Vacuum Fixtures

[barrowj]

I need to make several individual hold down vacuum fixtures. Ideally a 12"x36" and a 24"x24" with the ability to seal off what I won't be covering. I have not gone down this route so not sure what is the best way to do this. I don't have any vacuum setup at all so would probably buy a small vacuum pump. Any ideas or suggestions would be greatly appreciated.

[steve_g]

Joe…
I think you’ll be better off making several small “pucks” and ganging them up in series… This method plays well to the advantages of a high vacuum / low volume pump and you can rearrange these at will or leave them as a permanent setup on a sub-base.
SG

[barrowj]

Steve, what material did you use for the pucks, that is a great idea btw and makes more sense that several larger ones. I was looking at 1/2" hdpe and a 3cfm or 5cfm 2stage vacuum pump, any thoughts?

[bobmoore]

Pucks are nice for some materials and/or sizes but if you have a flexible material (1/4 inch plywood) and get too far from the puck you will get vibration issues. Vacuum holddown is very material and project specific. If you are regularly making the same parts I recommend a dedicated fixture as that is the most efficient way to hold a project with vacuum. No system works for everything. If you are going to use pucks a 3/4 inch thick is more common because most of the vacuum tubing is 3/8 inch O.D. and 1/2 inch doesn't give you much room for the vacuum tube. HDPE is a fine material although any stable workable nonporous material works. Bob

[steve_g]

Joe…
Bob pretty much hit the nail on the head! One comment I’ll add is gasketing… Quick and dirty, you can just stick a gasket material on top of the puck. This leaves a gap that thinner material can be sucked down into. Even this is Ok for simple perimeter cuts, but if depth of cut is critical, use method two…
Method two uses an “O” ring gasket in a groove. The vacuum pulls the material down, compressing the “O” ring into the groove and leaving the material flat and undistorted…
SG

[barrowj]

Steve/Bob, both are great ideas, looking at 3/4" HDPE now. I will probably go with 2 12"x12" as I have a specific product that we are doing. The base is 11 1/8" x 28" so 2 would do that, then the tops are 2 1/2" x 12 and 2 1/2" by 20 1/2 so I will probably go 7/8 then plane or drum sand down to 3/4" or 13/16". That way I don't break the vacuum seal. Any thoughts on the a vendor for the "o" ring? Thanks for any advice, this forum is great..

[steve_g]

All Star Gasketing

http://www.talkshopbot.com/forum/showthread.php?t=20510&highlight=star (http://www.talkshopbot.com/forum/showthread.php?t=20510&highlight=star)

[scottp55]

Joe, Just learning myself, but met George Bradley from AllStarAdhesives at Shopbot Camp Saturday and Extremely helpful. Bet you a $1 that if you contact him and tell him what you are cutting/material/and bit, he or John have helped somebody set up something similar and could get you into production Fast. gbradley@allstaradhesives.com
One note, At Camp, Sallye mentioned when they first tried a small highvac/lowvolume cheapie pump---The main thing it pumped was oil into the shop air!! Pretty sure the small pump Dad bought for me is the "Oil Spewing" type:(. She mentioned another pump they settled on that works well, but I can't remember it "H something?"
I would be interested in small pump recommendations also, that don't cost an arm and a leg and would be suitable for Desktop sizes.

[barrowj]

Scott, TJ mentioned a Harbor Freight model 2 stage 3cfm on one of his training sessions. There are a number of those type on Amazon (Prime, my favorite) and I will get one of those and let you know how it works. I also found 3/4" HDPE on Amazon 12" x 24" for $33 (Prime again), cheaper than even eBay... All I need now is to nail down the gasket and I will make my purchases either today or tomorrow and hopefully be up and running by next week. I will keep you informed.

[scottp55]

Joe, PRETTY sure that the "Oil Spewer" Sallye from Shopbot mentioned WAS a harbor freight(95%sure). Try emailing TJ and asking what pump they eventually used as standard.

[steve_g]

http://www.talkshopbot.com/forum/showthread.php?t=19559&highlight=gast

The Gast pumps have been well spoken of in the past

sg

[bob_dodd]

What you do not want is a vac pump for service air cond . as they are rotary vane type with a oil res. ,, One like joewoodworker.com is a dry diaphragm type and cycles on and off as needed

[Ger21]

Gast oil less rotary vane and Thomas diaphragm pumps are the most common. Most of the cheap pumps on Amazon are the oil spewing variety.

[Burkhardt]

Get one of the oil-less GAST or Thomson pumps that are being sold refurbished on e-bay for $150 or so (Google). They usually come with starter capacitor and power cable (check). No oil and they can run for days continuously. I guess they are more industrial than a Chinese consumer device.

HDPE is fabulous for pods but since I have unintentionally destroyed a few I just use 3/4" Baltic or even solid wood. The porosity is insignificant compared to other leakages (work piece, seals etc.). Another advantage is better friction on the table. The HDPE pods tend to slide around on my aluminum table when not bolted down well. I use 3/8" foam o-ring cord from McMaster. The o-ring channel is undercut with a ball end bit so that the o-ring is captive and can not jump out.

I use a standard size pod (5x5" or 5x9") for surface cuts that don't go through and where the material is rigid. For through-cuts and flexible material I make disposable "spoil adapters" that sit on top of the pod with a few through holes and adhesive 3/16" flat gasketing tape around the known un-cut areas. To avoid flexible material to be sucked/bowed in between the gaskets, I may create a gasket grid pattern that supports the entire surface evenly. I heard Allstar is good quality gasket but have not tried it yet. I usually take the rubber foam weather strip (Frost King R338H) from the hardware store that compresses under vacuum to less than 20/1000" but will recover. When replacement is needed it scrapes off with a chisel easily

[GeneMpls]

The ones on ebay seem to be 1/3 HP- how much of a vac fixture
will that support? Thinking 18x36" approx. Thanks Gene

[Ger21]

Depends on how much leakage you have, and/or how porous the material you're holding. My 1/4HP Gast is rated at 3CFM.

[Burkhardt]

The ones on ebay seem to be 1/3 HP- how much of a vac fixture
will that support? Thinking 18x36" approx. Thanks Gene

I have one that is 3/4 hp and it can do four 5x5 pods holding solid wood or plywood.

For 18x36 you will need more volume. For such a large surface you may be better off with a Fein or Lighthouse.

[bobmoore]

Yes gasketing should pull down to 0. Makes your Z much more predictable. I use 3/8 O.D. surgeons tubing (like you used to make sling shots out of). I have even used the round weather seal material from Home Depot in a pinch. Allstar gasketing sells excellent vacuum stuff although a little pricey it works great (try their cover gasket for dedicated fixturing with a central vac motor). Brady Watson and some others did extensive research and writing about vacuum on this forum if you can search the archives. Bob

[gbradley]

We are working on making up half rolls for the folks that are not in the high production end of the cnc world. Hope fully that will make the cost more affordable to the guys with the smaller machines.

[barrowj]

Bob, is that the same as Latex Surgical tubing, Amazon sells 50' of 1/4"id - 3/8"od for $28 Prime

[barrowj]

I've ordered a 12" x 48" HDPE and the Vacuum Pump that joeswoodworking site has along with various accessories. I am trying to decide if I want to make the last foot on my bot a dedicated area for my vacuum since I won't be needing the whole table. I really have very few plans on using a full sheet of plywood and when I do I can keep the cuts to 6-7' of it. I will set it up for a 4 station system but will probably only use 2 at a time. I have no issues doing cuts with an onion skin as I have a 24" dual drum sander to clean the last bit up and with tabs the smaller pieces won't just fall out. I will post my progress and final setup for anyone that is interested. Thanks for all of your suggestions.

[scottp55]

Interested Joe, post pics and results please:)

[bobmoore]

Yes Joe that is the stuff. I route a groove for it .325 deep with a .375 ball nose bit and the vacuum will pull the last .050 down flush with the fixture. Cut the gasket a little long and square, compress it into the groove and the butt jointed end doesn't have to be glued. BOB