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View Full Version : Broke 3rd lense in 4 months. HELP!!



Jim Beachler
11-21-2009, 5:48 PM
I have had my ULS pls 6.60 for just over a year. Have been doing lots of engraving on wood and some cutting. Never cracked a lens.

When I am cutting the wood, it is already painted and lacquered so I was putting tape over the top to cut down on the scorching. Pulling off the tape of each little puzzle piece was getting to be a real pain and taking time.

Hooked up the air assist with cone and small air pump from Grainger recommended by rep. Installed a water separator to get rid of moisture.
Broke one lens when I forgot to turn the air on. Since then have set the program to default to air on. Have cracked 2 lenses since then. At $230 each this is getting more expensive than pulling tape off each piece.

What am I doing wrong??

Bruce Volden
11-21-2009, 6:14 PM
Jim

I have 3 machines, oldest from 1995 and have never cracked a lens. The only things that comes to mind is something (moisture, smoke, some form of contaminant) is getting on the lens and absorbing the energy :confused:

Bruce

Scott Shepherd
11-21-2009, 6:45 PM
I agree, it's either moisture or it's forgetting to have the air on for a brief second. When the lens is cracked, is it clean or dirty (when you remove it)?

A moisture trap may not do the trick. It needs to be very clean, dry air. A trap isn't what I'd consider dry air. Install a dryer in the system just before it goes to the laser. If the lens is dirty when it's cracked, I'd say it's being run without air and the nose cone on. If the lens is clean, my guess would be a drop of water made it through the system and got on the lens.

Just my guessing.

Richard Rumancik
11-21-2009, 11:14 PM
Maybe talk to a few local body shops and ask what they use to dry the air for their spray guns. They may be able to suggest something. Most desiccant-type dryers require cartridges to be replaced as they become saturated or ineffective.

I use an inexpensive version like this

http://princessautoelearning.com/ch3_002c.html

It uses loose pellets, but I put the pellets into a perforated tube to make it more like a cartridge. Harbor Freight might have something similar if you don't want to pay $200-$300 for an automotive type unit.

For the unit I have, you need to cool the air before it hits the pellets. Not a bad idea anyway: if you can cool the air (and ensure the condensate goes into a sump, not the laser) then that alone will help remove some of the moisture. In the link, it says to have 25 feet of tubing between the compressor and desiccator - I used a length of nylon coiled air compressor hose and just wrapped it tight around the desiccator body itself. So moist air enters at the top of the nylon coil; the moisture condenses and runs down to the bottom of the sump, while the air is forced up through the pellets which collect additional moisture. This drips down into the sump. At the top of the steel tube it exits and goes into a filter (you must have a filter after the desiccator.) The unit is drained of water at the bottom.

In addition to water droplets, depending on your compressor type, you might have got some oil on the lens. Not sure if oil could get past your separator or not.

George Brown
11-21-2009, 11:56 PM
I have a 25 ft hose from the compressor (oilless compressor). Then a separator/filter, then a silica gel drier, then another separator/filter. I also keep the air in the room at about 60 percent relative humidity with a dehumidifier. Have not had any problems. If you're interested, I can send details on the silica gel drier (home built, not purchased).

Dave Johnson29
11-22-2009, 9:49 AM
Hi Jim,

Are the cracked lenses cloudy from paint residue? If so, then smoke and junk is getting back into the cone somehow.

Is there a strong flow of air from the nose of the cone? With the cone in place it needs to provide cooling air to the lens. Maybe smoke and junk is being sucked back into the top of the cone by venturi action.

Can you cut upside down on a cutting table and with a good extraction system?

Mike Null
11-22-2009, 10:18 AM
Jim

I've been engraving for 12 years and never had a cracked lens. Two of the three machines I've operated didn't have air assist. I'm wondering if it's possible that the lens has been installed upside down or if it needs to be cleaned with more frequency.

In terms of moisture in the air, we are just a few miles apart and I have never used any kind of dryer in my system.

I'm on the north side of town once a month or so if you think I might be of any help.

Bill Cunningham
11-22-2009, 2:36 PM
Maybe talk to a few local body shops and ask what they use to dry the air for their spray guns. They may be able to suggest something. Most desiccant-type dryers require cartridges to be replaced as they become saturated or ineffective.

I use an inexpensive version like this

http://princessautoelearning.com/ch3_002c.html

It uses loose pellets, but I put the pellets into a perforated tube to make it more like a cartridge. Harbor Freight might have something similar if you don't want to pay $200-$300 for an automotive type unit.

For the unit I have, you need to cool the air before it hits the pellets. Not a bad idea anyway: if you can cool the air (and ensure the condensate goes into a sump, not the laser) then that alone will help remove some of the moisture. In the link, it says to have 25 feet of tubing between the compressor and desiccator - I used a length of nylon coiled air compressor hose and just wrapped it tight around the desiccator body itself. So moist air enters at the top of the nylon coil; the moisture condenses and runs down to the bottom of the sump, while the air is forced up through the pellets which collect additional moisture. This drips down into the sump. At the top of the steel tube it exits and goes into a filter (you must have a filter after the desiccator.) The unit is drained of water at the bottom.

In addition to water droplets, depending on your compressor type, you might have got some oil on the lens. Not sure if oil could get past your separator or not.

The pellets look like molecular sieves. When their fresh, and you put one on your tongue it will feel hot.. You can reactivate them and save some money by baking them in a oven at ab.t 400+ for 35-40 min. Let them cool, then seal them in a can.. The bottom part of the dryer (water trap) can be filled with marbles to increase the surface area by many times, and increase the amount of water collected..

Mark Winlund
11-22-2009, 3:09 PM
The best type of dryer is a refrigerated dryer. While expensive, there are no cartridges to forget, and they are very good at what they do. I have heard of people making a "poor mans" dryer with an old refrigerator and some copper tubing. The commercial ones use concentric (tube within a tube) systems. refrigerant is forced one way through the small tube, and compressed air goes the other way through the larger tube, ending at a water trap. Graingers sells them for around $500.... a small cost compared to the laser system and it's lenses. I have been running mine for 5 years or so with no problems.

Mark

Anthony Lembo
11-22-2009, 5:03 PM
One thing to check is if you have adequate air pressure. I have a ULS V-460 and the psi requirements are pretty high for what it does (50psi if I remember correctly). Are you sure you're getting enough air to the lenses?

An epilog machine can use a small air pump, but the universal systems need a compressor.

Hope that helps.

Anthony

Todd Suire
11-23-2009, 9:43 AM
Jim,

When you connect the air assist cone, make sure the valve at the connection (above the lense cover) is open. I always turn on the air pressure (at the compressor) and place my finger under the cone to make sure I'm getting air all the way through.

I also always use my ventilation system; it pulls the flames and heat away from the cone and lense as the piece is lasered.

Hope this helps.

Ron Nametko
11-23-2009, 9:46 AM
When running air lines you should try to avoid using rubber hoses. The moisture can build up a lot in them. You should use black pipe. You need to create a trap just before your water separator. The water will fall to to the drain valve instead of getting into the water separator. (An old trick learned while using airtools). Google "how to run air lines" and you will find several diagrams to show you what I am talking about. The best diagram is on tptoolsdotcom. It will eliminate almost all your water problems and save your water seperator too.:D

Zvi Grinberg
11-23-2009, 1:50 PM
In addition to:
Dry and clean air
Enough pressure in air-assist lines (you can sense at the cone tip)
Good blower - very important. If your hose is too long or has 90 degrees bendings, use a stronger blower that can overpower the internal compression.
I would add - NEVER touch the optics after finishing a job. Don't clean it, don't check it. Just let it cool down for a few minutes, before you take it out for inspection or cleaning.
After the cleaning - wait a few minutes to let the cleaned surface dry from the moisture of the cleaning solution.

Jim Beachler
11-23-2009, 5:12 PM
Thank you all for the info. I'm sorry that I haven't responded sooner but I was doing a local show all weekend and have been playing catch up with the orders from the weekend.

The compressor that I am using is a oil-less diaphragm pump. It is supposed to put out a steady stream of 60psi. As far as checking to see if air is coming out of the cone, my laser doesn't let the air come through until it starts moving. So I cannot check to see if it is coming through. I presume it is as I can see the flame and smoke going away from the cut.

I was using shop air from my shop compressor. Have 25 feet of 3/4 inch copper pipe before the water separator on the line. Then it is another 30 - 40 feet to the laser system. I had a drip leg, a water separator and a desiccant filter at the laser area. Still cracked a lens. That's when I went to the diaphragm pump. Thought that would solve the problem.

I do get a lot of build up on the cone as we are cutting through material. Is this normal?

I will install either a dryer or desiccant filter on the line this week.

Mike Mackenzie
11-23-2009, 6:26 PM
Jim,

My guess is you have a leak in the air line system within the laser. If you have even a pin hole leak what the system does is act like a vacuum instead of a pressurized air system. Thus sucking up the debris instead of blowing the debris away.

Look over all of the connections to the hoses and there connectors listen carefully and or feel around these connections to see if there is any air leaking from them.

Lower your table so you can put your hand under the air cone then send a file running at a slow speed. LEAVE THE TOP DOOR OPEN and start the file you can then check to see if air is coming through the cone. As long as the top door is opened the laser will not fire.

Scott Shepherd
11-23-2009, 6:26 PM
Build up on the cone is pretty normal from what I have experienced.

So when the lens cracks, is the cracked lens dirty or clean?

Zvi Grinberg
11-24-2009, 2:05 AM
If you could put images, we could have a look at the cracked lens. It can tell a lot.

Cracked lens is many times a result of quick transition between high and low temperature. Such as cleaning or touching when it's hot right after completing a job.

Dave Johnson29
11-24-2009, 4:06 PM
It is supposed to put out a steady stream of 60psi. As far as checking to see if air is coming out of the cone, my laser doesn't let the air come through until it starts moving.

The more important thing is the CFM rate for the pump.

Is there a safety shutter for the laser? If so flip it into the beam path then set it running. Make sure the beam is not cutting using a Popsicle stick under the cone and then try with a finger. My first guess is not enough air flow.

Have to ask again, was the cracked lens cloudy? If it was not you may have a metal lens mount that is too tight or missing a plastic washer and as it expands with heat, it is cracking. If it is cloudy then the junk is getting back into the cone some how.

Rob Bosworth
11-24-2009, 4:16 PM
It might be one or all of the things offered up from previous posts. Here is one more possibility. Maybe you need to align your air assist cone. Maybe it is a little off center, and the beam is clipping the side of the aluminum air assist cone. It heats up pretty quickly. And the heat travels up. Maybe it is nothing more than heat build up that is cracking your lens.