rhb
Aluminum
- Joined
- Apr 27, 2019
- Location
- A small town in central Arkansas
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.
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.