I have just finished the last components of my vacuum work holding system, and am sharing some images and videos of the machining and testing for those interested. I got inspiration for products manufactured by Pierson Work Holding and Nemi, the latter have a great video series sharing valuable information on the design and uses of vacuum work holding systems.
Jump to two video links at the end (machining the aluminum vacuum plate and testing the holding ability) if the details of the vacuum system are of no interest.
In a previous post I shared the large block of aluminum that makes up the base of my vacuum system, and this also serves as the base to which my SMW mod vise/plate is attached. The vacuum is available through one M6 threaded hole that can be plugged when not using the vacuum system.
I have a source for 5/8" cast aluminum plate - 12" X 18" - which are off cuts from this small machine shop and very affordable. My goal is to make a variety of vacuum plates from this material that will sit on top of the base block, and these in turn will use various vacuum pods specific to different jobs.
The bottom of the plate has a 1/8" perimeter gasket and a hollowed out area to help establish the vacuum. Here is an image of the recess being machined:
The top of the vacuum plate is made up of a 20 mm square grid, with 6 holes to allow the vacuum through the plate. I found a source for push in o ring plugs, and these, along with a second o ring, are used to seal the vacuum ports when not in use. They are easily pushed into the slip fit hole, and are also threaded, so a small screw is all that is needed to pop them out. Here are images of the top of the finished plate and plugs:
The vacuum grid plate can be used to hold stock that will be machined on the surface. For machining through the surface and the full edge of stock material, I plan to use riser pods of various sizes and configurations. Here is an example of a prototype made from 6 mm acrylic. (On a side note, I highly recommend the Datron 4 in 1 single flute end mills for machining aluminum and acrylic. They are expensive - especially for Canadians - but the finish they leave is excellent, as seen in the image of the riser that follows). The image shows it located on top of the aluminum grid plate, ready for stock to be held on top by vacuum. The stock is held a few mm off the grid plate so that the perimeter can be machined without damage to the plate. The bottom of the plate has 4 thin ribs that slip fit into the grid pattern grooves to aid the holding of stock. I can create custom plates/riser pods for jobs requiring through machining.
Here as well are some F360 CAD files of the components:
The vacuum is generated by a rotary vane pump, and my testing of the new plate with 6 vacuum ports installed shows that it will hold vacuum indefinitely - which was a happy surprise. With the prototype riser and a test piece of acrylic on top of one open port, the vacuum drops from 25 "Hg to the relay trigger set point of 20 "Hg in about 8 minutes, with the pump running only about 10 seconds to reestablish full vacuum to the system.
I used a digital force meter to test the holding power of the vacuum system, and I am very pleased with the results. The grid plate with 6 o ring plugs installed did not move a 2 micron dial indicator at all when applying over 120N of force - I stopped there as it was difficult to push the meter that hard by hand. The real test however was to plate the riser plate and acrylic stock on top, and see how the stock held. I stopped at about 70N as there was no movement. I may try again using a clamp to increase the force to the point of failure, but see no need at this point as I will use real time machining as the next test.
Here are two videos showing the machining of the aluminum grid plate (all tool paths), as well as the two force tests I did: