Chucking.

In this area, I will endeavour to explain several different ways or mounting stock in the lathe. I have also included the instructions for constructing a vacuum chuck

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The Index

Jam Chuck

This is ideal for finishing off bowls etc, but can be adapted to cater for repetitive jobs, where the stock is all prepared to a set size, and a tapered Jam can be utilised to hold the stock .For bowl bottoms, or any turning, you can either jam inside or outside, depending on the shape of the turned article As the name implies, this is a friction chuck principle where the holding is done either by jamming the stock inside a recess or over a spigot. This principle is not limited to initial stock mounting , but lends itself to various phases of turning, (see lidded box) Simply turn the recess or spigot to accommodate the size of the other part. If you make the recess too big or the spigot too small, they can be helped to fit by wetting, which will lift the fibres and take up some of the slack, or if it is still loose, use a few layers of toilet tissue or paper towel or serviette to do the job

Glue Chuck

This system is ideally suited to mounting bowls, plates, platters etc, where the bulk of the turning is not to far away from the mounting surface. It allows you to make the most of the stock that is available to you, as you don’t waste material by turning a foot or spigot. For the simple glue, you need a turned spigot as shown above (Glue Block) or a faceplate mounted block, with a clean outer face, slightly concave. I generally nail a small brad into the centre of the Glue Block face, cutting off all but 1mm. This makes centralisation easier,locating this pin into an appropriate recess in the centre of the piece to be turned As for the glue, the world is your oyster. I prefer to use PVA (Poly Vinyl Acetate) which takes a couple of hours to dry. Some of my fellow turners use Hot Melt Glue, while others with full pockets and little time use the "Super Glue" type of products. Again, please think out of the normal here. Using the Hot Melt Glue for example, is an ideal way of reverse mounting bowls as well, particularly rough edge turnings, or "holey ones" that won’t lend themselves to Vacuum chucking. Simply Hot Melt Glue the Glue Block to the finished surface, mount and turn as you will, and then when you want to get the block off, apply a little Mineral Turpentine, wait a few minutes, and the glue will soften allowing the block to be removed.

Glued Jam
This is good where you need that little extra strength, perhaps because you are turning further away from the mounting. (doing things like candle sticks, bud vases etc), essentially short spindle work This makes the best of both the Glue and the Jam Chuck, and by using the Jam Chuck recess, you increase the glued surface. Unfortunately, with this method, you loose the lower end of the stock (what's in the recess) but it is ideal if you don’t have a normal chuck, in which you would loose the bit at the bottom anyway

Glue and Paper Chuck

This has been around since the beginning. Essentially the same as the glue chuck, except that the inclusion of a layer of "brown paper" facilitates the easier separation of the glue block when required. The down side is a possible reduction in the strength of the bond Can be used in the same situations as the simple glue mount. This type of mount is not suited to using Hot Melt Glue, but any other seems to work. (needs a lot of super glue though

Faceplate

Not a lot to this really. Simply find the centre of the work, and secure the faceplate to the work, (centralised of course) using screws. I prefer to use "Gib Screws" which are a very sharp screw with an aggressive pitch and depth of flute. (or whatever the screw equivalent is) Take care as always with the lathe speed, as out of balance work is dangerous

Between Centres

Between centre turning is just that and therefore needs a tail stock. Mount a spur drive centre in the headstock and use a centre in the tailstock to force the turning stock onto the drive centre. It is important to ensure that the stock is fairly well balanced, or the speeds are low or else you could well end up wearing your turning stock. Having said this, there are a range of off centre turning projects that can create a range of effects by deliberately using different centres for different parts of the same piece. A simple jig can be made for finding the centre of work and details of this are shown in my tools and jigs page

Screw Chuck

This method is ideal for holding bowl blanks to turn the outside of the bowl. To call this screw chucking is really a little bit of poetic license. A specially machined "coach screw" is locked into the chuck, and a piece of stock with an appropriately sized hole is screwed onto it, thus holding it against the closed jaws of the chuck. A derivation of this that I have seen is where a special faceplate has been made with the screw as part of it, so the area of support is greatly increased

Press mount

This is another way of reverse mounting bowls to finish the bottom. It can also be used to hold stock while a dovetail or spigot are turned on the base for mounting in a chuck For bowls, a padded faceplate is used, and the work is pressed against it by the centre of the tailstock. Friction drives the turning. I have a wooden disk that I attach to my faceplate, and it is covered in 1" thick foam rubber. Different sizes can be made to suit different sized turnings. For turning spigots etc for mounting, the work can be held between the tailstock and the bare metal faceplate, or even the chuck jaws. If you are going to be using this method to clean off the bottom of a bowl, help your self by marking the centre of the bottom of the bowl when you are turning the outside. This makes centralising it when remounting a very simple task, by just bringing the tailstock centre back up to the mark

Vacuum Chuck

A very simple way to reverse mount work for cleaning off the bottoms. This article is in four parts

  1. Common Equipment (faceplate etc)
  2. Vacuum Chucking arrangement using a Vacuum Pump (car air conditioning)
  3. Vacuum Chucking arrangement using a Domestic Vacuum Cleaner
  4. Getting it together (making your own)

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 suck, a large platter, especially thin walled, can suffer a collapse if an air bleed is not provided.

So what are the common components ?



A suitable faceplate


My Large Face plate, which attaches to the small one with clips. (See next picture) 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 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 Cond. 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 (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.


A vacuum coupling device.

This is a shot of the coupler, 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 vac gauge and this unit will pull 27 inches of mercury. (what ever that is) Please note that the vacuum hose is plain "OLD" garden hose, cheap and firm. I have never had any problems collapsing it. Other plumbing is clear plastic hose, (3/32 wall) and irrigation dripper hose. Its all cheap


Some assorted plumbing

The key piece is the junction (centre right, scavenged off an old automobile engine. It was something to do with the emission control and was a cooling water fitting.
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.
Vacuum cleaner vacuum chucks work on a different philosophy than the pump varieties, as the vacuum cleaner is a low vacuum (but still enough to hold and even damage thin walled articles) but high volume.
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 pull it off by the tenon that we were about to remove.
Given that the turning speed when chucking this way should be reduced to a "sane speed", (under 300 RPM) then 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 (as the shaft of the lathe has a hole through it to facilitate locking) 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. (see below)

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 centring to be achieved, or with a bit of force, the work removed... (as shown here)


The soft vacuum bleed valves must be left operable and open to allow some air flow to allow cooling. (see note in red above)

And that is all there is to it

Now that you have seen the pictures of mine, here is how to make one, not quite the same, but something you can do without a lot of hassle, using things you have at home. Three of the components are the same, (you don't need the oiler) just their construction differs

A suitable faceplate

I use a normal faceplate with a wooden (3/4’ MDF) disk attached.
A hole is drilled (1") in the centre 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 1.5mm thick). The film used to wrap computer equipment is ideal, or else 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 even though the work is attached to the vacuum chuck, it will not be as stable as possible.

A vacuum source

Simple. Use your vacuum cleaner, or acquire an old vacuum cleaner from wherever. It doesn’t need to be flash, and even an old reject from the house cleaning duties, will perform perfectly.
An alternative which I have (only because it came with my lathe), is a vacuum pump made out of an auto air conditioning unit, and an electric motor. This is overkill, nice but still overkill, and the risk of collapsing your work is even greater.

A vacuum coupling device.

The ways of doing this are many and varied, but this is one idea.
Get 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 (depends on the lathe manufacturer) 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 centre of the block
The second needs to be a tight fit into the centre of the bearing, and at the other end, accommodate the end of the vacuum cleaner hose. Again, drill a 1/2 inch hole through the centre 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. (see next bit)
Now all you need to do is create an air bleed to stop the vacuum cleaner destroying itself. (they rely on the air flow to cool). This is for two reasons, firstly to facilitate cooling and longevity of life for the vacuum cleaner, and secondly to regulate the amount of suck, for large pieces.
Drill two holes in the solid section of the vacuum hose, 1@ 3/8 inch and the other a couple of inches away at 1/2 inch. 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 away. Centre your work as described in the Press mount explanation above.
Another way is as pictured above, using a piece of copper pipe glued through the centre of an appropriately sized round wooden block, set up to take the vacuum attachment from the vacuum,e cleaner

A couple of things to watch here.
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 1000lbs if you are using a vacuum pump with no bleed and a leak proof system).
This gives you an idea of the forces involved. (will your bowl stand the weight of you standing on it, or one wheel of the car? )
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
The bearing is also an optional nicety, and the vacuum cleaner system shown above works very well.
A very simple way to reverse mount work for cleaning off the bottoms.

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