Extendable nose cone

[Bill George]

On my laser It has a extendable nose cone. I have been doing all my work so far with the cone all the way up. I made my focus gauge with it up in that position.

What happens to the focus and laser performance when that cone is moved so its down toward the work more, like an inch or so, maybe more? Do I lose power or does the focus just need to be re-calculated /tested and a new gauge made?

[David Somers]

Bill,

I am asking out of ignorance. Is the lens mounted in the extendable cone? Or is it mounted in the stationary part of the tube?

Dave

[Bill George]

Me Duh. I went out and looked, yes the lens is in the cone, and when I removed and went over to the work bench and looked at object, it appeared to focus at more or less the same distance that my focus gauge was set at. But alas even fully extended on the laser head there was not enough clearance to allow me to slide something under the rails.
I'm guessing now I will need to get a lens and cone that will allow that clearance, otherwise I am limited to the bed size.
My machine has pass thru doors front and rear, also the left side opens allowing material larger than the bed to be processed.

[David Somers]

Bill,

I am sorry....I am being dense.
Do you have a motorized table? A manually raised and lowered table? Or a fixed table?
Normally, you would be put your object on the table and raise it with the motor or manually raise it to the focal height using your gauge to set the distance. Your lens would be fixed.
Some folks have a static table and they raise and lower their lens to achieve the right distance to the object. That typically works OK when you work with objects of a very limited thickness.
Someone on the forum had talked about having purchased one like that in order to save $$ and because they saw limited thickness objects in their future. I think it might have been Kev?
And he developed a lens tube that gave hims some better range of motion in the tube. And he also had several focal length lenses with tubes for each.

Or am I really misinterpreting what you are saying??? Which wouldn't surprise me much today!

Dave

[Bill George]

Manual table crank up and down. But it would make no difference in this problem. I can and will put objects on the table that will extend beyond the table dimensions, and therefor the table can not be raised past the rails. The existing tube and cone can be extended down to the limits of the tube length but it is not a solid stable fit. It will still work all the way out but not well as I think the lens alignment is off at that setting. The focus setting never changed from the original.

I see on LightObject dot com I can purchase a longer focal length lens, it would give me about 22 mm more reach which should be about right.

Anyone with suggestions is welcome to educate me on this.

[David Somers]

I think I have the picture. Because your object extends beyond the boundary of the table it strikes the rails above as it is raised and can't go past that point, and therefor the surface of the object is below the focal plane of your lens. And your lens, which has some adjustment on it through the use of a sliding tube, can't be extended low enough to compensate either.

Thanks for being patient and explaining that Bill.

Dave

[Bill George]

I think I have the picture. Because your object extends beyond the boundary of the table it strikes the rails above as it is raised and can't go past that point, and therefor the surface of the object is below the focal plane of your lens. And your lens, which has some adjustment on it through the use of a sliding tube, can't be extended low enough to compensate either.

Thanks for being patient and explaining that Bill.

Dave

Correct. And now what I need to find out is.... if the laser beam comes out of the cone, say 1/2 or 3/4 inch (13-20 mm) will that be a problem? I think the air flow would not make a difference.

[Kev Williams]

Bill, does your lens tube (? for lack of the actual name) look like these? If so, consider having some extras made like I did. The shortest one was the original, that I cut down. The 3rd one is a duplicate of the original, the other two I had made longer.

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Because I have a vertically immovable table, that I often remove to engrave non-typical items (like the stainless container shown below), I needed a way to be able to focus on parts other than stacking shims under them. Triumph charged me $120 for the 3 tubes. Money well spent for me. In this pic below I'm using one of the longer tubes. I actually use the shortest more than any of them, because it allows me to engrave thicker items on the table than I could with the 'standard' tube. If you DON'T have a similar lens setup, post up some pics--

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[David Somers]

Many thanks Kev! That was the photo and info i was trying to remember for him!!!!

Dave

[Bill George]

Here is what I have. Question, if I purchase a lens with a longer focal length like a 75 mm instead of the 52 now installed, that would change the distance from the lens to the work material. That would mean if I am thinking correctly, the distance from the cone end to the work would be greater. The beam exiting would be exposed more than it is now, would that be a problem?

If I could find a longer cone of course that would solve the problem as I can just use the same lens I have now.
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[Dan Hintz]

Yep, a new (longer, or wider tip) cone would be needed...

[Bill George]

Yep, a new (longer, or wider tip) cone would be needed...

So purchasing the lens with a longer focal length and having the cone tip 3/4 inch above the work instead of 1/4 inch or so won't work?

[David Somers]

Morning Dan!

Just being sure I follow this. When you say "a new (longer and wider tip) cone would be needed." Do you mean the tube the cone is part of would have to be longer rather than needing an elongated cone? If you meant the cone itself needed to be elongated I am not sure I follow the reason for that?

It seems like Bill wants a longer tube so that his lens, which is in the cone itself, can be extended down further to reach the object on his table which can't be raised beyond a certain point. In other words, he is moving the focal plane down to the objects surface by lowering the lens rather than by raising the surface of the object up to the focal plane using the table.

If that is the case, and he is still using the same focal length lens, why would the length and width of the cone need to change? The lens is still mounted in the cone in the same position and in theory wouldn't the size and shape of the beam coming through it remain the same? The only change is how far the laser beam has to travel from the mirror on the tube mount down to the lens. And in theory that beam is relatively coherent and roughly the same diameter when it reaches the lens as it was when it left the mirror above? I can see where if he changed the actual focal length of the lens he would want a different cone to match the new shape and size of the focused beam, but is a different cone called for when using the same focal length lens in this case?

Whew! Need a cup of coffee!!!

Thanks Dan!

Dave

[Bill George]

I did some Searching on here and found out if you go to a longer focal length lens you will lose some sharpness in detail when laser engraving. But this will be only a 22 mm difference so I am wondering since the long distance work will be mostly wood ( at least for now) if that would be a big issue.

Ideally IF I could find a longer tube/cone assy that would be the solution.

[David Somers]

Bill,

Since Kev had Triumph make some new tubes for him would it be worth your while to contact GWeike for the same thing?

[Bill George]

Well heck I own a metal lathe, I can gather up some aluminum round stock and just make a extension tube for the existing one. One that slips into the mounted laser head and has the other end sized to go over the tube on the cone end. Easy peasy. The machined end of the tube is a sloppy fit anyway and I can correct that when I build my own extension.

[Dan Hintz]

Dave,

If he wants a longer focal length lens, he'll want either a longer cone, or a similar-length cone with a wider hole.

[Jerome Stanek]

doesn't your laser have an up and down bed like the say in the specs. I use the bed to set the focal length and just fine tune it with the the lens tube.

[Kev Williams]

Your lens tubes are essentially just like mine, so there ya go...

Your 52mm lens is essentially a 2" lens (2.04"=52mm), this means the distance from the lens itself to the work surface should be 52mm to be in focus. However, ramp testing should be done to find "true" focus. A 75mm lens is roughly 3", a 100mm is roughly 4".

I took your pics and doctored 'em up a bit. The yellow lines are approximately where the lens is located inside the tube. With a 2" lens, the cone ends up pretty close to the material. Good for air flow when cutting. When moving to longer length lenses, the tip of the cone will obviously be much farther from the work. With a 100mm lens the distance becomes a country mile! If you're using air assist thru the cone, this is why you need a longer cone, so the air will actually reach the work. And a wider hole in the cone is good to compensate for the wider focused beam. Note that using a 4" lens with a short cone means the beam has only started focusing down, and the sides of the beam will likely hit the sides of the cone.

Me, I don't use the cone, I have my air (when I use it) routed around the lens with a tube, pointed at the work. For focusing I just have a bunch of 1/4" thick plastic posts cut to length and labeled, they fit between the bottom of the tube and the work...

http://www.engraver1.com/erase2/glens.jpg

[Bill George]

But if I just make an extension tube like my post above on the lathe. I can still use the same lens? Correct? It just extended the distance the beam has to travel by 1 inch or 25 mm from the mirror on top of the head. Or will that make a difference in the power?

I am just making a 1 inch (25mm) extension, not the entire tube and cone, lens holder and all.

The only issue for me anyway is finding some solid round aluminum bar or heavy tube stock. I have lots of 2x2 inch square on hand but gee that's a lot of machining to make it round. Trying to buy some here locally might be a waste of time.

[David Somers]

Dan,

Gotcha. Phew! I was just getting confused. It sounded like you were saying he needed a new cone with wider tip even if he used the same lens but with a longer tube or barrel, but you were really referring to the use of a longer lens requiring a different cone/wider tip.

Thanks!!!!!

Dave

[Bill George]

Ok got the proto type done and now in testing. It did not seem to lose any power and the Extension was done on the lathe on the fly via measurements from the cone slider and holder still mounted in the machine. Really don't know how close the Chinese CNC machines hold tolerances but I tried my best to make it fit snug. In fact the lower part where I added the 8-32 US Allen screws held in without the screws.
Used what I had on hand, sometime I will pick up official thumbscrews, and the longer air hose to the cone is a piece of snowmobile fuel line I had on hand also but works very well. I added a "O" ring to the top part of my Extension so it could be pushed up tight to the top and when the gold thumb screws tightened seem to hold tighter.
Minimum gain is 40 mm and it could be adjusted further out, but the OEM end has to much play to be really stable too far out.
The test cut was repeating a job I did yesterday with it at normal height.

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