Turning A "No Chuck" Bowl

[Bob Hamilton]

Since the discussion got going on faceplate turning I decided to go out to the shop and turn a bowl without using my chuck. I took some pictures and put together a step by step of the way _I_ did it. I'm probably not the right guy to do it since this is only about the third time I have used a faceplate for bowl turning, but it is there if anyone wants to have a look. The format is a bit different because I used much larger pictures than I usually do, so there is not too much text on each page. But there's quite a few pages....

http://bobhamswwing.com/Articles/No%20Chuck%20Bowl/No%20Chuck%20Bowl.htm

The bowl is a small one from ailanthus. It is about 5 1/4" in diameter and 2 1/2" high.

http://bobhamswwing.com/Articles/No%20Chuck%20Bowl/No%20chuck%20bowl/100_9008-640.jpg

Take care
Bob

[Edward G. Burlington]

Well done Bob! I have been doing that ever since I started doing the Bowl from a board method (well over a year now) and I concur with your tutorial. Two slight differences however.

1. The glue block in my case is a 1 - 2 inch piece of maple attached to a 3 inch face plate then turned flush with the outer edge of the faceplate. I turn a recess on the outer facing end leaving ½-3/4 inch wide raised flat on the outside face diameter. The recess takes the squeeze out glue leaving just the outer flat ring in contact with the bowl blank. When I am ready to attach the bowl blank to the face plate, I put a bead of thick CA glue on the maple rim and spray the bottom of the bowl blank (in the area where the glue will contact) with accelerator. I then place the center point of the blank over the live center in the tail stock and push the blank against the glue block and crank the tail stock tight against the blank. This centers the blank and holds it in position for a few seconds while the glue sets. It is quite easy to break off the completed bowl using a small hammer and chisel leaving a smooth bottom to finish. The accelerator does two things. First it speeds up the set up of the glue (less than 5 minutes to full strength) and second reduces the adhesion to the bowl blank making the separation easier and cleaner.

2. To finish the bottom I use a vacuum chuck, but your jam chuck is just as effective and not as expensive to set up.

I highly recommend this method for dry wood blanks. I find since I do a lot of turning with dry wood blanks this method speeds up things and leaves me with no waste on the bottom which is important to me. I keep 2 prepared face plates ready at all times (as I often do 2 bowls at a time). . I always remove (turn off) the left over glue from the face plate and re-cut the recess ready for the next bowl right after removing the bowl. The left over glue can be very sharp and cause cuts if handled without cleaning up first.


I have not tried this method on wet wood to date, and do not recommend it without first testing the adhesion to the wet wood. It should work as long as the wet wood is sound and solid.

14891

E.G.

[Bob Hamilton]

Hi, Edward:
That looks like a great idea for larger pieces. On this one I fully intended right from the start to demonstrate that the glue block was expendable by cutting in to it so I didn't want to have to worry about cutting past the glued area. That big pink disk on the last two pages actually is one of my vacuum chucks and I cheated by turning on the shop vac to hold the bowl while I cut off the stub and sanded the bottom.

Take care
Bob

[billh]

Bob,
Excellent presentation which should give a lot of new turners good direction on how to do things without a chuck.

CA glue works well on wet wood but the turning should be done right away. If left, say overnight, the drying, contracting wood will break or severely weaken the bond. CA bonds tend to be brittle and do not "give".

I use my home-made drum vacuum-chucks as friction-drive chucks with the tailstock a lot. They are easily made by cutting a groove into a piece of MDF or suitable wood to fit the diameter of a black ABS pipe connector or even a chunk of ABS pipe. Epoxy the ABS into the groove, mount on lathe and true up the outer rim. Glue some foamy or other closed-cell material on the outer rim to make the seal.

I use 3/4" MDF which I tap so it will directly thread onto my spindle.

billh

[Edward G. Burlington]

Hi, Edward:
That big pink disk on the last two pages actually is one of my vacuum chucks and I cheated by turning on the shop vac to hold the bowl while I cut off the stub and sanded the bottom.

Take care
Bob

Neat Idea to use the shop Vac. It is much cheaper than a vacuum pump.:thumbup:

What do you use as a swivel joint for the outboard side?

E.G.

[Bob Hamilton]

Hi, Edward:
The Teknatool vacuum adaptor for Nova lathes is specifically intended for use with a shop vac as the vacuum source. It is simply a sealed bearing that is sized to fit the recess in the outboard handwheel with a stub of pipe sticking out that is sized to fit inside a standard 1 1/4" shop vac hose.

http://www.bobhamswwing.com/justpics/vacuum%20test/100_8253-400.jpg

There are a couple of holes in the side of the pipe, one for a retaining bolt and one for a bypass air flow hole that require drilling matching holes in your vac hose.

http://www.bobhamswwing.com/justpics/vacuum%20test/100_8256-400.jpg

I bought the adaptor when I bought my lathe, but I took a look at it when it came and really didn't think that something that simple could really work, so I stuck it in a drawer and forgot about it for a couple of years. Then I turned a large platter that was too big for my donut chuck and I decided to try out the vacuum adaptor, figuring a platter wouldn't put too much strain on it. I made up that disk with a ring of self adhesive closed cell weatherstripping for a gasket and gave it a try. I was quite impressed with how well it held the platter and started using it for other projects as well.

When I first started using it I did not bore the hole for the bypass air flow in my shop vac hose, because my shop vac used room air to cool the motor. It was one of the low end Shop Vac brand units that I had had for 7 or 8 years. The system worked fine for about 11 months and then the motor on the shop vac started loudly announcing that it did not care for that kind of treatment. I pulled the motor apart and lubed the motor shaft bushings and that quieted it down for a while, but the noise came back.

I wound up buying a new shop vac that is bigger and more expensive, so hopefully is a little better quality. I also went ahead and bored the bypass air flow hole. I was very surprised to find that the deliberate leak did not seem to have much affect on the holding power of the chuck. The new vac is not showing any signs of distress after almost a year of service.

Obviously a shop vac is not going to develop the kind of "inches of mercury" that a proper vacuum pump can generate, but for the kind of thing I use it for it seems to be perfectly adequate. In response to a query on another forum I did some very rough and probably highly inaccurate tests using an old fishing scale and a string to pull a piece off the chuck that seemed to indicate that I am only getting something like 5 inches of mercury, which would translate to about 2 1/2 lbs/sq.in. of pressure holding the workpiece. I was quite shocked at how low the numbers were when most folks using vacuum systems talk about getting 22" to 25" of vacuum.

When I thought about it though, I realized that it is the square inches that is important. On this little bowl that is 5 1/4" in diameter and assuming for the sake of simplifying the math that it is hemispherical, there are about 43 sq. in. of surface area that the atmosphere is acting on. At 2 1/2 lbs/sq.in. that means just over 100 lbs. of force holding the bowl to the chuck. I think that is adequate for nibbling off that little stub and sanding the bottom.

Take care
Bob

[billh]

I'm going to quibble a bit about the calculation above. Even though the surface area of the hemispherical bowl may be 43 sq in, the only component that matters is the one that is projected back towards the spindle - the surface area of the opening of the bowl since all of the bowl interior is under vacuum. (If a 3" dia drum chuck was being used then this area would be that of the drum chuck opening.)

So the actual pressure is:
(5.25/2)**2xPi=21.6 sq-in. The pressure is roughly 0.46psi/inHgx5inHg which gives a pressure of 49.8 lbs. This is where the rule of thumb comes from: Holding pressure = 0.5 the inches of Hg X the area.

This pressure is parallel to the axis of rotation. There is virtually no holding pressure perpendicular to the bed. This is easy to demonstrate by putting the bowl against a hard surface and pulling the vacuum (which may be hard to do without a good seal). You will find that you can easily slide the bowl sideways even though it will be difficult to pull off. It is the embedding of the rim into the sealing material and the friction of the sealing material against the rim the holds the bowl in this direction.

billh

[Bob Hamilton]

Hi, Bill:
I'll accept your numbers because my math and physics skills are pretty rusty. I probably shouldn't have put the numbers in at all because my point was that whatever the actual numbers the bowl is held strongly enough for the light cutting and sanding I use the vacuum chuck for.

I also agree that it is the friction between the bowl and the gasket that prevents it from shifting off centre or rotating. That is why I use a resilient, high friction material for the gasket. The forces acting on the sides of the bowl are just as great as those acting on the bottom, but they are exactly balanced in opposite directions so the sum of those forces is 0.

Take care
Bob

[billh]

Hi Bob,
I was also going to mention that even though your use of a shop-vac doesn't provide large vacuums compared to a vacuum pump, it does have the advantage of being able to such a lot of air and maintain some sort of vacuum.

It doesn't take much of leak to wipe out the "large number" vacuum from a pump. I'm always amazed at how much leakage there can be just through the grain of some types of wood like butternut especially if no finish has been applied.

I plan on making a dual hookup for both a pump and shopvac source.

Bill

[Leo Van Der Loo]

I'll quibble a bit also, yes anything outside the vacuum chuck/drum does not create any hold to the object (bowl) as the pressure is equal to all sides and no it is not directional but uniderectional a cylinder turning on the lathe with an opening on it's side can have a disk held by the air pressure just as well as if it is on the end or any other place, it is the area that has the lower pressure that rules the amount of area that is pressurized.
In the case with the bowl there is hardly any "side area" to have pressure placed on it, so it will slide sideways without hardly any area changing by the displacement/sliding of the object.