Update on Vacuum Chucking Systems

[Grant Wilkinson]

Bill has it right, John. It's simply a solid piece of wood for the back, onto which you mount a face plate. The pressure plate is like yours. It is another piece of wood with a "donut" hole cut out of the middle of it. The bowl is placed rim down onto the back piece, the donut piece is placed over the bowl and long bolts hold the two pieces together. The bowl can be centered using the dimple on the bottom of the bowl and the tail stock. When the bolts are tightened, the bowl is firmly hold and the bottom is easily accessible for finishing.

 

[Richard Jones]

John,

The leakage is occurring at the other end, where the new handwheel slides up and locks on the spindle with two set screws. Isolating components shows that this new piece, that replaced the factory handwheel, is the culprit. I believe that the spindle locking collar, which is a split ring locked on the spindle shaft, is the weak link. Any air leaking around the spindle shaft has an almost unimpeded escape, or ingress in this instance, through this collar. I'll play with it some more and see what I can do.

Rich

 

[Bill Boehme]

.... Other turners have switched to a threaded 3/8" pipe (used for lamps) through the spindle and sealed at the end of the spindle. I belive Bill mentioned this in an earlier post above. There are commercial versions availble also. I think that I bought one from Craft Supply for usage in one of my demonstrations...

It is just a small variation from what you described, but it does make a difference in leakage --instead of sealing at the end of the spindle and then still having the problem of leakage around the chuck threads to contend with, I seal the threaded lamp rod inside the chuck by having a hole just large enough to pass the lamp rod. I then counterbore from the inside of the chuck body to fit a shouldered rubber bushing with a 3/8" hole. I glue a steel washer on top of the shoulder. Now, after the lamp rod passes through the snug fitting hole, I screw a 3/8 - 27 nut onto the rod. This compresses the soft rubber bushing tightly around the threads and it also has the side benefit of snugging up the rotary coupler on the handwheel.

When I bought my new lathe a couple months ago, I also bought a commercial rotary coupler that just pushes into the handwheel side of the headstock and has two small O ring seals. I have not had a chance to see how well this "store bought" rotary adapter works.

This now leaves me with the problem of sealing at the chuck. I am thinking of making a tapered bung with a hole in it to fit the spindle MT socket and extend out far enough to be compressed slightly by the chuck when it is screwed onto the spindle. A tapered connection at the chuck body would work better than a flat mating surface.

Another idea is an expanding rubber bung such as used in vacuum bottles.

 

[John Giem]

John,

The leakage is occurring at the other end, where the new handwheel slides up and locks on the spindle with two set screws. Isolating components shows that this new piece, that replaced the factory handwheel, is the culprit. I believe that the spindle locking collar, which is a split ring locked on the spindle shaft, is the weak link. Any air leaking around the spindle shaft has an almost unimpeded escape, or ingress in this instance, through this collar. I'll play with it some more and see what I can do.

Rich

There are two commercial rotary adapters that I am familiar with one from Oneway and the other from JTTurning Tools. Oneway has o-rings in it that seal against the outboard end of the spindle. JTTurning Tools takes a different approach. The factory hand wheel is replaced with a custom hand wheel which has a bore that is the same as the bore in the Powermatic 3520. This way he only needs to make one sized rotary adaptor. This adapter uses o-rings to seal against the inside bore of the handwheel. When I installed the new handwheel on my JET 1442 I could not detect any method of sealing the threads between the handwheel and the outboard spindle. My engineering training took over. I did not want to take any chances for leakage so I grabed a tube of silicone bathroom calk. After I cleaned the outboard shaft the best I could with alocohol, I place a liberal amount of calk on the shaft, mounted the handwheel, secured it and wiped off the squeezed out excess. As stated earlier, I do not expect any problems when and if I need to remove the handwheel since the silicone calk has a low shear strength allowing joints to be easily disassembled. I am also using a custom sized push in rotary vacuum adapter with my Vicmarc lathe. I have had good performance with both. For the AW Feb 2011 article on vacuum chucking, I did all of the testing on the Vicmarc lathe using this pushin adapter. As stated in the article, I was able to push the leakages in the system down far enough that I could place an aluminum plate on the vacuum chuck, pull a vacuum and then isolate the pump at the manifold. I was able to achieve in excess of 5 munutes for the fall-off test. I use the silicone calk when ever I have a difficult sealing task. Yes, it sometimes gets messy but it works. Note: all of the silicone calks that I have worked with fail rapidly when exposed to any oil product.
As near as I know, both work equaliy well so it is a matter of personal choice as to which one you use. Another difference in the two adapters is the size of the bore into the spindle.

John

 

[John Giem]

I finally got my gast pump connected, completing my Nova 3000 vacuum chucking system. I put a 3 inch piece of hard maple over a faceplate / plywood chuck and turned up the vacuum.

Voila, 19 mm Hg! Totally unimpressive. A sneeze would send it flying...

Ernie Connover in "The lathe book" says, "Oh, just plug the pores with a coat of lacquer"

What if I don't really want to seal the wood just yet?

Admittedly, I have end-grain over the faceplate but shouldn't hard maple be less porous?

Any ideas on how to adhere the piece to the lathe without sealing?

The hard maple is kiln-dried from a local lumber distributer.

Joe, in rereading your post, I see a different intrepretation than I did before.When you use 'faceplate', it sounds like you may have an aluminum or steal faceplate mounted on the spindle and want to hold your wood on it. The faceplate is acting like a flat vacuum chuck or this is the first step in making a vacuum chuck. In either case then you need to use some sort of gasketing between the faceplate and the wood to be mounted. I can think of at least two solutions. The first would be to use a layer of foam between them, something like the Funky Foam mentioned earlier. The second, and my preference for a permenant mounting, would be to use a bead of silicone calking between the faceplate and the wood.
John

 

[John Giem]

John,

I'd like to learn more about the practical aspects of using a vacuum chuck: How can vacuum chucking be used for odd-shaped items (one of the topics you cruelly suggest you'll discuss only to leave us hanging), can vacuum chucking be used (safely) for multi-axis turning, can it be used for holding small items like reverse-chucking box lids, does vacuum chucking have a place in spindle turning, what can be done to make it easier to properly center an item that lacks a "tailstock dimple", when, if ever, should a turner us masking tape to "back up" the vacuum chuck, etc.

!

David, I'm revisiting one of your earlier posts to follow-up on some of your questions;
1. odd shaped items - holding small items: Did my description of the Complient Vacuum Chuck answer these issues?
2. multi-axis turning - here again the Compliant Vacuum Chuck should help with this. Using a different technique, I also use vacuum chucking to do offset inlay work on coasters, tirvets, etc.
3.use masking tape to back up the vacuum chuck - I'm assuming that you mean to hold the turning on the chuck incase of a catch or a power failure for the vacuum pump. (I once poped a circuit breaker for the vacuum pump and the lathe kept running.) Safety first, always, always, always wear a face shield. I seldom need to use backup holding with tape. For unusal cases, like an out of balace piece, it may be necessary to use a little extra help. Masking tape or painters tape is too weak. For applications like this, I prefer to use fiber glass reinforced packing tape and wrap it around the chuck and the workpiece. One problem though is that tape usually leaves a residue behind when removed. To protect the wood, first wrap it in plastic. Use the streach film plastic like that used for preparing items for shipping. It can be found in the big office supply stores in the packaging and shipping area. (the streach film plastice has many other uses for us also, later.If you don't have any of the plastic, you can wrap your tuning using painters tape for protection and them put the fiber tape over it for strength.
4. Proper centering an item without the tailstock dimple - I'll suggest several methods and let you choose that which fits.
a. if your piece has a tenon and can be remounted in a chuck, use a centering punch. A cenering punch is a machinist tool that looks like a long smooth punch except that on the end is a small point at the center. It is used to mark the center of a hole of a top part onto the bottom part. The punch is placed in the hole on top, tapped with a hammer leaving a punch mark on the bottom part that can be used for drilling, etc. For us to use it we need to make a guide plug that snugly fits into the threads of the chuck. the guide plug has a hole in it correctly sized for the centering punch. Simply insert the punch, tap it and the center of the workpiece is marked.
b. Use a combination square fitted with a centrering head to find and mark the turning. Similiarly, use one of the many centrering tools available on line or at a woodworking store.
c. Make a template by turning a disk on your lathe marking the center. Drill a small hole at the center and use is to mark the center of the turning. (I have made a full set of these and routinely use them to layout bowl blanks for cutting on the bandsaw.)
d.Use the tool rest as a gauge - Place your turning on the vacuum chuck and apply a low level vacuum, just enough to hold it while centering it by eye. Move the tip of the tool rest close to the base of the turning. Turn your piece by hand while watching the varing gap between the tool rest and your piece. Find the closest point and carefully move the tool rest in until it almost touches. Verify that this is the closest point. Put your finger on the vessel next to the tool rest and keep it there while rotating the vessel 180 degrees. The gap between the vessle is now at the widest position. Using a rubber mallet or equivalent, tap the vessel on the opposite side toward the toolrest. Remember the vessel is being lightly held by the vacuum. Quit tapping the vessel when the gap is 1/2 the width as when you started. Repeat the rotate, measure and tap until the variation is the gap is as small as possible or it is 'good enough'.
I hope this helps, let me know if you have any questions.
John Giem

 

[John Giem]

This now leaves me with the problem of sealing at the chuck. I am thinking of making a tapered bung with a hole in it to fit the spindle MT socket and extend out far enough to be compressed slightly by the chuck when it is screwed onto the spindle. A tapered connection at the chuck body would work better than a flat mating surface.

Another idea is an expanding rubber bung such as used in vacuum bottles.

Bill, I'm having trouble visualizing this. I thought that the lamp drawbar with gasket sealed the end of the spindle and covered the chuck/spindle thread joint. Can you expand on your description?
John

 

[egsiegel]

John,

The leakage is occurring at the other end, where the new handwheel slides up and locks on the spindle with two set screws. Isolating components shows that this new piece, that replaced the factory handwheel, is the culprit. I believe that the spindle locking collar, which is a split ring locked on the spindle shaft, is the weak link. Any air leaking around the spindle shaft has an almost unimpeded escape, or ingress in this instance, through this collar. I'll play with it some more and see what I can do.

Rich

Rich,
Are you using the Oneway rotary adapter on your 1642? That is what I have and I'm sure I'm having the same leak issue so I'd be interested in knowing if you find a solution.

Also...while we are on the subject...do you remove the adapter when you are not using it? if not, how do you deal with removing MT centers from your headstock?

Ed

 

[davidwalser]

John,

Thank you for your detailed answers to my questions. I've inserted my responses to your answers withing the quoted material, below.

David, I'm revisiting one of your earlier posts to follow-up on some of your questions;
1. odd shaped items - holding small items: Did my description of the Complient Vacuum Chuck answer these issues? DKW: Yes. Your description addressed the question. Thank you. I'll admit I didn't follow your description well enough for me to have a clear idea how I'd build my own complient chuck (pictures would have been nice) -- but I'm sure I could build my own once I have enough time to fiddle around in the shop.
2. multi-axis turning - here again the Compliant Vacuum Chuck should help with this. Using a different technique, I also use vacuum chucking to do offset inlay work on coasters, tirvets, etc. DKW: One of the questions I have is how securely is the work held with a vacuum chuck as opposed to other methods of chucking. It's very helpful to know that you've successfully used vacuum chucking for offset inlay work, but I still think the turning community lacks a good resource for information on when "x" is safe or unsafe. For example, a lot of turners turn small disks for use as pendants and use offset turning to decorate the pendants. I'm confident there's enough surface area on a 6" disk to do that kind of work, but what about a 1.5" disk? It may well be that there are so many variables that it would be impractical to summarize the various parameters in a chart or table, but such impracticalities have never prevented wishing it weren't so.
3.use masking tape to back up the vacuum chuck - I'm assuming that you mean to hold the turning on the chuck incase of a catch or a power failure for the vacuum pump. (I once poped a circuit breaker for the vacuum pump and the lathe kept running.) Safety first, always, always, always wear a face shield. I seldom need to use backup holding with tape. For unusal cases, like an out of balace piece, it may be necessary to use a little extra help. Masking tape or painters tape is too weak. For applications like this, I prefer to use fiber glass reinforced packing tape and wrap it around the chuck and the workpiece. One problem though is that tape usually leaves a residue behind when removed. To protect the wood, first wrap it in plastic. Use the streach film plastic like that used for preparing items for shipping. It can be found in the big office supply stores in the packaging and shipping area. (the streach film plastice has many other uses for us also, later.If you don't have any of the plastic, you can wrap your tuning using painters tape for protection and them put the fiber tape over it for strength. DKW: Thanks
4. Proper centering an item without the tailstock dimple - I'll suggest several methods and let you choose that which fits.
a. if your piece has a tenon and can be remounted in a chuck, use a centering punch. A cenering punch is a machinist tool that looks like a long smooth punch except that on the end is a small point at the center. It is used to mark the center of a hole of a top part onto the bottom part. The punch is placed in the hole on top, tapped with a hammer leaving a punch mark on the bottom part that can be used for drilling, etc. For us to use it we need to make a guide plug that snugly fits into the threads of the chuck. the guide plug has a hole in it correctly sized for the centering punch. Simply insert the punch, tap it and the center of the workpiece is marked.
b. Use a combination square fitted with a centrering head to find and mark the turning. Similiarly, use one of the many centrering tools available on line or at a woodworking store.
c. Make a template by turning a disk on your lathe marking the center. Drill a small hole at the center and use is to mark the center of the turning. (I have made a full set of these and routinely use them to layout bowl blanks for cutting on the bandsaw.)
d.Use the tool rest as a gauge - Place your turning on the vacuum chuck and apply a low level vacuum, just enough to hold it while centering it by eye. Move the tip of the tool rest close to the base of the turning. Turn your piece by hand while watching the varing gap between the tool rest and your piece. Find the closest point and carefully move the tool rest in until it almost touches. Verify that this is the closest point. Put your finger on the vessel next to the tool rest and keep it there while rotating the vessel 180 degrees. The gap between the vessle is now at the widest position. Using a rubber mallet or equivalent, tap the vessel on the opposite side toward the toolrest. Remember the vessel is being lightly held by the vacuum. Quit tapping the vessel when the gap is 1/2 the width as when you started. Repeat the rotate, measure and tap until the variation is the gap is as small as possible or it is 'good enough'. DKW: Thanks, those were the kind of suggestions I hoped you'd share.
I hope this helps, let me know if you have any questions.
John Giem

 

[Richard Jones]

Rich,
Are you using the Oneway rotary adapter on your 1642? That is what I have and I'm sure I'm having the same leak issue so I'd be interested in knowing if you find a solution.

Also...while we are on the subject...do you remove the adapter when you are not using it? if not, how do you deal with removing MT centers from your headstock?

Ed

Ed,

No, I'm using the JT handwheel and adapter. The adapter does not leak at all, but the handwheel does where it abuts the locking collar. For the life of me I can't see how it can't leak. I removed the collar, cleaned everything well, and reassembled it with some silicone caulk, both in the locking collar threads and in the collar "split" area. Some improvement, but still am losing about 1 or so between the handwheel and the chuck. Plenty of vacuum for about anything, but we always seem to want more power, eh?

 

[Bill Boehme]

.... Would you, and others, mind sharing the approximate cost and time required to set up your first vacuum chucking system?

I got my rotary vane vacuum pump on eBay from a company that makes foot orthotics for $50, but the shipping added about $25 more. The vacuum pump was in like-new condition. I spent roughly another $100 for electrical stuff, tubing, valves, 5 micron air line filter, vacuum gauge, quick disconnects, manifold, and all of the little parts to make my own rotry coupler and vacuum chuck. I figure that I saved quite a bit by making my own rotary coupler from hardware store parts for about $20 total. The most expensive parts were a pair of double rubber sealed bearings. I learned that I could turn brass and PVC quite easily with my lathe tools. The chuck was about the same cost with the most expensive part being an aluminum faceplate. The rest was MDF and PVC sewer pipe couplings.

 

[Bill Boehme]

Ed,

No, I'm using the JT handwheel and adapter. The adapter does not leak at all, but the handwheel does where it abuts the locking collar. For the life of me I can't see how it can't leak. I removed the collar, cleaned everything well, and reassembled it with some silicone caulk, both in the locking collar threads and in the collar "split" area. Some improvement, but still am losing about 1 or so between the handwheel and the chuck. Plenty of vacuum for about anything, but we always seem to want more power, eh?

You might want to check that set screw and put some clear RTV sealant over it too. It is amazing how much air leaks through threads even if they seem tight. The crests and valleys of threaded couplings do not meet and that is where the air leaks through.

 

[Doug Wolf]

Would you, and others, mind sharing the approximate cost and time required to set up your first vacuum chucking system?

Thanks,
John

I have a 3520b lathe and bought a used Gast pump and made my own adaptor (see link), http://www.pueblowoodturners.org/Me...uum Adaptor For A Powermatic 3520b Headst.pdf
and all of my chucks (see link),
http://www.pueblowoodturners.org/Members/wolfd/How To Make Vacuum Chucks.pdf
myself.

I have about $150 in the system.

 

[Ron Sardo]

When I wrote the article on vacuum chucking systems for the Feb '11 issue of the AW, it generated a lot of discussion. Since then I have continued to investigate and work with vacuum chucking systems to solve serveral questions that have come up.
For example: "I don't worry about leaks in my system since I have a large capacity pump and will overpower any leakage." The measurements I have made have proven to me that this is a false statement.

FWIW and not to take away any credit from you, here is a vacuum chuck I built.
http://www.woodturnersresource.com/extras/projects/VacuumChuck/index.html

I use a rotary vane pump from an old printing press. This pump is designed to run 3 shifts a day and indeed can overpower any leaks (Gast 1550). I even had to install a bleeder to leak vacuum on purpose.

I'm very interested in your Compliant Vacuum Chuck and read your "teasers" on building one.

I enjoyed your past article and look forward to your upcoming article next year.

 

[Bill Boehme]

Bill, I'm having trouble visualizing this. I thought that the lamp drawbar with gasket sealed the end of the spindle and covered the chuck/spindle thread joint. Can you expand on your description?
John

OK, I shifted gears on you and perhaps it wasn't clear enough that I was now talking about the situation on my new Robust lathe where I have a commercially made rotary adapter and, hence, no lamp rod drawbar to take care of the sealing at the chuck issue. I am mulling over some ways of getting a tight seal between the spindle bore and the interior of the chuck without the nuisance of trying to wrap Teflon tape around the threads.

BTW, for those who use Teflon tape, there is a thicker yellow colored version specifically made for sealing threads on gas pipes. It give superior results with fewer wraps.

 

[Doug Wolf]

I am mulling over some ways of getting a tight seal between the spindle bore and the interior of the chuck without the nuisance of trying to wrap Teflon tape around the threads.

Bill,

I tapped my wooden (Poplar) vacuum chucks with a 1-1/4" X 8 TPI beall tap and just put beeswax on the threads. Haven't have any leakage since.

 

[John Giem]

Rich,
Are you using the Oneway rotary adapter on your 1642? That is what I have and I'm sure I'm having the same leak issue so I'd be interested in knowing if you find a solution.

Also...while we are on the subject...do you remove the adapter when you are not using it? if not, how do you deal with removing MT centers from your headstock?

Ed

I have a JT Turning Tool adapter on my JET lathe using the adapter handwheel. When installing it, I used an excess of silicone calk including the set screws. As near as I can tell, it does not leak.

Both the Oneway and the JT Turning Tool rotary adapters are designed to be removed when not needed so that the knock out bar can be used to remove the MT drivers.

John

 

[John Giem]

I guess that I will start looking for some bees wax and yellow teflon tape.
John

 

[John Giem]

Photos, Compliant Vacuum Mandrel & Chuck

As 'suggested' here are some photos for you. The empty chuck has has a removable plug in the bottom for the filter. I used a coffee filter reinforced with screen wire. The other two photos are of a Compliant Vacuum Mandrel and Chuck. The securing and sealing of the plastic film is what I described above. These work quite effectively. As hinted at before, I have found some new materials that work quite well, fewer leaks from perforations and I have eliminated the need for the hose clamp around the perimenter. I'll probably reserve that technique for the upcomina AW article. That will give you something to look forward to.

 

[John Giem]

Vacuum Pumps

Several of you indicated that you are interested in Vacuum Pumps and optomizing your systems. This thread is getting a bit long so it seems reasonable to start another thread for vacuum pumps and the overall system.
As a 'teaser' I will address pair of common statements, "What size vacuum pump should I buy for my vacuum chucking system?" and "I have a large vacuum pump so I don't really care about leakage, I'll just over power them."
I'm in the process of finalizing my measurements and analysis and will do some posting when completed. Oh, the size of vacuum pump, for a lot of systems it just doesn't matter, in a lot of cases anything more than about 2.5 SCFM or 3 SCFM is a waste of resources. The second statement about overpowering leakage is false. Did I get your attention?

Happy Turning,
John Giem

 

[John Giem]

I have a 3520b lathe and bought a used Gast pump and made my own adaptor (see link), http://www.pueblowoodturners.org/Me...uum Adaptor For A Powermatic 3520b Headst.pdf
and all of my chucks (see link),
http://www.pueblowoodturners.org/Members/wolfd/How To Make Vacuum Chucks.pdf
myself.

I have about $150 in the system.

Doug, I like both of your articles, well written with good photos.
Apparently, the bore through your adapter appears to be 1/4" ID. The size of your tubing is unspecified. When you have a perfect seal and the wood in your turning does not leak then the air flow will be zero, hence the vacuum drop through your adapter is negligable. A lot of the stuff I work with does leak and perfect seals are difficult to obtain so there is some air flow through the adapter along with the corresponding vacuum losses. I'm going to start a new thread on vacuum pump and vacuum systems showing how all of the components work together to determine the system capability and how to optomize the performance. In my investigations while working with the vacuum systems, I discovered that every little bit counts, they add up. When I build my own vacuum adapter (and I will for the experience) I will follow your design but will increase the diameter of the bore as much as possible to reduce losses.

Several turners in this area, Colorado, have been using decking material that is a blend of recycled plastic and wood fiber with good success. I think that it may be called Trex. Cut offs are cheap and they are in various thicknesses and widths. They seem to make good chucks like your wood ones, they do not need to be sealed and the threads seem to last longer than wood. Otherwise the disigns closely follow what you are doing.

Keep up the good work,
John Giem

 

[Bill Boehme]

... Bill is correct that a valve or other restriction can act like an orifice and limit the FLOW to a constant rate under the correct conditions. Typically, an orifice is a sharp edged hole through which a gas flows. At low differential pressure across the hole, the flow through the hole is low. As the pressure (vacuum in our case) increases the flow will increas also until the speed of the gas through orifice reaches supersonic speeds and beyond this point the flow rate is constant no matter how high the pressure increases.

The highlighted statement appears misleading because it seems to imply that the mass flow rate is limited. The vena contracta* reaches a minimum effective diameter at sonic flow and the flow velocity does not increase any further with increase in pressure differential. However, mass flow rate still continues to increase with increase in differential pressure.

For compressible gasses, sonic flow occurs when the ratio of absolute upstream pressure to absolute downstream pressure is between 1.7 to 1.9 depending on the gas. I don't recall the ratio for air, but this range is sufficient for this discussion.

You are correct that a flow control valve is not, per se, a pressure control device, although pressure control valves are essentially flow control valves with a pressure feedback loop closed around the valve to modulate the orifice. The statement that I was trying to make in my post that you referenced is that the system is in an essentially quasi steady state condition with leakages and vacuum source not changing very much at all when a turning is mounted on the vacuum chuck. In such a case as that, using a needle bleed valve serves the purpose of setting a reasonable vacuum level at the chuck.

I am afraid that I don't see the need for the precision pressure control that comes from using a pressure control valve. In my limited experience, the only modifications that I would need to apply to otherwise using as much vacuum as your system can produce would be not so much vacuum that the vessel becomes distorted, implodes, or suffers a "chuck bruise" (a.k.a., ring around the tub). Avoiding those problems doesn't appear to necessitate precise regulation of vacuum.

* not wanting to lose any innocent bystanders, the term vena contracta is simply the effective orifice size. The actual vena contracta location occurs slightly downstream of the physical orifice and is the result of flow effects that are a function of flow velocity through the orifice.

 

[Doug Wolf]

Apparently, the bore through your adapter appears to be 1/4" ID. The size of your tubing is unspecified.

When I build my own vacuum adapter (and I will for the experience) I will follow your design but will increase the diameter of the bore as much as possible to reduce losses.

John, I'm glad you could follow my write-up.

The tygon tubing from the adaptor to the vacuum pump is about 4 feet of 3/16" ID x 5/16" OD. The reason I used this size is because the bearings I used had a 5/16" ID. I originaly built the protype using rollerblade wheel bearings of this size and quickly found out that the bearings must be double sealed (which roller blade bearings are not) in order to prevent leakage. The reason for two bearings in the adaptor is to give the vacuum a double pressure drop to atmosphere. It is important to use two bearings.

The adaptor is drilled through with a 1/4" hole because I was concerned that when I cut the two O-Ring grooves on the outside of the adaptor it might weaken the material. If you want to increase the diameter of the through hole, you might skip the two shaft O-Rings and just use the O-Ring on the face toward the handwheel.

I notice that depending on the outside temperature, 35 degrees to over 100, the adapator fits tight or loose in the headstock. And this is with the double O-Rings on the shaft. In the case of fitting loose, the O-Ring on the face is the one that provides the seal.

 

[Ron Sardo]

The second statement about overpowering leakage is false. Did I get your attention?

Happy Turning,
John Giem

I would agree if I didn't have a pump that that does overpower leaks. If you are thinking about the small pumps used in laboratories, then you are right. But using an industrial rotary vane pump such as I mentioned the above. I need to "bleed" or create a leak in my system when turning dense wood, other wise I would crack a 1/8" thick wall of wood.

I remember reading that engineers back in the 1800s thought if a railroad car went faster then 60 mph a vacuum would be created in the compartment and the passengers would suffocate.

Thanks for the photos, it really clears up how your donut chuck works. Very ingenious.

 

[Joe Cornell]

Thanks John

Joe, in rereading your post, I see a different intrepretation than I did before.When you use 'faceplate', it sounds like you may have an aluminum or steal faceplate mounted on the spindle and want to hold your wood on it. The faceplate is acting like a flat vacuum chuck or this is the first step in making a vacuum chuck. In either case then you need to use some sort of gasketing between the faceplate and the wood to be mounted. I can think of at least two solutions. The first would be to use a layer of foam between them, something like the Funky Foam mentioned earlier. The second, and my preference for a permenant mounting, would be to use a bead of silicone calking between the faceplate and the wood.
John

Thank you for this and your previous reply. I do indeed have your article and will pay more attention to it. I especially appreciate your comments about how to troubleshoot leakage.

I know it sounds like a bad idea, but I put my palm over the bottom of maple piece while it showed 19 inHg (I misread the gauge previously). This pulled my hand onto the piece and caused the piece to seal to the face plate with 26 inHg. It seems clear to me that the majority of the leakage is through the pores in the maple. I will definitely try the aluminum plate approach and make sure there isn't some other issue.

 

[Bill Boehme]

Thank you for this and your previous reply. I do indeed have your article and will pay more attention to it. I especially appreciate your comments about how to troubleshoot leakage.

I know it sounds like a bad idea, but I put my palm over the bottom of maple piece while it showed 19 inHg (I misread the gauge previously). This pulled my hand onto the piece and caused the piece to seal to the face plate with 26 inHg. It seems clear to me that the majority of the leakage is through the pores in the maple. I will definitely try the aluminum plate approach and make sure there isn't some other issue.

Twenty six inches of mercury is all the vacuum that you can expect to gt from most type of vacuum pumps and for woodturning purposes could be considered a "hard" vacuum. Nineteen inches of mercury is sufficient for almost anything that you might need to do although more is always nicer.

BAD PUN WARNING: It is interesting that only in vacuums and in UNIX would "LESS" be the same thing as "MORE".

Here is an example assuming that your system could achieve 19 inches of mercury vacuum with your maple bowl. I don't know the inside diameter of your plywood chuck, but for this example, let's say that it is 4 inches.

First of all, let's convert inches of mercury to pounds per square inch. Since 2.036 in-Hg = 1 lb/in², we get 19/2.036 = 9.33 lb/in².

Next, we calculate the inside cross section area of the face of the chuck using A = pi X (d/2)²
Plugging in the numbers gives, 3.14 X (4/2)² = 12.566 in²

Finally, to find the total axial force pressing on the bowl, we multiply the pressure by the area, 9.33 lb/in² X 12.566 in² = 117 lb
​

A force of 117 pounds is quite substantial. In fact, a thin vessel could easily crack with that much force being applied.

Now, just for grins, close your books and let's have a pop quiz. Calculate what the force would be if the inside diameter of the chuck were five inches while all other parameters are the same. (The correct answer is 183 pounds).
What? You can't see the answer? That's because I used invisible ink. OK, if you must cheat and look at my paper, click and drag across this paragraph and the answer will be revealed. Does it agree with your answer?

Extra credit questions: Do you think that the bowl is likely to fly off the lathe from insufficient vacuum? Do you think that the bowl might break?

 

[Joe Greiner]

I hope you realize your invisible ink might not work if the forum changes "skins" or allows user-selectable (as used in some other VBulletin forums). BTDT.

Also, it's XXX pounds, not PSI. (XXX = I won't spoil the fun.)

 

[egsiegel]

Both the Oneway and the JT Turning Tool rotary adapters are designed to be removed when not needed so that the knock out bar can be used to remove the MT drivers.

On most lathes the Oneway uses a threaded adapter for mounting. On the Jet 1642 the adapter has no threads and has an O ring to make the seal on the shaft. The first time I put it on it was TIGHT...really tight. I figured it was on forever. I had to pull it off one time and it came off fairly easily. Putting in back on was not as difficult as the first time (maybe I just knew what I was doing). My concern is that removing it and remounting it will ruind the seal and I'll have leaks. Am I just being overly concerned?

Ed

 

[Grant Wilkinson]

I accept that it's important to know how much pressure we are applying to vessels.

However, no matter what my gauge reads, and how many pounds that means are being applied to my bowl, I've found that:

small diameter vacuum chuck + large diameter bowl + too many rpm + too heavy cut = orbiting bowl.

Until I saw John's vacuum donut chuck idea, I had not figured out how to use a vacuum chuck confidently on larger pieces with small bottoms. I have been using vacuum chucks that are small enough to mate with the inside bottom of the bowl. Many times, that means that a bowl of 14" or more is being held by a chuck of 3", since that is the biggest chuck that will snug up to the bottom of the bowl. Maybe I'm just too aggressive, but I find that it does not take much to dislodge a bowl of that size being held by a chuck that small. Now, with John's pressure plate concept, the pressure will be applied against a much larger surface.

 

[davidwalser]

...

However, no matter what my gauge reads, and how many pounds that means are being applied to my bowl, I've found that:

small diameter vacuum chuck + large diameter bowl + too many rpm + too heavy cut = orbiting bowl.

... I have been using vacuum chucks that are small enough to mate with the inside bottom of the bowl. Many times, that means that a bowl of 14" or more is being held by a chuck of 3", since that is the biggest chuck that will snug up to the bottom of the bowl. Maybe I'm just too aggressive, but I find that it does not take much to dislodge a bowl of that size being held by a chuck that small. ...

Grant,

A 3" chuck is too small to securely hold a 14" bowl. The question I have is why are you insisting on using such a small chuck? A large bowl can be supported along the rim (using a platter shaped chuck) or along the inside sides of the bowl -- the chuck doesn't need to reach to the inside bottom of the bowl. As a general rule, I wouldn't use less than a 4" chuck for a bowl.

 

[Bill Boehme]

I hope you realize your invisible ink might not work if the forum changes "skins" or allows user-selectable (as used in some other VBulletin forums). BTDT.

Also, it's XXX pounds, not PSI. (XXX = I won't spoil the fun.)

Thanks, Joe. It was either way past my bedtime or much too early to get up and I completely missed that one. I don't suppose that you would believe that I purposely put that there to see who was alert? You get extra credit. I also made a spelling error, but if I go back to edit the post, it will create more problems than it is worth because I entered the numerical code for some ASCII characters that can't be found on the keyboard and editing will result in the ASCII code showing up rather than the intended character (for example, superscript ² would become &#178).

 

[Joe Greiner]

Test of invisible ink in a quote with different background color.

Now, just for grins, close your books and let's have a pop quiz. Calculate what the force would be if the inside diameter of the chuck were five inches while all other parameters are the same. (The correct answer is 183 PSI)
What? You can't see the answer? That's because I used invisible ink. OK, if you must cheat and look at my paper, click and drag across this paragraph and the answer will be revealed. Does it agree with your answer?

[Judge for yourself]

 

[Grant Wilkinson]

David: On the couple that I tried the small chuck on, the bottom was the only place solid enough to attempt to pull a vacuum. Between voids and punky wood, trying to get a vacuum chuck to seal somewhere along the insides of the bowls was not on. Since the rims were natural, going the flat plate route would not have worked, either. The best solution for these so far seems to be a simple jam chuck between the inner and outer surfaces of the bottom. For the less fragile pieces, the pressure plate approach that John has shown here may work.

 

[John Giem]

Grant,
From your description, I believe that the Compliant Vacuum Chuck would work for your application. The major problem I see is the size of the vacuum chuck that would be needed. Maybe you can use the concept and come up with a solution for large bowls that don't need a vacuum chuck larger than the turning you are working on. I am very much interested in what you come up with. Let me know if you need to bounce some ideas off of me.
John

 

[John Giem]

I am afraid that I don't see the need for the precision pressure control that comes from using a pressure control valve. In my limited experience, the only modifications that I would need to apply to otherwise using as much vacuum as your system can produce would be not so much vacuum that the vessel becomes distorted, implodes, or suffers a "chuck bruise" (a.k.a., ring around the tub). Avoiding those problems doesn't appear to necessitate precise regulation of vacuum.

.

Bill,I agree with you. I don't see a vacuum regulator as being needed for most cases. I view a vacuum regulator as another tool available, if needed or desired. To be honest, after I got it working I was wondering if it was a solution to a problem or a solution looking for a problem. With that said, why did I go to the trouble to make a vacuum regulator? I received an email from a Turner looking for a vacuum regulator. I don't fully understand his situation but the best I recall is that he was using vacuum to hold some rather large and fragile items. He was looking for a more reliable method for protecting his work from vacuum level changes. In summary, a low cost shop made vacuum regulator does exist and is available when and if your application needs it.
(Beside the Engineer in me could not resist the challenge.)
John Giem

 

[John Giem]

I would agree if I didn't have a pump that that does overpower leaks. If you are thinking about the small pumps used in laboratories, then you are right. But using an industrial rotary vane pump such as I mentioned the above. I need to "bleed" or create a leak in my system when turning dense wood, other wise I would crack a 1/8" thick wall of wood.

.

Ron,
I don't see how your statement shows that you can over power leaks. In effect you are telling us that you have a good working system but it is unknown whether or not your system has a leak to overcome. I'm interested in the free flow capacity of your pump, can you enlighten me?
The performance of a vacuum chucking system is dependent on everything in the system, not just the pump. In the new thread I am going to launch, I will try to help the readers understand the effects of the system hardware. Yes, we all seem to have a 'gut feel' for how these things work but no numbers to evaluate to determine if the extra effort is worth it. I am planning on providing methods and numbers to measure the effects of any changes we make, i.e. when we make changes we will be able to measure the effects of that change and not just 'it seems to be working better'.
John Giem

 

[John Giem]

Twenty six inches of mercury is all the vacuum that you can expect to gt from most type of vacuum pumps and for woodturning purposes could be considered a "hard" vacuum. Nineteen inches of mercury is sufficient for almost anything that you might need to do although more is always nicer.

...

Finally, to find the total axial force pressing on the bowl, we multiply the pressure by the area, 9.33 lb/in² X 12.566 in² = 117 lb
[/INDENT]A force of 117 pounds is quite substantial. In fact, a thin vessel could easily crack with that much force being applied.


Extra credit questions: Do you think that the bowl is likely to fly off the lathe from insufficient vacuum? Do you think that the bowl might break?

Bill, you forgot that some of us do not live at sea level. Here in Colorado, I live at an altitude of 5000 ft. Allowing for a loss of aproximately 1 in Hg per 1000 ft, the maxumum vacuum I could get here is about 26 - 5 = 21 in Hg. Even that depends upon the pump, different types of pumps and their wear can further degrade the maximum achcievable. To add a bit more confusion, most of the vacuum gauges woodturners use are not calibrated to all read the same. Last spring, I bought five inexpensive 2 1/2 in vacuum gauges at one time. Upon delivery, only two of them read zero, I adjusted them accordingly. Then when they were all connected in parallel to a vacuum source, the readings, at near maximum atainable of 21 in Hg, varied between the gauges about 1 1/2 in both high and low. I view the typical 2 1/2 " gauge as an indicator that can show me that something has or has not changed. I do not use these 2 1/2 in. gauges in my vacuum system testing measurements.

Above, you estimated an axial force of 117 lb. That is the force parallel to the axis of rotation and the force that could crush the bowl. Most Turners forget that when a bowl is disloged, it is the force perpendicular to the axis of rotation that does the dirty deed. This ability to resist the sideways force depends on the axial force and the coefficient of friction between the bowl and the sealing gasket. The coeffiecient of friction varies between .4 and .6 for most materials with some designed that will go down close to 0 and upwards approaching 1. If we assume the coefficient of friction = .5 then the available force to resist perpendicular forces is 117 * 0.5 = 58.5 lb. We could get into torque calculations but not now, just realize that the force resisting the cutting action of your gouge is about 58 pounds. If your gouge has a handle 12 in long and the tool rest is 1 inch from the tip of the gouge, then the force the Turner must supply at the end of the handle is between 4 and 5 pounds when the bowl is disloged from the chuck. So, when using a vacuum chuck, use a light touch and support the work with the tailstock when possible.

John Giem

 

[John Giem]

A word about Safety.

Always, always, always wear a face shield whenever you are turning on the lathe.
When using the Comliant Vacuum Mandrel, one slip of my gouge cut a nice ring in the plastic sheet creating a beautiful display of flying rice. All bets are off as to what happens to work the piece. The risk can be reduced by taping a protective ring aroung your work and over the exposed plastic sheeting (cardboard, thin plywood, thick stiff plastic sheeting, etc.)
It is a good idea to also use a protective ring on the Compliant Vacuum Chuck to protect the plastic sheeting. So far, I have not lost a turning off of the Compliant Vacuum Chuck. It seems that the way the plastic sheeting is wrapped around and secured, it provides extra holding power when the vacuum is lost. Yes, I have inadvertenly cut the plastic with my gouge and lost the vacuum but nothing interesting happened, yet.
So, always wear a face shield, we never know when we will get to experience an exciting event. A face shield will hopefully allow you to learn from the event and not make a trip to the ER.

John Giem

 

[Bill Boehme]

Test of invisible ink in a quote with different background color.

I see that the invisible ink effect is beginning to fade. I actually did momentarily consider inserting C code to reference the current background color.

... Last spring, I bought five inexpensive 2 1/2 in vacuum gauges at one time. Upon delivery, only two of them read zero, I adjusted them accordingly. Then when they were all connected in parallel to a vacuum source, the readings, at near maximum atainable of 21 in Hg, varied between the gauges about 1 1/2 in both high and low.

I am surprised that they were that close. The typical vacuum gauge that most of us use costs $10 - $15 and are not exactly laboratory instruments. I have found gauges with an accuracy of ±0.5% including NIST calibration certificate for about $120 and calibrated gauges with ±0.25% accuracy from around $300 and up.