Rotary Laser centre finder

[Alan .204Participant @alan-204]

Nuts.

Al.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

The basic version of this laser centering device can be improved considerably by use of a contained beam instead of an open one .

Basically transmit laser beam from source to very near work using a light pipe of controlled diameter and only have the beam out in the open for the last 10 mm or so above the workpiece .

Optical diameter of light pipe can be as little as 10 microns but realistically you could use 0.5 mm and that would produce a sharp spot 0.5 mm diameter .

Optic fibre is easiest to use but there are other possibilities .

Optic fibre has to be suitable type to transmit the laser wavelength but that should not be a problem – plenty of data available from manufacturers .

Won’t work with a plain pipe with a small hole through unless hole is exceptionally clean and straight – best to use the optic fibre .

MikeW

Edited By MICHAEL WILLIAMS on 26/01/2014 17:51:18

[Clive HartlandParticipant @clivehartland94829]

During my career as an Inst. Tech I have carried out the centering of Lasers through Optical Plumbs. I cannot tell for what reason as it was very hush hush at the time but led to the development of Phalanx. The original requirement was to establish an almost perfect vertical aiming mark, but failed as the physical structure was not stable enough. Wind pressure and thermal heat on one side etc. The measurements were done over 30m and an X/Y sensor measured the deviation. The best I could achieve was 0.15mm over 30m. The optical plumb itself was rated at 1 in 30000, that is 1mm over 30m.The resolution was so sensitive it was measuring the vibration of the element in the illumination bulb which was then changed for an LED.

In general a tube Lasers beam is too big in dia. and any development should be carried out using a diode Laser. These vary greatly in quality of beam and its shape, mainly a lozenge shape which has to be corrected by filter and a collimation system.

Please take care and do not view the Laser beam directly and if working use green goggles. Laser power is usually safe below 0.9Mw for 0.25sec. but NOT recommended. Flashing around is not nice either.

The rotating Laser is a good idea as it gives a static coherant image, the Cone or the ball are equally effective and quite common in aircraft jig setting up with SMART Laser system which is self seeking. This has a theoretical 'jig' in the PC and the measurements are put through the PC in real time and any deviations are measured for correction. All the big aircraft makers use this system and they require calibration quite often. It all has to be traceable.

Clive

[Clive HartlandParticipant @clivehartland94829]

Michael, I have made fibre optic light pipes and you need a method of transmitting the beam into the fibre. I did it with a glass tube and a glass window and an oil meniscus. Quite complex to set up but could measure the difference in length of a Fibre optic cable using an EDM measuring device. Used industrially for some time.

Clive

[Michael GilliganParticipant @michaelgilligan61133]

Posted by MICHAEL WILLIAMS on 26/01/2014 17:47:59:

Optical diameter of light pipe can be as little as 10 microns but realistically you could use 0.5 mm and that would produce a sharp spot 0.5 mm diameter . Optic fibre is easiest to use but there are other possibilities .

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Sorry, Mike … I don't believe it works like this

The exit angle from a fibre optic is usually in the order of 60-70 degrees [included], so the spot will be greatly increased in size at 10mm distance.

You would need optical element[s] to collimate the light, and maybe more to focus it.

MichaelG.

[FMESParticipant @fmes]

Posted by Michael Gilligan on 25/01/2014 23:19:44:

Posted by Lofty76 on 25/01/2014 23:11:15:

Why do you need to have the offset angle?

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Did you watch the video that John linked in his original post?

Angle produces cone … Cone makes useful patterns on various shaped workpieces.

MichaelG.

Sorry Michael, No I hadn't as my laptop wouldn't spool it properly, but I have now.

It would be very difficult to use this rotating unit on our mills (Bridgeports) as the guards keep you well out of the way and the machine will not work if they are not closed, additionally the lighting would make it very difficult to see the laser.

I know its not on the same lines, but people have been mentioning 'marking out'.

Recently I built one of the Stirling engines our apprentices do as a test piece, as a leaving present for one of the EDF energy directors

With the exception of the marble base , all machining was carried out by using my single spot laser edge finder to find a datum corner to set the DRO and then all dimensions were taken directly from the DRO, not one single piece was 'marked out'.

So I think there is a lot of room for developments of this kind and it will be most interesting to see whats forthcoming.

[IanTParticipant @iant]

Just spent a good piece of today watching all 18 videos from this guy – but am having to regretfully accept that I may never have a water-cutting machine of my own….much as I'd like one.

Very much enjoyed watching them all and there were quite a few ideas/hints (that hopefully) I can remember and utilise should the need arise. Never heard of "flextures" before (for instance) but I'm sure they will find a use one day…

IanT

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Lofty76 on 26/01/2014 18:27:19

I know its not on the same lines, but people have been mentioning 'marking out'.

Recently I built one of the Stirling engines our apprentices do as a test piece, as a leaving present for one of the EDF energy directors …. all machining was carried out by using my single spot laser edge finder to find a datum corner to set the DRO and then all dimensions were taken directly from the DRO, not one single piece was 'marked out'.

< condensed quote >

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Lofty,

We're in agreement there !!

With a DRO [or on a decent analog machine], and one good datum point, there should little or no marking-out required … use the Mill more like a Jig Borer.

That's what was underlying my "a very good place to start" comment when I mentioned the Ickey Ball.

MichaelG.

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P.S.

The little Stirling engine looks good … I hope EDF-man was suitably impressed.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Just quickly :

(1) If milling machine axes DRO’s are provided with absolute reference facility then you don’t of nescessity even have to find the edges of the workpiece – certainly not on repetition work and often not for one off’s .

There are several ways of doing it but absolute reference means that table is always in an exact unambiguos position as shown by DRO reading .

Some scales can be set up for absolute reference directly but precision micro switches for bump zeroing are often used and work just as well .

If table can be guarantee to always be where you think it is then work can be positioned relative to blocks and pins on the work table or more usefully on a sub table .

(2) Ends of optic fibres can be cut off at any angle required . Square on and basic polish will make the spot described in earlier posting .

Components for coupling light sources to optic fibres are available off the shelf now thanks to extensive use of optic fibres for communication cables and use of optic fibre/laser combinations in science research .

MikeW

[Billy MillsParticipant @billymills]

I do not see why you need to introduce a fibre. The discussion is about rotating a source in air to generate a cone then observing the intersection on a cylinder, cone or sphere target. We are not into precision metrology, we don't need DRO's, we are not into absolute measurements or taking gravitational levels. This is about a bloke in a shed with a poundshop pointer lining up a drill, mill or Lathe.

The sensitivity geometry is simple, the shallower the angle of illumination the higher the sensitivity. For cones and rods a Tan term gets in there so the gain increases very rapidly towards infinity around zero degrees. With a sphere the sensitivity function then includes the diameter of the sphere. Although a ball can be placed over a hole as an alignment target we might not need a ball target too often. A hole can be the target, we can set the pointer to cross the axis of rotation to produce two cones, with points touching, the lower cone can then illuminate a bore.

A point that may have escaped- pointers often have non-round beams and fuzzy edges. However because we are rotating the beam, the defects only produces a wider ring when the cone hits something. Say the beam was a small picture of David Clarke, as we rotated the beam it would then appear to be a series of rings but always rotating around the true axis of rotation. Often the spot is so bright that it appears fuzzy, TURN UP the background lighting then you will reduce your eye sensitivity and the spot will appear tighter. Always better to use pointers in the brightest illumination usable.

Billy.

PS thanks Sir John for your comments, Others got there before me.

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

Re the Gelbart video, been there done that. He clearly has some imagination and intelligence and is open minded to new or different ideas, unlike some of those on youtube who fall short in those departments. He does though sound, on first listening, a little too dogmatic but I shall reserve full judgement till a later date.

I can recommend the idea of one size collet usage, ie the TTS system from Tormach but I standardized on 20mm collet instead of 3/4". He could make life easier if he shortened the shanks to about 30mm anything more is a waste as the collet only grips about an inch. Not having power feed on the Z on my mill the extra shank length was a pain.

All this hole location fiddling about, set ABS to 0,0 on DRO on one corner of fixed jaw on vise, if you want a centre hole just dial in radius and hey presto dead nuts on, really simples

Having now spoken it's back to the silent order monastery for me.

chriStephens

PS Hi Billy, long time no see..

[Michael GilliganParticipant @michaelgilligan61133]

Chris,

Re: your first paragraph … it's worth reading the biographical note that I struggled to link, earlier in this thread.

MichaelG.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Billy ,

Not all people in sheds and not all people on this site are complete morons .

Anyway I can’t be bothered anymore so I’m going to be a very infrequent visitor from now on .

Regards ,

MikeW

[John McNamaraParticipant @johnmcnamara74883]

Hi All

Hi Michael

You raise some interesting points:

Fibre optics have got me thinking.

And an absolute reference system using micro switches is also a good idea. I was at a factory a couple of weeks ago that made kitchens and the like. Thy had an amazing CNC router, yes I drooled…. The work was fed onto the table by a robot that pushed it against steel pins that popped up as a positive stop. then disappeared again when the vacuum took hold.

Now there is another idea. A spring loaded pin that popped up from a machined base that hid within a T slot the work could be located against that.

It is strange how discussions in this forum lead to other worlds……..

————————————————————————

Gee I am glad they invented CAD

A couple of links on cones intersecting.

First for a brush up……
**LINK**

Then if you are a masochist….
**LINK**
**LINK**

Regards
John

Edited By John McNamara on 27/01/2014 10:48:33

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

Got a dispensation from the Abbot to speak again, Only watched half a dozen of Mr. Gelbart's videos so far, he gets my vote for "videos to be viewed watched" for all aspiring machinists/hobbyists. I particularly like the way he questions classic assumptions that have been trotted out as gospel, by the old guard, for generations.

My only gripe is that not all of us have the mega-bucks to throw at our interests the way he has, whether it's his or his company's. Translation, I am jealous!

chriStephens

[IanTParticipant @iant]

If you look him up Chris, you will find that he has been an extremely successful serial entrepreneur, founding (and selling) a number of companies.

**LINK**

I first took him to be running a University Lab (I know that at some US institutions like MIT – money is not a problem) but I suspect that the videos were actually shot in his own workshop. Probably still cheaper than a fleet of luxury/high performance cars though – and much more fun!

Regards,

IanT

[chris stephensParticipant @chrisstephens63393]

Hi IanT,

I'm still, if not even more, jealous but i don't begrudge him a single iota. Wish he was my next door neighbour so I could do the machinery equivalent of borrowing a cup of sugar, but I fear I could not even afford to live in the same town let alone road. If had his brains and money I would certainly have an equivalent shop and not buy sports cars either.

chriStephens

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John McNamara on 27/01/2014 10:31:29:

————————————————————————

Gee I am glad they invented CAD

A couple of links on cones intersecting.

First for a brush up……
**LINK**

Then if you are a masochist….
**LINK**
**LINK**

Regards
John

.

John,

For what it's worth [which probably isn't much] … that third link of yours properly describes the shape that I had in mind when I wrote: "What I was hoping was that the circle of light would become emphatically ovoid when the ball was displaced from centre."

Wolfram's maths, and particularly the resulting diagram, do a much better job than my words! … Given that we are especially good at recognising certain shapes [*], I wonder if there might be a visual "microswitch effect" when the alignment is correct and pure circle appears.

MichaelG.

[*] the Gestalt Effect

Edit: added footnote hyperlink

 

 

Edited By Michael Gilligan on 28/01/2014 08:34:53

[John McNamaraParticipant @johnmcnamara74883]

Hi All

Hi Michael Gilligan
I think were on the same page when we thought about the geometry involved.

On Gesault

May I first digress, when we had a wholesale business it specialised in making custom items for the building and design trade, mainly furniture Bedding and elaborate drapery all made to customer order we supplied to retail and designers. If you are wondering how Engineering fits in it was designing and building special machinery for the business. Training staff to develop an eye for balance and proportion was quite difficult, We were lucky if we got drawings and a specification for an order, most of the time it was a sketch that we had to interpret. Many an hour was spent pondering over a ragged page trying to interpret it. Some staff got the design intent straight away while others struggled to visualise it in the finished form. I put it down to lack of experience in life. We were for ever training.

As always there are exceptions, From time to time certain individuals joined us that were exceptional I remember one young woman who with no previous experience joined us as an apprentice. her perception of form and proportion was remarkable. She worked in the drapery department making period window coverings like the ones you see in the film Gone with the wind. There were not many like her. We were lucky to met a few some people are gifted.

The underlying theory of the so called Gestalt effect relates to the brain viewing objects or concepts holistically. I think it does. Reading this page we see words not individual letters. The result is however limited (with some exceptions) to the sum of the experiences a particular individual has had. That is why we had trouble with training some individuals and not others. If you have not been exposed to good design you will have more trouble recognising it. If you do not have a working knowledge of the physical world with a smattering of history and philosophy (My academic wife would say a lot of history and philosophy!) and enthusiasm you will not do so well.

There has been a lot of work done in this field. This search leads to research on Eye perception.
**LINK**

Getting back to the Rotary Laser centre finder, As soon as I watched Dan Gelbarts Video It got me thinking, but it was not because of the aesthetic form of the patterns produced it was (why) the various patterns were produced. Thinking back to school geometry, which I rather disliked! Made me think of the intersecting cones and other shapes they tried to drum in,,,, Hmmm well at least I remembered some of it. Throw in a bit of engineering experience and the Idea for cone on a slightly different cone came out. And most of all a bit of stand back and why is this so thinking. Experience joined the dots.

Regards
john

Edited By John McNamara on 28/01/2014 12:55:41

[Michael GilliganParticipant @michaelgilligan61133]

..

Posted by MICHAEL WILLIAMS on 26/01/2014 21:50:51:
Just quickly :
.

.

.

(2) Ends of optic fibres can be cut off at any angle required . Square on and basic polish will make the spot described in earlier posting .

Components for coupling light sources to optic fibres are available off the shelf now thanks to extensive use of optic fibres for communication cables and use of optic fibre/laser combinations in science research .

MikeW

.

Mike,

You say:

"Square on and basic polish will make the spot described in earlier posting ."

Forgive me for responding in my best Pantomime voice:

… "Oh no it won't" …

As I referenced earlier; the light exiting a circular Fibre Optic light guide with a square-on polished end will be a diverging cone with an included angle of [typically] 68 degrees. … This is also the acceptance angle at the input end [assuming, in both cases, that the other medium is Air].

The light guide in the two pictures below is a 1mm diameter multi-fibre bundle, in a 2mm plastic sheath; and the ferrule is just under 3mm diameter. The bundle is Epoxy-potted and finely polished [they were made by Schott; so the quality is pretty good].

The light input for these pictures is a Green LASER pointer.

.

First; the exit angle:

Now, the spot size, at a distance of 10mm

.

As you will see; this is not a 1mm spot.

… If you want the small spot size, you will need additional optics. … It's all "do-able" but can quickly get complex and expensive when compared to a Pound's worth of LASER Pointer.

MichaelG.

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P.S. Don't abandon us !

[Billy MillsParticipant @billymills]

There are devices called quadrant photodetectors which are now very cheap and common, you can find one in the optical block of a CD/DVD player. As the name suggests the detector is four adjacent square detectors now made in the surface of one IC.. Lets call them a,b,c & d going around the centre. If you electrically add (a+b) but subtract (c+d) then you detect misalignment along one axis, adding (b+c) but subtracting (a+d) gives misalignment at 90 degrees to the first axis.

Using a small rotating beam painting a circle around the quadrant detector gives a constant brightness spot, Misalignment varies the proportion of the rotation that a quadrant is illuminated so we get a modulated signal which can be AC coupled to reduce steady state drift. So we could have two meter pointers, when both were reading no signal the circle would be rotating around the centre of the detector.

The quadrants are around 2mm square in some blocks, it is trivial to display microns with this arrangement.

Before anyone explodes off a high chair, this is a very well known set up with non-rotating sources. The Optical disc player uses a variation to recover height information . The player has a focusing lens driven by a coil actuator. The light from the lens is then sent through a round rod to create spherical abberation, the rod is at 45 degrees to the quadrants.

When the lens is focused on the disc surface the detector gets a round spot hitting all four quadrants equally. When the track is off then the detectors use the axis data to servo the lens to track the pits on the disc.

The focus is performed by adding (a+c) but subtracting (b+d), when the lens is too high the output is positive and proportional to the error, lens too low the out put negative. This is because of the cylinder lens abberation, out of focus the spot becomes eliptical, the major axis twists 90 degrees each side of focus.

This stuff was originally developed by Philips/Sony for the 12" video disc but was then recycled for CD & DVD players. The method of using servo's and quadrant detection is needed because you need micron accuracy to track the pits as they go around very fast on a disc that can go up and down several mm and also have the same kind of eccentricity. An all for ten quid for the player and electronics!.

You can use the rotating source and the quadrant detector to align co-axial shafts. A fixed beam can be rotated into a parallel rotating beam by rotating an inclined glass slide in the beam, that will scan the beam but it will not rotate a shaped beam. No fibers, no time domain measurements

Billy.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Stevenson on 26/01/2014 14:47:42:

So we have to thank Sir Billy for the patent rights to this design.

… so where do I send the royalties ?

< condensed quote >

.

John,

I'm guessing that your remark was just a good-natured nod to Billy, but [on the off-chance that you might consider making these commercially]; I think you would discuss royalties with Dan Gelbart … his patent is dated 2007.

MichaelG.

 

Edited By Michael Gilligan on 29/01/2014 08:33:06

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Billy Mills on 29/01/2014 01:09:38:

There are devices called quadrant photodetectors … <etc.>

.

Fascinating stuff, Billy

Inspired by your description, I found this very interesting [and practical] article.

MichaelG.

[WALLACEParticipant @wallace]

At the risk od sounding nanny-ish, beware – or at least gen up – on the risk of cutting fibre optics.

Glass, being glass, will readily fracture and if you contaminate your eye by, say, rubbing, the glass splinter is in there for ever as an irritant !

It can’t be removed as it’s invisible in the watery conditions !

W.

[Michael GilliganParticipant @michaelgilligan61133]

Very wise words, Wallace

I generally prefer to use ready-prepared light guides [obtained cheaply, as-and-when I find a bargain] but, for anyone interested in experimenting with small diameter "data" fibres … this video is worth a look.

Warning: It's a lot of faffing-about, and the consumables are expensive.

MichaelG.

[Author]

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