Invested in vacuum chuck bits and pieces...

[Jeff Hornung]

any tricks or tips? Talked to my mentor Kirk DeHeer who suggested running off a vacuum pump instead of a vacuum generator. Assorted kits and pieces ordered. Will be using the Oneway chucks, Gast Vacuum gauge kit and the rotary adaptor for my Powermatic. Currently using a free but worn Central Machinery pump. When it dies a horrible death I’ll probably upgrade to a Robinair.
Thoughts from the membership?

 

[Hy Tran]

Hi, Jeff,

I use the "cheap vacuum chuck" from frugalvacuumchuck.com. This particular style of vacuum chuck has the rotary seal in the chuck, rather than the rotary adapter plugging into the handwheel on the back side of the Powermatic headstock.

In any vacuum chuck, you'll still want a flexible seal between your bowl or plate and the chuck itself. An inexpensive flexible seal is craft foam sheets from Michael's, Hobby Lobby, or Walmart. Cut them to be a bit bigger than the vacuum chuck, with a hole in the middle. (Keep some extra bits handy in case you're trying to vacuum chuck ambrosia maple, to plug the beetle holes!)

For the pump, you're looking for two things: (1) Amount of vacuum pressure (I know, that's an oxymoron) that the pump can pull, and (2) flow rate. You need to be able to pull a good amount of pressure, but you don't need a lot of flow--but your pump needs to be able to handle large flow at small pressure differentials as you place the workpiece on the chuck, start the pump, and initiate the vacuum. You will want a venting valve, so you can modulate how hard you suck (if you've made this really thin plate, you don't want to suck too hard...). You'll also want to run a filter between the chuck and the pump, to catch large dust/chips/shavings and prevent them from going into the pump.

A word about pressure: Atmospheric pressure is about 30 inches of mercury, or 760 Torr, or 101 kilopascals. Pure vacuum is 0 inches of mercury, etc. Some folks specify pumping capacity in terms of how many inches of vacuum the pump can pull, for example, they might say can pump 27 inches when they mean that it will pull to 3 inches of pressure (27 inches away from atmospheric pressure)--others will mean that it will pump from 30 inches to 27 inches (3 inches away from atmospheric pressure). Be careful reading data sheets!

The advice to avoid vacuum generators is correct. Vacuum generators will suck huge amounts of either compressed air or water to generate small amounts of differential pressure from atmospheric.

Some vacuum pumps require oil lubrication, and will spew oil out into the atmosphere (and will need periodic replenishment of the oil). You'll want to put a filter (and probably a muffler) on the exhaust of your pump. I suspect the Central Machinery pumps require oil.

Look for an oil-less vacuum pump. Either vane-type (think of an enclosed propeller) or piston-type pumps will provide sufficient vacuum and flow; piston will typically be able to have greater pressure differential. Frugal uses rebuilt oxygen concentrator pumps; you can probably find surplus or rebuilt oil-less piston pumps on e-bay. Look for being able to pull 27" of vacuum (have a 27" pressure differential, or have the vacuum at 10% of atmospheric pressure), and ~3 cfm or more at unrestricted flow (wide open). Thomas and Gast are solid brands.

Best,

Hy

 

[Dean Center]

Jeff, if you've already had your system set up, disregard. Assuming you have not, be aware that you will need to remove the handwheel on the Powermatic (and not be able to replace it) which can be tricky. The oneway insert is special for the Powermatic. I was concerned about losing the handwheel, but the oneway adapter is a large enough diameter that it is a satisfactory replacement.

 

[Gerald Lawrence]

Jeff, if you've already had your system set up, disregard. Assuming you have not, be aware that you will need to remove the handwheel on the Powermatic (and not be able to replace it) which can be tricky. The oneway insert is special for the Powermatic. I was concerned about losing the handwheel, but the oneway adapter is a large enough diameter that it is a satisfactory replacement.

If you go with the Frugal Chuck system or build that type this is not a problem. As a matter of fact the price of the Frugal with everything set up is very attractive and no further searching or shopping needed. By the way that is what I have and it works very well.

 

[Bill Boehme]

JT Turning Tools has a rotary coupler that simply plugs into the hole on the handwheel side of the lathe. There is no need to remove the handwheel. I use a similar coupler on my Robust American Beauty. They make couplers that fit most popular lathes.

Frugal Vacuum Chucks is an outstanding place to get a complete vacuum system for a low cost. I bought my ¼ HP Gast dry rotary vane vacuum pump on eBay for a really low price (don't remember the exact amount, but it was somewhere between $50 and $75). I think that the shipping was more than the cost of the pump. I've had it for about ten years and am very pleased with it. I make my own vacuum chucks. It's easy to do using PVC couplers, a faceplate, and MDF and doesn't cost much.

An ideal pump for vacuum chucking would have a high flow capability because some wood leaks air like a sieve. Most air-conditioning type vacuum pumps can produce high vacuum, but sometimes not enough flow to keep up with really leaky wood. A rotary vane pump like mine doesn't produce a really hard vacuum, but it can produce a differential vacuum at sea level atmospheric pressure of about 27 in-Hg and has an open port flow rate of about 4.5 CFM.

When it comes to measuring vacuum there are many different units of measure. The most common for our purpose is inches of mercury (in-Hg). Some others include pounds per square inch (PSI), centimeters of mercury, inches of water, centimeters of water, atmospheres, megapaschals, bars. Standard day sea level atmospheric pressure is 29.92 in-Hg or 14.7 PSI, but many of us aren't at sea level so don't be surprised by low readings on your vacuum gauge. It's sort of interesting when we're talking about pressure from an air compressor we use PSI, but use in-Hg when talking about a vacuum pump.

We really don't care about absolute pressure from a vacuum pump because what is more important is how hard is the atmosphere pressing on the piece of wood on the lathe. The vacuum gauge is actually displaying the difference between atmospheric pressure and the vacuum produced by the pump minus losses due to leaks. This relative vacuum is also called gauge vacuum. It is not possible to produce a vacuum that is greater than whatever the local air pressure might be. In other words, the pump can't create a vacuum that is below absolute zero pressure. If you live at a higher altitude such as Denver where the standard day air pressure is about 24 in-Hg, the best that any vacuum pump would be able to produce is -24 in-Hg. So, if you live at high altitude don't worry that your vacuum pump isn't working as well as someone else's pump at sea level. Just blame the atmosphere for not pushing as hard on your bowls.

In addition to air leaks through the wood, there are other leaks around the vacuum seal on the chuck, between the chuck and spindle, the rotary coupler, and the bleed valve. You can minimize leakage through the wood by covering most of it with blue painters tape.Leaks around the rim seal of the chuck is a balancing act. A thick seal reduces leaking, but it also means that the bowl can move around. A thin seal gives a solid hold to keep a bowl from squirming around, but it might mean that there will be a lot of air leaking if the bowl is warped even the slightest amount. Finding a happy medium is the never ending quest of vacuum chucking.

 

[Gerald Lawrence]

Great synopsis Bill. I had not thought about the fact that thick seals allow movement. Thanks

 

[Dean Center]

OP said he already has a Oneway adapter.

 

[JeffSmith]

For what its worth...I’d advise against using the oil-type pumps in the shop without a good oil suppression muffler system. If you keep your eyes open, good pumps like the gast rotary vane models are often available at very reasonable prices as surplus stock from industrial/medical installations that have to maintain spares and rotate them occasionally. As Bill mentioned, I bought one for $89.00 several years ago on eBay. When it arrived, it was a brand new pump in the original packaging.
The rocking piston pumps often used in water treatment systems are also commonly available. These are rated for continuous duty, are very reliable and have the added benefit of being very quiet when running. I found one on ebay - it was my first pump - for $35. Its still in use on the carving stand.
Rebuild kits with the seals and parts that commonly wear out for both of these pumps are also available on eBay.
With good options readily avaible online and from industrial liquidators, I can’t see putting an oil-spewing rig meant for limited duty servicing ac systems in the shop.

 

[Bill Boehme]

OP said he already has a Oneway adapter.

He also asked for thoughts from the membership. It never hurts to get information about what others are doing.