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Discussion Starter · #1 ·
I am almost ready to pull the trigger on a vacuum chucking setup but was wondering which type of vacuum pump I should use: diaphram, rotary vein, etc. What are the pros/cons of them? I see diaphram being more expensive and oilless but quieter while rotary vein has been noted as being louder and uses oil but a much better price for a given CFM. Looking at between a 4 and 6 CFM pump.

Right now I am leaning towards this pump with the plumbing kit below on the same page: http://jtturningtools.com/vacuumpumps-kits

Just trying to get the best deal I can find for a good setup.

Thanks for your insights!
 

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I am almost ready to pull the trigger on a vacuum chucking setup but was wondering which type of vacuum pump I should use: diaphram, rotary vein, etc. What are the pros/cons of them? I see diaphram being more expensive and oilless but quieter while rotary vein has been noted as being louder and uses oil but a much better price for a given CFM. Looking at between a 4 and 6 CFM pump.

Right now I am leaning towards this pump with the plumbing kit below on the same page: http://jtturningtools.com/vacuumpumps-kits

Just trying to get the best deal I can find for a good setup.

Thanks for your insights!
Dry rotary VANE is the preferred type for woodturning because of the high flow capacity and good vacuum performance even wit some air leakage. Oil type rotary vane pumps are less desirable because of oil contamination from wood dust and also because they produce an oil mist.

DIAPHRAGM pumps are less tolerant of air leaks and are slower to recover vacuum although the one that you indicate seems to be better than average. Diaphragm pumps are generally the lowest cost of the three main types. Typically, diaphragm pumps do not produce as strong a vacuum as rotary vane or piston pumps.

Piston pumps are for pulling a hard vacuum, require oil, and have lower open port flow rate than rotary vane and diaphragm pumps.

I found this pump on ebay and wonder if it is work a shot for the price. Would say it is made in China, but considering: http://www.ebay.com/itm/5CFM-1-2HP-...d=100010&rk=4&rkt=19&mehot=pp&sd=231702288123
The main drawback is that it is an oil type rotary vane pump.
 

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Discussion Starter · #4 · (Edited)
Thanks for the info, Bill. I appreciate the clarity.

My minion at my day job has a couple of rotary vein pumps he is going to check on the CFM. If they are not more than a 4 or 5, I will pass them on since everything I have read says that 4CFM is the minimum for reliable hold even when the wood allows for some leakage. I understand the issue with the oil filled pumps. That was one of my concerns as well. As far as the oil mist or noise, it is not much of a problem as my minion at work has let me know of what sort of performance and noise he had from these pumps. I was going to give me a deal of $35 if one of them met my CFM requirements. We'll see what happens--had my budget slashed rather severely and I am trying to salvage my chance of doing this. Otherwise I would have just gone with the setup at jtturningtools.com for the pump and plumbing.
 

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I hope that I'm not being too "vain" when I say that it is rotary "vane" and not "vein". :laughing: Sorry, I couldn't help myself. ;)

The internal workings has four vanes that slide in and out of slots in the rotor as centrifugal force pushes them outward against the edge of the oval (maybe elliptical) chamber somewhat like a Wankel engine combustion chamber.

I think that the Gast series 0523 pump has an open port flow of about 4.5 CFM which has been fine for everything that I have done over the past 7 or 8 years. A rating of 3 CFM would be marginal I think.

I'm not sure where my minion is now. I donated him to Beads of Courage.
 

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Just for the record, the JT pump which nodemaster linked to in the original post has been around for a while and is both durable and quiet.

Although it pulls less vacuum than a rotary vane unit like the Gast (just like any diaphragm pump will), it still pulls plenty for woodturning purposes. I've never once suffered from inadequate vacuum causing a lack of holding power.

It has only slightly less flow rate than the Gast pump too. (4.2 vs 4.5 cfm)

And you can buy two of the JT pumps for the price of a single Gast and have enough money left over for a decent bowl gouge.
 

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Discussion Starter · #9 ·
I was also looking for that functionality as well as for vacuum pot stabilization. If the one from my coworker is not up to the task, I found a 5CFM unit online that I will go with.
 

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I ought to mention that if you get a vacuum level of about 18 inches of mercury that should be plenty adequate for most things. Holding smaller things is more of a challenge than larger pieces where you can use chucks with a larger diameter.

The EZ rotary coupler is OK, but it seems to be a bit pricey. Also, it uses only a single bearing which means that any side loading where the vacuum line connects to the hose barb fitting will probably lead to some leakage through the bearing and some loss of lubricant from the bearing.

I built several single bearing type rotary couplers before it occurred to me that was the main reason that all of the grease was being sucked out of the bearing and resulting in early failure as well as excessive air leakage. The best rotary couplers have at least two bearings and shaft seals so that overhung loads are much less of a problem. I found that I can buy a really excellent rotary coupler from JT turning tools for about $100 or I can make one myself for about $50 and 100 hours of work that isn't as good as the store bought one from JT Turning Tools.

Something that you can do to minimize any overhung loads is to insert a street ell between the coupler and the hose barb fitting and then clamp the hose to your lathe in a way that insures only minimal side loads are being placed on the coupler. Flexible hose is also better than stiff hose in this respect.

If nobody has mentioned it yet, tailstock pressure should be used in conjunction with vacuum chucking to help keep the piece from shifting around and help save the day if vacuum is suddenly lost for some reason ... and it can happen when you least expect. My vacuum pump suddenly shut off in the middle of vacuum chucking. Fortunately the tailstock pressure prevented a flying bowl. The problem was that I had been using vacuum chucking for several hours without stopping long enough between bowls to let the pump cool and it was a hot summer day. When the motor reached the point of egg frying temperature, the thermal overload switch shut it off and I had to wait about an hour or so before the thermal cutoff finally reset. So now I pay much closer attention to how hot the vacuum pump is getting ... and the Gast dry rotary vane pumps do get really really hot.
 

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Discussion Starter · #11 ·
Thanks for the info, Bill. Yes, I do plan on using the tailstock for support and have ordered a reversing mandrel for the 4 jaw chuck--it was an option for the chuck kit I ordered from Holdfast. The kit I got has aluminum ends with bearing in each for the vacuum adapter. I also ordered extra seals and such. It comes with a 3" and 6" chuck cups with the 1 1/4" x 8TPI of my lathe. I should hopefully know Monday if I will be ordering a vacuum pump or getting a second hand one form a coworker--he is just having a bit of trouble locating it at home. Once the pump and everything arrives, I will get the plumbing fittings locally and see what happens.
 

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It's interesting to compute the holding power of a vacuum chuck.

Roughly speaking, you get almost 1/2lb/sq in of holding force from every 1" of mercury of vacuum. (It's a tiny bit less than that, but not much less)

So 20" of mercury pulling on a 6" diameter chuck adds up pretty quick;

0.5 x total inches of Hg vacuum (20) x area of chuck (3.142 x radius squared)

0.5 x 20 x 3.142 x 3 x 3 = about 280 lbs or so.

Quite a bit, which is why a bleed valve is an absolute necessity so you can back off on the vacuum for fragile work, otherwise it's entirely possible to have the workpiece simply implode.

Like Bill mentions, when the chucks get smaller the holding forces drop in proportion to the square of the diameter, so if you halve the chuck diameter to 3", you get only one-fourth, about 70lbs in this example, of holding force.

That's plenty for a smallish workpiece, but kinda spooky for a larger one.

So it's important that the chuck diameter matches the piece being turned. Much more so than with mechanical chucks which tighten on a spigot or tenon.
It's usually not a problem to hold a 12" diameter bowl with a 3" tenon in a 4-jaw chuck, but trying to hold that same bowl with a 3" vacuum chuck is asking for an adventure you probably don't want.
 

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Discussion Starter · #13 ·
@9kfeet: That was why the set I bought came with a 3" and a 6" head.
 

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@9kfeet: That was why the set I bought came with a 3" and a 6" head.
Understood.

It's quite easy to make vacuum chucks bigger or smaller than that, as you find you need them, and very inexpensively too.
Especially if you have a tap the size of your spindle thread — 1 1/4 x 8 or whatever.

I think I might have something like 8 or 9 homemade ones, the smallest being barely 1.5" and the biggest around 10" or so.

You're going to like vacuum chucking. It's really versatile.
 

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As 9K' said making a vacuum chuck is easy and can save you a bundle of money. The details depend on how you connect the plumbing from the rotary coupler at the hand wheel to the nose of the spindle. The two most common choices are using a lamp rod and just using the hollow spindle. The sealing requirements are different for those two methods. Here is a link to a thread on Wood Online where I describe my solution for building a chuck for my Robust. Since I am using a JT Tools rotary coupler, I can't use a lamp rod for the plumbing through the headstock. As a result, I needed a way to create a seal at the spindle nose. You can skip posts 9 through 18 since they are about rotary couplers including how I did it for my old Delta 1440 Iron Bed Boat Anchor. Posts 19 through 22 provide more details about my chuck design.
 

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Discussion Starter · #16 ·
Understood.

It's quite easy to make vacuum chucks bigger or smaller than that, as you find you need them, and very inexpensively too.
Especially if you have a tap the size of your spindle thread — 1 1/4 x 8 or whatever.

I think I might have something like 8 or 9 homemade ones, the smallest being barely 1.5" and the biggest around 10" or so.

You're going to like vacuum chucking. It's really versatile.
I figured there would be in between and outside sizes I would need for those short bus special projects. At least with this set starting out, a wide swath of bases would be covered. And with the vacuum adapter, I can easily add my shop built versions as needed.

Can't wait to get my toys. Might even make one for the misses.......:blink:
 

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Discussion Starter · #17 ·
As 9K' said making a vacuum chuck is easy and can save you a bundle of money. The details depend on how you connect the plumbing from the rotary coupler at the hand wheel to the nose of the spindle. The two most common choices are using a lamp rod and just using the hollow spindle. The sealing requirements are different for those two methods. Here is a link to a thread on Wood Online where I describe my solution for building a chuck for my Robust. Since I am using a JT Tools rotary coupler, I can't use a lamp rod for the plumbing through the headstock. As a result, I needed a way to create a seal at the spindle nose. You can skip posts 9 through 18 since they are about rotary couplers including how I did it for my old Delta 1440 Iron Bed Boat Anchor. Posts 19 through 22 provide more details about my chuck design.
I like your pic for the expansion plug for the #2 morse taper. Very cool. I did my homework on the adapter that came with the starter kit I bought and the initial version had its issues but the current version I bought is made out of aluminum and has a lot of very happy customers. I saw the exact kit on Carl Jacobson's YouTube channel and got the same kit less the venturi vacuum generator. From what I saw, it is a great kit to start with.

At the moment, I have 3 or 4 bowls that are in need of the vacuum chuck so I can make the recess for my branded medallion--That is the first and main reason I ordered a vacuum chuck was so I could make that recess.:thumbsup:
 

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Discussion Starter · #18 ·
When using a vacuum bag to pull down a veneer my friends used an old pump out of a fridge.
johnep
I have my minion from my day job checking the 2 vacuum pumps he has (used to do refrigeration stuff in his dad's auto shop) to see how many CFM they handle. If they are above 4, I will go that route because of the great price and I trust his knowing they are rather expensive and good quality pumps that work. If they don't meet my CFM needs, I have an alternative lined up but would prefer to go with someone I trust--and KNOW WHERE THEY WORK! :laughing:
 

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Discussion Starter · #19 ·
Just for the record, the JT pump which nodemaster linked to in the original post has been around for a while and is both durable and quiet.

And you can buy two of the JT pumps for the price of a single Gast and have enough money left over for a decent bowl gouge.
Those were the reasons I was really looking at those.

My minion in my day job is a submarine hydraulic and HVAC engineer who mentioned his complaints about the diaphragm pumps--which, after his explaining to me everything, I completely wrote off diaphragm pumps as an option.
 

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Discussion Starter · #20 ·
I hope that I'm not being too "vain" when I say that it is rotary "vane" and not "vein". :laughing: Sorry, I couldn't help myself. ;)

I'm not sure where my minion is now. I donated him to Beads of Courage.
You donated your minion? Was it incompetent? If not...what a horrible evil genius...wait a minute...I guess you would be exactly as intended at that point.

And, yes, I get it: vein. Vane. :laughing:

Had both spellings on the sites I was checking and used what looked right. Guess I was wrong. Left?
 
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