I'm a ways from it like everything else these days but I have access to some nice solid plastic drops, 3", 5" and 6" rough OD cylinder shaped drops if I remember correctly, also some one inch thick plastic plate. The round stuff is a little oversize to clean up at the call out sizes, the one inch plate has already been precision cut to one inch. Along with the plastic I'm thinking about babbett bearings and O-rings to keep oil where I want it and vacuum where I want it. I will use the job shop metal equipment to shape the plastic. A wood lathe would do most of it, all of it really, but accuracy, ease, and speed make the metal lathes and mills more attractive for tooling builds.
You didn't say it, but I am guessing that you jumped from describing your idea for a vacuum chuck design to your idea for a rotary coupler design.
I'll volunteer my opinion about using a Babbitt bearing in the rotary coupler. I think that you will have better success with a rotary coupler that uses ball bearings. I am not sure how you would incorporate O-rings into a Babbitt bearing and besides you also need to consider the effect of the vacuum on the Babbitt metal which I think would have a greater tendency to erode away under vacuum.
Here are some of my minimum design rules for a rotary vacuum coupler -- at least two bearing assemblies along with shaft seals and O-ring seals for the perimeter. I have seen quite a few different design for rotary couplers for woodturning vacuum chucking systems and most of them do not measure up to these design guidelines -- they either forget about the shaft seals or they forget that two ball bearing assemblies is the minimum.
.... the best pressure we can get is theoretically somewhere around a negative 14.6 or 14.8 PSI normalized for a lot of things only scientists and engineers care about. I'm more interested in few connections, a decent vacuum to begin with and a vacuum reservoir and bleed valve to stabilize things. Figure that I can maybe get 12PSI raw pressure and hope to keep pretty much all of it except what leaks through the bowl or vessel and what leaks at the connecting joint between the bowl or vessel and chuck.
Theory? This isn't some mystical prediction of the unobtainable, such as the quest for seeing how close we can get to absolute zero temperature where matter disappears. We're talking about the weight of the atmosphere. We can feel it and measure it ... and with atmospheric pollution, we can see it too.
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For practical applications we deal with gauge pressure as opposed to absolute (WRT a vacuum). Gauge pressure is referenced to local ambient pressure which is in constant state of changing with the weather (or to be more precise, it is this changing that causes weather).
.... I should get a little mechanical help too by applying cutting pressure directly towards the headstock as much as possible.
I think that you have really confused yourself here and talked yourself into a bad idea because it appears to not be a bad idea if taking a quick casual assessment of what is going on. Applying a force towrds the headstock is the force that you feel yourself exerting on the tool, but that isn't the end of the story. As the wood is rotating around, the force it "feels" from the cutter is vertical from the toolrest. The net resulting force is the vector sum of the components. So, save yourself from bad newbie cutting technique and instead make light slicing cuts. Your bowl will thank you and so will your vacuum chuck.
An aside from someone that hasn't worked with fresh cut wood much, the cherry was a tree just a few months ago. I'm amazed at the amount of color that is all through the wood already. Kinda amazed at some punky areas too but can't have everything.
One of the wonderful perks of being a woodturner is that you get to see hidden beauty that nobody else gets to see. The color and chatoyance of fresh cut green wood changes very rapidly as moisture evaporates.
I'm not amazed at the amount of knowledge and assistance so freely given on this forum anymore but I do remain deeply grateful. You guys and gals are the best, in more ways than one! Thanks to each of you, as always I read and reread every post and thread when I start these things.
...... You will at least want to true the contact surface between chuck and wood to your wood lathe's mechanicals. Remember to do this before you apply the seal!😀
That would only apply if your lathe does not have an alignment registration shoulder on the spindle. Most lathes do and in that case a chuck that runs true on one will run true on all lathes that provide an alignment reference.
