Update on Vacuum Chucking Systems

[John Giem]

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. Depending upon the deisgn and implentation of the hardware between the pump and the vacuum chuck, you cannot achieve more than about 2 SCFM at the chuck.
Another turner asked about a vacuum regulator since he couldn't find one. Neither could I, so I figured out how to build one.
In another case, I had interesting shapes on the outside of a burl. I wanted to turn a bowl from it without damaging the exterior. I figured out how to use a vacuum system to mount any shaped blank, with or without perforations (holes) and turn it. My method allows me to shape the blank without damage to any surface other than that whicn is needed to accomplish the configuration desired, i.e. I cut no tenon, do not use any glue, screws or nails. For a bowl, only the top rim and interior are cut and shaped and it is not really necessary to touch the top rim. All of the other surfaces are untouched.
Vacuum pumps have two major specifications, maximum vacuum and free air flow rate. Measuring the maximum vacuum is easy, just hook up a vacuum gauge and block off the input. Measuring the flow rate without spending a lot of money is not so easy. I figured out how to measure the flow rates of a vacuum pump cheaply using common items found in most shops or at most at the local hardware store.
I have borrowed a lot of vacuum pumps from friends and characterized them measuring the flow rates at diffeent vacuum levels. I have found some strange things. Not all pumps are created equal. I have test results indicating that a significant number of pumps do not come close to meeting their flow rate specifications in free air.
I've thrown out a lot of ideas here without much detail. Is anyone interested in discussing them? If so, where do you want me to start? Which are of most interest?

John Giem

 

[Bill Boehme]

.... I have borrowed a lot of vacuum pumps from friends and characterized them measuring the flow rates at diffeent vacuum levels. I have found some strange things. Not all pumps are created equal. I have test results indicating that a significant number of pumps do not come close to meeting their flow rate specifications in free air...

Of course, the specs would be for a brand new vacuum pump since there is no reasonable way to assure specific performance as the pump wears. To make matters worse, I have seen a number of "interesting" hook ups by woodturners and these installations sometimes use unsuitable filters which are not always installed in the optimal location. The result can be a lot of wood dust being ingested which accelerates wear on a pump.

It is not unusual for a huge amount of air to be sucked through a vessel that is vacuum chucked and fine sanding dust will go right through the pores in many species of wood. There is a lot of silica in wood dust and adequate filtration is very important.

I would guess that rotary vane pump max vacuum performance would be likely to suffer from wear faster than that of a diaphragm or piston pump, but the advantages of a rotary vane vacuum pump are that they seem to have higher flow capacity than the other types. Additionally, vane replacement on a rotary vane pump is a simple job.

A needle valve makes a perfectly adequate regulator since the flow is through a small orifice. The important thing is to put the vacuum gauge at the right place. I have seen some installations where the bleed valve is somewhere downstream of both the gauge and the air filter.

One area where leakage is a problem is at the chuck threads. I devised a solution for problem by using a threaded lamp rod that goes through a friction fit rubber seal in the chuck and then a nut on the lamp rod to compress the seal. I will try to get a picture of the set up. I make my chucks using a small aluminum faceplate, MDF, and sewer pipe couplings.

I am still interested in finding the perfect gasket material for the rim of the chuck that does not "squirm" too much as the vacuum seats the turning, yet makes a good seal. I am currently using a thin closed cell material, but do not remember what the source of this stuff is.

 

[John Giem]

Bill and All,
Personally I don't like suprises. I want to make it clear up front that I have several reasons for starting this thread.Yes, I'm interested in sharing what I have learned but I an also gathering questions, information and ideas toward writing a book on vacuum chucking systems. I am an engineer with many years of industrial experience. I am applying that experience to my woodturning, in particular vacuum chucking. In doing so, I think that I have pushed my capability beyound what can be found in the literature and on the web. I have found that in reading this forum and others, I am leariing a lot of usefull things that are otherwise 'hidden'.

Bill, the comments from you (and others) are helping me to understand the issues as seen from outside my local circle of friends. Your questions are helping me to refine my thinking. The points you made above are good ones and I'll try to respond to each of them. In order to keep these responses reasonable in length, I will break them up into seperate responses for each of your points.

Being an engineer, I also like to put numbers on things when possible rather than just generalities. I have developed simple and inexpensive methods to measure those things that I am discussing. In the following responses, when possible, I will quote measurement numbers to back up my statements.

Later,
John Giem

 

[GLENN ROBERTS]

John, I have just completed the building of a vacuum pump unit for various uses around the workshop ( eg: chucking, flat panel work and veneering etc) what I have noticed that most of the information shows a filter placed in locations where any 'bleed' air would bypass the filter and be sucked into the pump or tank. And/or potentially be trapped in the gauge etc.
I took the trouble of sourcing numerous parts, including filters from a USA veneer supplier to hopefully improve the design of my system to alleviate the potential dust problem. These parts are difficult to source in Australia. I wonder if turners have a problem sourcing suitable parts and/or they follow the existing information available without thinking about how the dust laden air could get in. So a book or article etc would be a great help.
Glenn

 

[John Giem]

Glenn,
The primary reason for having a filter on a vacuum chucking system is to protect the valves and seals in the vacuum pump. The amount of air that flows into and out of the vacuum gauge is so small that for practicle purposes it can be ignored. Therefore, ALL of the air that goes into the pump should go through the filter. I have not yet looked into the available filters to be used for these vacuum systems. We know that we want to trap fine particles but how fine is good enough? And, what is a good source for them? In genral we also want a large surface area to minimize vacuum losses, also the input and exit connections should not neck down and provide restrictions.
Does anyone out there have any words of wisdom here? Filter recommendations, sources?

I purchased the two filters I am using from www.jtturningtools.com.

Regarding a book, I'm working with a publisher toward that goal but no contract yet.

John Giem

 

[John Giem]

Vacuum chuck gasket material

Bill,
I plan on addressing each of the points you brought up. Just remember I don't have all the answers but I do know what works for me and what I have investigated.

For sealing the rim around the vacuum chuck, I have had good success with Funky Foam obtained in craft and hobby stores. It comes in Sticky Back Foam Sheets, 2mm thick, 9" x 12". It is a closed cell foam and does not squirm for me. I use white so that it will not mar my turnings.
Most people place their chuck on the sheet and cut a circle a bit larger than the diameter of the chuck, peal of the protective sheet and stick it onto the chuck smoothing it down. Afterwards, they cut a hole in the center and start using the chuck.
This method is fine if the diameter of the chuck is smaller than the size of the available foam. When I made a large diameter chuck for a special project, I had to find a different method. I cut the foam sheet into 1 1/2" strips. With the chuck on the lathe, I drew a guide line about 1/2" below the rim. I carefully wrapped the foam around the outside of the chuck following the guideline letting the opposite edge stick out. I found that at the joints between the strips, I would get adequate sealing by overlapping the joints by about 1/32". After going around the complete perimeter, I carefully smoothed over the foam wrapping it into the inside of the chuck while carefully maintaining the overlap at the joints.
This is the primary method I use for putting sealing foam on all of my chucks no matter what the size. It works and minimizes waste.
The foam has a memory and tends to lift itself off of the interior and exterior sides of the chuck. Applying a heavy rubber band around the outside keeps it in place. On the inside, I use blue painter's tape to hold the foam down onto the surface.
When the gasket needs to be replaced due to wear or damage, It can easaily be removed using a heat gun.

What experiences have others had in this area?

I hope this helps,
John Giem

 

[Bill Boehme]

Funky Foam is what I am currently using, but I made the mistake of getting the kind that does not have adhesive on the back. I used spray adhesive, but it is a bit messy. I think the product is OK, but it seems a bit slick and I have had some turnings slip when using it. I bought some shower pan liner. It is about the same thickness as the Funky Foam. It can be obtained in either PVC or CPE (chlorinated polyethylene). The CPE tends to be a bit more compliant than PVC.

 

[Bob Chapman]

When i built my vacuum system I spent a long time experimenting with different materials to seal the rim. The best alternative I found was thick walled rubber tubing, about 5/8 in external diameter. I bought this from a science teaching supply company, where it was sold as 'pressure tubing'.

After measuring the diameter of the chuck I cut the required length and glued the two ends together with CA adhesive which bonds rubber very well. Placing the 'doughnut' flat on the bench I then used a craft knife to cut down into the hollow running through the tubing. This could then be pushed over the front of the chuck and fixed in place with more CA glue. I used plastic sewage pipe (4 in diameter) for the chuck so there was no problem doing this. It's worked perfectly for about five years now, and turns very true.

Bob

 

[davidwalser]

Answer: All of the above

John,

For some reason, I couldn't respond to your poll question. If I could, I would have answered "all of the above". In particular, 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.

I've lots of questions and no definitive answers. Unlike most other chucking methods, there aren't many well-understood rules-of-thumb for vacuum chucking. Each turner seems to be left to learn from his or her own experience what works and what doesn't. Such trial and error learning tends to be "eventful".

Good luck with your book!

 

[Grant Wilkinson]

John

I've been using my vacuum chuck system solely to hold the bowl to remove the tenon and finish the bottom. I would really like to hear your advice on using vacuum chucks for odd shaped pieces and smaller pieces. I don't seem to be able to draw enough vacuum to hold small pieces very well.

As for sealing around the bell, I tried the foam pieces and had some luck with them. However, I found that they did not hold up all that well. Now, I am using surgical tubing. I use it like Bob Chapman uses his tubing. I cut a piece to length, glue the two ends together to form a donut, slit the donut and slide it over the end of the bell. A couple of dabs of hot glue hold it place.

 

[Bill Boehme]

John

I've been using my vacuum chuck system solely to hold the bowl to remove the tenon and finish the bottom. I would really like to hear your advice on using vacuum chucks for odd shaped pieces and smaller pieces. I don't seem to be able to draw enough vacuum to hold small pieces very well.

As for sealing around the bell, I tried the foam pieces and had some luck with them. However, I found that they did not hold up all that well. Now, I am using surgical tubing. I use it like Bob Chapman uses his tubing. I cut a piece to length, glue the two ends together to form a donut, slit the donut and slide it over the end of the bell. A couple of dabs of hot glue hold it place.

I like the surgical tubing idea.

I have used various types of rubber weatherstripping (not the open cell plastic foam stuff) and also some garage door weather stripping. Most of it is a bit too spongy for vacuum chucking, but I did find one that I liked -- unfortunately I can't seem to find it now at the hardware store. The biggest problem with black rubber seals is that they often leave a black ring on the wood.

NOTE to David Walser -- were you looking at the voting screen or the results screen that shows the bar graphs? If you are viewing the voting results, you need to go back to the previous view. If you inadvertently click on the Vote button before making any selections, that is counted as voting and you will no longer be able to access the voting screen.

 

[John Giem]

One area where leakage is a problem is at the chuck threads. I devised a solution for problem by using a threaded lamp rod that goes through a friction fit rubber seal in the chuck and then a nut on the lamp rod to compress the seal. I will try to get a picture of the set up. I make my chucks using a small aluminum faceplate, MDF, and sewer pipe couplings..

For every problem there is more than one solution, some are just harder to find and each person should use the solution that they are comfortable with. When I encountered spindle thread leakage, I fell back on my experience working with pipe threads. I found that by applying multiple layers of teflon tape on the threads solved my leakage problem. I have multiple vacuum chucks of variying sizes and have found that not all threads are created equal. When screwing a vacuum chuck onto the spindle with teflon tape, some screw on loosely and others are rather tight. Sometimes I need to go back and adjust the number of layers of tape.

John Giem

 

[Malcolm Zander]

Sealing vacuuum chuck ends

I have made a number of my own chucks, and I seal them with a neoprene gasket which Oneway sells for their chucks. This neoprene comes with a sticky back, revealed by peeling off a protective wax paper strip. It lasts very well indeed. It is thin (about 1/16") so seals very well with no give. The only drawback is that it does not come in a sheet - I use the one designed for the largest (6") Oneway chuck - it has the form of a large fat O and is about 7" diameter and the useful part is 1.75" wide. For any chuck whose business end is less that 1.75" I just trace the outline on the gasket and cut the piece out, and then separately cut the centre hole. For larger chucks I cut separate pieces of the gasket and butt them together.

 

[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.

I've lots of questions and no definitive answers. Unlike most other chucking methods, there aren't many well-understood rules-of-thumb for vacuum chucking. Each turner seems to be left to learn from his or her own experience what works and what doesn't. Such trial and error learning tends to be "eventful".

Good luck with your book!

David, I picked out your post since you asked for solutions for a very broad range of problems. To further tease you, I have solutions for most of the issues you asked about, but to give adequate/useable rfesponses will take multiple posts.

Note: I have not been able to find anything in the literature or on the web that does anything like the following Compliant Vacuum Mandrel and Chuck.

I have aluded to a Compliant Vacuum Chuck. Along with this is the Compliant Vacuum Mandrel. These two tools will solve most of the difficult tasks you listed. Conventionally, the turning must be shaped to fit the chuck or mandrel being used. A mandrel, to me, is something that provides a surface that the tailstock can push the turning against and hold it for shaping.The problem is that some surfaces of your turning could be damaged by the ridgid surface of the mandrel. For the Compliant Vacuum Chuck and Mandrel, the term 'compliant' reflects that the mandrel will deform to fit your project and will hold it, with low risk of damage, while you turn it into the desired shape. The Compliant Vacuum Chuck and the Compliant Vacuum Mandrel use similiar techniques. I have written an article for the American Woodturner on how to build and use these devices. I've been told that it will be published early 2012. For now, I will explain the priciple behind the mandrel and expand on the chuck later. Both of these devices will expand your tool set so that you can do more but will not replace what you are doing now.
Most of us have seen vacuum packed coffee, or other foods, in plastic bags. Before opening, the coffee seems hard and fixed in it's shape. Once the vacuum is realsed, the coffee can be easily moved around. When under a vacuum, the coffee is tightly packed together and interlocked by the outside air pressure against the plastic bag. This is the princicple utilized by the Compliant Vacuum Mandrel to conform to and support your turning. It took me over a year to develop the vacuum mandrel and chuck. There a too many details for now but here is an overview of building the Compliant Vacuum Mandrel. Place your vacuum chuck on your workbench with the bell upwards. Build and place a filter over the opening going to the spindle at the bottom of the chuck. Fill the chuck with dry rice, other materials may work but they must be 'clean' and non-packing. (Coffee did not work.) Loosely place a sheet of plastic over the top of the chuck enclosing the rice. Bring the plastic down around the outside of the chuck, secure it to the chuck and provide a good vacuum seal. Mount the mandrel (the chuck has been converted into a mandrel) onto the spindle. Provide support to prevent the plastic coming off. Notice that at this point, the rice and plastic sheet can be easily moved around. Upon applying a vacuum, the plastic sheet pushes up against the rice and everything gets ridgid and can not be moved or molded.
Release the vacuum and place the project against the plastic and hold it in place with the live center in the tailstock. You can move the turning around, position and orient it any way you please. By rotating the chuck, applying a light vacuum and molding the rice with your fingers, you can achieve a good solid positioning of your turning. When you have it where you want, apply full vacuum. Recheck and start turning.
Challenges: getting a good seal of the plastic sheet around the chuck, learning how to position the work on/in the mandrel and preventing the work from puncturing the plastic sheet. It took a lot of research, work and time but I have solved thes problems.
To Be Continued...

John Giem

 

[Doug Wolf]

Bill,

For sealing the rim around the vacuum chuck, I have had good success with Funky Foam obtained in craft and hobby stores. It comes in Sticky Back Foam Sheets, 2mm thick, 9" x 12".
John Giem

I also use the Funky Foam, but the larger size sheets (12" x 18") without the Sticky Back. I coat each surface with rubber cement, let dry completely, then press together. The rim of my PVC chucks are only about 1/4" wide and I've never had it come loose. It comes in two thicknesses and I use the 2mm not the 5mm which I thought might give me to much movement. I use a Fram fuel filter for my Gast pump.
The foam can also be found on Hobby Lobby on-line and is called "EVA Foam Sheets", sku# 570192, Price: $5.99. There are 12 foam sheets; two of each color in a package. Color Primary Colors Size 12" x 18" - 12 Sheets

 

[davidwalser]

Very cool. I (not so) patiently await the next installment.

 

[Grant Wilkinson]

John: If I've understood your description, the vacuum is not acting on the piece being turned. It is acting solely to create a surface against which the piece can be held by the tailstock.

Is this right?

 

[Dave Peebles]

Good evening,

As for material for the vacuum chucks, I have recently found these from rubberchucky.com

http://www.rubberchucky.com/index.php?option=com_content&view=article&id=80&Itemid=112

I have used just about everything on the Oneway drum chucks, from Oneway's, to the funny foam sheets with some sucess.

These look good to me, and I will soon give them a try.

Just another option,

Dave

 

[Bill Boehme]

... There a too many details for now but here is an overview of building the Compliant Vacuum Mandrel. Place your vacuum chuck on your workbench with the bell upwards. Build and place a filter over the opening going to the spindle at the bottom of the chuck. Fill the chuck with dry rice, other materials may work but they must be 'clean' and non-packing. (Coffee did not work.) Loosely place a sheet of plastic over the top of the chuck enclosing the rice. Bring the plastic down around the outside of the chuck, secure it to the chuck and provide a good vacuum seal. Mount the mandrel (the chuck has been converted into a mandrel) onto the spindle. Provide support to prevent the plastic coming off. Notice that at this point, the rice and plastic sheet can be easily moved around. Upon applying a vacuum, the plastic sheet pushes up against the rice and everything gets ridgid and can not be moved or molded.

Very clever way to create an instant jam chuck of any shape and size.

 

[John Giem]

John: If I've understood your description, the vacuum is not acting on the piece being turned. It is acting solely to create a surface against which the piece can be held by the tailstock.

Is this right?

That is correct. Later, when I get into the Compliant Vacuum Chuck, I will start from here and tell you how you can mount unuasual shaped items with or without perforations at just about any orentation. Your primary limitation will be your iminagation.
As stated earlier, the Compliant Vacuum Chuck will not replace a conventional vacuum chuck but will complement it. I will make a significant contribution to your ability to mount items on the lathe.
John

 

[John Giem]

A needle valve makes a perfectly adequate regulator since the flow is through a small orifice. The important thing is to put the vacuum gauge at the right place. I have seen some installations where the bleed valve is somewhere downstream of both the gauge and the air filter.

I really like the discusions we have going here. The quote from Bill (Bill, I'm not picking on you, you just identified an important topic) above is an example of where a true statement is applied in a way for which it does not apply. 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. In our case, at low vacuum levels we are most likely not in the constant flow performance region. Also, we want to regulate or control the vacuum level at the chuck to a constant value. The actual vacuum level at the chuck depends upon the pump design, all of the connecting hardware and how much air we provide to the starving pump. If the amount of air flowing into the pump changes, then the vacuum level also changes. As far as the pump cares, the air coming from the bleed valve is just another source of leakage. IF you want to regulate or control the vacuum level then you must adjust the amount of air available to the pump. the constant flow from a fixed valve can not compensate for changing leakages elsewhere in the system, such as your turning.
Anything that is going to control the vacuum level must be able to control or adjust the amount of air that is available to the vacuum pump. Presently, you adjust the available air for the pump by turning the control valve.
Remember we are talking about vacuum chucking SYSTEMS. If we want to get the most out of our systems and use them in new ways then we need to understand the pieces of the system and how they interact.
I will be revisiting valves, pumps, orifices and vacuum regulation later.
I hope this discussion clears up some misconceptions that are floating around out there.
One of you indicated that you use your vacuum system primarily for mounting and turning off the bases of your bowls. I feel that these systems are too expensive to be only used for that. Personally, I have set myself a goal to find as many new ways to use my vacuum system with my lathe as possible. As we progress, I plan on sharing some of these new applications with you.
There are many misconceptions about vacuum chucking systems. When I find them, I want to correct them without offending anyone. Hopefully, some more will crop up and we can discuss them also.

Have a Good Day,
John Giem

 

[John Giem]

John

I've been using my vacuum chuck system solely to hold the bowl to remove the tenon and finish the bottom. I would really like to hear your advice on using vacuum chucks for odd shaped pieces and smaller pieces. I don't seem to be able to draw enough vacuum to hold small pieces very well.

Grant, the force holding your piece on the chuck is a function of the vacuum level and the surface area upon which the vacuum is applied. Force = area * Pressure (our vacuum).
We have strict limitations on how much vacuum we can generate and even that changes with leakage, the weather and altitude. To increase the force the only thing left is to increase the area upon which the vacuum is applied.
I've described the Compliant Vacuum Mandrel. I'll build on that and describe how the Compliant Vacuum Chuck functions. With some ingenuity on your part, I think that it will help you solve your problem. We will eliminate most of those troblesome restrictions we are fighting with now. Recently, I discovered an enhancement to the Compliant Vacuum Chuck that simplifies it, reduces the parts count and makes it more reliable. I will be describing the principles of the chuck in the near future but some of the refinements will need to come later.

Have a Good Day,
John Giem

 

[Grant Wilkinson]

Thanks for your replies to my direct questions/statements, John. As you say, pumps and all the peripherals are pricey enough that it is a shame to use a vacuum chuck only as I now do - to remove the tenon and finish the bottom. If I can learn how to fabricate one that I can be confident will hold for other turning purposes, I'll be one of the first to jump on it.

 

[John Giem]

Thanks for your replies to my direct questions/statements, John. As you say, pumps and all the peripherals are pricey enough that it is a shame to use a vacuum chuck only as I now do - to remove the tenon and finish the bottom. If I can learn how to fabricate one that I can be confident will hold for other turning purposes, I'll be one of the first to jump on it.

Grant, I percieve that there is a wide range of investments in the vacuum shstems out there. Would you, and others, mind sharing the approximate cost and time required to set up your first vacuum chucking system?

Thanks,
John

 

[John Giem]

Compliant Vacuum Chuck

OK let's put one together. I'm going to describe a simple wooden fixture to hold a sphere and then transform the fixture into a Compliant Vacuum Chuck. Set your Compliant Vacuum Mandrel to one side for now. We'l be using it later. OK, you have a three inch sphere that you want to clamp down to work on. Get two conveniently sized plywood sheets and cut them into disks, say 6" or 8" in diameter. In the center of both disks, cut a 2" diameter hole. Around the perimeter, drill 3 or 4 holes equally spaced for bolts. Place the 3" sphere in the center hole of one of the disks and then place the other disk on top. Now place screws through the perimeter holes and tighten. Sphere is now firmly held between the two disks so that you can work on it. Note that we know that the sphere is being clamped between the disks but there is no convenient way to measure or caluclate the magnitude of the force, repeatablity is difficult and we could crush a fragile object. But this is not on the lathe so we need to transform the fixture into something that can be mounted. Label the top disk "force disk". Note that you can hold most anything in this fixture by cutting the appropriate size and shaped hole in the force disk. Remove the bottom disk and place the shpere and force disk on your Compliant Vacuum Mandrel. You still have the sphere captured so that you can work with it. The problem is that there is no force on the force disk to hold the sphere stable. Set the force disk to one side. On the Compliant Vacuum Mandrel, detach the plastic sheet from the sides of the vacuum chuck. Keeping the sphere in place, wrap the plastic sheet up over the sphere bunched up pointing upward. A rubber band helps here. Place some extra rice around the sphere building it up as much as possible. Now place the force ring around the bunched up sheet and down onto the sphere. Spread out the plastic sheet, bring it down over the sides of the vacuum chuck, attach and seal it as before. Mount the assembly onto the lathe spindle and apply a vacuum. You can reposition the sphere using the tailstock and the same methods we used with the Compliant Vacuum Mandrel. You have just built a Compliant Vacuum Chuck and firmly held a shpere with it.

Let's look at some of the features and challenges of the compliant chuck. 1. the plastic sheet is under the sphere against the rice, wraps around the sphere up through and over the force ring and back down to the side of the vacuum chuck. 2. no vacuum will be applied directly to the sphere so any leakage through the wood or holes are don't cares. 3. the rice provides conformal support for the sphere, helps keep the plastic sheet from imploding, and keeps the plastic sheeting out from under the force ring.
When you applied the vacuum, you probably noticed that everything sort of shrunk inward. The plastic sheet on top of the force ring has the atmosphere on one side and a vacuum on the other so it trys to move toward the spindle. But it can't because the force ring is in the way. All of the force the plastic is applying to the force ring is transfered to the sphere holing it in place. It is important to have enough rice under the force ring to keep the plastic from imploding but not so much as to keep the force ring from moving inward. You have complete freedom to replace the sphere with anything else you wish to hold, just cut the center hole in the force ring the appropriate size and shape. Just remember that some very large forces can be generated and applied to your work being held by the force ring. How much force? Remember that force = area * pressure. Example: the force ring is 6" in diameter with a center hole of 2". This calculates out to an area of about 25 square inches. If the applied vacuum is 20 in Hg then the pressure differential applied to the disk is about 10 psi. Force = 25 sq in * 10 psi = 250 pounds.
When you look at this you realize that you can control the holding force by adjusting the area of the force ring and the vacuum level. This may help you to understand why I am interested in vacuum regulators. As long as the item to be mounted has something that the force ring can push against, then you should be able to mount and hold it. There are no limitations other than your imagination. You can mount and turn, reorient, remount and return to your hearts content.
One of the limitations of what is presented here is that it is difficult repeatably remount the project in exactly the same position each time, like if you are turning a chinese ball. Don't worry I have a solution for that also.
Comments or questions, let me know.
Happy Turning
John Giem

 

[Grant Wilkinson]

John: Well, someone must go first. I bought a very used Gast on Ebay for about $125 as I recall. I started out from there with one of the many vacuum adaptors using lamp rod. Mine came from Woodcraft and was about $60. I made my chucks from scrap. My vacuum gauge and assorted pipes, tubing and valves likely added up to $30 or so. I didn't like the lamp rod thing for long, so I went to JTTools and got a custom handwheel and vacuum adaptor for my Vega lathe. They ran me about $200, and one of John's chuck adaptors was $70. Again, I made my vacuum chucks from pvc pipe and surgical tubing that I had lying around.

So, my total may be less than others and more than some. So far, I have somewhere around $500 in this. Not a princely sum, I suppose, but it's a lot for me when all I do with it is turn off tenons.

 

[Grant Wilkinson]

John: I seem to be the only village idiot here, always asking questions or making comments.

I have used donut chucks on bowls since my first course with Bill Grumbine, so the concept of your force ring is familiar. It would seem that a large issue to overcome would be leakage around the plastic sheet where is meets back at the vacuum chuck. You have all this plastic coming back from around the force ring. It is being scrunched up around a smaller, tubular vacuum chuck. There are lots of pleats and folds. Do you simply use an elastic band or three to seal it, or are you keeping us in suspense awaiting another part of the puzzle?

 

[John Giem]

Grant,
My original method for sealing the plastic sheeting to the sides of the chuck worked but it seems awkard looking back on it. What I did was extend the the foam sealer down from the rim of the chuck for a total of about 3/4". I used a rubber band to help manage the sheeting while I clamped it in place. I used a strip of thick flexible plastic around the plastic sheeting directly over the sealing foam. The plastic strips were to prevent puncturing the plastic sheeting by the hose clamps I placed around it and then tightened the h____ out of it.
Problems encountered: awkard to assemble and frequent holes punched in the plastic sheet and hose clamp failures. I could not reuse the sheet but always had to replace it. It was a trade off between being thick enough to resist punctures and thin enough to handle. The good news is that it really worked. This is the design that I demonstrated at the RMWT Symposium in Loveland in Septermber this year. It is also what I wrote up for the American Woodturner article.
Receintly, I discovered a different plastic sheeting that looks promising. Preliminary tests look quite good but I need to do some more testing. Presently, it looks like I can signficantly reduce the number of components, easier and faster to assemble and fewer leaks. For example: in the past, leaks would always develop before I was finished which dropped the vacuum level at the manifold to around 15 or 16 in Hg. With the one trial that I did this last weekend with the new material, my initial vacuum was 19 in Hg and stayed there until I was finished. For my system that translates to a final leakage of about 1.3 SCFM for the old method and about 0.5 SCFM for the new method. I do not use my system below 5 in Hg at which my pump is pulling about 1.7 SCFM. This translates to a margin of 1.2 SCFM for the new method versus a margin of 0.4 SCFM for the old method.
After I do some more testing with the new material and assembly, my confidence should improve afterwhich I'll post the details.
The new material I 'found' has a lot of promise for improved performance in this application. Once I'm convinced that it works as good or better than before, I will post the results, the material used and how to use it.
As you may have picked up from this post, system performance is all about controlling leakage. The amount of leakage in turn determines the resulting vacuum levels. But we usually talk more about the vacuum levels because it is easier to measure. Later, when I discuss vacuum pumps and the interaction with the rest of the system, this should be easier to understand.

Happy Turning.
John Giem

 

[John Giem]

Bowl turned using Compliant Vacuum Chuck

Attached are some photos from different views of a bowl turned using a Compliant Vacuum Chuck. I used the original method of mounting and sealing the plastic sheeting. Again, on the surfaces away from the hollowing, they are completely unharmed, no cuts, screws, tenons, glue, etc. Only the hollowed out area and the rim were modified while turning the blank. Granted, some of the side surfaces where there were chainsaw cuts were sanded.

John Giem

 

[John Giem]

John: I seem to be the only village idiot here, always asking questions or making comments.
QUOTE]
Grant, the only way we learn, grow and share information is by asking questions and making comments. So, keep it up.
The only dumb question is the one that is not asked.
Besides, by your asking questions keeps me motivated and guides me toward what you want to know.

Thanks,
John Giem

 

[Joe Cornell]

Porosity, water content, pore blocking

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.

 

[Bill Boehme]

19 mm Hg is less than one inch of Mercury. Your system has a major problem somewhere. The wood can't be responsible for that much leakage. You should incrementally troubleshoot the system.

 

[John Giem]

I have used donut chucks on bowls since my first course with Bill Grumbine, so the concept of your force ring is familiar.[
/QUOTE]

Grant, you refer to 'donut chucks' for mounting your bowls. I am not familure with donut chucks, perhaps I know them by a different name. Can you describe them for me?
Thanks,
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, I like challenges. I am assuming that you can get a copy of my vacuum chucking article printed in the Feb 2011 issue of the American Woodturner.
My first reaction was that you misread the vacuum gauge. If the reading is correct then we need to divide and conquer. From your information it is not obvious where the problem is, is the excess leakage in your system or the wood? When I start to use my vacuum system each day, I do a health check on it. I keep an aluminum plate near my lathe. I place it on the vacuum chuck and turn the pump on. I look for two things; what is the vacuum level achcieved and how much leakage do I have. The achieved vacuum at the chuck should be the same as obseerved by placing a vacuum gauge directly at the input of the pump with the rest of the system blocked off. I'll discuss this achievable vacuum later. I get a rough estimate of the leakage by watching the rate of decrease in the vacuum level when the pump is turned off or isolated. I've done a lot of work on my system to reduce the leakage. If I wanted to wait long enough, the aluminum plate on the vacuum chuck will stay there in excess of five minutes. If the leakage is on the vacuum system side, then the article listed above will help you to isolate and fix the problem. Earlier in this thread, several materials for making a gasket around the rim are given. Instead of an aluminum plate, you can use nearly anything that is smooth and non-porus but be careful. A friend of mine used one of his wife's saucers from the kitchen. The saucer sealed off the chuck so well that the vacuum achievd caused the saucer to implode.
In reviewing your post, I see that the vacuum chuck is made from plywood. Not all plywoods are created equal. check the plywood to verify that there are no cracks or voids in it. Usually, wood vacuum chucks need to be well sealed. If in doubt about the body of the chuck leaking, wrap it with Saran Wrap while the vacuum is applied. This is also a good way to check out joints or parts that are suspected to be leaking.
Good luck and let me know if you need more help.
John

 

[Bill Boehme]

If I am not mistaken, a donut chuck is just two pieces of plywood, one of which has a hole in the center for the bottom of the bowl. Long bolts and wingnuts hold everything together. The "hole" idea gives me the willies, but some folks like them.

 

[Richard Jones]

John,

Great article in AW, really helped a lot.

After some isolation I've determined that my leakage is occurring where the adapter fits onto the spindle (Jet 1642). I've tried tape and pipe dope, to no avail. I am losing about 2 lbs at this point.

Any thoughts?

Thanks.

Rich

 

[george morris]

try some vasaline on the o rings if you are using a plug in adapter on the head stock. I also use blue painter tape to seal the bottom of the bowl while I use the vacuum chuck.

 

[John Giem]

John,

Great article in AW, really helped a lot.

After some isolation I've determined that my leakage is occurring where the adapter fits onto the spindle (Jet 1642). I've tried tape and pipe dope, to no avail. I am losing about 2 lbs at this point.

Any thoughts?

Thanks.

Rich

I have a couple of ideas that may help.
1. Some venders sell a plastic washer to place on the spindle. The idea is to seal the chuck to the shoulder of the spindle. It aslo helps to keep your scroll chuck from binding up making it hard to remove.
2. If this is a shop made vacuum chuck, many of them are, check the threads that screw onto the spindle. There should be a 1 1/4" (or what ever size spindle you have) mortice cut into the base before the threads start. If you look at the threaded part of the spindle, on most lathes the threads do not go all of the way to the registration shoulder so the mortice is needed to allow the proper seating and registration when a tool is screwed onto the spindle. The threads themselves should be in good shape without any chipouts. 3. I have made many vacuum chucks turned from wood and they work fairly well. It is important that the threads you tap are into side grain not end grain. Threads tapped into the endgrain of wood tend to chip out and fail early.
3. If the above are OK then teflon tape should work. With the different vacuum chucks I have, I've noticed that there is variation in size amoung them. I usually use three complete layers of tape the full length of the threads. Maybe you will need a fourth. When wraping the tape on the spindle, wrap it in a clockwise direction so that when you screw the chuck on, it will tighten the tape wrap and not just push it out of the way.
4. If you really get desperate then put a bead of silicone sealer (bathroom calk/sealer) around the base of the threads on the spindle. Use a paper towel to remove the squeeze out. The installation is messy but it works. Removal of the chuck is not a problem since the sealant is very weak under shear stresses and will 'fail' when you remove the chuck. This is the technique I use with all threaded plastic pipe joints. Usually, the plastic threads are so slick that any teflon tape wraped around them just pushes off when you try to make up the joint. After making up the joint, do not 'adjust it' after the silicone has setup or you may create leakage.
5. 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.
Rich, let me know what method you used to resolve the leakage.

Happy Turning
John Giem

 

[John Giem]

try some vasaline on the o rings if you are using a plug in adapter on the head stock. I also use blue painter tape to seal the bottom of the bowl while I use the vacuum chuck.

George, are you applying the tape on the inside bottom of the bowl or where the bowl rests against the vacuum chuck gasket?
I know of some turners that are successful in sealing off known small flaws by placing painters tape over the flaw on the inside of the bowl.

John

 

[John Giem]

If I am not mistaken, a donut chuck is just two pieces of plywood, one of which has a hole in the center for the bottom of the bowl. Long bolts and wingnuts hold everything together. The "hole" idea gives me the willies, but some folks like them.

OK, now I know what the correct name is. This is the starting point I used to describe/explain the Complient Vacuum Chuck.

John