Double Sided Gasket vacuum Fixture

[diyengineer]

I have seen some large table use only 5 or 6 inch PVC for manifolds. That would hold a good volume of air and be far less prone to collapse than a cheap tank.

They then run zones off that main with valves for each. I have seen several different styles of these back when I was researching them. I think the bulk was on Youtube. Some where here at the Zone.

Would i just use 5" or 6" PVC end caps glued onto the ends. then tap a large fitting on one end?

I will do some more research tonight.

[LeeWay]

I think so, but no need to do any drilling and tapping. They use fittings to come off with smaller pipe to the zones, so you could hook the air line up like that too.
The more fittings, the stronger the pipe I would think. If I get a chance, I will look for some of those systems and post my findings.


Here is the first one I saw on Shopbot.
http://www.shopbottools.com/mProduct...umholddown.htm

[diyengineer]

Below is an Awesome article on the use of Schedule 40 & 80 PVC under vacuum. It is certified for full vacuum use.

This answers lots of questions:
The Vac FAQ: Frequently Asked Questions About Vacuum Presses

I also found a mini vacuum info and education:
Do-It-Yourself Vacuum Veneer Press


Free Vacuum Plans here:
DIY Vacuum Press - PDF Downloads

These can be modified for use on any type of machine. These are specifically for veneering, but the concept is the same.

I stopped by Home Depot and picked out a few prices.

Sch 40 2" PVC 10' (burst pressure of 280psi) $5.87 each.
Sch 40 1.25" PVC 10' (burst pressure 370psi) $3.81 each.
Sch 40 1" PVC 10' (burst pressure of 450PSI) $2.72 each.
Sch 40 1/2" PVC 10' (burst pressure of 315psi) $1.65 each.

Volume: (all lengths are in 10' sections) (pi x r^2 x h)
2" - 376.8 cubic inches
1.25" - 147.2 cubic inches
1" - 94.2 cubic inches.
1/2" - 23.55 cubic inches

Cubic inches to gallons: (1 cubic inch = .00432)
2"- 1.63 gallons
1.25"- .637 gallons
1"- .407 gallons
1/2"- .101 gallons.

Price per Cubic Inch:
2"- $ .0155 per cubic inch
1.25"- $ .0258 per cubic inch
1"- $ .0288 per cubic inch
1/2"- .0700

The above is obvious that the 2" PVC pipe will give me the most volume per dollar. Since this machine is huge and there are a lot of unknown variables, i will calculate for a 60 gallon storage capacity. I want enough that i wont run out, and my pumps wont be working so hard.

I would need: 36.80 10' 2" tubes for 60 gallons (well round down to an even 36). I was thinking about using 4 rows of 9 tubes. This would give me 4 reservoirs of 15 gallons each.

I already have Six 24 volt 1/2" orifice honeywell skinner valves i could use. One on each reservoir to control each individually, and then maybe use the last 2 valves to fill up the tanks up?

Anyways, that is my initial thoughts.

I have a lot of material to read through tonight, well see what i learn from it. I also would like to contact a plumbing house and see if i can acquire the PVC for any cheaper, along with the end caps it takes.

[diyengineer]

The Gast pump seems to be a hair cheaper, and they have been a reliable pump manufacture for ages. It flows 5.5CFM, but can do 28" of mercury.


Gast 5.5 CFM Vacuum Pump Model 72R645-V160-D303X

VS:

The Dayton is a bit more money, probably not as high quality as the gast, flows 7 CFM, and pulls a hair less pressure @ 25Hg.
Evacuation Pump, 1/2 HP, 7.0 CFM, 3440 RPM - Vacuum Pumps - Air Compressors and Vacuum Pumps - Pneumatics : Grainger Industrial Supply

I would like to buy 2 pumps, in case one dies, i'll always have at least 1 pump. Remaining. Who knows maybe i will buy 3 Gasts since the price is a bit less.

Also, taking my Altitude into the equation. I live at 605 feet above sea level.

I'll continue to read about the overall design here:

Basically this little design except on steroids.

Project: EVS - The Concept

I also will call around and find 4" PVC pipe. That will require less pipes overall.

I wouldn't mind using Sch80 pipe since it has thicker walls.

[chuck_hobby]

From my experience, it's very difficult to hold thin, flexible material with vacuum. To get a good seal, the gasket needs to compress a little, and if the material is too flexible, it won't compress evenly, which causes leaking.

One thing I've had smashing success with is taking a page from the o-ring principles used in mating vacuum fittings in mass-spectroscopy and other lab research instrumentation (day job).

Basically, there are 2 rules of thumb. The first is that for a good seal a large mating area is better than narrow (this translates to thicker/larger diameter gasket material in this application) and the second is that the o-ring doesn't support anything dimensionally but only forms a seal (which translates into choosing the correct hardness of gasket/resistance to deformation, and depth of recess/allowing o-ring to properly deform. Also, the larger the vac opening/hole, the better (assuming sufficient support to prevent bowing of the stock).

Sorry for the long version. Essentially, there are formula/tables for the width and depth of slot for a given size gasket profile, so that it compresses completely into the slot and forms only a seal, rather than pushing the stock up off the surrounding fixture.

h##p://www.allorings.com/gland_static_axial.h#m
for a quick example.

I did a run of what I consider thin (0.007 heavy foil) aluminum last year with great results, although admittedly the total area was like 12in x 6in for a couple dozen parts. Handling those afterwards however is obnoxious...don't drop it on its corner! Had to do a half run afterwards...picked up my shop notebook and 4 slide off onto the floor and made some extra scrap at like 9pm! $#@$

Happy chip making!
Chuck

[chuck_hobby]

The Gast pump seems to be a hair cheaper, and they have been a reliable pump manufacture for ages. It flows 5.5CFM, but can do 28" of mercury.


Gast 5.5 CFM Vacuum Pump Model 72R645-V160-D303X

VS:

The Dayton is a bit more money, probably not as high quality as the gast, flows 7 CFM, and pulls a hair less pressure @ 25Hg.
Evacuation Pump, 1/2 HP, 7.0 CFM, 3440 RPM - Vacuum Pumps - Air Compressors and Vacuum Pumps - Pneumatics : Grainger Industrial Supply .

I would go with more flow over deeper vacuum level. My 2 cents. Gast are OK, I love KNF Neuberger diaphragm pumps myself. Not cheap although used on ebay I've seen some sweet deals.

[diyengineer]

I started researching the dayton pumps a little bit. Grainger is infamous for overcharging for just about anything it seems like, and i remember the last dayton product i bought fell apart (i dunno when they sold out to china but they did like most everyone else). I read a few negative comments about dayton pumps in general, motors failing, pumps failing, ground wires not working and getting shocked, etc. I don't know if i want to go down that road and take the chance for the extra 1.5cfm. I would have to many eggs in one basket. haha I would rather buy an extra gast pump and play it safe.

The Gasts are made in the USA (opposed to china) and have been around since 1921. By Using more then one Gast pump that would offset the CFM difference easily. Plenty of people use them off that website as well with no complaints.

3 Gast pumps would give me 16.5 CFM, theoretically capable of 28" Hg max, and cost $1016.09 shipped to my door. I'm waiting to hear back from a few different vendors. Maybe tomorrow i'll get to pull the trigger and order.


(also fooled around in solid works playing with some different types of hold down solutions). They use a gasket around the outside of the part, and also have a pocket milled out so the panel can be profile cut all the way though, and not eat the board. This was just a tester with random shapes, nothing serious.

[diyengineer]

GAST 72R645-V160-D303X (5.5 cfm open flow 60hz)
http://www.gastmfg.com/pdf/rockpist/...1R72R_twin.pdf

$324.50 Each:
Gast 5.5 CFM Vacuum Pump Model 72R645-V160-D303X

[Phife]

If you are going to use the Gast pumps, I recommend trying out the Thomas brand pumps.

I have 3 on my gasketed vacuum table, I can use 1 or all 3 at the same time, they have similar specs as the Gast (6.6CFM open and 27.7"HG) but only cost around $50!

So you could buy a whole bunch of these for the same price as 1 Gast.

I have 4, only 3 hooked up and 1 backup. Ive been using the 3 for about 100H runtime so far and no issues!

Keep in mind that these are used pumps, but for the price they cannot be beat!

Thomas Compressor Vacuum Pump 2650 2660 Pond Aerate | eBay

there are several other listing on ebay, just search Thomas Vacuum pump, go for the 2600 series.

Hope this helps.

[rowbare]

Check out the ShopBot forums. There are a few threads there on DIY pumps build from commercial vacuum cleaner motors. Something like that might be a good first stage pump to get the bulk of the air out and suck down the sheet. After you could switch to a pump with less volume but more suction.

Also check out CNCCookbook. There was an article posted recently about doing some carbon fibre work. There are a few pics of the vacuum system used for the bagging.

bob

[LeeWay]

There was also a thread somewhere where a guy reversed the valves in an air compressor to make it pull vacuum instead. I don't recall where I saw it, but it was on a forum. Here there or some other one. Not much help as it's been a few years, but I thought that was rather cool.

[Phife]

There was also a thread somewhere where a guy reversed the valves in an air compressor to make it pull vacuum instead. I don't recall where I saw it, but it was on a forum. Here there or some other one. Not much help as it's been a few years, but I thought that was rather cool.

A compressor can work, but its not designed for vacuum so the valves get damaged fairly quickly, I used one at the start and it didnt last long.

I tried to take it apart and reverse the valves but it wasnt possible with the compressor I had, I think you can do it on some, but most compressors you wont be able to reverse the valves.

You do get suction on the intake port and you can reverse the plumbing so it pulls a vacuum instead of compressing but dont expect it to last long if you cannot reverse the reed valves.