Sonotube for vacuum chuck

[Josh Allen]

I've been vacuum turning my bottoms for some time. Using some home made by vacuum Chuck's with PVC. Worked very well. I have a large bowl that I need to make a new vacuum chuck for, looking at 10" or 12" diameter, with 12" length. Thing I'm wondering is, would sonotube be rigid enough for this? I looked at some 12" plastic pipe but it not cheap, and I can't seem to locate any offcuts from a plumber. Or is there something else out there? I am in Calgary Alberta. Home Depot has nothing above 6" diameter.
Any help appreciated!

 

[hockenbery]

I have made a few using sona tube. its been years since I’ve used them.
i glued the tube in channel cut in plywood then cut the top of the tube square with a skew point down..

its easy to make one from kiln dried wood too.

i’ve made them from 3” thick poplar 12” OD for platters so the rim has a wide curve.
one of the poplar ones is glued to plywood So it can be clamped to a bench to hold platters for carving. Has a hole drilled in the side and ann air fitting screwed in the hole.

also have several turned from a stack of 3 face glued construction 2x8s and 2x10s. These are are easy to return for other tasks
I use these to hold balls for hollowing so they get opened up inside to fit larger balls. I like the ball to almost fit inside but not get sucked into the chuck.

the wooden ones leak air through the end grain until they are wrapped with duct tape.
duct tape is ugly even in the designer colors. But it sure beats the time it would take to make a stave constructed wooden chuck.

also sonatube is great for shipping delicate turnings. A bubble wrapped turning snug in the tube, foam disc in each end. Put one or several in another box. For the double box protection..

 

[Michael Anderson]

I don’t have any vacuum experience, so nothing personally significant to add, BUT I know @Tom Gall has mentioned using a flat universal-ish vacuum chuck disc before. Not sure how big your bowl is, or what the limits are if his setup, but that could be an option.

 

[Tom Lucas]

No experience with sonotube for anything other than concrete forms. It's also not so cheap, for what it is. I use a holdfast 8" chuck for anything that it'll fit. Of course, it's more costly than homemade. But if you expect to have a lot of bowls and such where you want to reverse vacuum, a durable commercial solution might be warranted.

 

[Sam Fleisher]

New Frugal vacuum system up and running

And another lesson learned...... No matter how bad you want to stick your hand in front of the vacuum chuck just to see how strong it is...... Resist that urge! I didn't have the bearings sealed in yet so it wasn't at maximum but first thought was obviously OUCH! second thought was Wow...

www.aawforum.org

Post #12

If your bowl has a flat rim with no holes.

 

[Chuck Kubin]

I've been vacuum turning my bottoms for some time. Using some home made by vacuum Chuck's with PVC. Worked very well. I have a large bowl that I need to make a new vacuum chuck for, looking at 10" or 12" diameter, with 12" length. Thing I'm wondering is, would sonotube be rigid enough for this? I looked at some 12" plastic pipe but it not cheap, and I can't seem to locate any offcuts from a plumber. Or is there something else out there? I am in Calgary Alberta. Home Depot has nothing above 6" diameter.
Any help appreciated!

Sonotube is an excellent choice -- cheap and made to stand up to concrete work.

 

[Chuck Kubin]

Sonotube is an excellent choice. Cheap, available in large diameters and made for concrete work.

 

[robo hippy]

A plumber will not have off cuts of PVC in that size. Road building crews may have them. They probably throw them away because you can get too many scraps.

robo hippy

 

[JeffSmith]

Just eyeballing it, that's about 1,600 psi to hold a bowl so you can turn the bottom? Overkill? The biggest vac chuck I have is 6" pvc on an aluminum hub (a little under 425 psi if I'm doing the math right - I'm nearly at sea level) and it's held up to a 24" Dia bowl just fine. The suggestion of using a flat plate of MDF covered w foam sheet seems most appropriate as long as the rim is reasonably flat. I'd suggest using tailstock support as long as possible, keeping the toolrest close and light cuts whatever you choose to use to hold it. Whatever you do, keep an eye and ear out for cracking - that's more than 3/4 ton of pressure...

Just a quick edit - my math was way off on the original post...(radius squared x 3.14 x 15 = total psi)

 

[Asher Langton]

Just eyeballing it, that's about 1,600 psi to hold a bowl so you can turn the bottom? Overkill? The biggest vac chuck I have is 6" pvc on an aluminum hub (a little under 425 psi if I'm doing the math right - I'm nearly at sea level) and it's held up to a 24" Dia bowl just fine. The suggestion of using a flat plate of MDF covered w foam sheet seems most appropriate as long as the rim is reasonably flat. I'd suggest using tailstock support as long as possible, keeping the toolrest close and light cuts whatever you choose to use to hold it. Whatever you do, keep an eye and ear out for cracking - that's more than 3/4 ton of pressure...

Just a quick edit - my math was way off on the original post...(radius squared x 3.14 x 15 = total psi)

The PSI doesn't change with chuck size, only the total holding force does.

 

[JeffSmith]

The PSI doesn't change with chuck size, only the total holding force does.

True - the equation is for the holding force…in pounds, not psi. Thanks for pointing that out. It is also for sea level, or near - adjust for your location.

 

[William Rogers]

I think my math is right. I have a 5” vacuum chuck and at 23 in.hg. that gives me 221 1/2 pounds force holding. There will be some leakage reducing that force. I can get most accomplished with tailstock support and only have to worry about the remaining center nub. I can take light cuts or just sand it down. I could even take it off the lathe to sand. What I don’t understand is the need for a 12” length.

 

[Sam Fleisher]

I think my math is right. I have a 5” vacuum chuck and at 23 in.hg. that gives me 221 1/2 pounds force holding. There will be some leakage reducing that force. I can get most accomplished with tailstock support and only have to worry about the remaining center nub. I can take light cuts or just sand it down. I could even take it off the lathe to sand. What I don’t understand is the need for a 12” length.

Maybe he needs it to stand off from the headstock?

 

[William Rogers]

Maybe he needs it to stand off from the headstock?

That is a possibility I guess, but 12”! That would be one “deep” bowl.

 

[Richard Coers]

10-12" vacuum chuck will pull so much vacuum it may actually collapse the sonotube. I'd do a test before putting in all the labor to make one. I've worked on 18" bowls with the Oneway 5 1/2" chuck and had excellent results. If you want PVC cutoffs, go to the plumbing supply house. They can have damaged pipe laying around.

 

[DON FRANK]

I would bet money a vacuum will collapse a sonotube. They are not that strong. If you are familiar with fiberglass resin you could put a layer of resin and cloth around the tube and that would probably work. Around here our main water lines are 12" or bigger. Usually any water tower around here has a pump station where they store pipe and there is always cut offs and short pieces that you could talk a worker out of.

 

[hockenbery]

I would bet money a vacuum will collapse a sonotube.

maybe at max vacuum. But a platter i might put on something that large would crack before the sonatube failed

I tested my vacuum set up when I first got it on a heavy weight plastic bucket the kind that 300 pound guys stand on. Put it on a foam covered disc
I totally closed the bleeder valve to see max vacuum
About 30 seconds later it imploded with a loud pop

Max vacuum will break a lot of work pieces
when using lager chucks I use less vacuum

I use enough vacuum to pull the work piece a 1/16” from the tail center

 

[john lucas]

You don't really need 12" in diameter. 8" will hold a huge bowl or platter. You can buy pvc adaptor pieces like the one on tge far right in this photo.

 

[Josh Allen]

Wow! A ton of replies! Really appreciate the spectrum of thoughts here. To answer some questions. This is a large live edge bowl, about 18 inch across and 16 inch tall. Biggest thing I've turned. I like using the vacuum chuck to do bottoms on most bowls I do, and I think this will work best here as well. I am concerned about stability and while the sonotube seems pretty tough I am worried about it extended out from the headstock, so using a tail stock in conjunction should make it stable. Someone suggested a construction sight for bigger tubing, and I did walk on to a big apartment biuld site and yep, site supervisor gave a 3' length of 12" diameter waste line (I think). About 1/2" thick. Going to make a chuck this weekend, let you know how it goes...

 

[Dwayne Watt]

I am going to parrot the earlier responses with more data. A 12" diameter tube used as a vacuum chuck will exert upwards of 1400 lbs or 6.22 kN of total force on your bowl at normal barometric pressure (roughly 12.8 psi or 88.2 kPa) in Calgary. Even if the PVC tube doesn't fail, it is very possible your bowl will if you use all the vacuum pump capacity. IMHO, a 6" tube would provide more than adequate holding force in excess of 300 lbs and still have the potential to crack your bowl. Be very, very careful!

 

[Josh Allen]

I do hear you. My vacuum set up is home made with a bleeder valve I use to control my vacuum. While I could pull 21 inches, there is no need to! I have no intention of destroying the bowl. That being said, it would make sense with the larger volume vacuum chuck to run some tests, see what bears out. Shouldn't be to much trouble to run some different thicknesses of wood from the planer and see how they distort on the chuck. I think this could give one a good guideline for setting how much vacuum to pull. Could also see how different vacuum settings can control how much movement I get on the pieces under load, and of course if I get any deflection on the chuck itself. This is starting to sound like it needs a chart to graph it. Not my favorite thing to do. But probably worth it.

 

[Darryl Fective]

I keep wondering, is there any reason a block of dry wood couldn't be used to make the "cup" part of a vacuum chuck? Extra thickness would allow a more radiused contact area-- Potentially more versatile and gentle in the workpieces. I haven't done any vacuum chucking at all, but I do have a pump, adapter, and a few 1 1/4" nuts that I thought could be used to make my own cups.

 

[hockenbery]

I keep wondering, is there any reason a block of dry wood couldn't be used to make the "cup" part of a vacuum chuck? Extra thickness would allow a more radiused contact area-- Potentially more versatile and gentle in the workpieces. I haven't done any vacuum chucking at all, but I do have a pump, adapter, and a few 1 1/4" nuts that I thought could be used to make my own cups.

I use wood. Have 4 or 5. Mine are poplar and face glued construction 2x10 or 2x8
wood leaks though the endgrain so a wrap of duct tape makes them leak proof in seconds.

6 of us in my club started vacuum chucking at about the same time almost 30 years ago. 3 built pumps from various salvaged equipment and bought chucks from ONEWAY. The other 3 bought pumps and made all their own chucks. I was in the make your own chuck group.