The red dot question

[John Finnegan]

Ok, folks, does the through-lens red dot reduce the power of the laser?

According to my vendor, yes it does, and I should choose the head mounted red dot.

Need an answer soon, please.

What say you, sawmill creek users?

Thanks,
John

[Gary Hair]

Ok, folks, does the through-lens red dot reduce the power of the laser?
Absolutely not, but I'd sure like to hear his reasoning!


According to my vendor, yes it does, and I should choose the head mounted red dot.
Time to find a new vendor.

Gary

[John Finnegan]

For the through-lens red pointer: According to my vendor, the through-style 'gold' mirror will be required next to the laser tube and will reduce the power of the 100W tube somewhat.
Conceptually this makes some sense, but I'm new at this so I thought I should check.

Thanks for your reply,
John

[Rich Harman]

Since the only way to get a red dot laser to be coincident with the CO2 laser is to place a mirror in the beam path, there will be some power lost as the CO2 beam passes through that mirror.

Does it make a difference? I think that is going to depend upon the quality of the beam combiner, and personal preference.

[Rodne Gold]

We removed the red dot thru the laser path mirror as it was causing some issue with the diode itself, had a meaningful increase in cutting speed etc , removed it on our other chinese machine for an increase as well..approx 10% faster.
I think the red dot is somewhat a "frill" , the nozzle shows where the laser is going to fire . However the red beam , if aligned 100%, IS useful for alignment and maybe for positioning but its not a deal breaker for me. We don't care about autofocus or red beams....in ALL our lasers...
What you have to be careful of if mounting the diode at the head , is that it doesn't become a mission to remove the nozzle to clean the lens.

[Dan Hintz]

Ok, folks, does the through-lens red dot reduce the power of the laser?

According to my vendor, yes it does, and I should choose the head mounted red dot.

Absolutely (sorry, Gary ;))... any time you put a coating on a lens/mirror that reflects one wavelength and passes another, there is bound to be some loss (no matter how residual). Is it enough to make a noticeable difference? In Rodney's case, yes... I think it may have been a bum coating or they got the angles wrong (depending upon the coating, it can be very sensitive to entrance angle). In most cases, there should be very little difference, but it's something to be aware of.

[Mike Null]

If there is a difference it is undetectable to me. And, the red dot is very important in my operation.

[John Finnegan]

Thanks for all your advice, I think I'll go for the head mounted style.

-JF

[Mark Ross]

Not having the pass through would make alignment a nightmare for me. I'll vote for the pass through.

[Gary Hair]

Absolutely (sorry, Gary ;))... any time you put a coating on a lens/mirror that reflects one wavelength and passes another, there is bound to be some loss (no matter how residual).

I guess it depends on how they implement the dot into the path. On my GCC it is not done through another lens, it is introduced at a slight angle into the first mirror and then adjusted to be coincident with the beam. So, in my case, absolutely no change in power.

[Dan Hintz]

it is introduced at a slight angle into the first mirror and then adjusted to be coincident with the beam.

How is that done (without using coatings that have different angles of reflection for visible and IR)?

[Rich Harman]

On my GCC it is not done through another lens, it is introduced at a slight angle into the first mirror and then adjusted to be coincident with the beam. So, in my case, absolutely no change in power.

I don't see how that is possible. Can you post a picture or diagram?

[Scott Shepherd]

It's like that on most mainstream lasers. If I recall correctly, the Epilog's were like that, I don't know on the Universal, but I'm 100% sure on the Trotec's, that it's introduced into the system externally. I know because I just adjusted it.

[Gary Hair]

How is that done (without using coatings that have different angles of reflection for visible and IR)?

Here is a picture I found with the red dot assembly. I added the notations - both the red dot and laser beam reflect off the mirror and exit through the hole indicated. It works quite well and there isn't any power loss by using a reflective/pass-through type lens.

Gary

246043

[Rich Harman]

I still don't get it. I can see how that system can get close to a colinear beam but not all the way.

Two beams reflecting off the same spot on the first mirror but from slightly different angles cannot be colinear. If they don't reflect off the same spot, they still can't be colinear but I can see how they could be adjusted so that it works for a limited area of the table.

[Gary Hair]

I still don't get it. I can see how that system can get close to a colinear beam but not all the way.

Two beams reflecting off the same spot on the first mirror but from slightly different angles cannot be colinear. If they don't reflect off the same spot, they still can't be colinear but I can see how they could be adjusted so that it works for a limited area of the table.

As long as the dot and laser beam hit the third mirror in the same place then they will remain colinear, or pretty dam close, and they are aligned at any position on the table. You start by removing mirror 1 and burning a spot on something about 10' away. Then you adjust the dot to be slightly above the burn spot, or maybe it's below, I can't remember which without looking at the manual. You then burn a spot at mirror 2 to get the beam centered, and then at mirror 3, adjusting the red dot when you get to mirror 3. This will keep them aligned to hit mirror 4 and the lens in the right position. Maybe it doesn't make sense, but it works.

[Dan Hintz]

Here is a picture I found

246043


I can see how that system can get close to a colinear beam but not all the way.

Ah, i get it now. Rich, instead of trying to bend the red beam just once off of the main mirror, they bend it twice... once off of the "red dot" mirror, then off of the main mirror. By bending it twice, the entrance angle can be less than 90 degrees... think of it as two 45 degree bends.

[Rich Harman]

I was thinking that too, so I went to draw it out and I can't make it work...

[Lee DeRaud]

Ok, folks, does the through-lens red dot reduce the power of the laser?

According to my vendor, yes it does, and I should choose the head mounted red dot.I'm willing to believe it reduces the power, but I suspect the amount of that reduction is an order of magnitude less than the variance in power from one randomly-selected tube to another.

But I'm 100% sure that (1), the lasers your vendor sells use the head-mounted dot and (2), if you asked him how much it reduced the power, he wouldn't have a clue.

[Rodne Gold]

Our problem is the 1/2 silvered mirror was promoting some scatter of the beam for some reason and the scatter was impinging on the plastic lens of the red diode and melting it a bit , making the red beam blurred or scattered it'self.
Easiest solution was remove the system.
The GCC way is great , you can adapt the chinese lasers to do it that way , but it requires another adjustable mirror holder (I brought in 3 extra .. princely sum of $22 each) or just a conventional mirror and a way to adjust it in 3 dimensions (GCC use a normal glass mirror for the red beam)

[Greg Holt]

Since the only way to get a red dot laser to be coincident with the CO2 laser is to place a mirror in the beam path, .............................

Not true. There is another way.

When the lid is open, the laser pointer drops into the path and becomes in effect coincident with the CO2 laser.

Safety mechanisms prevent the CO2 laser from firing while lid is open and the pointer is in the path.

Lid shuts and laser pointer lifts clear of the CO2 laser path. No mirrror in the beam path.

[Dan Hintz]

Wow, that is...er, ugly, to say the least, Greg. :-/ Moving the laser with the lid screams inaccurate to me... maybe "accurate enough" for many, but for my money I want a beam that's guaranteed to be in the same spot each time, and such a mechanical solution precludes that.

[Greg Holt]

Wow that's a pretty big call.....seeing as you have not used it........and never even seen it working. :)

On the other hand I have been using it for a year now and find it does a great job.

[Lee DeRaud]

Since the only way to get a red dot laser to be coincident with the CO2 laser is to place a mirror in the beam path, there will be some power lost as the CO2 beam passes through that mirror.(sitting around waiting for the turkey to thaw...)
What if it's done the other way around? It doesn't matter if the pointer beam incurs some loss: have it go through one of the main-beam mirrors from the back.

[Dan Hintz]

Greg,

How do you align such a thing? If the lid is closed, you no longer have access, which means a lot of open/adjust/close/try/repeat...

[Rich Harman]

Greg,

How do you align such a thing? If the lid is closed, you no longer have access, which means a lot of open/adjust/close/try/repeat...

It appears that the red dot is attached to the front lid. It should be pretty easy to adjust it while watching through the window of the main lid.

Neat idea, wouldn't work for me because I don't have the lid closed half the time when I am using the laser.

[matthew knott]

Another common method is to have a clear optic made from ZnSe with anti-reflections both side fitted at 45 degrees right at the output window of the CO2 laser, the laser goes straight through (pretty much). You can then fire the red beam down onto this optic and it will be reflected off the optic at 45 degrees on the same path as CO2 beam, you simply take a burn at a long distance then adjust the red beam to land on the spot.

[Greg Holt]

Greg,

How do you align such a thing? If the lid is closed, you no longer have access, which means a lot of open/adjust/close/try/repeat...

Oh I thought someone who says, sight unseen, from the other side of the world, "screams inaccurate" and "such a mechanical solution precludes that" would have a better idea of how it worked. :rolleyes:

The laser pointer drops into place when the lid is open. And besides the laser tube, first mirror and laser pointer are all in a separate compartment on the back of the machine. Not accessed through the main lid at all.

It was actually surprisingly easy to align because of the way the mount is designed. If I remember correctly, I have only once in a year, gone back to tweek the adjustment.

:)

[Greg Facer]

Looks good to me!

I'm sure you could also rig something up that was not tied to the lid but still allowed you to swing the dot pointer in place. Add one limit switch of some sort tied into the water alarm / lid alarm circuit and you couldn't laser it either. Solenoid or air cylinder come to mind as workable, although a pivot, adjustable stop, some string and a spring work would probably work too. Something to play with if I think I need it.

As Rodney says, the red dot (on the Chinese machines) makes the lens harder to get at and also needs readjusting for thickness. I haven't removed it yet, but thought about moving it off the lens barrel. Through the nozzle would be even better. However, as the pointer doesn't really show up well on clear acrylic, the whole pointer thing and its use is still a work in progress.

[Dan Hintz]

Oh I thought someone who says, sight unseen, from the other side of the world, "screams inaccurate" and "such a mechanical solution precludes that" would have a better idea of how it worked. :rolleyes:

My point was any time you move the alignment of the two beams every time the lid is opened, there are bound to be inaccuracies introduced... a solid bump to the lid, for example. Don't think I have any issues understanding how it works, I just don't think it's a sound idea.

[Greg Holt]

No not a sound idea. It just works. :)

[Rich Harman]

Looks good to me!

I'm sure you could also rig something up that was not tied to the lid but still allowed you to swing the dot pointer in place. Add one limit switch of some sort tied into the water alarm / lid alarm circuit and you couldn't laser it either. Solenoid or air cylinder come to mind as workable, although a pivot, adjustable stop, some string and a spring work would probably work too. Something to play with if I think I need it.

That's a really good idea. I was also thinking to put a switch on it series with the water alarm. Using the air assist and a small pneumatic cylinder would be an efficient method of moving it out of the way.

[Rich Harman]

My point was any time you move the alignment of the two beams every time the lid is opened, there are bound to be inaccuracies introduced... a solid bump to the lid, for example. Don't think I have any issues understanding how it works, I just don't think it's a sound idea.

Only one beam is being moved. Certainly it would have to be well made to retain accuracy but that should not present an insurmountable problem. Our lasers already have two mirrors that are in constant motion, they maintain alignment pretty well.

[Ross Moshinsky]

I don't see any issue with Greg's solution. It seems pretty effective to me.

[Bill Cunningham]

I use the red dot to match the engraving point on the table with the location on the computer screen. Why would it bother the power of the laser itself, when you can simply turn it off before engraving. You don't need it 'while' engraving, only for setup.. Or, is the Epilog unique in the fact that you can turn it off from the front panel?