It’s Textbook Tuesday! This is “Porous Graphite Air-Bearing Components as Applied to Machine Tools”. I mentioned this fantastic 1974 report to SME in my recent interview on the @withintolerancepodcast
The article discusses many aspects of the application, design, fabrication and testing of aerostatic bearings (ie those which use externally pressurized air). But its primary topic is an aerostatic hemispherical spindle developed at the Oakridge Y-12 plant. This is where air bearing spindles were first developed in earnest, so this is a fascinating insight into the history of precision machine design.
But the thing I love about this article is that it is full of practical information - basically everything you need to know to build your own air bearing spindles. The information is presented clearly and concisely. Even the math is explained in such a way that someone with minimal math background can understand it!
One of the key nuggets in this article is the discussion of flowrate through aerostatic bearings. It was found that the spindle had a weird self-excited vibration. After investigation, the cause was identified as “pneumatic hammer”. Basically, this is a result of the air flowrate through the bearings being too high.
In simplified terms, what happens is that the pressure between the bearing and the surface pushes the bearing up until enough separation forms between the two that all the air blows out and the pressure drops. The bearing then comes crashing back down until the gap is small enough that the pressure can build back up. And the cycle continues.
The solution is to restrict the air flowrate into the bearing area. In conventional air bearing designs, this is done with precisely-sized orifices and slots. In porous media air bearing designs (for example, those which use graphite), this is done using the many tiny air passages in the media itself.
You could purchase specially-made graphite with the right permeability. Or you could purchase any old porous graphite and tune it with lacquer!
#textbooktuesday#kinematics#airbearing#precision#metrology#inspection#machining#machineshop#machineshoplife#instamachinist#engineering#design
.1 micron resolution in discrete steps 🤯
I was playing around with our Kern MMP microprecision milling machine donated by @kernprecision and finally it clicked in my head just how utterly ridiculous it is that the resolution of the axes goes out to four decimal places. I am used to using machines in inch mode, where four decimal places is normal. That’s just ten-thousandths of an inch. No big deal. But this machine is in millimeter mode!
.0001mm is .1 micron, 100 nanometers! Or for us inch folks, that’s 4 microinches, 4 millionths of an inch! That’s such a tiny value!!
I was slightly disbelieving at first. I thought, “This must just be the resolution of the glass scales. There’s no way this thing can actually move in such tiny discrete steps.”
BUT IT CAN!
Verified with a high resolution indicator measuring displacement of the table, when the table is jogged .1 micron it actually moves .1 micron!
Why is this so amazing? Because of friction. This machine uses conventional technology in its construction: timing belts, ballscrews, linear guide rails with rolling elements, etc. There’s a lot of sliding and rolling friction in an assembly like that. This leads to lost energy and a phenomenon known as stiction. This is the result of lost energy when breaking free two surfaces in contact when they begin to move relative to one another. It is like a sort of stuttering effect of the machine travel when trying to make small movements. The machine builds up energy to crack the surfaces loose, but then as soon as the surfaces move the energy is dissipated. The machine lurches forward and then stops suddenly.
Stiction makes it really hard to make small adjustments in precision mechanisms. One way around this is to back off the table a little to get it moving and then advance it forward to its new position. But the fact that the axes on this machine can be moved in individual .1 micron movements is incredible! This is what’s possible with a really well-designed, dialed-in machine.
#kernmmp#microprecision#precision#machinebuilding#machining#cncmachining#machineshop#machineshoplife#instamachinist#engineering#design#metrology#inspection
Thank you @livermore_lab 🙏
Yesterday was the last day of my internship in Target Fabrication where they build nuclear fusion experiments for the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). Truly one of the most memorable experiences of my entire life! It was a never-ending parade of awesomeness 🤯
I didn’t really know what to expect when I first arrived. I thought maybe they would let me look over the machinists’ shoulders as long as I stayed out of the way. And I would have been quite satisfied with that.
But instead they told their most senior machinist, “Your job for the next two weeks is to teach this guy anything he wants to learn.” And then they set me loose on the machines 😳 So I was milling foams on a Kern with end mills no bigger than a human hair and turning sine waves on a Moore Nanotech with diamond tools! (This is all after the proper training of course, and there was a lot of training…)
Everyone I met was welcoming, friendly, level-headed, patient, open to sharing their immense knowledge and open-minded about trying new techniques and pushing the boundaries of what can be done in a machine shop. It was an absolute joy to work with the crew!
The internship was a unique and critical opportunity for Livermore Lab to share knowledge with the machine technology department at Laney College, so that we can prepare our students for machinist positions at the Lab and help promote open positions at the Lab with our students.
I believe our department is especially good at training entry-level machinists for R&D environments which require a broad range of technical skills, tight tolerance work and high level critical thinking. And it seems the Lab agrees, since they hire so many of our graduates for their apprenticeship 👍
If you want to build the best foundation of knowledge and skills as a machinist, you go to Laney College. If you want to build on that foundation and work at the highest level of the trade, you go to Livermore Lab.
Photos from LLNL site.
#ultraprecision#precision#micromachining#machining#machineshop#machineshoplife#instamachinist#engineering#design#metrology#inspection
PSA: You should understand the rules before you break the rules. We see a mountain of techniques on the gram on hair cutting. A lot of what we see is dry cutting an texturizing from our favorite cutters. We have to remember that the people we see doing these amazing cuts have a strong base in the principles of cutting a foundation. It is through that understanding and core principle knowledge our favorite cutters are able to make there haircuts look easy and effortless. My suggestion start with the wet cut bob. Cut this to perfection and then cut it again and again and again... This will give you a understanding of lines shape and symmetry..✌🏽
@hayalbrecht hair was cut with @arcscissors phantom II
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#precision#precisionhaircut#bobhaircut#goodhair#hairinspo#haireducation#ruskrevolution#minneapolisstylist#evolove612