Author Topic: Wire Alignment  (Read 12833 times)

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Offline John Mac

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Wire Alignment
« on: November 25, 2008, 09:26:09 PM »
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
« Last Edit: November 25, 2008, 09:48:08 PM by John Mac »

Offline RICH

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Re: Wire Alignment
« Reply #1 on: November 25, 2008, 10:46:45 PM »
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.



 

Offline Hood

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Re: Wire Alignment
« Reply #2 on: November 26, 2008, 02:46:23 AM »
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

Offline Ian Ralston

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Re: Wire Alignment
« Reply #3 on: November 26, 2008, 05:32:00 AM »
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
« Last Edit: November 26, 2008, 05:37:50 AM by Ian Ralston »

Offline John Mac

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Re: Wire Alignment
« Reply #4 on: November 26, 2008, 06:30:34 AM »
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
« Last Edit: November 26, 2008, 07:19:46 AM by John Mac »

Offline John Mac

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Re: Wire Alignment
« Reply #5 on: November 26, 2008, 06:58:07 AM »
Thank you Ian

I made up a grinding device and ground it. Having a known reference line and levels allowed me to work to those. This lathe has double v’s for the saddle. The tailstock uses a V and flat. Total run out for the tail stock ways was about .005 end to end not bad for 30 years. I used that for the grinding head guide. The important point was knowing the error I could allow for it as I ground to compensate. It was a slow process.  It is not perfect, but good enough for most of the work I give it. The saddle was bedded with Moglice. Epoxy bearing material No scraping there. Sending it out for a regrind in Melbourne Australia would almost cost more than it would cost to replace the whole machine. With an Asian built machine.  Don’t forget freight both ways for a crane truck. No I would not do another but learnt a lot in the process. 

Cheers

John Mac

Offline Ian Ralston

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Re: Wire Alignment
« Reply #6 on: November 26, 2008, 04:12:31 PM »
John,

You wrote :-
"No I would not do another but learnt a lot in the process. "
But you have to do it to prove that you can. :)

This quite a practical group, have a look at the Show and Tell section. They do like pictures here. I for one would like to see your carriage grinder setup.

Ian




Offline John Mac

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Re: Wire Alignment
« Reply #7 on: November 26, 2008, 07:44:53 PM »
A couple of images of the precision level and the measuring stage cludged up from scrap.

Cheers

John Mac
« Last Edit: November 26, 2008, 07:47:19 PM by John Mac »

Offline RICH

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Re: Wire Alignment
« Reply #8 on: November 26, 2008, 11:44:04 PM »
How did you know the wire was true about the lathe head axis / front and rear bearings of the head?
Maybe another way of saying it, what's assumed correct?
RICH

Offline John Mac

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Re: Wire Alignment
« Reply #9 on: November 27, 2008, 02:46:12 AM »
Hi Rich

For testing: I first leveled the bed in the X and Y direction, then mounted the wire using some blocks milled from mild steel at each end of the bed. They were adjustable to enable the wire to be positioned exactly.
By moving the wire (not the jig) that aligned the wire to the bed, end to end. The wire was set low, level with the centre of the V’s horizontally, making all 3 in line, to avoid parallax errors.

The head axis is aligned to the bed by the front and rear V ways which showed the original manufacturers scraping marks, it is not adjustable I do not have an Autocollimator so used a precision 18” inspection grade square and a dial indicator swung on a bar mounted in the chuck, the alignment to the bed was fine. Horizontally it appears fine using a test bar.

The saddle prepared to be set in Moglice http://www.google.com.au/search?hl=en&q=Moglice&meta= by fitting inverted V blocks  with cap screws to the 4 corners of the saddle. They were adjusted jacking up the saddle until it was perfectly aligned in all planes using the level and careful measurement to set the lead screw and control bars back on axis. Then all that remains is to very carefully remove the saddle and apply the Moglice to the saddle V’s and replace it over the bed. The next day the saddle was removed and the squashed out epoxy trimmed away. Am trying to find the CD to post some photos.

Cheers

John Mac