Using a Vacuum chuck is a good way to hold work on your lathe. No screws are required and neither a mortise nor a tenon is required to hold your work. The system described here may be used on most lathes. The only restriction is that your work is not so porous or has so many wormholes as to preclude forming a vacuum, and even then there are tricks that may enable you to overcome some of these difficulties. Of course the surface of your work must be sufficiently smooth to allow the gasket to seal to the vacuum chuck.

A vacuum chucking system has 4 components:  

1. Vacuum pump
2. Control manifold connecting pump to the lathe spindle adapter
3. Spindle adapter allowing lathe to spin while manifold connection remains stationary
4. The vacuum chuck itself

Figure 1

Examples of these are shown in Figure 1: the control manifold (2), spindle adapter (3), and a vacuum chuck (4) holding a large bowl. The control manifold is in the left of this figure. The vacuum hose from the pump attaches to the control manifold at the bottom. Next is a valve for controlling the level of vacuum applied (as shown on the vacuum gauge).

To the right and below the gauge is a toggle valve which when opened allows air (through a sintered metal dust filter) inside the chuck for quick release of the bowl. (All of the threaded pipefitting's in the manifold should be sealed with plumbers Teflon tape.) From the left a vacuum line leads from the manifold to the spindle adapter.

Figure 2

The spindle adapter appears at the left of the headstock. This hose connects to a rotate-able ball bearing seal. The function of the spindle adapter on this lathe is to allow the vacuum hose to remain stationary while the spindle rotates, and to convey the vacuum through the headstock to the rotating chuck.

A different system is shown in Figure 2 to the left. The grey plastic chuck is screwed onto the lathe spindle. A gasket of closed cell-plastic foam forms a seal between the rim of the chuck and the bowl. The low pressure inside the chuck results in atmospheric pressure outside the bowl pushing the bowl tightly against the chuck.

Mickey Goodman has written about vacuum chucking. See his extensive and helpful article at http://cnew.org/tips_techniques/vacuum_chucking.htm. Goggle can bring up more information. Our purpose here is to provide practical information aimed at turners who would like more information about some part, or all, of a vacuum chucking system, including making your own vacuum chucks. Off the shelf commercial systems may be purchased at 4-figure prices. The information here enables you to make a fine system that may exceed the performance of the most expensive systems because it can be custom made to your needs and to your lathe. Depending on your choices you may build a fine system at cost two orders of magnitude less than that of commercial systems.

Figure 3

The spindle adapter may be purchased complete for $57 and $79 (in the same catalog!) 800-683-8876 and is also available for $75 at 800-551-8876.

Figure 4

To work on the inside a bowl, for example, involves a gasket that makes an airtight seal between the bowl’s bottom (or side) and the vacuum chuck. An airtight seal between the inside of the bowl and the chuck would allow you to work on the outside or bottom of your bowl. By evacuating air inside this seal the greater atmospheric pressure outside forces your bowl against the chuck. As was explained with a graph in Part I, this force can be considerable and can resist significant force from a gouge or sanding. Admitting air into the sealed space releases the bowl from the vacuum chuck. Mounting and unmounting the bowl can be done quickly and conveniently so your vacuum chuck system should be designed with efficacy and convenience in mind as well as economy.

Figure 4 shows the inside of a shop made chuck together with a foam gasket. This chuck has been tapped with threads that fit the lathe spindle. The gasket of closed cell foam is readily available as packing from U-Haul for example. The foam is glued using contact cement. Rubber cement also works. The bottom is maple and the body of the chuck is from a length of plastic plumbing pipe fastened with epoxy to the bottom. This chuck is quickly assembled using scrap materials and pipe chosen of a diameter to fit the current turning project.

Figure 5

Figure 5 shows three vacuum chucks, two of which have been made from PVC plumbing material. They are 2 ½ inch diameter by 5 inches tall and 4 inches diameter by 4 inches tall. The 7¼ inch by 4 inches deep grey chuck was cut down from a derelict piece of plastic. A 4 inch diameter oak disk was screwed and epoxied onto the end and then it was threaded. Air leakage along the wooden threads or through the oak disks has not been noticeable using the shop made vacuum pumps described in the first part of this series of articles. With raw chuck material in hand, special purpose vacuum chuck can be easily assembled as the need arises. Various pieces of PVC pipe and fittings 2”, 3” and 4” in diameter are waiting in my junk box.

Figure 6

Figure 6 shows larger raw chuck material available free at my recycling center: three aluminum pots and a cutoff length of PVC drain pipe 8 inches in diameter by 10 inches. Two of the pots are about ten inches in diameter; one is 5 inches high. The largest is a derelict canning pressure cooker12.5 inches in diameter and 8 inches high. Projections can be reduced with a metal saw and smoothed once mounted on the lathe. An oak or maple disk can be screwed and epoxied centered on the bottom. Applying threads will be discussed next.

You will be pleased once you own a tap of size for the spindle threads on your lathe as you can then make faceplates and other spindle fittings for your lathe.

Figure 7

These are not cheap, however the cost per use diminishes rapidly once you begin making fittings of your choice.

Figure 7 shows three taps from Grizzly (800-523-4777) on the left and a 1¼ x 8 tap from Woodcraft (800-225-1153) $17 to $27 depending on size. Carbon steel works just fine for wood and aluminum. The usual rule of thumb is to drill the base hole at 80% of the tap diameter. However with the one tap Beall tap on the right the hole in wood should be drilled 1/8^th inch smaller in diameter than the tap size. A piece of waste backing (with hole) behind the hole to be tapped is needed to allow the tap to fully penetrate through the oak or maple piece being threaded.

Alignment of the tap is critical.

Figure 8

The best plan is to drill the hole on the lathe holding the wood with a 4 jaw or faceplate and the bit with a chuck in the tailstock. Then using a rotating center in the tailstock carefully align the tap in the hole and apply pressure with the tailstock as the tap is rotated with a wrench.

Figure 8 shows this setup, including the oak backing block between the faceplate and the maple disk being tapped. While tapping the spindle is locked. No need for a special tap wrench here as an end wrench works just fine with the end of the tap supported by the tailstock.

Figure 9 shows a vacuum chuck supporting a bowl from its inside. The closed cell foam gasket is clearly shown providing a good seal between the edge of the PVC chuck and the cherry bowl.

Figure 9

Returning to the situation in Figure 9, initially the tailstock was used to center the bowl on the chuck before applying vacuum. While the bowl is firmly held by the vacuum chuck the tailstock may be withdrawn and the tenon removed.

This completes our two part series on the vacuum chuck. In the first part I showed how you could make your own fine vacuum pump, inexpensively. In the second part we discussed the control manifold-- the plumbing for applying vacuum from the pump to your lathe and for adjusting the strength of vacuum applied. Next we discussed the spindle adapter that is needed on most lathes for conveying vacuum through the headstock to the chuck. Lastly we discussed the vacuum chuck itself. Making your own manifold and chucks offer opportunities for custom designs and the greatest savings.

Chuck Force versus Inches Vacuum

My graph below shows how force varies with inches of vacuum and chuck diameter. A common unit to describe the strength of vacuum is inches of mercury. At sea level a perfect vacuum can support a column of mercury 30 inches high, which corresponds to 14.7 pounds per square inch. This is atmospheric pressure at sea level. The force on a bowl with an area of 50 in² (about 8” in diameter) under a vacuum of 25 inches of mercury (abbreviated 25 ” Hg) would be 613 pounds (50 x 14.7 x 25/30 = 612.5). This is a considerable force and helps explain the effectiveness of the vacuum chuck. For example at 20 inches vacuum and with an 8 inch diameter chuck the graph shows that the force holding the bowl to the chuck is 500 pounds, or 275 pounds force for a 6 inch diameter chuck. With 15 inches vacuum a 6-inch diameter chuck would provide the holding force of a good size person standing on your work pushing with their weight down against the chuck. As shown in this graph the larger the diameter of the chuck the greater is the holding force for a given vacuum.