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  #1  
Old Sun 28 April 2013, 19:36
David Bryant
Just call me: David #99
 
Western Australia
Australia
What size vacuum pump

Hi
What size vacuum pumps are being used?

Absolute pressure?

meters cubed per hour, for a particular table area?

Power?

Thanks for putting up some data with what works, and does not.

( My vac cleaner hold down had very limited success...)

Thanks
David
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  #2  
Old Mon 29 April 2013, 11:11
nisma
Just call me: chris
 
bz
Italy
There are two types of vacuum holding. Those that build the vacuum and donīt allow
no leaking, then hight absolute pressure is needed. This usually have one O-Ring or a
rubber gasket in order to limit the vacuum area. This sort of vacuum table has only a
limited amount of holes.
The other type of vacuum table have many holes, mostly two sized holes, one larger and
inside this larger hole one smaller hole to the vacuum. With this type of vacuum, only
the high meters cuber per hour matters and the vacuum table has many holes to the
vacuum supply.
This two types of vacuum table holdings are different from user point of view. With the
first, itīs not allowed to drill/break the vacuum holding area, the holding is stronger.
The second system one can drill/route trought the vacuum.
There is a third system of amorph plastic/ light mdf that allow pass the air trought the panel and itīs identical to the second option.
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  #3  
Old Mon 29 April 2013, 18:43
David Bryant
Just call me: David #99
 
Western Australia
Australia
Thanks for the summary Chris.

I have an MDF Base board and was thinking of a vac system under the MDF.
I also do some composite work so am hoping for the vac pump to also be used for Vac bagging etc. currently using two old fridge vac pumps in parrallel, very low flow rate

As the primary job for the new vac pump is to be the hold down on a 1200mm X 2400mm MM table I was hoping to find out what people are using successfull in this situation.
Regards
David

Last edited by David Bryant; Mon 29 April 2013 at 18:44.. Reason: Spelling
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  #4  
Old Mon 29 April 2013, 21:00
Tom Ayres
Just call me: Tom #117
 
Bassett (VA)
United States of America
My limited experience says that you will need higher volume than vacuum especially if you're planning to go directly through the mdf (and you'll need the ultra light mdf to get the volume needed). You'll also need to seal edges and areas not being used to control volume loss. What I Can Not tell you is what size pump or mfg (I have no idea what your needs will be)
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  #6  
Old Mon 29 April 2013, 22:22
David Bryant
Just call me: David #99
 
Western Australia
Australia
Thanks for the comments and GREAT links
David
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  #7  
Old Tue 30 April 2013, 04:48
Surfcnc
Just call me: Ross #74
 
Queensland
Australia
Hi David

I have some practical experience with the low flow higher vacuum side of things but the shopbot guys have done their homework on the high flow side.
The Black Box is a favourite on that site.
http://www.talkshopbot.com/forum/showthread.php?t=11813

The motors they use are basically good quality ducted vacuum motors.
The Black Box is designed to separate the intake and outlet flows and maybe provide a little silencing but not much.
The over the hump system they talk about is very smart stuff that provides both high flow low vacuum and low flow high vacuum.

I have used venturi type vacuum systems for vac bagging, as long as you get a good seal and have a resevoir to stop rapid cycling.
Leaks will cause these systems to use massive amounts of air over time, so if you can't get a good seal a more conventional vacuum pump is needed.
Butyl mastic is killer for sealing bags made from most everyday plastic films and a blobs of it very effectively seal spot leaks.

The oil type pumps incl the fridge compressor hack all have issues with oil aspiration. Makes things a bit dirty unless it can be controlled.
I have played with three good quality Robinair pumps and if the leakage in the system is high they will aspirate lots of oil.
Strangely if you get a good seal they don't have so much oil passing by the pump and into the air.

The best for the high vacuum low volume stuff is the oil free dry type pumps.
Like everything top shelf expect to pay plenty in comparison to an oil type Chinese pump.

One of our members on the forum has just built the Shopbot Black Box hold down pump, you might also want to follow that up for some user feedback.

Regards
Ross

Last edited by Surfcnc; Tue 30 April 2013 at 04:50..
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  #8  
Old Tue 30 April 2013, 07:06
darren salyer
Just call me: Darren #101
 
Wentzville mo
United States of America
I built the Black Box project. (Painted MM blue, of course.. )
Works really well.
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  #9  
Old Wed 01 May 2013, 04:33
Robert M
Just call me: Robert
 
Lac-Brome, Qc
Canada
Send a message via Yahoo to Robert M Send a message via Skype™ to Robert M
Darren, any pics for us ?
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  #10  
Old Wed 01 May 2013, 07:14
darren salyer
Just call me: Darren #101
 
Wentzville mo
United States of America
Don't know if I'll get in trouble for this, but heres a link to a 13 page thread on the Black Box construction that covers everything. Only thing I did different was to hook the vac motors to a 240v relay and powered the 110v coils through a RF remote outlet. I can position the work and start the vacuum using a keyfob remote.
Towards the end of the thread there are basic cut files posted, I think.
The design goes through a couple iterations, so read it through to the end.

http://www.talkshopbot.com/forum/showthread.php?t=11813

Edit: I see Steve linked to it in post#5 above as well.
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