Kinematic support of major machine tool components
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    Default Kinematic support of major machine tool components

    For those not familiar with the term, in this instance a kinematic support is one which imposes no stresses on the part other than gravity. The concept was first formally described by James Clerk Maxwell in 1871 and has been widely used in the design of scientific instruments ever since. And probably even before Maxwell did his analysis.

    Richard King has written quite well on the need for 3 point support, however, there is a bit more to it if one wishes to secure the machine component from moving while it is being worked upon. Wood blocks, saw horses and gravity have limitations. Connelly calls attention to the need to check regularly to be certain that things have not moved.

    An object in space has 6 degrees of freedom, commonly stated as 3 rotations and 3 translations although the translations are sometimes more usefully considered as rotations about an axis at infinity.

    I am exploring design concepts for a mounting system which will accommodate an arbitrary machine component and hold it firmly so that the surface being worked is precisely (fractional arc second) level and immobile, thus making the use of a high precision level vial a satisfactory means of testing the surface. This is not a substitute for a spotting master, but rather a means of augmenting such so as to ensure that one is scraping straight down. And ultimately, automating the work such that a machine can do the grunt work leaving the human user's work to the mensuration of the result. If a machine can make a glass surface accurate to a fraction of a wavelength of light, a suitably designed machine can do the same for a worn machine tool.

    As the case of a lathe bed is trivial, I wish to focus on the problems posed by a milling machine or other machine in which a surface which is vertical in normal use is made horizontal for the reconditioning work.

    There are several issues which must be addressed:

    - the work must be supported at 3 points with an equal load on all 3 supports to minimize deflections

    - the work must be secured against movement while being worked without the connections imposing moment forces

    - the system must accommodate any arbitrarily shaped part

    - the system must permit correction of the deflections caused by rotation of the machine part from vertical to horizontal

    Temperature gradient effects are neglected in the analysis even though the may be of similar or greater magnitude than the deflections due to rotation because they should be well understood and readily addressed by proper temperature control.

    Aside from a kinematic connection to the machine component, precise leveling of a surface to fractional arc second accuracy requires that the support system use differential screws to adjust the supports.

    I propose to solve the equal loading requirement by use of hydraulic jacks modified to read the pressure. A movable and adjustable height load cell if you will.

    Fastening the work without bending moments can be accomplished by means of simple swivel joints.

    Arbitrary shapes can be accommodated by fixtures made to suit which manage the interface between the support and the work piece.

    At present I do not have a satisfactory scheme for addressing the changes in deflection due to rotation. This is routinely done with guitar necks by luthiers, but guitars are rather lighter weight. However, I have significant knowledge of sensors and electronics design, so though unresolved, I do not perceive this as a serious obstacle.

    There is no question of my ability to do what I have outlined without outside assistance. I do not need help. I would like to discuss the problem with peers for the simple pleasure of conversation with someone who understands the work. I do not expect others to know as much about certain aspects of the work as I do, nor do I think that I know more about other aspects of the work than they do. I'd like to have a conversation with smart people who have a range of practical experience related to the topic in the hopes that as a group we can do better than any one of us could do alone.

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    The problem with massive objects is friction.

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    Quote Originally Posted by rhb View Post
    There is no question of my ability to do what I have outlined without outside assistance. I do not need help.
    .
    .
    I do not expect others to know as much about certain aspects of the work as I do,....
    .
    . I'd like to have a conversation with smart people who have a range of practical experience related to the topic
    That's what is called a "Catch 22" situation.

    Any "smart people" who truly ARE avoid engaging a nutter... lest they be seen to NOT be "smart".

    Or would simply waste less time and take more pleasure in wandering down to the loo for a good s**t.

    Not hard to confirm that. Just see if you can get Thales of Miletus to even return an e-mail about "three point" stuff.

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    Could this machine be applied welding?
    I had a heck of a time getting at a forklift the other day
    It would have shure been nice to position it at a more convenient angle/elevation
    20190618_082933.jpg20190618_082914.jpg20190618_135515.jpg20190618_135625.jpg

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    Quote Originally Posted by Hbjj View Post
    Could this machine be applied welding?
    I had a heck of a time getting at a forklift the other day
    It would have shure been nice to position it at a more convenient angle/elevation
    20190618_082933.jpg20190618_082914.jpg20190618_135515.jpg20190618_135625.jpg
    Yahbut..... don't even think about a patent.

    Some indigenous organization in Australia had 4 million years of prior-art before the latest genius decided he's The Anointed ONE to re-invent 3-point support. The Macropus clans can probably outsmart him as well.

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    CSRIO

    Imagine a sphere of defined radius as the definition of a unit of Mass.

    We do live in the silicone age......

    But why not a noble gas at a defined volume, temperature and pressure?

    or......

    To the OP

    Neutral, as opposed to negative and positive compliant supports are a significant philosophical dilemma.

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    Quote Originally Posted by CalG View Post

    We do live in the silicone age......
    God dammit, is there no safe refuge from Kardashian references?!

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    From "Machine Tool Reconditioning" by Edward F. Connelly

    connelly.jpg

    QED

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    Quote Originally Posted by rhb View Post
    ...I propose to solve the equal loading requirement by use of hydraulic jacks modified to read the pressure. A movable and adjustable height load cell if you will.

    Fastening the work without bending moments can be accomplished by means of simple swivel joints...
    I think using scales, hydraulic jacks with pressure gauges, etc. could be a good idea to identify three points with equal weight distribution, especially if you need to achieve levels of precision much greater than most people.
    However, I'm lost with your next sentence: the three point chosen could be still far from reachable and the surface directly above them is likely to be the area requiring scraping.

    Just a general comment: this thread and the conceptualizing how to hold things on the perfect three points for automated scraping is likely a solution looking desperately for a problem.
    Automated scraping machines have been already invented and mostly forgotten, mostly due to each scraping situation being slightly different from any other and the impossibility to create a machine as flexible as an human being. Not much return for the investment.

    As pointed out elsewhere, Connelly did a fantastic job putting together that reference material contributed by many experts in the field. however, as Richard has pointed out in several occasions, the author himself didn't have much practical experience in scraping and I think the cited page demonstrates it clearly.
    If I recall, in other places in the book, rightfully, recommends to use for the leveling machined surfaces that won't be touched by scraping. Probably I'm clumsier than others and, for sure, I am the strong believer in Murphy's law. But, anytime I do have something leveled rested on three points, I always assume that it will move either because somebody bumps into it or because the floor moves with changes in humidity, temperature, etc.

    Generally, when scraping something, I will rest it as accurately as possible on three points in order to evaluate it. But I will move it to a more rigid and stable setup (or add extra supports and cribbing to the pieces that are too large/heavy to be moved). And, if I need to use precision levels to assess the alignment to other features, I would use as leveling reference a surface I am not scraping at the moment. If the level is used only to assess the flatness of the feature I am scraping, there is no issue in re-leveling the item before each survey.

    Another thing to consider is that the three point principle (or the kinematic mount in general) is not something of absolute validity. For instance, if you are scraping the bed or the saddle of a lathe, you are better off doing it with the bed resting where the legs/base bolt to it and where the saddle rests on the ways. Otherwise, after having re-scraped them perfectly on three points, you could have the unpleasant surprise that they sag in the middle.

    Paolo

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    Perhaps you could use this technology instead of scraping

    https://www.google.com/url?sa=t&sour...=1562120549818

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    Quote Originally Posted by Milland View Post
    God dammit, is there no safe refuge from Kardashian references?!
    It was meant to draw smiles
    I

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    Quote Originally Posted by Hbjj View Post
    Perhaps you could use this technology instead of scraping

    https://www.google.com/url?sa=t&sour...=1562120549818
    Total misapplication. There is more to the process then what Gehring is saying. Most of it is proprietary to the end customer and use of proprietary coatings.

    Huffman actually has a more usable process that was developed for aerospace in the rebuilding of turbine blades. They laser map the existing part profile then laser weld the surface to buildup the worn surface with the appropriate alloy of filler material. The idea is for minimum weld stress and to minimize finish machining.The cost is relative to the value of the part especially when most of the parts are made from unobtanium.

    The problem with all of these hi-tech solutions is that we need to know all of the desired finish dimensions to an extremely precise amount.

    The idea of scraping is to compensate for wear on the wear surfaces and get the machine to hold the desired tolerances and accuracy with the least amount of cost.

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    Quote Originally Posted by thermite View Post
    The Macropus clans can probably outsmart him as well.
    What's the season on Macropus clams and where do they grow ?

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    Quote Originally Posted by EmanuelGoldstein View Post
    What's the season on Macropus clams and where do they grow ?
    If ever there was a seagoing version of a kangaroo, it probably evolved into a Royal Australian Navy CPO....


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    Quote Originally Posted by Ziggy2 View Post
    ...
    The problem with all of these hi-tech solutions is that we need to know all of the desired finish dimensions to an extremely precise amount.

    The idea of scraping is to compensate for wear on the wear surfaces and get the machine to hold the desired tolerances and accuracy with the least amount of cost.
    I keep not following you: first, you state that one of your goals is to build a machine to automate scraping. And now you discount possible already-existing alternatives of scraping as expensive? How much do you think would cost the development of your scraping machine, solving all the issues and bugs (at least in theory, already done in off-the-shelf processes)?

    The major time saver in scraping is to map the surface and perform several rounds of step-scraping without spotting in between. This is indeed where an automated process of mapping and laser-etching could be faster and more efficient than scraping.
    Moreover, laser etching (or, for what matters, micro-welding to build up the worn surface) would generate significantly fewer side forces and you could keep the piece on your kinematic mount all the time.

    Paolo

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    Quote Originally Posted by Paolo_MD View Post
    I keep not following you: first, you state that one of your goals is to build a machine to automate scraping. And now you discount possible already-existing alternatives of scraping as expensive? How much do you think would cost the development of your scraping machine, solving all the issues and bugs (at least in theory, already done in off-the-shelf processes)?

    The major time saver in scraping is to map the surface and perform several rounds of step-scraping without spotting in between. This is indeed where an automated process of mapping and laser-etching could be faster and more efficient than scraping.
    Moreover, laser etching (or, for what matters, micro-welding to build up the worn surface) would generate significantly fewer side forces and you could keep the piece on your kinematic mount all the time.

    Paolo
    I never said that the goal was to build a machine for automatic scraping.

    The OP posted a link to a new Gehring add relating to honing that was using a laser for part of the process and the OP thought it could be applied to scraping. I was trying to make the point that the Gehring technology is a complete misapplication of what they are doing. This is a hone and the sizing is only relative to the cylinder center line.

    The hone process does not measure the cylinder bore diameter directly. The actual size check is done at the next station using an air sizer which gives feedback to the hone expansion system as a correction factor.

    The Huffman technology is quite a bit different in that it is doing the surface mapping with the laser and then immediately doing the surface buildup where needed. The problem with this is that you need an exact 3-D model of the part which needs to fit inside of the machine cabinet.

    The whole process is done with an inert atmosphere. the tolerancing is submicron and really out of the realm of any scraping applications. The machine costs close to 2million dollars with the required software.

    If you want to automate mapping a surface for scraping, use a CMM but you will have the same problem, you need a 3D model to begin with.

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    Paolo,

    If you bolt a machine part to a support e.g. an odd shaped section which requires putting some frame around it to provide a secure means of holding it, the bolt will exert a bending moment if it is not perfectly vertical. Good luck with the "perfectly" part of that sentence.

    The best points for support will be the points which place an equal load on all 3 supports. Machinery's Handbook only treats 2 point beams, but the same principles apply for 3 points. By equalizing the loads the deflections of the part under its own weight are minimized.

    I'm looking at this from the context of the reconditioning work extending over a long period of time such as a small CNC job shop where reconditioning work is only done when the operator is not otherwise occupied. So being certain that the machine does not move after being set up is important. In my case, I have an Armor JM horizontal mill I want to rebuild. However, I do not relish the thought of working on that full time until it is done.

    In the page from Connelly that I posted, he points out that in order to "scrape straight down", the first surface that is going to be scraped is the original surface used to level the part. So if it is bumped or humidity changes or wood bends under load, using a level as a means of measure courts disaster as you rightly recognize. I intend to include an adjustable reference surface which is leveled at the time the original leveling is done so that if the machine needs to be moved for some reason part way through the work that can be done accurately.

    I do not consider machines as a substitute for human intelligence. The machine only does what a human told it and, having been responsible for fixing 2.5 million lines of other people's scientific software, I am acutely aware of how often the software is wrong.

    As I noted in the start, a lathe bed is the trivial case and other than single point supporting one end and not applying a bending moment when securing the machine, nothing more need be done. Leveling is not reliable because the bed might well be warped at the start of the work for any number of reasons. So a kinematic mount matters.

    The real reason for this is that a level vial is a very sensitive instrument. With electronic magnification it can easily detect a millionth of an inch over a distance of several inches. There is nothing else at the price that can do that. It is so sensitive that temperature control becomes a major obstacle to exploiting the accuracy.

    My Clausing lathe has a hardened bed, so scraping it is very difficult at best. Sufficiently so that it is not considered possible, although I expect a carbide scraper could do it. But a weighted lap operated by a stepper motor can gradually lengthen the stroke as the high spot gets wider and then stop until the results have been checked. A machine that does that is simple and fairly inexpensive. I can build one for much less than the cost of hauling my 4902 to DFW for grinding.

    A magic machine that rebuilds a machine without human oversight is a fantasy. There are far too many variables. The great value of experience is all the mistakes you remember making. But measuring how much metal a new piece of silicon carbide paper removes per cumulative inch of travel is simple enough. So long as the machine stops before it goes to far, it can do the pure labor part.

    At the moment my chief concern is designing a fixture to hold the work which is sufficiently flexible that anything which needs to be leveled can be, and once leveled will stay that way indefinitely. As a consequence I need to take into account that the floor is not infinitely stiff and moves when someone walks nearby or a car pulls into the parking lot and probably tilts after a rain.

    To reiterate, this is intended to be useful to a small job shop where machine tool reconditioning is only done when there is not paid work to be done. Builders buy and rehab houses so they can keep their crew busy if there is a gap between projects or the weather precludes outdoor work. Same concept.

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    Quote Originally Posted by rhb View Post
    To reiterate, this is intended to be useful
    Not new...

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