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[MonkeyHead]

Youd be MUCH better having a fixed laser position and a gimballed mounting containing the material requiring cutting...

[TSTwizby]

I'd guess you could do it, but the loss of precision and consistency would be significant over a basic horizontal moving arm style setup. I'd worry that changing the angle and height would mean a very inconsistent energy delivery over a pattern, which may or may not matter that much depending on the material and overall laser power. Off the top of my head a 45 degree rotation would be a roughly 30% drop in power at the extremes, assuming the distance change is negligible compared to the angle effect. You may need to compensate with more sophisticated control than usual for your burn time, and that would be hard given the motor setup.

For any sort of precision (and to avoid cable problems) I'd certainly go for rotators rather than a ball and external motors. It's more guaranteed that there won't be slippage and it's easier to calibrate.

Not to mention, purely from a safety POV, that a free floating hamster ball would be a huge risk. If the laser is even capable of coming to the horizontal (or worse, above it) you would want the system well contained on top of basic precautions (effective eye protection, no reflective objects in it's firing range). The chances of it firing outside of your expected area means you need to make the entire room laser safe, or at least absolutely any theoretically possible firing angles. Having it more directly connected to a motor setup with a hard maximum elevation would vastly reduce the hazard.

You can probably build around a lot of these issues, but they are complications that reduce the viability of the build in my eyes.

I'm not sure what you're saying with respect to laser power. Again, I'm not especially familiar with lasers, so could you explain why having it at an angle would reduce the power?

With respect to the safety concerns, it is very easy to put a 'ring' around the ball which prevents it from rotating more than some amount upwards.

By a rotator, do you mean something like a pair of motors placed at right angles to eachother? I considered building something like that instead, but while it would reduce the amount of random errors that would pop up while the laser turned around I'm pretty sure it would also be much harder to calibrate. I decided to go with the ball because it was a stabler design, in the sense that fewer of its parts are moving around. Am I wrong about this?

Youd be MUCH better having a fixed laser position and a gimballed mounting containing the material requiring cutting...

The two main problems with doing this is that it would take a lot more space and materials to build and it would introduce a hard upper limit on the size of things I can cut. If I have the laser pointing down on a circular platform with radius R, then I can cut any shape I want to of square size up to almost 4R by cutting one quarter(ish) of the material at a time. With the material spinning around, within a sphere of radius R, it would be impossible to cut anything larger than a square size 2R, and very difficult to cut most things of size larger than about 1.4 R. Also, it would do the opposite of two things I am trying to do with this: namely, taking up less space and making scaling easier to handle.

[Shazbot]

I'm concerned your cuts will be sloppy and of irregular width given the constantly changing angle of incident with the material. Furthermore cutting paper is an interesting science fair project, but if you intend to have a commercially viable product, you have to be able to cut heavier materials consistently. For an X-Y table-type laser cutter, the math is simple to figure out how fast the laser can travel through the cuts and still go through the material. For this arrangement, heavier materials hit at an angle may be incompletely cut if the machine isn't going slower at the high-incident points of the cut. Also, I imagine cutting anything thick is going to leave the outer edges actually sharp. 45 degrees is a knife edge.

[TSTwizby]

I'm concerned your cuts will be sloppy and of irregular width given the constantly changing angle of incident with the material. Furthermore cutting paper is an interesting science fair project, but if you intend to have a commercially viable product, you have to be able to cut heavier materials consistently. For an X-Y table-type laser cutter, the math is simple to figure out how fast the laser can travel through the cuts and still go through the material. For this arrangement, heavier materials hit at an angle may be incompletely cut if the machine isn't going slower at the high-incident points of the cut. Also, I imagine cutting anything thick is going to leave the outer edges actually sharp. 45 degrees is a knife edge.

I don't see what the angle will affect except for small changes in the size of the dot at the end. I'm not intending to make a commercially viable product, at least not yet. For now I just want to test the principle. This would not, of course, work for cutting thick materials due to the problems you mentioned with aiming at an angle. Thanks for pointing out the problem with sharpness, I hadn't thought of that.

[kaenneth]

I'm not sure what you're saying with respect to laser power. Again, I'm not especially familiar with lasers, so could you explain why having it at an angle would reduce the power?

Same reason it's colder on earth as you go north/south away from the equator;the angle of incidence can cut the power/area ratio considerably.

[GalenEvil]

I approve of this project. I am going to suggest that a very low-power laser be used during the initial prototype phase. If I can get a decent picture of my other suggestion I will add it also later.

[TSTwizby]

Just in case people missed it, this isn't something I'm working on at the moment, or something I intend to do in the near future even (I was going to use it as a summer project, but missed out on funding). If I get a chunk of money and/or access to a 3D printer/lathe then I'll have something to work with.

I am going to suggest that a very low-power laser be used during the initial prototype phase.

DEFINITELY THIS. Good lasers are expensive, probably more expensive than the rest of this project put together. Also, dangerous.

[GalenEvil]

If you go with a few sets of gears you can probably get some high-precision laser guidance, in both horizontal and vertical rotation, and then have an arm for the gears to be attached to for horizontal and vertical movement also powered by high-precision gears. If I can get something set up in Blender that looks right I'll post a picture of what I am talking about. It might be a little easier to control than your hamsterball on bearing-ring. It will also have a defined range of motion along the horizontal and vertical axis of rotation.

[TSTwizby]

I think I understand what you're saying, but I'm pretty sure that there's a major problem with that system that the hamsterball system doesn't have, which is calibration. For the hamsterball it's easy; put a sensor in the middle of the base, make the laser shine on the sensor. For a pair of motors however, the motors also need to be very precisely aligned so that the laser not only points directly at the center, but also rotates directly around the center, which is a significantly harder problem.
That said, the advantages with regards to ease of control and more precise movements might overshadow this.

[Osmosis Jones]

I am going to suggest that a very low-power laser be used during the initial prototype phase.

DEFINITELY THIS. Good lasers are expensive, probably more expensive than the rest of this project put together. Also, dangerous.

You can get the example laser for our calcs before (a whopping 20W) for a few hundred bucks. It's pretty well impossible to get cheaper than that, even a good laser pointer that could possibly burn paper is gonna cost as much if not more.

[palsch]

I'm not sure what you're saying with respect to laser power. Again, I'm not especially familiar with lasers, so could you explain why having it at an angle would reduce the power?

The power delivered by a laser is spread across the spot area. Increase the spot size and the power density per unit area is decreased. Let's say that to burn through a sheet of paper you need 1 Watt per mm^2 delivered over 1 second (so 1 J/mm^2, just to make things easy here). You have a laser with a spot size of 1mm, delivering 1 Watt of power and calibrated to fire on each spot for 1 second.

Now you increase your angle to 45 degrees. Your power is being delivered over an area ~40% larger (spot is elongated by 1/sin(45) so a factor of ~1.4) due to the angle the beam is at with respect to the target. Now you need to calibrate it to linger over each spot for longer to compensate and ensure an equal burn for each spot.

Obviously not an issue if your laser is overpowered for your purpose, but if you are doing fine control work it's an extra calibration factor to take into account. Where power delivery matters angle matters.

NB: I'm assuming here you have a tophat beam profile with constant energy throughout the profile, as commonly used in cutting lasers. Likely you will have a Gaussian beam which complicates these calculations a little. It might also matter less depending on that beam profile. But it's something that would need to be checked.

By a rotator, do you mean something like a pair of motors placed at right angles to eachother? I considered building something like that instead, but while it would reduce the amount of random errors that would pop up while the laser turned around I'm pretty sure it would also be much harder to calibrate. I decided to go with the ball because it was a stabler design, in the sense that fewer of its parts are moving around. Am I wrong about this?

I'm pretty sure a pair of good quality motors would be easier to calibrate and control than any hamster ball setup. You would need fine power control to the motors, but that's going to be needed in any case. You already need direct computer control and once you go that far it's mostly a programming problem.

Realistically calibration is going to be easier due to removing the risk of slippage and variation in rotation of the ball. You could use sensors to determine exactly where your hamster ball laser is pointing, but determining the exact power to deliver to the motors to make a precise movement is going to be far harder. You would need to rely on real time correction, which isn't great when you are trying to do timed and precise burns. If you have calibrated motors you can have real time response as an additional safety check, not the primary method of control.



Just on the safety front again, I'd recommend doing some basic laser safety reading. Lasers not fixed in a horizontal plane (at waist level, nowhere near eye level) are usually viewed as significant safety risks and often required to be fully enclosed. Cutting machines often have full covers to keep their classification low; a class 4 fully contained can be used as a class 1. Correct eye protection is essential for anything classed 3B or above; a not fully contained cutter will be in this class. Having a lower power mode (usually achieved with an attenuator in front of the laser itself) for calibration and alignment is essential, but the beam should still be treated as a full power one as far as is possible. No shiny/reflective material other than required mirrors in the same horizontal plane as the laser itself; even reduced reflections can be some risk in higher powered lasers. Setting up an interlock to shut down the laser if the enclosure is opened (or if the room the laser held in is opened if you are allowing users with eye protection to use it without full containment) is pretty much required.

[Virex]

I don't think the rotation itself is that much of a problem if you're working at short distances, we can get to sub-millidegree precision nowadays, which probably would yield a deviation less than the diameter of the beam spot. A bigger problem would be that delivering a reliable voltage to a rotating system may be difficult. This can be solved by not rotating the lasing cavity, but shining the laser on a prism or mirror and rotating that. The problem of uneven laser intensities could be fixed by modulating the intensity of the laser depending on it's rotation and distance from the target.


However, since getting high precision with this system probably requires the use of advanced mechanics and the system can't reach around corners, I'm not sure it'd be better than a mechanical arm. One advantage could be that it's a lot smaller, requiring only a laser and a prism with suspension. Such a system could be carried in a suitcase and deployed on-site, for example, for rapid prototyping or on-site machining.


Also, have you done a patent search yet? I'd be highly surprised if no one ever thought of a similar system?

[kaenneth]

I just thought of a cool effect your could potentially achieve with this system;

Cutting through a thick material or multiple layers spaced out, you could make an image that could only be clearly seen from an eyeball positioned exactly where the center of the 'hamster ball' was, when there is a diffuse light from behind the material.

Then, you shift the frame the distance between two average human eyes, and cut a second, slightly different image.

Result: a 3D image cut into the material that can only be seen from one precise point.

Or, cut a series of images the make an animation for people walking past, using the slitted fence effect. but that would be harder to keep the material solid enough.

[Lord Shonus]

This would not only hold no benefit over a traditional design, it would be far worse in nearly every way. Simple is better, and most lasers do not like being moved while in operation. (Plus, the massive size of a laser compared to a mirror assembly (for example, the 10 watt sealed laser I used five years ago was ten times longer and about thirty times as heavy as the mirror mounting) means that you would have to scale up everything at a huge cost, any cooling tubes (or, if you're not using a sealed model, the gas feed) would have to be designed for the movements you want, and you risk damaging a very expensive bit of equipment if something doesn't move right.

[PTTG??]

How disappointing.