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My 2 x 3 Vacuum Former
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sulla
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Joined: 30 Oct 2009
Posts: 75
Location: Indianapolis, IN

PostPosted: Fri Mar 12, 2010 8:48 am    Post subject: Reply with quote

Found a used Viot VPBS3 1 stage 3CFM pump locally. It's light duty according to the VIOP site (second from the left).
http://www.viot.us/showmanual.php?model=pumps
Is this one too dinky to use on a 2 x 3 former with a 20 gal (aprox) tank? I am not too concerned with how long it takes to empty the tank.


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stormtrooperguy
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PostPosted: Fri Mar 12, 2010 11:06 am    Post subject: Reply with quote

my concern would be that 3CFM would take forever to evacuate the tanks.
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sulla
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Joined: 30 Oct 2009
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Location: Indianapolis, IN

PostPosted: Fri Mar 12, 2010 11:55 am    Post subject: Reply with quote

My thoughts too. It was a great value though, slightly used for $50...
I think I may hold out for at least a 5CFM or better.
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sulla
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Location: Indianapolis, IN

PostPosted: Fri Mar 12, 2010 12:27 pm    Post subject: Reply with quote

How about this one!

**edit**
Whoops, it's a Robinair 15600 6CFM 2-stage vacuum pump.
**edit**

Used, needs oil, still works. Local guy selling it for about $100.
6CFM, Emerson

NM - found that Robinair label, was able so see it a ebay and a few other place to get an idea. I think I will haggle it a bit see what I can get.




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jdougn
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PostPosted: Fri Mar 12, 2010 6:12 pm    Post subject: Reply with quote

There's formulas that will calculate how long it will take any give cfm pump to evacuate any give volumn tank. Here's a link from cnczone that does a good job of explaining the math.
http://www.cnczone.com/forums/showpost.php?p=602066&postcount=14

Two issues with the pump size come to mind. First, how long is the wait for the pump to evacuate the tank. For most pump/tank combos that is probably not an impossibly long wait unless thin, fast heating plastic is being used. The second issue is a funtion of the thickeness and/or type of plastic being used. The 10cfm pump on my 2'x4' two stage vac former has saved my hind end more than a few times when a pull went wrong. The capacity of the pump was enough to complete the pull even though a vent hole blew out, or an edge pulled loose. However, this is working with 3/16" ABS on big molds so keep this in mind when deciding upon your system. If nothing else, a second pump or additional tanks can always be added later.
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spektr
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PostPosted: Sat Mar 13, 2010 8:14 am    Post subject: Reply with quote

This formula isnt accurate. Mathematically it is correct, but it doesnt take into account the reality of pumping down tanks. If you were pumping a liquid with a non changing density, you'd be there. However you aren't. You are pumping an ever decreasingly dense "fluid" per se.

The pump will move 6 cfm of "air" at AMBIENT PRESSURE. Efficiency of the pump go's down dramatically as the density of the "fluid" falls. Some pumps will take 20 minutes to get from 24 to 25 inches of mercury on a 30 gallon tank, when they get hot, they may never get there.

Just thinking out loud;........

Scott.
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stormtrooperguy
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PostPosted: Sat Mar 13, 2010 11:06 am    Post subject: Reply with quote

spektr wrote:
Some pumps will take 20 minutes to get from 24 to 25 inches of mercury on a 30 gallon tank, when they get hot, they may never get there.


YIKES! I guess I got lucky on mine. I'm only using 20 gallons, but I get down to 26 inches in a minute and a half or so!

I don't understand the math well enough, but is there any difference between 1 20 gallon tank and 2 10s, assuming that they are both open?
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sulla
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Joined: 30 Oct 2009
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Location: Indianapolis, IN

PostPosted: Sat Mar 13, 2010 2:49 pm    Post subject: Reply with quote

Well, I talked the guy down to $75, so I bought it. We'll have to see how well it does when I find a tank. I was curious about the double tanks set up as well. Maybe I need to read more about the vacuum system in the plans and that will tell me.
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93RMW
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Joined: 26 Sep 2009
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Location: Tulare, CA

PostPosted: Tue Mar 16, 2010 10:01 pm    Post subject: Reply with quote

[quote="spektr"]That will do the job. It has a habit of spitting oil into the air while it's running. A very fine mist that is hard to stop. You should be fine if youre in the garage and you put a vent line on the outlet . Ever ask why it has 3 bottles of oil included with the pump???????

If you really dont mind waiting a few minutes, the 79 dollar 3 cfm pumps work pretty well.. I have 2 of them and besides the sloppy exhaust issue, they pull 26 or 27 inches most of the time.. Perfectly fine for low volume use....

Scott.[/quote]

Scott, I was worried about my Gast 1065 pump putting oil mist into the air. it has a filter before the muffler, but was thinking about building a small box from Filter Pads around it. I share my garage with a lot of stuff, and I don't want to get it oiled up. Any thoughts on how that might work? Back pressure?

For the little Harbor Freight style pumps try this out
[url]http://viot.us/HVAC/product_info.php?cPath=27&products_id=212[/url], for 17 bucks you run this and a lenth of hose to any where you want. Hope that helps Fredo.
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sulla
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Location: Indianapolis, IN

PostPosted: Tue May 04, 2010 11:52 am    Post subject: Reply with quote

Part of my uncle's entrepreneurial 'job' is building custom race car chassis. He has been helping me go the steel and aluminum parts of my 2 x 3 proto-form machine.

He got us all the steel tubing needed for $189 (he has the flat plate needed for the tabs.) I am paying for it regardless, but I was just wondering if anyone whose constructed the proto-form finds this to be a good or bad price for the steel.
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Bryan
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Joined: 12 Jan 2009
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Location: Oklahoma City

PostPosted: Wed May 05, 2010 8:58 pm    Post subject: Reply with quote

sulla wrote:
He got us all the steel tubing needed for $189 (he has the flat plate needed for the tabs.) I am paying for it regardless, but I was just wondering if anyone whose constructed the proto-form finds this to be a good or bad price for the steel.


I don't know how much steel the Protoform requires, but $189 would buy about 275 pounds of A36 around here.
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sulla
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PostPosted: Thu May 06, 2010 12:42 pm    Post subject: Reply with quote

I checked with my uncle, we bought a bunch of 14ga in mostly 24' lengths, so I may have some extra. Maybe so I can make some mistakes. Smile
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kayaker43
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PostPosted: Fri May 07, 2010 7:57 am    Post subject: Reply with quote

All the A/C service pumps tend to blow awater vapor/oil mist out the exhaust. They usually come with a crude exhaust trap but some don't. I've been selling rebuilt Robinair pumps for years and the 10 CFM unit comes with a screw in trap. I was able to find a limited number of older style traps that are no longer made but work a bit better. I can't sell these separate, I need them for pumps I sell.

One trick that helps a lot if you can unscrew your trap. Use two 90 degree elbows between the trap and pump. This creates a labyrinth of sorts and adds some length. As the misty air turns corners and rubs along the walls, much of the oil drops out of suspension and drains back. I haven't had time to experiment but it seems like similar ideas should also work? maybe a couple of elbows with a lawnmower muffler at the end?
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Doug Walsh
www.build-stuff.com
Hobby-Vac and Proto-Form machine plans

Also other plans books and videos for people who like to build things
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sulla
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Joined: 30 Oct 2009
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Location: Indianapolis, IN

PostPosted: Wed May 26, 2010 6:56 pm    Post subject: Reply with quote

I spent 11.5 hours last Sunday at my uncle's place welding up my machine (he runs an at-home custom racing fabrication shop called Mac Racing - he's currently working on a land speed record car). We got pretty close to finishing before we lost the light.

Almost everything follows the plans perfectly except for a few things, and the handle bar and angle steel is just what ever he had in his shop to save money.

You can see in the pix that we notched the angle bar on the carrier frame to fit around the glide tube since it's a little large, but forgot to notch it to fit around the uprights. That will be adjusted and I still need to make the top part of the carrier frame along with a few dozen little details. I will make the smaller carrier frames too, after the full size machine is all built and tested.

That will all be tackled in July when I get back over to his shop. For now I am going to get the cart done and start on the platens and clean up the weld-nerds and what-not.




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TK 109
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PostPosted: Thu May 27, 2010 10:23 am    Post subject: Reply with quote

nice! This seems to be taking off! Very Happy
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