Laser Centre Finder

Just finishing a quill type angled laser centre finder. The cheap laser pen has a beam diameter bigger than I would ideally prefer. Is it possible to add a smaller aperture to the beam end to reduce same? I have considered using an adjustable dioptre which is to hand.

Are there any obvious dangers or "no no`s" please?

This, in the present condition is a very valuable asset. Easy and very cheap to make. If you have not already. Check it out on U Tube.

Rod,

It is difficult to improve the shape a laser pointer spot. The "proper" way is to use Spatial Filtering, but that gets rather bulky [and can be expensive]

Unfortunately: Simply adding a pinhole is most likely to be counter-productive, because of diffraction.

... If you haven't already done so; may I suggest you read through this recent thread.

MichaelG.

Edited By Michael Gilligan on 09/03/2014 08:33:55

With the small Lasers now they are diode lasers and the shape of the diode gives the shape of the beam. Mostly they are lozenge shaped and in the Surveying instruments one end of the laser spot is used as a reference. You cannot focus a laser as it is coherant light and will travel through an optical system in which ever direction it is inserted. In most cases I can use a 3 to 4 mm beam at 35M. At 1.8M the beam is usually about 1mm and we adjust to rotate about one end of the image.

There may be better defined Laser tubes so you will have to pick and choose among them.One thing you have to watch is the intensity of the beam as if it is too strong it will scintillate and be hard to define, better to reduce the intensity with a polaroid screen to allow better definition of the point where it strikes the surface. With short distance this is a problem.

High quality Lasers are available but not in our price range and again bulky size is the problem.

Clive

Clive- you have stated that you cannot focus a laser as it is coherent light- that is simply not true. Light from a laser can be reflected and refracted in exactly the same way as any non-coherent source excepting that laser sources are normally substantially monochromatic (i.e. single frequency/one colour) so chromatic aberation is not the issue it is with wide spectrum sources so focus can be much better. The coherence will make diffraction issues much more obvious however that is a useful property in many ways.

As was indicated in the previous thread, the beam intensity often makes lines appear much wider. By increasing background light levels the apparent line width will decrease. Bright illumination is also good from an eye safety viewpoint.

Billy.

Hello Billy, My intention was to point out that the Laser beam can be put through an optical system at any point around the optics, it does not have to go through the Pole of the optical system. Focusing of the Laser beam is done at the source with a field lens and this makes it a parallel beam. It becomes a diode/lens module and is carefully set at manufacture. Over running reduces the life considerably.

I find that higher ambient light levels do not help me to set the Laser on to a point. In fact the lower the intensity the better I am able to set it. Instruments I repair/adjust have a mode where the light beam can be increased in steps so that over longer distances the beam intensity is increased.

Actually I would still prefer to locate a point of a target using a cross hair and have in fact made one from an optical plumb from a Tribrach.

Clive

I have just tried shinning the beam from a laser pen through various magnifying devices, watchmakers eye glass 10x, stamp viewer 8x, another magnifier15x and they all enlarge the diameter of the beam "spot". This happens with both glass and plastic lenses.

I know nought about optics but when I knocked up a version of this following the previous thread the laser spot from my £2 ebay laser pointer was too big so I punched a small disc of thin, probably 0.5mm, copper and drilled a 0.6mm hole in it before gluing it over the diode. Worked a treat in reducing the size and apparent brightness of the spot to a usable level.

Andy

I bought one of the purpose made laser centre finders, it has a polaroid filter to "focus" down to a spot.

In any event, I find it only useful for setting edges true (ie squaring up a mill vice). Every other setting up task I use conventional (ie old fashioned) methods as they tend to be quicker and I feel more confident in the accuracy of the setup.

Steve

I bought (for a pound) a cheap laser pointer, several years ago. It came with some very cheaply made plastic end caps, each of which contained a cartoon hologram that made the laser project a simple picture. At least one of those is a fine cross hair, if only I can find where I put it..

Neil

It's worth [briefly] exploring diffractive optics.

... Very clever stuff.

MichaelG.

Hi Everyone:

For those interested in building a laser center finder, as seen in one of my videos, please note the following:

-You need a laser diode module that has a focus adjustment, so you can bring the laser to a sharp focus about 100mm from spindle. A laser pointer will work if you add a lens (focal length about 100mm) but better to buy a module with focus adjustment such as found on Ebay by searching "red laser diode module 3V focusable". Price is about $5 including shipping.

-Design device to be balanced so you can run at high speed

-Ability to change beam angle is a must.

Cheers,

Dan Gelbart

i've recently watched on (australian) abc 'catalyst' program a segment on cheap laser pointers. Despite legislation limiting power to 1mW or so, many labelled as such were in fact much higher. So What? well, a simple demo pointed such a laser at a balloon. In very few seconds, the balloon burst. Eye damage can occur in a similar time. So make sure that no-one looks directly at it. A bit sobering, really.

-russell

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Good to see you on this forum, Dan

MichaelG.

I concur with the previous post. We test all our laser pointers at work and the cheapo imports do often exceed 1mW by a large factor so do be careful. Retina's are not replaceable items. If you cannot get it tested try to buy from a trusted source and don't just go for the cheapest. If you can reduce the output don't run the device any harder than you need to.

Regards Martin

I second and third that. Some of the most common sense, useful and educative videos I've ever seen on YouTube.

If you read this Dan please could you post a link to them. I find the You Tube interface to clever for its own good and somehow I seem to end up loosing track of what I have seen and not seen.

Ian P

Imported one of these from California when first available 10 yrs ago and never used since.

Have a look at the videos to see how useless they are, need a small narrow beam 0.1mm or less for precise work most are of the order 1mm with spatter so can have error of +/-0.5mm at extremes. Stick to the wiglers or electronic edge finders. If lining up on punch marks spinning a centre drill will be more accurate. Or just touch edge of work with a cutter and take readings from there, easy.

**LINK**

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Jon,

... not to be confused with the item under discussion, as patented by Dan Gelbart.

MichaelG.

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P.S.  You may find it worth reading the earlier thread. ... There were some digressions, but much of it is interesting.

Edited By Michael Gilligan on 12/11/2014 22:12:05

Edited By Michael Gilligan on 12/11/2014 22:12:49

I agree with john, after the original article I made one and found that I was using my eyes to see if the alignment wasCorrect. The  feeler guage I use was much more accurate and repeatable on setting up. For centre points I use a wiggler again it is more accurate especially if used with a dial guage.  I keep the lazer on my key ring to point things on white boards. An inexpensive toy.😳

Bri

Edited By Boiler Bri on 12/11/2014 22:26:02

Hi
How do line up or fit or hold the laser beam to be on the centre line of the milling /drilling machine to pick uo say a scribed X line or an edge for that matter ?
Nobby

Edited By Nobby on 12/11/2014 22:32:18