a vacuum on the cnc (even my pieced together setup).
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