Questions for Existing Users of Vacuum Chuck Systems

[Laurence Giglio]

I am thinking of getting a Oneway vacuum chuck system with a Gast pump but I have some questions regarding if it will be useful or not in my needs.

I turn mostly pecan bowls using the “turn wet-turn dry†method. Most of my bowls are in the 10 to 15 inch diameter at the rim and about 5 to 7 inches deep. I turn wet blanks using a faceplate and mostly leave ¾ to 5/8 thickness through out the entire bowl when turning wet. For larger 15-19 inch bowls, I will leave ¾ inches of wood thickness wet. After about 3 or 4 months drying time I re-turn them dry, I am currently using a 19 inch ¾ inch plywood base attached to a faceplate and jamb sandwich of a second ply disk using 6 carriage bolts and wing nuts. I first turn the bottom tenon, getting it true and also turn as far up the side as I can safely turn then sanding it thru 220 grit before removing the bowl from the jamb chuck sammywich, placing the now round tenon on the chuck and completing the turning outside and in.
My expectations of using a vacuum chuck is to make the turn dry work go faster so as to reduce the time fidgeting with the jamb chuck getting it centered putting the bolts on, adjusting them, then taking them off when done. So…

I have a question. Can the vacuum systems hold a rough turned bowl blank that is dry, but not smooth as it has warped a little in the drying process and hold the bowl well enough to allow me to retrue the bottom tenon and lets say get about a third of the way up the bowl on the outside? If I cant do that then there is no reason to get it, granted, I know that if I wanted to turn off the bottom tenon after its all complete then the vacuum system is great, but I am more interested in using it to hold dry rough turned bowls for final turning/sanding. Has your experience shown this to be doable with the vacuum systems out there or will I be disappointed?

 

[Michael Mendelsohn]

Generally, the short answer is no.

A rough turned bowl is not able to seal against the vacuum chuck until it is turned true.

As far as dealing with rough turned bowls is concerned, I use a plywood donut which I mount in my chuck (expansion mode) that is roughly the size of the inside of the bowl. I place the tailstock center in the center of the tenon. This provides a good enough mount to true up the outside and the tenon so I can reverse it to turn the inside of the bowl.

The vacuum chuck is used to hold the bowl while removing the tenon and turning the foot. I can also do some final touchups to the outside of the bowl in this mounting.

 

[john lucas]

Well I don't turn many rough turn bowls but I don't have a problem holding them with a vacuum chuck. Centering gets interesting. The reason I can hold them with my vacuum chuck is that I use an extra sheet or two of closed cell foam to compensate for the warp. I cut the foam into a square larger than my vacuum chuck face. I cut a hole in the center to conduct the vacuum. Then I just lay this over the face of the chuck and move the bowl into position. You can grab one of the square corners of the vacuum to "fiddle" with the foam if it slips out of position. Turn on the vacuum and see if it is enough to compensate for the warp. If not use 2 sheets.
I have some reasonably thick foam tubing on one of my vacuum chucks and it will hold many warped bowls without the extra foam. The reason is the bottom of the bowls don't warp as much as the sides so even though the sides go out of round by 3/8" or more the bottom is not that far off.
I start my bowls between centers so there is always as tailstock mark left. When I go to put it on the vacuum chuck I just bring the tailstock up and put in back in the starter hole. Then push it against the vacuum chuck and turn on the vacuum. At the very least I can true up the tenon and a little around it but many times I can turn the whole outside.
I rarely turn bowls as big as your so they might be a different problem.

 

[Bill Boehme]

+1 to what Michael said about the purpose of a vacuum chuck. I think that you would be much better served by using a large scroll chuck to turn the dry wood. Depending on the size of what you are starting with, it might also be a better choice for turning the green wood.

I have a vacuum chuck system and would not trade it for anything, but it is primarily for removing the tenon and shaping the foot. The Oneway vacuum chucks are nice, but you can make your own for pocket change. It also is not a big deal to design and build a rotary coupler for much less than the cost of buying one.

 

[hockenbery]

Vacuum chucking has trade offs. To hold an out of round piece requires a seal that can conform to the out of round surface. Thicker foam or a chuck made of flexible material like sona tube( round concrete forms) will get you the grip. However this flexibility make for a spongy feeling when turning.

A method I prefer for returning bowls is one I learned from Al Stirt.

I open up the chuck about halfway put the bowl over the chuck jaws bring up the tail stock to the tenon. I do a quick rim check to get the high and low points of the rim equal distance to the headstock. I slide the bowl on the chuck with the tenon against the tail center to align the rim's end grain peaks and side grain valleys then tighten the tailstock. This jams the bowl over the chuck jaws which then drive the bowl.

Then I square off the rim this gets the bowl in near balance, turn the tenon round, turn the outside to round, add any beads etc. and sand the outside. put the bowl in the chuck, finish turn the rim, the turn the inside, and sand the rim and inside.

This is quick, effective, safe, The open chuck makes a few marks but you turn these away finish turning the inside. Re chucking on the chuck will get the rim and tenon centered real quick and the hold will be much more solid that the vacuum chuck hold which will have to flex to hold and will flex while you turn.

I have a ONEWAY vacuum system and it is great! I sometimes use it to turn off the chuck tenon and finish the inside of the foot. I make all of my own chucks from wood, PVC, sona tube, depending on what I want them to do.

Al

 

[hockenbery]

One caution if you use vacuum on an unfinished bowl you can suck sanding dust and dirt into the wood.
Leaves sort of a bathtub ring.

 

[Don O. Jr.]

Vac systems are great for final turning of the bottom of bowls using light cuts. The tailstock and center should be used as long as possible especially if your vac level is not great. I emphasize LIGHT cuts only. Vac chucking is not meant for heavy cutting/shaping. I would use the method described by Al H. It works well and is fast to put bowls on & off and do the entire outside in a single mounting. The open jaws of the chuck act as a large drive spur.

Vac chucking is wonderful but has its limitations.

 

[Tom Coghill]

L,
you bring up a lot of good questions and they are well addresed by others here. My reason for adding is that purchased the system you are talking about and I have been VERY happy with it.

I find the control and flexibility of what I want (centered and offset centered turnings) to be terrific. I have found it to be excellent for all my finish work. For what you are going to re-mount the work, I would do that between centers then after true-up, use the Vac system.

Tom

 

[john lucas]

Well I'm turning a Walnut second turned bowl right now. Used the vacuum chuck to turn the tenon. Worked like a charm using a 6" vacuum chuck. In fact I roughed out the entire outside to get it round. Had just a little chatter to clean up but I was taking some pretty good cuts. I made a final pass as a push cut and only had a little chatter out towards the lip to clean up after I reversed it in the chuck.
Remember with a vacuum chuck you get 14lbs per square inch so if you use a larger chuck you get a huge amount of holding force. I have a 10" chuck and you could hog all day with that thing on. I also have one that's 8" that I use for platters. I don't have any trouble taking quite large cuts with it.
That being said I do keep the tailstock up just fore safety sake but on the 10" chuck I don't think you can pull that bowl off of there.

 

[Mark Mandell]

Well I'm turning a Walnut second turned bowl right now. Used the vacuum chuck to turn the tenon. Worked like a charm using a 6" vacuum chuck. In fact I roughed out the entire outside to get it round. Had just a little chatter to clean up but I was taking some pretty good cuts. I made a final pass as a push cut and only had a little chatter out towards the lip to clean up after I reversed it in the chuck.
Remember with a vacuum chuck you get 14lbs per square inch so if you use a larger chuck you get a huge amount of holding force. I have a 10" chuck and you could hog all day with that thing on. I also have one that's 8" that I use for platters. I don't have any trouble taking quite large cuts with it.
That being said I do keep the tailstock up just fore safety sake but on the 10" chuck I don't think you can pull that bowl off of there.

Not right John! You only get 14 Lb/SI if your pump is pulling full hard vacuum at sea level; never seen that on a wood lathe setup due to limits on the pumps and leaks in the system. If your vacuum gauge reads 20" of hg, you're getting about 9 Lb/SI pressure. Depending on the diameter of your seal, that could still be plenty. A 10" chuck would give you 700Lbs. of pressure at 20" of vacuum; more than enough to crush a thin turning. The larger the chuck, the less vacuum you need.

 

[john lucas]

Your right Mark and I'm above sea level as well. I draw about 22 according to my gauge if I get a really good seal. I went to a lot of effort to make my system as leak proof as I could.
One time on a smaller thin cone shaped turning I felt a funny vibration as I was making some final passes on the outside. I stopped the lathe and there was a quarter sized depression about to implode. I reduced the vacuum to about 15 and it leveled itself back out. I decided it was time to sand and no more cutting. That Cone was only 5" in diameter at the big end and held with a 4" vacuum chuck.

 

[Laurence Giglio]

Tenon and mortise naming in error, my bad.

OK, due to my misnaming some important terms regarding mortises and tenons, what I meant to say is that I turn bowls using the chuck grabbing the dovetail cut on the inside of a mortise, an "inny" so to speak. I used the word tenon, meaning where the chuck attaches to the tenon using a compression or crushing force, which I dont use. Long ago I thought that using a tenon would eventually reduce bowl depth so I went with the mortise, making it part of hidden. That allowed me in some instances to leave the element in place permanently, as a foot with a decorative element on the very bottom for visual effects.

However I can see that when doing wet then dry turning, its easier to true up the OUTSIDE of a tenon where the tailstock center isnt in the way, get it true and round, attach to the chuck, complete the turning, use a jamb chuck or a vacuum chuck, turn off the tenon and finish the piece. In my method, trying to clean up the INSIDE of a mortise is impossible (for the 2 inch ID diameter I use, with the center in the tail stock in place. That is what I was hoping to do since in half of my bowls, I leave the mortise in place, albeit shorter than what I used to turn the piece as a design element. I cut two or three rings on the bottom, allowing me spacing to add the species, date and my name. By using the mortise, I can turn larger diameter bowls using the smaller 2 inch mortise for the chuck grabbing element, but place a foot for the bowl to rest on wider, as wide as needed for larger diameter pieces such as platters. The sitting rim hangs lower than the mortise, making the piece stable, but it allows the same jaw set to be used for 90% of my work.

So from what I am hearing is that I may be able to do it but I also may not. I have learned that the larger the chuck diameter, the greater the holding force due to the pressure differential and the surface area that the pressure is applied to. The roughness may allow it to work on some bowls, but not on all. In other words, i may get it and find that I cant use it as often as I woukd have hoped for. I have 50 odd bowls waiting to be completed and while I may be able to use it, I may just do them all in jamb chuck fashion. Its not really the cost factor, is time. With my health circumstances, I have much more money than time. But something to be said for the slow deliberate method I use. I dont need to turn, its just what i want to do with he time I have left. It been said that he that dies with he most toys wins, I would add the following, he that dies with the most unfinished work wins. Somthing fo the next guy to complete.

 

[john lucas]

I made a special tool to return rebates with the tailstock in place. It's just an allen wrench with the short leg ground into sort of a metal lathe cutter tip. I use a longer tip on my Nova live center but could still probably get in there with the allen wrench tool using my Oneway love center.
I use the vacuum chuck mostly to finish the bottom of finished bowls but it sits on the headstock end of my lathe ready to go so I'll use it for all sorts of things.

 

[hockenbery]

L,

Now you know why very few bowl turners use a recess. When turning from stabbed blanks the recess can save some wood. When turning from 1/2 logs the recess takes more wood than the tennon.

You can still jam chuck over the open chuck and make a tool like john suggested to scrape your recess round. I would take the point out of my center and use the cup to position and hold the blank for truing and the clean up the mark made when finishing the bottom.

In the future if you want to use recesses you can leave a proud center area marked with a center point - say 3/4" diameter 1/4" tall inside your recess to speed things up.

If you don't want to deal with the mark made by the tail center you can make a small wooden cover for most live centers.
I use these all the time for turning balls and makes sets for use in workshops I put leather on the face that contacts the wood.

Rubberchucky.com sells a variety of profiLes of non marring material that screw onto the ONEWAY live center.

Al

 

[Laurence Giglio]

OK, I have 50 odd bowls turned wet that are ready to turn dry. ALL have mortises that were sized for a No 2 Oneway stronghold chuck set at minimum diameter. What I do now is I take each dry bowl blank and with an angle grinder and a sandpaper flap wheel (36 grit) I set the bowl on the table, rim side down and find the high spots and sand down these high spots on each end until the bowl no longer rocks on the board. I dont do the entire rim, just the 2 or 3 inches at each of the end grain that stick up when it dries. Now when I place it on the jamb chuck, it is solid, wont rock and it establishes a close to final edge for reference. I determine the center of the mortise using a compass and then apply the live center to hold the bowl onto the base plate of the jamb chuck. Secure the other half of the jamb chuck, tighten the bolts, and remove the tailstock. Now the bowl is sitting solid insiode the jamb chuck, its realitvly wobble free. Using a bedan, I true up the mortise, then using a dovetail scrapper clean up the dovetail add some decorative elements and sand the bottom to 220 grit. Remove the bowl from the jamb chuck, set in on the Oneway chuck, turn the bowl.

Now this method does have some disadvantages, especially on larger bowls. The reference point is the newly established rim, which sets the bottom of the mortise and then when its turned over and placed on the chuck, may create an angle that is off to what the original wet turned bowl had established. If I turn the outside of the outside surface when on the jamb chuck, going maybe a third of the way p when i chuck it on the Stronghold chuck, and finish turning the outside, the two surfaces dont stay in alignment. There is often some alignment issues that makes me have to use a scraper to feather out the differences. I try to turn the outside at one time, but its hard using the No 2 chuck. Perhaps the tower jaws might make that easier. This was the reason for the vacuum chuck all along, but I see that I have to make other adjustments as I go.

The next 20 blanks waiting to be turned wet will be done with a tenon foot and I will see if that method helps.