A vacuum chuck is a very simple way to reverse mount your work for cleaning off the bottoms. This article is in three parts:
1. Common Equipment
2. Vacuum Chucking arrangement using a Vacuum Pump
3. Vacuum Chucking arrangement using a Domestic Vacuum Cleaner

A word of caution.
The amount of suction is proportional to the surface area of the article being held. In layman's terms, this means that even with an ordinary household vacuum cleaner providing the suction, a large platter, especially thin walled, can suffer a collapse if an air bleed is not provided.

So what are the common components ? The first thing that you need is a suitable faceplate.

My Large Face plate, which attaches to the small one with clips.	This picture shows the small faceplate attached to the rear of the large one. The rubber on the small plate forms a perfect seal with the back, and doing it like this removes the necessity to tie up two lathe faceplates

I use a normal faceplate with a wooden (3/4' MDF) disk attached. A one inch hole is drilled in the center of the disc to allow a clear passage through the faceplate and the headstock when the face plate is attached. The surface of the faceplate is covered in thin rubber about 1.5 mm thick. The film used to wrap computer equipment is ideal, or else something similar to a very thin wet suit material. A corresponding hole needs to be cut in the film as well. You do not want the covering to be too thick or else even though the work is attached to the vacuum chuck, it will not be as stable as possible.

The rest of the elements are specifically tailored to the type of vacuum source you are using. Please read on to see what I mean.

Vacuum Chucking using a Vacuum Pump (Auto Air-conditioning unit)

This is my pump mounted on the base of my stand. Please note the oil container underneath that acts as an oil reservoir for the auto air conditioner pump. These pumps are designed to run "wet" so it is necessary to keep some oil going through it. I use the vacuum to draw the oil up out of the tank via the thin black pipe heading up the wall, through the pump, and back into the tank. The flow, which doesn't need to be much, is regulated by a small irrigation "dripper" valve. Total cost of all the plumbing for this project was less than the quart of auto transmission oil that is in the tank.

This is a shot of the coupler, which is made from brass. I wouldn't have gone to this excess, but it came with the lathe (second hand). The "T" piece is the bleed valve. The gauge is a cheap auto vacuum gauge and this unit will pull 27 inches of mercury. Please note that the vacuum hose is an ordinary garden hose, cheap and firm. I have never had any problems collapsing it. The other plumbing is a clear plastic hose (3/32 wall), and an irrigation dripper hose. Its all cheap !

The plumbing as seen behind the headstock. The key piece is the junction (center right) scavenged off an old automobile engine.

It has two 1/2 inch ports and two 1/8 inch ports. The black lead going through the clamp on the wall, is the oil feed, one end going into the junction, and the other going via the dripper tap, into the oil reservoir. The green hose goes to the coupler on the spindle. The fine clear hose goes to the gauge, and the other clear/reddish pipe heading down from the junction goes to the vacuum side of the pump. The last black lead is the power lead (rising vertical) The output side of the pump is then put back into the tank (oil container), and this has a vent to the air on the opposite side to stop the plastic tank bursting. An essential element is that your lathe must have a hollow shaft in the headstock.

Vacuum Chucking using a Vacuum Cleaner

The theory is exactly the same here as before, you need a vacuum source and a way to feed it through to the faceplate. Chucks using a vacuum cleaner work on a different philosophy than the pump varieties, as the vacuum cleaner has a low vacuum but a high volume. However there is still enough to hold and even damage thin walled articles. This has the advantage of allowing less than perfect seals and still providing sufficient suck to hold. I have held cracked bowls on this type of vacuum chuck.

This type of chuck, as featured in the pictures following, will hold a 10 inch bowl with such a force that it cannot be removed by trying to physically pull it off. The turning speed when chucking this way should be reduced to a "sane speed", under 300 RPM, so that the risk of loosing a piece, short of a "dig in from hell" is very minimal.

It is essential to provide an air bleed (a deliberate leak) in this type of system to prolong the life of the vacuum cleaner as the motor relies on the air flow to keep cool.

If you have a perfect seal, you will burn the cleaner motor out. For this reason, coupling devices are a lot less engineering feats and more of a hit and miss affair as this picture shows.

This coupler consists of a piece of copper pipe that goes just about through the head stock with a piece of wood attached that is a snug fit for the vacuum cleaner hose, which in this case has been extended using standard PVC pipe fittings. This set up has the added advantage that the copper pipe which rotates freely in the spindle shaft of the lathe, can be withdrawn when the lathe is stopped, greatly reducing the vacuum and allowing minor centering to be achieved, or with a bit of force, the work removed. The soft vacuum bleed valves must be left operable and open to allow some air flow to allow cooling.

Here is how to make the vacuum coupling device. The ways of doing this are many and varied, but this is one idea. Get a hold of an old ball bearing race, with a minimum of about a 1 inch hole in the middle. Turn a pair of wooden blocks as follows. The first, needs one end to either be a tight fit into or over the headstock shaft, depending on the lathe style and what fits best. The other end needs to accommodate the outside of the ballrace, again a snug fit. The race can be glued in if you want, but it needs to be firm. Drill a 1/2" hole right through the center of the block. The second needs to be a tight fit into the center of the bearing, and the other end turned to accommodate the end of the vacuum cleaner hose. Again, drill a 1/2 inch hole through the center of the block. With the two pieces connected to the bearing, you have a rotating joint. Don't worry if the thing isn't completely airtight. Now all you need to do is to create an air bleed to stop the vacuum cleaner from destroying itself. The air bleed is set up for two reasons: firstly to facilitate cooling and longevity of life for the vacuum cleaner, and secondly to regulate the amount of suction, for large pieces. Drill two small holes in the solid section of the vacuum hose, one 3/8 of an inch, and the other a couple of inches away 1/2 an inch in diameter. The 3/8 hole is the bleed, and should never be covered. The 1/2 inch hole can be covered when holding smaller objects, and uncovered when turning large surfaced areas or those with thin walls. Put the whole thing together and you are off and away. Center your work as described in the press mount explanation above.

A couple of things to watch here.

Don't ever turn the vacuum source off while the lathe is turning or you will wear your precious turned piece.

When mounting your work, start with the maximum bleed (Minimal vacuum), and check the vacuum. If you can't move it then its fine. If you can, re-centre and then increase the vacuum by adjusting your bleed system.

As an indication of the forces applied, I understand that a 12 inch platter mounted by this system is subjected to the equivalent of about 200 lb. weight bearing down on it if there is no air bleed available (with a vacuum cleaner), and about 1000 lbs. if you are using a vacuum pump with no bleed and a leak proof system. With the system working properly, and and a reasonable level of suck from the old Hoover, you will be hard pressed to move a 12 inch platter, even with the vents both open.

Rex Haslip