laser level for line on curved surface?

My wife does gourd crafting and wanted to make a table out of one. The gourd was flat on the bottom but the top and sides were irregular and she needed to cut the top so it was flat. The solution I made was to put the gourd on a shelf. On the shelf above I clamped a board with a marking pen sticking down. Now all she had to do was rotate the gourd on the shelf and keep bumping it gently against the marker to make a line all the way around that was parallel to the bottom. If you don't have a shelf unit that would work, the basic concept is to get a marker firmly fixed to a point in space and then rotate the object against it. Take a look at a height gauge in the metalworking section on eBay to get the idea.

Steve.

Absolutely! Just make certain the cut you take is flat; that is to say, parallel to the horizon or perpendicular to the vertical. If the hemisphere is not perfect, you may wish to position it in such a way as to include the most pleasing parts of it. Visualize an orange with a small rotten spot. You'd want to turn it so that the laser illumninated another portion in order to leave out the bad spot. In other words, you position the subject (or the laser) in such a way that the area of interest is illuminated.

Bob Swinney

Yes, the "Strait-line" style lasers will work for something like this.

Yes. Although much narrower than that other light sources, the beams of these cheap lasers do diverge noticeably. The ones with a finer aperture have thinner beams. If you can modify one to have a very fine aperture (I.e, very narrow slit in very thin material), it should be able to do what you want, within reason. You'll still get a diffraction pattern, but the main line should be pretty clear for reasonable distance.

Doesn't matter. The lasers in those things are too weak to pose any serious hazard. It's about as dangerous as looking at something illuminated by a red flashlight.

Cheers!

Jim

Actually that is not true. Those cheap lasers are surprisingly good, between

1 to 2 mrad divergence. This is the same for ordinary HeNe gas lasers.

You cannot narrow the beam by passing it through a slit. A slit will cause the beam divergence to increase. The divergence is a function of the width of the wave front. A narrower wave front (beam with) will result in a increased divergence. This is a result of wave theory and is not specific to lasers.

Pete.

||Catherine Jo Morgan wrote... ||> Could a laser level lay a straight ||> line onto the curved surface, so I could mark it for cutting? || ||Yes, the "Strait-line" style lasers will work for something like this. || ||> Are the lines or dots always smaller the closer you are? || ||Yes. Although much narrower than that other light sources, the beams of ||these cheap lasers do diverge noticeably. The ones with a finer aperture ||have thinner beams. If you can modify one to have a very fine aperture ||(I.e, very narrow slit in very thin material), it should be able to do ||what you want, within reason. You'll still get a diffraction pattern, but ||the main line should be pretty clear for reasonable distance.

How would one go about that? I have 3 different laser levels, all have a beam that is about 1/8" - 3/16" at

6 feet. I'd like that to be under 1/16" at 15 feet. Rex in Fort Worth

The old boat builders used strings to scribe water lines on hulls.

Use two string lines. For ease of setup have the strings parallel and level to where you want the line to go. Site through the strings onto the hemisphere and make a pencil mark every 6 to 8 inches. (an extra person helps) Get a flexible baton (thin, straight stick) and connect the marks.

Good luck.

Eide

That may be, but I have a few of these things and some of them diverge noticeably more than others. Perhaps it's in the optics.

I disagree and offer the following for consideration:

I didn't place a ruler in the setup, but I believe the effect is clear.

This is true, but like I said, within reason, the beam width itself can nonetheless be decreased by a slit. To be fair, the definition of "beam width" is debatable, but for practical purposes -- as in the OP's application, it can be narrowed.

Jim

I would screw two pieces of thin brass or steel to a couple of cross members. Make one edge easily adjustable, say, with elongated screw holes. Then attach the "slit" to the laser so that it lies in the path of the beam. You may need to fiddle with the rotation to get the result you want.

Seems to me that this should be possible.

Note that there's no free lunch here. The slit will markedly decrease the brightness of the beam. This limits the maximum distance at which it's an effective tweak for you. Can't hurt to play around with it though.

Good luck!

Jim

P.S. I uploaded a couple photos to my web site, in response to another fellow's post in this thread. You might take a peek, to make sure we're on the same page and that something similar might work for you. They're at:

"Eide" wrote: (clip) Site through the strings onto the

^^^^^^^^^^^^^ I have a level with a laser beam which shoots out one end. If this were mounted on a tripod, and adjusted to level, and axis vertical, then rotating it would sweep the spot across the curved surface you intend to cut. As suggested above, make pencil marks as close together as you desire.

Or, you could mount a rifle-scope-sight on a tripod, and do the same thing by directing someone with a pencil to make the marks.

Or you could use a surveyor's transit or level to do the same thing

I have, but have never used, a pair of transparent tubes that can be used with a water-filled garden hose, that can be used to carry a level reference. Probably less accurate than the other methods, though.

I have seen those devices. The plastic lens that produces the divergence in one axis that gets you the line also increases the divergence somewhat in the other axis. You cannot get better than the 1 to 2 mrad divergence with a lens or a slit or the expensive lasers would do it. Have a look at the spec's for lasers in the Edmund's Scientific catalog. They are all in that range for red lasers no matter what the price.

Pete.

I would think that a good old fashioned height gauge would be the proper tool to use. A laser would only illuminate 1/2 the hemisphere and you would have to reposition the light or the item being marked. Do you have any metalworking books that show the use of a height gauge used for laying out? Pretty simple instrument for what it does. From looking at the art work that you are doing I would think that you could fab up something that would do what you need to do. You only have to hold the marker at a fixed height while you move it around the piece being marked out, while the piece being marked is held steady and the sliding marker is on a flat surface that is parallel to the to the line you wish to draw. For precision metal work this is done on a surface plate. You could probably get away with a piece of glass or a good flat counter top. I could send you pictures if you like. lg no neat sig line

I understand, and you are correct, of course. I did not mean to suggest anything else. I only intended to advise the OP that she could get a finer line with a slit, as she in fact may well be able to do.

To be sure, beam divergence is always increased by any close aperture, including a slit. I hope I didn't lead anyone to think otherwise.

When a slit does effectively narrow the beam, I suspect it accomplishes this by blocking part of the diffraction pattern produced by whatever is already in the optical path. If this is the case, my additional suggestion that the slit should be very narrow was bad; it should be no narrower than the "main" beam width at the point of the aperture. This should minimize the beam divergence caused by the slit.

I should also point out that there is some distance at which a slit would only worsen the problem, and that the farther the slit is from the laser source, the better.

Jim

My usual solution to this problem is a lot less technical.

First, stand your object on a flat table, preferably clamping it so it can't move, with your intended cut plane horizontal.

Then, hold a pencil horizontally on the top of a block of wood, with the point sticking out over the edge a bit. Pick the height of the block so the pencil point is at the cut height.

Now you can slide the block around on the tabletop all you like, and the pencil tip is always at the same height. Just slide the block round the object, drawing your cut line as you go.

It's not a super-accurate solution unless your table is very flat, but it's probably better than marking from the laser line.

Hi, Have a look at something like this

I bought one of these and find it very good for this sort of thing. This one's in Australia, but they should be elsewhere as well.

As far as the width of the beam goes, I dont think it matters if all you are after is a straight line just mark to the center or edge of the dot or line in this case.

I found a bit of two inch masking tap stuck up around the side of the laser will stop it from throwing the laser in directions you don't want it to go.

This thing comes with shaded glasses, but they are to help you see the laser in sunlight, not to protect your eyes, as like someone else posted this one doesn't seem powerful enough to do any damage, just don't ask me how I tested it! I think the rotary action is safer again for a given power laser, because it is only blinking at you, not staring a hole in you.

regards,

John

WRONG - some tiny ones - but there are laser pointers and industrial spinners that will blind or spot your eyes.

When I got my laser level it came with glasses because of the class of laser. A friend of mine just got a 'green' laser pointer - and it can be seen 7 miles away on a water tower at night. That is 14 miles of round trip and droppoff by the square of the distance.

Martin

With luck it will hyper link to hyperphysics - I found this on my private copy and then went to the public version for this group.

Single and double slits are different, but energy is lost in the scattering to each side.

Martin

My understanding is that because that is not a point source, the 1/R(sq) law does not apply. Of course it's still a long way for a laser pointer like that.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

What I *think* is happening is that the divergence follows a curve -- I believe it is a "sinc" function -- with the most energy per unit area in the center, and decreasing amounts as the divergence increases -- up to the point at which it drops to zero and starts back up -- to produce rings for a single beam, or parallel lines for a beam which would otherwise produce a line.

What adding the slit will do is decrease intensity at *all* points in that function, and reduce in a narrower part of it being above the threshold of detectability -- which is probably a function of the ambient illumination. So -- it gives the *user* a narrower apparent beam.

I have observed this effect with a laser pointer and a set of pinholes from an IR blackbody illuminator, designed to control the total illumination received by the device under test.

I have not had a laser set up to produce a line, so I have not experimented with the same effect there. I would probably attempt it using a pair of double-edge razor blades -- or perhaps even blades from injector type razors -- if such are still made with a single blade. (I haven't shaved since about 1977 or so. :-)

Enjoy, DoN.

The pointer is a =5mw model. It is really an UV that is blasted in a Yag xtal. So in a way, the UV is pumping the Yag xtal and it is the laser.

Back in the dark ages - aka '68 - we got a couple of lasers for the lab and they were listed at 5mw - just a tweak under the legal limit or just on it - for mandatory restrictions.

Naturally, we hauled it up to the roof and shot the water tower with it. Worked nice. :-) Nowadays, a pocket holds one, back then it was a He OO IIRC.

Martin