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    Default Wanting to design a vacuum fixture.

    I plan to make a vacuum fixture for this part (see picture)I need a vacuum source either a pump or a venturi type source. Cycle times I expect to be around 5 minutes or less. I will probably make 20 to 50 at a time. Right now I have a fixture made that uses some corner shop made clamps allowing me to drill and tap the holes in the interior,I add hold down screws through those drilled holes and cut the profile. I would like to put the blank on held by vacuum and do the whole part to get the cycle time down.

    I use vacuum on a router table but it is a high CFM low pressure system that allows a lot of air leakage. This fixture I plan to be a high hold down pressure no leakage or very low leakage system. Of course I want to get by as cheap as possible. I plan to machine the fixture specifically for this part. I have a couple Harvey "O" ring cutters and some "O" ring material. The part is cut from a 19.5" x 11.75" X .250" 5052 AL blank it has plenty of surface area for vacuum the part is bent after machining.

    I have been looking on my local CL for a vacuum pump but I don't really know what type I need other than it needs to be continuous duty. I am not sure which type are designed for continuous duty. I have heard the venturi type vacuum source use a lot of air.

    vacuum-fixture.jpg

    Would this work? GAST Vacuum Pump DOA-V720-AA Oil-less Diaphragm Pump Air Compressor with Vacuum | eBay

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    Quote Originally Posted by gundog View Post
    I plan to make a vacuum fixture for this part (see picture)I need a vacuum source either a pump or a venturi type source. Cycle times I expect to be around 5 minutes or less. I will probably make 20 to 50 at a time. Right now I have a fixture made that uses some corner shop made clamps allowing me to drill and tap the holes in the interior,I add hold down screws through those drilled holes and cut the profile. I would like to put the blank on held by vacuum and do the whole part to get the cycle time down.

    I use vacuum on a router table but it is a high CFM low pressure system that allows a lot of air leakage. This fixture I plan to be a high hold down pressure no leakage or very low leakage system. Of course I want to get by as cheap as possible. I plan to machine the fixture specifically for this part. I have a couple Harvey "O" ring cutters and some "O" ring material. The part is cut from a 19.5" x 11.75" X .250" 5052 AL blank it has plenty of surface area for vacuum the part is bent after machining.

    I have been looking on my local CL for a vacuum pump but I don't really know what type I need other than it needs to be continuous duty. I am not sure which type are designed for continuous duty. I have heard the venturi type vacuum source use a lot of air.

    vacuum-fixture.jpg

    Would this work? GAST Vacuum Pump DOA-V720-AA Oil-less Diaphragm Pump Air Compressor with Vacuum | eBay
    I'm going to say that pump wont work way too small. but i could be wrong. I think a a/c pump from the chiness ebassy would work just as good as that one.
    venturi systems do use lots of air.
    if you have or can find one an old 2 stage air compressor with tank alot of guys make vacumm pumps from them and they work pretty darn good. would be cheaper.

    in all honesty you want a double reed pump at a minimum.

    Edit **** this should have said rotary vane** brain fart

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    I would never buy a used vacuum pump unless you can test it out somehow.

    I've been running this pump for years with no problems at all. PLATINUM 7 CFM VACUUM PUMP - JB Industries, Inc.

    Run good oil in it, and change the oil the second it looks any different than brand new: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    Plumb a reservoir between the work and the pump so the pump doesn't digest any coolant if your vacuum seals spring a leak. Mine is 10 gallon.

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    What can work fairly well is if you get yourself an old or surplus compressor tank, and pull that tank down with your (relatively small) pump. That way you have a lot of vacuum capability (instant hold when you open the valve), but you can still get away with a small-ish pump.

    PM

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    If you are going electric then you want a rotary vane pump. The ones I have used were good for 25" mercury. 1/4hp is plenty for fixtureing that will fit on your cnc mill. For my money I use a venturi pump, up to 27" mercury and .5 cfm at 60 psi, or .4 cfm at 80 psi. Either way you want a coolant collection container so your pump doesn't ingest coolant. With a venturi pump it will drop the vacuum while the coolant goes through it, anything else you should stop and clean it out very well. A rotary vane you can just run some cleaning solvent through it so have it on hand. YOU DO NOT WANT A PUMP THAT CAN BOIL WATER!!!! If you pump uses oil then you are supposed to change the oil after every day of use, and that is assuming dry use, not what you will be doing with it.

    Foamed cord stock is worth gettting, way more compressible than solid. You can design in a lot more compression with foam stock which is a big help for extruded material that is not perfectly flat. With solid .005" of compression is about max for 3/32" or 1/16" cord. Your part is big enough but you have a lot of features that will reduce your vacuum surface area. It would be a good idea to do you heavy milling, say the outside perimeter, with the part located with solid stops so it can't move around. For your part probably pins in holes would work best. A little movement won't bother holding the part down but will show up in your finish. Keep in mind when profiling the outside of a square plate the corners are where it will lift or shift, more leverage with less hold down. I would strongly suggest using a corn cob mill to rough the profile out. Less side loads and less lifting. Garr makes a real nice 3/16" stub version and you can get them to coat it with Tib2 or whatever it is, which may well be worth it with 5052. You do not want to use bigger than a 1/4" end mill on your part, the bigger the mill the more force is transferred to the part. I ran the Garr 3/16" stub mills at .015" feed per rev at .235" doc in 6061 on a big production job with no problems machining 1/4" plate on a vacuum fixture that the part was blocked in place so it wouldn't move. Garr is the only one that I found that makes corn cob stub mills for aluminum under 1/4" diameter.

    PS My coolant reservoir holds about 12 oz and is way too big for my needs. It will be getting replaced with a 2 oz compressed air water separator. If your seals are good you shouldn't leak much coolant, maybe .5 to 3 oz a day.

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    Quote Originally Posted by [email protected] View Post
    I've been running this pump for years with no problems at all. PLATINUM 7 CFM VACUUM PUMP - JB Industries, Inc.
    +1 on this vacuum pump. Been using the same for 4 years without issue.

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    You can get the specs for that Gast pump online. Gauge reads as a vacuum pump and if it can pull 24" it will do an excellent job. Rotary vane is not just overkill, but more complexity than you need. Big volume rotary vane are used with spoil boards without gaskets. Rule of thumb is you get apx 1 pound of atmospheric hold down force for every 2" mercury. A pump pulling 24" = 12 psi. hold down. Both McMaster and MSC will have .250 EPDM closed cell cord stock, I buy 10s of thousands of feet of the stuff every year from Allied Seals.
    You will prob run coolant so you will need a tank between vac chuck and pump, with a sight glass to monitor fluid level inside. Make your chuck grooves with a 5mm or 7/32 bit maybe a bit deeper than 3/16. Make sure the through holes have either a EPDM O ring around them, or just wall them off. Cover the face of your chuck with peel and stick fine sandpaper. It will not mark the material and your parts will not move. Use superglue to join the ends of the EPDM.
    Buna N O ring cord stock will also work but you will need a seriously bigger pump and groove depth can be critical. Your part needs to make a perfect seal with the gasket to work and the soft compliance of the sponge cors helps a lot. Or stock is much harder to use and will totally suck (bad joke) if there is the slightest warp in your stock. You also may have the edges around the cord stock raised up a bit at the pressure holding the part down may not compress the Buna into the groove.
    Your chuck with thap pump can easily apply 2000 pounds holding your part in place. Just remember that is total force applied inside the gasket. You could stick a jack knife under a corner and break the seal and releasing the part. So be careful with high helix cutters. Your thickness is not so bad to cut with a down spiral bit. I use them a lot in 5mm cutting 3/8 canvas phenolic sheets, and 1" x 5" parts.

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    Air-Vac Store: AVR SIngle Stage Models:

    I have the AVR062H, and it works great. Make sure you add a muffler if you end up going with one.

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    Question about the venturi vacuum generators once they pull max vacuum do they continue to use a lot of air? I was at HF yesterday buying cloth gloves and they have a 5 gallon and 10 gallon air tank for filling tires would one of these work for a vacuum reservoir?

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    Quote Originally Posted by gundog View Post
    I was at HF yesterday buying cloth gloves and they have a 5 gallon and 10 gallon air tank for filling tires would one of these work for a vacuum reservoir?
    Exactly what I'm using for mine, although not from Harbor Freight.

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    Yes, the venturi vacuum generators continue to use roughly the same amount of air regardless of the vacuum level. I prefer the venturi style because all of the workload is on the compressor, which should already be rated to put out air continuously. We used Vacmagic fixtures from Mitee-Bite, with built in vacuum generators that were tolerant of coolant ingestion. They would just suck up the coolant and spit it out teh other side and keep going. They were also a good source for the foam gasket and diamond/round locating pins and bushings. I will say I was rather unhappy with the flatness of the base fixture (about .002" from corner to corner if I remember correctly), and disassembled it to mill each section flat in place. I had dozens of fixture plates that went on that base, including one with a 6" Kurt vice so I wouldn't have to ever disassemble it. My normal workflow was to mill the bottom of the part flat, finish the sides, then drop it in a sized pocket to finish the top and details. The grid base was also good for one off pieces, held in place with their bolt down "fingers".

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    The venturi, or any other pump for that matter, uses the same amount of energy when in use. How much air it uses depends on what you get, .3 cfm to 40 cfm. You can save a lot of air by turning the pressure down but your level of vacuum will drop as well, but sometimes you don't need 27" to hold your part in place. My mill uses 8 cfm so .5 for my pump is not noticed in my shop. I do not like using a vacuum reservoir, I like to control my vacuum by turning the pump on or off. If you have a venturi pump then you want the smallest coolant catcher needed so when you turn it on it pulls full vacuum right away. Venturi pumps don't mind ingesting coolant but it WILL significantly lower the vacuum level while doing so. Keep in mind that venturi pumps don't move much air, about as much as they use or less, so if your seals are not perfect they will not work.

    For an electric pump rotary vanes are about as simple and efficient as you can get for part holding, kind of like an air die grinder motor. The only problem with ingesting coolant in one is it may make it a bit sticky so the vanes don't slide right. Running some of the correct solvent through it is all you need to do to clean it up. Ingest some coolant in a two stage oil bath pump and you will be doing a lot more to recover.

    Source for cord stock. I use 1/16" or 3/32" for all of my work. For fixtures to hold smaller parts in production I will try to design around molded O-rings so I don't have to splice them together. Also molded O-rings typically have a .003" diameter tolerance, the tolerance for cord stock of the same diameter is typically double.

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    This is probably overkill since you're only talking about 50pcs at a 5 minutes cycle ... But I have used this product in the past and it worked pretty well. At the very least it might give you some ideas .... Vacmagic(R) VM100 | Mitee-Bite Products LLC.

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    If you are really concerned with how how much air the venturi type use, get a large and small one, and plug them in parallel, with on/off valves. Use the large one, to do the initial evacuation, then turn it off, and have the smaller one connected during the machining process.

    I would rather set the money aside for a vacuum pump, and put it towards a better compressor if your current one isn't adequate.

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    Here are some of the vac plates I have made and some of the other stuff that is needed.



    This is a 5/8" thick plate I made to hold some plates while I machined them. I used dovetails to hold the plate so I didn't need to use as much vise pressure, so I didn't bow it. Worked just fine. There is a 90 degree push-to-connect fitting under it to pull a vacuum.

    vac-6.jpg

    This is my most recent pallet receiver. I use 1/4" dowel pins standing up .15" to locate and ream or mill the holes +.001" right in the aluminum pallets. Normally by the time the hole is getting trashed so is the pallet, this hasn't changed in 20 years. Cord for both fixtures is foamed 3/32" and is just right. I don't splice my cord stock for fixtures like this, I just cut it around 3/16" long and stuff it into the dovetailed slots which I cut a little tight. I use the larger neck Harvey cutters and don't worry about the plung hole.

    vac-7.jpg


    Here is my separator pot, vacuum gage and venturi pump with valve on the right side. The glass jar is turning out to be a poor idea, 2000 ipm rapids are tough on it. I have chipped the seal lip a few times so it is time to replace it. I am going to use a little air/oil separator I have laying around, it only has a 3 or so once bowl so it should make it a little faster at pulling 25". All the tubing is 1/4" push-to-connect and works fine, the air supply is 5/32" which is a little small but

    vac-8.jpg

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    I picked up a vacuum pump for my fixture I am designing. The pump is a 25 HG 3 CFM oil-less pump made by Becker. It is a fully self contained unit with a gauge and a 4 port manifold & vacuum reservoir. The unit was designed for the aircraft industry to supply vacuum to pods that attach to the side of aircraft to support a person while they work on the plane.

    img_1618.jpg

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    When it sucks in some coolant where will it go? How easy is it to see how much coolant it has sucked in and how easy is it to drain? IMO 25"s is perfect.

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    Quote Originally Posted by DavidScott View Post
    When it sucks in some coolant where will it go? How easy is it to see how much coolant it has sucked in and how easy is it to drain? IMO 25"s is perfect.
    I have not figured that out yet do you think a water separator made for compressed air would work?

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    I run 2 water filter separators at the pump both with filters then a 25 air gal tank then 1 separator(no filter its a waste) at each line . from there to the mold.
    one thing you ahve to do with the water filters bowls is epoxy the air relief in. other wise you will loose vacuum as they are push down to relieve air.
    The line coming out of the tank going to the vacuum pump is on the top(so coolant will stay in the tank)

    add'd pic
    red circle is what I epoxy from inside unit
    pentek_hfpp_112_pr10_01.jpg

    use clear ones , so you can see the fluid

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    Here is a picture of the vacuum fixture I have designed. Disregard the sharp corners of the channel for the cord I had to program this at the control and when I did I added the radius in all the corners. I tried to get a post processor to work with my current CAD/CAM (Vectric Aspire)(control Siemens 828D)that I use for the drawing and after many attempts and hours of trying I decided to cut my losses and program this at the control.

    The red line will be the EPDM 1/8" O ring channel. The black outline is the part being cut. The rectangle is the blank stock. The blue outlined areas are vacuum areas to hold waist material. The orange single lines inside the part will be vacuum channels cut in with a 1/4" ball end mill I have not decided depth for these channels yet. The hole where the vacuum channels all meet will be the vacuum port.

    vacuum-fixture-2.jpg


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