I wanted a vacuum chuck to give me a versatile system to enable me to hold as many different items as possible. I also wanted the system to be easily removable from the lathe so I could continue to use drive centres, knockout bars etc without anything obstructing access to the hollow spindle. I also wanted the system to be inexpensive but without that leading to me having to spend too much time fabricating the whole thing from scratch. Other than this, at this stage I had no preconceived ideas about making parts myself or buying a system off the shelf.
There are a number of useful articles on the web explaining all you need to know about vacuum chucks, DIY chucks and rotary adapters and the theory behind vacuum chucks. I used all I could find to decide on what to construct myself and what to buy off the shelf. A few useful links are listed below.
One of the main components of any vacuum chuck system is some means of creating and maintaining a vacuum in order to keep the work attached to the chuck. There are three approaches to this, the first one is to use a vacuum cleaner as the pump. This method has obvious cost advantages but also potential drawbacks too. Most vacuum cleaners rely on the flow of air to cool the motor. When in use with a vacuum chuck, the airflow will be minimal and this can cause the motor to overheat and cut out. The last thing you want is a loss of vacuum while your prized work is rotating on the lathe. However, some people have got around this problem by ensuring there is a small amount of air leakage in the pipe from the vacuum cleaner in order to maintain enough airflow to cool the motor. This will obviously reduce the effective vacuum but if done correctly, a workable system is achieved.
The second approach is to use a venturi type vacuum generator. For these, an air compressor is used as a source of compressed air and the air is fed through the generator to create a vacuum. These are cheaper than vacuum pumps but the downside here is that an air compressor is a) more noisy and b) uses a great deal more electricity than a vacuum pump. A vacuum generator will probably generate a higher vacuum than a cleaner but not as high as a vacuum pump.
The third approach is to use a proper vacuum pump. There are different types for different applications. Some are described as wet and require oil to be fed through the air intake to the pump, others are dry and require no oil in the air intake. There are also different types of pump but from my research, most sources seemed to recommend the dry rotary vane type.
I trawled the online auctions for a suitable pump. Many I found were either too big or too expensive but after a couple of weeks, I found one that seemed ideal. It could produce a vacuum of 25" of mercury and a flow rate of 8m3 per hour, exactly what I was looking for. I managed to win the auction and got my pump so I was on my way!
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