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Graham Taylor
02-22-2015, 8:10 AM
OK, I am not sure if this is another stupid question or not:

So I can cut 3mm MDF and 3mm ply with both my 1.5" and 2" lenses - the results look very simillar so which one would be the best to use or, because the results are simillar, does it really matter?

What thicknesses would I deffinately use the 2" lens on - 5mm and upwards?

Thanks for bearing with me.

Scott Shepherd
02-22-2015, 10:05 AM
The distance between the nose cone and the work stays about the same between those 2 lenses, since you change the mounting location for the 1.5, so I'd say it's just personal preference. I tend to keep my 1.5" for special things and use the 2" for general use. Technically, the 1.5 will have a little higher power density on the spot, but for something that thin, it's not much of a factor. I consider my 1.5" something to use for fine engraving, and don't use it for cutting too often.

I use the 2" all the way up to 1/2" material. I will go to a 2.5", but I don't go to the 4" because it puts the head so far from the work, the air assist isn't actually in the cut any longer and you get flare ups.

Just my opinion. Your mileage may vary.

Neville Stewart
02-22-2015, 10:48 AM
On the air assist topic, I wondered if you ran more pressure in the assist line would you get a deeper cut like a plasma cutter effect. I know it's not the same principle however I've often wondered.

Michael Hunter
02-22-2015, 11:00 AM
The 2" lens will give a little more tolerance if your material is not completely flat and for thicker materials it is definitely the lens to use.

On ply and MDF, the smaller spot size of the 1.5" lens is hardly going to make any difference as these are not "high resolution" materials.

One of the posters here (John Bion?????) said that he gets cleaner and deeper cuts in wood by using higher pressure on his air assist.
I don't have any control over the pressure on mine, so haven't been able to try this for myself.

Richard Rumancik
02-22-2015, 1:26 PM
On the air assist topic, I wondered if you ran more pressure in the assist line would you get a deeper cut like a plasma cutter effect. . . .

If you were running a laser with a concentric air assist (i.e. air exists through the nose cone) then I would expect that you could cut thicker material. But if the laser air assist is directed through a tube from the side, which I believe to be the case with the Speedy and many others, I don't think you could really get a directed airflow to eject material through the sheet.

The "nose cones" on commercial metal cutting lasers are highly engineered as the air is required to move molten metal out of the kerf. They are an integral part of the laser cutting head, as shown in this pic.

http://www.aml.engineering.columbia.edu/ntm/level1/ch03/html/l1c03s05.html


But the nose cones and/or air assist tubes on laser engraver systems were not really designed for that. It is mainly to keep dust, debris and smoke away from the beam path, and to keep debris off the lens.

Some of the GCC's have the air fed through the nose cone (like my Mercury) but I still don't see it as helping that much with ejecting material during cutting, (although I do use air assist for everything). The hole in the nose cone is quite large and I doubt it really creates much of a jet of air 1" or 2" below the nose cone.

For a material like acrylic, I think with a well-engineered nose cone may gain some advantage in cutting thicker acrylic, as acrylic cuts by turning the acrylic into vapor and then expelling the gas. The kerf can also act as a waveguide. So I think in theory it could help, but I don't think the nose cones on any small laser system are designed to do this. The downside of high velocity air is that the turbulence of the air could cause a rougher edge, as the acrylic will solidify quickly. So you could get more pronounced striations and swirl marks.

I would not have expected as much improvement with wood which tends to decompose rather than vaporize like acrylic, but the air will still remove char particles and smoke from the cut, which should make cutting more effective.

Scott Shepherd
02-22-2015, 2:03 PM
if the laser air assist is directed through a tube from the side, which I believe to be the case with the Speedy and many others, I don't think you could really get a directed airflow to eject material through the sheet.

Just for reference, the Speedy has the air blowing through the nose cone, not in from the side (that's an option that's available, but the standard air is through the nose cone).

I agree with you on the thoughts about the acrylic, and you are 100% correct, more air does causes more striations in real life. I think Synrad recommends 1 or 2 psi for acrylic.

Graham Taylor
02-22-2015, 2:42 PM
The distance between the nose cone and the work stays about the same between those 2 lenses, since you change the mounting location for the 1.5, so I'd say it's just personal preference. I tend to keep my 1.5" for special things and use the 2" for general use. Technically, the 1.5 will have a little higher power density on the spot, but for something that thin, it's not much of a factor. I consider my 1.5" something to use for fine engraving, and don't use it for cutting too often.

I use the 2" all the way up to 1/2" material. I will go to a 2.5", but I don't go to the 4" because it puts the head so far from the work, the air assist isn't actually in the cut any longer and you get flare ups.

Just my opinion. Your mileage may vary.

thanks for for the reply Scott, you have answered another question I was going to ask about the power level at the spot between the 2" and 1.5" lens.

Steve Morris
02-22-2015, 4:29 PM
Thanks for the answers guys, food for thought.

Thanks for asking Graham, as far as I'm concerned there are no stupid questions just stupid answers ;)

Richard Rumancik
02-22-2015, 7:19 PM
Just for reference, the Speedy has the air blowing through the nose cone, not in from the side (that's an option that's available, but the standard air is through the nose cone). . . .

I stand corrected. I did a quick image search on Speedy & air assist and I saw a side version which misled me.

I like pressurising the nose cone better than just a plain tube on the side as I think it protects the lens better. The downside is that if you don't have clean dry air, you could end up harming the lens rather than protecting it.

Graham, I didn't actually answer your question but I'd agree with Steve - save the 1.5" lens for precision work (marking and fine cutting of veneers, films etc) and use the 2" lens for MDF if it is working okay.

Scott Shepherd
02-22-2015, 7:52 PM
I like pressurising the nose cone better than just a plain tube on the side as I think it protects the lens better. The downside is that if you don't have clean dry air, you could end up harming the lens rather than protecting it.



Me too Richard. And also, don't leave the nose cone on with the air off. That's a recipe for a broken lens in record time (minutes, not hours or days).