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Re: [mill_drill] Re: Reposition the Head after a bit change.

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  • Malcolm Parker-Lisberg
    Rick There is always one.  I missed out the by between the word distance and laser. Malcolm I don t suffer from insanity I enjoy it! ... From: Rick
    Message 1 of 37 , May 9 5:18 PM
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      Rick

      There is always one.  I missed out the ' by' between the word distance and laser.

      Malcolm

      I don't suffer from insanity I enjoy it!

      --- On Tue, 5/10/11, Rick Sparber <rgsparber@...> wrote:

      From: Rick Sparber <rgsparber@...>
      Subject: Re: [mill_drill] Re: Reposition the Head after a bit change.
      To: "mill_drill@yahoogroups.com" <mill_drill@yahoogroups.com>
      Date: Tuesday, May 10, 2011, 1:10 AM

       

      Malcolm,

      Great article but I think there is a typo in your email. There were no lasers in 1939 ;-)

      Rick

      On May 9, 2011, at 4:12 PM, Malcolm Parker-Lisberg <mparkerlisberg@...> wrote:

      You could try a piece of chrome plated copper pipe mounted vertically.
      I have uploaded a file (1939) that shows how to increase the sensitivity over a short distance using a laser as the light source instead of a lamp and a convex mirror.

      Malcolm

      I don't suffer from insanity I enjoy it!

      --- On Mon, 5/9/11, Rexarino <rexarino@...> wrote:

      From: Rexarino <rexarino@...>
      Subject: Re: [mill_drill] Re: Reposition the Head after a bit change.
      To: mill_drill@yahoogroups.com
      Date: Monday, May 9, 2011, 9:11 PM

       

      If the laser were on the mill head, and the head (and laser) moved vertically, the laser would no longer point at the spot mirror.  Only a good quality accurately vertical cylindrical mirror would work.  Anybody ever seen one of those?  If it were convex, it might focus the spot...


      Perhaps better to use multiple mirrors to increase the path length and resolution (but the cumulative inaccuracy would increase also).

      Rex

      On Mon, May 9, 2011 at 10:04 AM, larycotten <lcotten@...> wrote:
      Idea on the laser sighting trick: Try putting a spherical "spot" mirror at the target location, and see where the reflected beam shows up. A laser hitting a spherical or cylindrical surface will greatly exaggerate the angular position.



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    • Paul Alciatore
      A Barlow lens is essentially the rear half of a telephoto lens. It is a negative lens and by mounting it somewhat behind a positive lens it effectively
      Message 37 of 37 , May 12 6:38 PM
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        A Barlow lens is essentially the rear half of a telephoto lens.  It is a negative lens and by mounting it somewhat behind a positive lens it effectively multiplies the focal length of the positive lens.  The advantage of  this arrangement, either as part of a telephoto lens or as an add on to a "normal" lens is the total length is shorter than it would be if a single, long focal length lens were used.  For instance, if you wanted a 500mm focal length lens, you could use a 250mm positive lens and a 2X Barlow and the overall length of the combination can be significantly shorter than the 500 mm effective focal length, perhaps only 300 or 350 mm.    A single positive lens with a 500 mm focal length would be a MINIMUM of 500 mm long from focal plane to the front of the lens. 

        Adding a Barlow lens to a lens that is already a telephoto (and hence already has a negative element in it) will produce image degradation: that's one of the tradeoffs.  I'm guessing that you will never see a spider web cross hair at 10 feet with such a lens and possibly not a line ruled with a standard pen or pencil.  It would become lost in the blur.  If you want to convert a telephoto lens into a small telescope you can simply add an eyepiece. 

        Or if you want a video image, just add a camera (web cam or just a plain video camera).  The inexpensive video cameras have rather small pickup devices so you don't need a really long focal length lens to get good magnification.  A 100 mm or 200 mm lens can produce very good magnification.  And it is this very small nature of the image pickup that makes the use of a good lens system critical.  A lens that has/had sufficient resolution for a 35mm film format will be trying to make an image on a pickup sensor that is perhaps 1/5 that size or even smaller.  So image resolution will suffer.  Adding additional elements, like a Barlow, will only make this situation worse. 

        How about this, use the laser on the mill head.  Use one that produces the vertical line so you don't have to worry about where it is vertically when it hits the target (wall).  Now, get a standard video or web cam and mount it a few inches from that spot on the target (wall), focused on the target and run the cable to the mill where you have a monitor screen for it.  You should be able to see the spot and target line on the wall quite well. 

        Or here's another idea.  Instead of focusing the camera on the wall, just take the lens off and mount it on the wall, facing the mill.  The laser line will hit the naked image pickup inside the camera and you should be able to see it on the screen as a band of light.  At 10 feet (120 inches) a 1/4" image pickup would subtend an angle of 0.11 degrees.  You need a resolution of about 0.0057 degrees for 0.001" accuracy at the spindle position, so you need to be able to position the laser line to 1/19 of the width of the screen.  The camera is definitely good enough to do that as even the cheapest ones can resolve several hundred lines across their image's width.  The limiting factor is the width of the laser line.  And having a nice big display screen at the mill head (a three inch screen is certainly big enough) would make it very easy to see it.  It won't get much cheaper than this; laser, cheap camera (B&W is OK), no lens, cable to mill, and display screen.  And it is as accurate as you are likely to get.

        Paul A.



        At 01:48 PM 5/12/2011, you wrote:
         

        John

        My other though for producing a telescope was to add a Barlow lens (bi-concave lens) to an old film camera telephoto lens, dirt cheap now. You can get Barlow lenses that will mount a web camera.
        Maybe a telescope focused on a ruled scale. Spider web makes the best cross hairs.
        I don't think you will get as good an angular resolution as with the laser, optical lever system, but I'm guessing.
        I use a soft hammer to finally position the head at the moment and it is not easy to achieve and a high resolution system would probably make it worse. So a compromise is needed between the system resolution and the ability to align the head.

        Malcolm

        I don't suffer from insanity I enjoy it!

        --- On Thu, 5/12/11, Paul Alciatore <palciatore@...> wrote:

        From: Paul Alciatore <palciatore@...>
        Subject: Re: [mill_drill] Re: Reposition the Head after a bit change.
        To: mill_drill@yahoogroups.com
        Date: Thursday, May 12, 2011, 6:44 PM

         

        Malcolm,

        I thought of that, but decided to keep it simple. 

        Paul A.



        At 06:13 AM 5/12/2011, you wrote:
         

        Paul


        A cheap video camera mounted on the telescope would solve the viewing problem and again provide a fiducial system. Maybe an old ex-government gun sight telescope could be used, they used to be available at low cost from surplus stores

        Malcolm

        I don't suffer from insanity I enjoy it!

        --- On Thu, 5/12/11, Paul Alciatore <palciatore@...> wrote:
        From: Paul Alciatore <palciatore@...>
        Subject: Re: [mill_drill] Re: Reposition the Head after a bit change.
        To: mill_drill@yahoogroups.com
        Date: Thursday, May 12, 2011, 1:44 AM
         
        I think that is a far better idea than any of the laser schemes.  But it is also more costly as rifle scopes are generally more expensive than lasers. 
        You would want to locate the scope so you can view through it while tightening the column lock down bolts.  A 90 degree eyepiece may be a good idea.  Hummm, perhaps a telescope sighting scope instead of a rifle scope.
        Paul A. 


        At 05:13 PM 5/11/2011, you wrote:
         
        Hello Just wondering if anyone has ever considered mounting a rifle scope to the side of the head, to sight a virticle line as far away as possible? just a thought. what you think? moose
        --- In mill_drill@yahoogroups.com, Malcolm Parker-Lisberg <mparkerlisberg@...> wrote:
        >
        > Paul
        >
        >
        > You are still missing the point.
        > If you are using a fiducial system, you are only using one small area of the mirror surface and returning the beam to the same position on the mirror that it it was before the column was displaced. The use of a line source means that it must produce an accurate vertical line so that when the column is lowered, a different portion of the vertical beam will fall on the same position, as previously, on the reflecting surface. The reflecting surface could be faceted, it would not matter, providing the displaced beam fell on the same portion, or facet, of the reflecting surface.
        >
        > Malcolm
        >
        > I don't suffer from insanity I enjoy it!
        >
        > --- On Wed, 5/11/11, Paul Alciatore <palciatore@...> wrote:
        >
        > From: Paul Alciatore <palciatore@...>
        > Subject: Re: [mill_drill] Re: Reposition the Head after a bit change.
        > To: mill_drill@yahoogroups.com
        > Date: Wednesday, May 11, 2011, 8:07 PM
        >
        >
        >
        >
        >
        >
        >
        > Â
        >
        >
        >
        >
        >
        >
        >
        >
        >
        >
        >
        > Malcolm,
        >
        >
        > A regards the use of chrome plated copper tube, you are obviously willing
        > to be satisfied by less accuracy than I would be.  That's you and
        > that's me. 
        >
        >
        > I mean consider the math.  You want to keeep perhaps a +/-
        > 0.001" alignment at the spindle.  A commoon figure for center of
        > the round column to center of spindle distance on round column mills is
        > about 10 inches so the +/- 0.001" spec. translates to +/- 0.0057
        > degrees (20.6 arc seconds).  This is a trruly small angle.  Now
        > lets say your mirror is about 8 feet away or about 100 inches.  This
        > means the beam will move +/- 0.010" on the surface of the mirror for
        > the same spec.  I am also assuming that tthe beam will travel another
        > 100 inches back to the mill head where it's position is observed.Â
        > So the question is, how much distortion in the mirror will cause a
        > similar deviation (20.6 arc seconds) in the beam.  Measuring this
        > distortion in terms of the angular error of the mirror's surface, the law
        > of reflection tells us that the angular difference in the mirror will be
        > exactly one half or the difference in the angle that the beam is
        > reflected by or 10.3 arc seconds.  We aree talking about a beam that
        > is, perhaps, 1/10 inch in diameter so we look at an area of the mirror
        > that is about that wide.  If the beam is not to be spread out in an
        > irregular fashion, that area of the mirror should be fairly consistent
        > (flat or uniformly curved).  So we look aat the amount of allowable
        > tilt that this assumedly flat area can have. The 10 arc seconds of
        > tilt translates to one side being only 0.00005" higher or lower than
        > the other side.  50 millionths of an inchh or gauge block
        > tolerances.  I personally do not have anyy expectation that a piece
        > of chrome plated tube or round would be consistent to such tolerances
        > over it's length. 
        >
        >
        > As regards to the metalized mylar, it is possible, with some care, to
        > obtain a good quality mirror that way.  IIt is one possibility that I
        > failed to mention and proves that two or more heads are better than
        > one.  The hard part with such a system woould be in getting the
        > vertical alignment needed to insure that the alignment is maintained when
        > the head is lifted or lowered.  Actually,, that vertical alignment
        > would be a problem with any cylindrical mirror system and that is one
        > reason why I would be more inclined to use a flat mirror.  Perhaps
        > someone can come up with a cleaver way of obtaining that vertical
        > alignment. 
        >
        >
        > I know that lasers are the latest and greatest, but you might also
        > consider mounting a vertical piece of flat ground stock at a 10 or 12
        > inch radius from the column and an arm mounted to the head that is kept
        > in contact with it.  The vertical flat woould be mounted on brackets
        > attached to the top and bottom of the column.Â
        >
        >
        > Paul A.
        >
        >
        >
        >
        >
        > At 05:54 AM 5/11/2011, you wrote:
        >
        >  
        >
        >
        > Paul
        >
        >
        > I beg to differ, if you use a line laser or a diffracting line generator
        > the mirror imperfections will make the image generated from the
        > reflecting surface still be an on average a straight line. Try a line
        > laser on a piece of chrome plated copper tube, it works with very little
        > deviation in the reflected image. You can make an excellent convex mirror
        > using a piece of metalised Mylar clamped in an oblong frame and
        > pressurised behind with fluid. If the fluid is a polymerised resin it
        > will set to a ridged mirror. Make it long enough so you don't use the
        > ends.
        >
        >
        > You can make convex mirrors good enough for optical telescopes by this
        > method.
        >
        >
        > Malcolm
        >
        >
        > I don't suffer from insanity I enjoy it!
        >
        >
        > --- On Wed, 5/11/11, Paul Alciatore
        > <palciatore@...> wrote:
        >
        >
        >
        >
        >
        > From: Paul Alciatore <palciatore@...>
        >
        >
        > Subject: Re: [mill_drill] Re: Reposition the Head after a bit
        > change.
        >
        >
        > To: mill_drill@yahoogroups.com
        >
        >
        > Date: Wednesday, May 11, 2011, 3:10 AM
        >
        >
        >
        >  
        >
        >
        >
        > Malcolm,
        >
        >
        >
        > If the mirror has slight deviations from flat, then you could set up
        > a reference point (line actually) at one vertical position on it and then
        > wind up using another vertical position on the mirror when the head is
        > raised or lowered.  The first position maay send the beam slightly to
        > the left while the second one sends it to the right.  If you are
        > going for the best precision (I would be) you want to avoid such
        > errors. 
        >
        >
        >
        > So you really need a high quality, first surface mirror.Â
        >
        >
        >
        >
        > Even if you could find the suggested cylindrical mirror, it also
        > would need to be very high quality as you would want it to reflect the
        > beam in the same direction at all vertical heights in order to maintain
        > accuracy.  I dare suggest that such a higgh quality, cylindrical
        > mirror would cost many thousands of dollars if new.  Polished,
        > machined surfaces that are accurate to thousands or even ten thousands do
        > not qualify.  We are talking millionths, like gauge blocks or even
        > better.  Optical methods allows such preccision to be achieved, but
        > not cheaply. 
        >
        >
        >
        > Paul A.
        >
        >
        >
        >
        >
        >
        > At 12:47 PM 5/10/2011, you wrote:
        >
        >
        >  
        >
        >
        >
        > Paul
        >
        >
        >
        > Small imperfections in the mirror surface don't matter, because you
        > are using it in fiducial mode, ie. returning to the same position. If you
        > use a piece of diffractive plastic off the child's toy that gives two
        > views of the image when you tilt it, you will get a nice line of bright
        > spots, alternatively you could use a line laser.
        >
        >
        >
        > Masking to a slot is a good idea.
        >
        >
        >
        > I don't suffer from insanity I enjoy it!
        >
        >
        >
        > --- On Tue, 5/10/11, Paul Alciatore
        > <palciatore@...> wrote:
        >
        > From: Paul Alciatore <palciatore@...>
        > Subject: Re: [mill_drill] Re: Reposition the Head after a bit
        > change.
        > To: mill_drill@yahoogroups.com
        > Date: Tuesday, May 10, 2011, 5:50 PM
        >
        >
        >  
        >
        >
        > If you use mirror(s), you will need high quality ones because small
        > optical defects will cause a variation in the angle of reflection.Â
        > You need the same angle at all vertical positions to allow for the very
        > change in head height that causes the alignment problem. 
        >
        >
        > You will search long and hard for a cylindrical mirror of such
        > quality and sufficient length to be of use. A better mirror idea
        > would be to mount a first surface, high quality, flat mirror in a manner
        > to reflect the beam back to the mill head and put your line on the head
        > itself.  This will double the distance annd accuracy of the method
        > and the position of the spot on the line will be easy to see as it will
        > be only inches away. 
        >
        >
        >
        > Some possible sources for high quality mirrors:
        >
        >
        >
        >
        > http://www.edmundoptics.com/
        >
        >
        >
        >
        > http://www.surplusshed.com/search.cfm
        >
        >
        >
        > www.
        > anchor optics.com
        >
        >
        >
        > A possible variation would be to mask the mirror to allow only a
        > small, vertical slit to show.  Then the bbeam would disappear except
        > when it was close to the desired position.Â
        >
        >
        > But my box/slit target would be cheaper and I would try it
        > first.  A test box could be made from carrdboard in a few minutes and
        > if it works well them make a better one. ;
        >
        >
        > Paul A.
        >
        >
        >
        >
        >
        >
        > At 02:39 PM 5/9/2011, you
        > wrote:
        >  
        >
        >
        > The unfortunate thing is it also increases the size of the spot,
        > making it difficult to find the position.
        >
        >
        > Malcolm
        >
        >
        > I don't suffer from insanity I enjoy it!
        >
        >
        > --- On Mon, 5/9/11, larycotten <lcotten@...> wrote:
        >
        > From: larycotten <lcotten@...>
        > Subject: [mill_drill] Re: Reposition the Head after a bit change.
        > To: mill_drill@yahoogroups.com
        > Date: Monday, May 9, 2011, 6:04 PM
        >  
        > Idea on the laser sighting trick: Try putting a spherical
        > "spot" mirror at the target location, and see where the
        > reflected beam shows up. A laser hitting a spherical or cylindrical
        > surface will greatly exaggerate the angular
        > position.
        >

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