Wire Alignment
John Mac:
Wire Alignment
________________________________________
Hi All
I posted this on CNCzone a while back. hence the references to a lathe.
I kept copies of all the docs so if anyone is int drop a line.
This note is about getting things straight…….Very straight.
Some time ago an old but looked after Heidenreich and Harbeck lathe came my way. The bed length is about 2 Metres and weighing at three and a half tons, this is a serious lathe!
Over time there is slight wear on the bed and I am contemplating scraping her back to perfection.
One day I went into a bookshop and found a new copy in the second hand section of Connelly’s book for 20 bucks. Yep I grabbed it. For restoring old machine tools I know none better. I have already used it as a reference. Scraping is not that difficult just hard work. and common sense. I found a couple in the US here
Amazon.com: Machine tool reconditioning and...
One of the mysteries of alignment is using a tight wire as a straight line.
How to do this this proved to be a bit harder to track down
However the following sites have helped a lot to understand the theory.
http://www.slac.stanford.edu/cgi-wra...-pub-11465.pdf (EDIT the link is down at the moment)
it is now here:
http://www.slac.stanford.edu/pubs/slacpubs/11250/slac-pub-11465.pdf
http://www.physicsforums.com/archive.../t-220848.html (EDIT the link is down at the moment)
It is now here:
http://www.physicsforums.com/archive/index.php/t-220848.html
http://www.spaceagecontrol.com/calccabl.htm (A good calculator)
I guess before the Egyptians they were using a string line
On a more 21st century note here is a link to a MIT
J. Paradiso is still there.
This would make an inexpensive electronic readout system for a tight wire alignment system. As used on linear accelerators. So it is quite accurate.
http://web.media.mit.edu/~joep/papers/WireReadout.pdf
There are other references on wire alignment on Google scholar
http://scholar.google.com.au/scholar...ment&hl=en&lr=
So now I have a plan!! The next bit is to get the time to do it, in the mean time. I would be most grateful if the CNC crowd had any further Ideas.
Cheers
Macka
RICH:
Dear John,
I am curious about the plan and what your planning on doing.
You may want to see a guy by the name of Michael Morgan has a web site if your intersted on scrapping techniques and information.
Does the lathe bed have hardened ways / bed?
Have you ever done any scrapping before?
How is the under carriage as compared to the ways?
Got the tools ( i assume you'll be hand scrapping it), the patience, and time to do it?
Sounds like a challenging endeavor and wish the wrist and elbow all the best.
RICH
PS: With a properly calibrated spindle mirror along with a autocollimator mounted on the carriage using optical
alignment via auto-collimation you can profile the bed rather quickly. Just another way of getting it straight.
Hood:
Suggest you maybe post a question on the Practical Machinist forum, one of the members there (Forrest Addy) teaches scraping and often has classes, in fact I think there is one soon but no doubt it wil be fully booked already. Should get a lot of god advice on the forum though if you post a question in the General New section, heres a link. http://www.practicalmachinist.com/vb/forumdisplay.php?f=38
Hood
Ian Ralston:
Macka,
Don't underestimate the time needed to do this job, it may be better to find a company that does slideway grinding!
My father, who had worked for Victoria Machine Tools and Central Tool and Equipment Company (Centec) here in the UK, decided that a small Victoria horizontal mill knee slide was too far out of alignment (0.030 ins overall) and that he would correct it by rescraping the slideways on the main casting. He only had a master square, a wide straightedge and my help.
The method he adopted was to square one vertical face to the spindle axis and worked from this as a standard to refer the other faces and dovetails. The job took about two days, if I remember correctly and was a lot of hard work. He only used rehardened and ground files as hand scrapers and a lot of time was spent honeing the edges of the scraper (mostly to give his muscles a rest from the scaping action - very tiresome, I know, I tried.). The final finish, for oil retension, was very professional with precise "z" shaped impressions neatly arranged on all working surfaces. After having my efforts unceremoniously compared to the scatchings of an old hen (chicken), my contributions were mostly restricted to making the tea.
I wish you every success but at 2 meters, it is going to be a very long job. ;)
Ian
John Mac:
Hi Hood
In retrospect I was a bit hasty in posting. It would be better if the references to a lathe were left out.
For the record I did use some Roslau piano wire .029 diameter. It appears to be available in most countries. Google search follows: http://www.google.com.au/search?hl=en&q=Roslau+piano+wire+germany&btnG=Google+Search&meta=
I strained the wire between two points and carefully aligned them to the Lathe bed using gauge blocks and used it as a straightness reference. To load it up a large gear maybe 25 pounds was hung just off the floor to tension it the wire did not break! Ideally it should be tensioned just short of breaking.
To measure the error, a measuring stage made from a 10 thou micrometer and a back lit slot only a couple of thou bigger than the wire. The stage was then mounted on a kinematicly correct frame two pairs of points on the v and one point of the flat of the lathe.
By moving the stage (carefully) until the slot was centered optically and then reading the micrometer it was possible to get repeatable measurements within about .0002. that cancels out any thickness error of the wire itself but The rosleau had no measurable error with a brand new micrometer. Obviously the slot and wire is not visible to the naked eye but no problem for a cheap student microscope. Set to about 50 power. Found one second hand for 10 bucks in a trash and treasure shop. The best way is to cut off the base and mount it on a steel support to fit your needs. (Keep the focus adjustment) The slot must not touch the wire. The bed is about 10 feet long with the headstock removed. Straight edges are out.
The horizontal plane is a different matter to check that a 10 second precision machine level (0.0005"/10 ") engineers level was used to level the machine. Buy working from both ends and averaging you can get a good result. For leveling machinery on a tight budget the only way to go. I have seen them on the internet for a couple of hundred bucks.
If you calculate the sag of the wire using the Catenary formula you can also use it to define a horizontal plane.
From reading some of the posts here there appears to be quite a lot of members building their own machines.
The wire method is not new as a browse of the internet will show, it produces outstanding accuracy.
An autocollimator would be nice but for 20 bucks a lifetime supply of wire is pretty cheap. I don’t reuse it. (When unwinding it off the coil make sure it is not kinked.)
The MIT paper Synchronous Proximity Detection for Stretched Wire Alignment Systems By J Paridiso, Link : http://web.media.mit.edu/~joep/papers/WireReadout.pdf
is very interesting as are many other posts on the internet using wire for the CERN linear accelerator for instance. It deals with reading the position of the wire electrically. That got me thinking? Could we sense the wire using a instrumentation amplifier bridge and use Mach 3 to read the error and position a tool? Even in the x plane if the Catenary formula was used?
Maybe this forum is more software oriented. And the practical side is of less interest to members. This post was made to possibly assist machine builder members on a budget. This method will allow sub thou accuracy over long distances. Not fast to set up but it works.
Cheers
John Mac
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