Compound lens with different lenses.

[Clyde Dale]

Hey all!

Been talking with Russ vai e-mail, but forgot that there was the forum here!

I'm wondering if it's possible to use different lenses with the compound setup?

I've been fiddling with a new 4in while waiting for a replacement 63 for my compound nozzle, and WOW, talk about more cutting power! I can crank it down to 20% (100W China Red OMTech) power and it will cut through 1/4th like butter no problem - I tried to drop it to 15 but it wasn't quite cutting through then.. but wow, before even with just the 38 I would have to use 45-65 depending on the wood. Of course I don't quite have the tiny point, so I was wondering.... why not use a 101 in the compound? Or a different combo of lenses? Additionally (I plan to try this out later when I can get out to the shop, but perhaps you'll respond with a "DONT DO THAT!" before I start if there's a reason not to lol) Additionally why not set the 101 at the higher point in the tube with the 38 still down in the nozzle? I don't know my lens optics worth a darn, but I'm not dumb.. Could one swap the lenses around and use the 38 in the 50 position and the 101 below? Or some combo there of? May possibly require lens positions that tubes don't have... What I'm trying to do is get the cutting power of a 4in into the point of a compound setup. While the 4in does an awesome job, it doesn't have the detail capability of the compound..and on the other side the compound is crappy for cutting through material of any decent thickness.. even with 1/8th inch the power has to be up pretty high and you get a lot of charring etc.. unless you make a lot of lower power passes. Seems if I could narrow down that more vertical walled beam from the 101 in a compound setup with the power behind it could cut out some very intricate designs with thicker material. I.E. Resolution close to the compound, but with the cutting ability of a 4in.

Thoughts?

C.D.

[Dave Vigness]

I don't have the nozzle for compound, but I love my 4" for thicker material, especially the GaAs. The narrow beam cone is amazing compared to the coated glass lens'. Only downside of the GaAs is if you have an integrated red dot, it doesn't pass visible light.

[Clyde Dale]

I'm actually using a GaAs 4in right now. IT does do a good job, but for example I tested it with a SVG pattern that had some pretty intricate detail work, and the smaller bits are just not high rez enough, get small details getting burnt or ablated away. Now..if can just narrow that beam down even more.... lol. Itching to get out to the shop and futz around with them and see what I can get. It would be awesome to get the cutting power of the 4in into the point of a compound.

[Clyde Dale]

Russ just got back to me on this for anybody who is interested:

"I have spent a lot of time experimenting with the LONG compound lens ie 4" at the top and something else at the bottom. I was convinced it would create a faster or deeper cutting system. It was a wasted 2 weeks of learning that wrecked 4 lenses and got nowhere...... but it did make me rethink my whole strategy for testing lenses. That redirection eventually led me to understanding how lenses actually cut AND it's not like the textbooks imagine. Along the way it taught me that if you pre-shrink the beam to a smaller footprint before hitting the bottom lens, two things happen, First, if you have a brown Chinese PVD lens you could well damage/crack it because you exceed its energy density capability. Second, because the light rays are not hitting the second lens in the way the lens was designed ( for PARALLEL rays) the converging beam dramatically shortens the focal length of the second lens. Short focal length lenses are great for engraving but crap for cutting to any depth. A single lens is much better for cutting. Why did you turn your power down?. In general for cutting you need to put your power up to its maximum allowable current for the tube power and then gradually increase the speed until your pieces do not fall out.The faster you run the narrower your cut will get and the cleaner your edges will be. Give it a try. Also I have discovered that of all the lenses in my vast collection, a 63.5mm gallium arsenide lens is the best cutting lens in the box. I use it for everything except photo engraving. Depending on whether you are running at 400mm/s or 20 mm/s your focal distance can change by as much as 2mm. Thus, do not use the setting piece, test the focus yourself."